Z- P. METCALI 
 
 LIBRARY OF 
 
 1885- IQ56 
 
/ 
 
 c 
 
 4. 
 
ENTOMOLOGY 
 
 FOLSOM 
 
ENTOMOLOGY 
 
 WITH SPECIAL REFERENCE TO 
 
 ITS ECOLOGICAL ASPECTS 
 
 BY 
 
 JUSTUS WATSON FOLSOM, Sc.D. (Harvard) 
 
 ASSISTANT PROFESSOR OF ENTOMOLOGY AT THE UNIVERSITY OF ILLINOIS 
 
 THIRD REVISED EDITION 
 WITH FIVE PLATES AND 308 TEXT-FIGURES 
 
 PHILADELPHIA 
 
 P. BLAKISTON'S SON & CO. 
 
 1012 WALNUT STREET 
 
Copyright, 1922, by P. Blakiston's Son & Co. 
 
 P R I NTED IN U. S 
 THE MAPLE PRESS 
 
PREFACE 
 
 This book gives a comprehensive and concise account of insects. 
 Though planned primarily for the student, it is intended also for the 
 general reader. 
 
 The book was written in an effort to meet the growing demand for a 
 biological treatment of entomology. 
 
 The existence of several excellent works on the classification of 
 insects (notably Comstock's Manual, Kellogg's American Insects and 
 Sharp's Insects) has enabled the author to omit the multitudinous 
 details of classification and to introduce much material that hitherto 
 has not appeared in text-books. 
 
 As a rule, only the commonest kinds of insects are referred to in the 
 text, in order that the reader may easily use the text as a guide to per- 
 sonal observation. 
 
 All the illustrations have been prepared by the author, and such as 
 have been copied from other works are duly credited. 
 
 To Dr. S. A. Forbes the author is especially indebted for the use of 
 literature, specimens and drawings belonging to the Illinois State 
 Laboratory of Natural History. 
 
 Permission to copy several illustrations from Government publica- 
 tions was received from Dr. L. O. Howard, Chief of the Bureau of Ento- 
 mology; Dr. C. Hart Merriam, Chief of the Division of Biological 
 Survey, and Dr. Charles D. Walcott, Director of the U. S. Geological 
 Survey. Several desired books were obtained from F. M. Webster, 
 of the Bureau of Entomology. 
 
 Acknowledgments for the use of figures are due also to Dr. E. P. 
 Felt, State Entomologist of New York; Dr. E. A. Birge, Director of the 
 Wisconsin Geological and Natural History Survey; Prof. E. L. Mark 
 and Prof. Roland Thaxter, of Harvard University; Prof. J. H. Comstock 
 of Cornell University; Prof. C. W. Woodworth of the University of 
 California; Prof. G. Macloskie of Princeton University; Prof. W. A. 
 Locy of Northwestern University; Prof. J. G. Needham of Cornell Uni- 
 versity; Dr. George Dimmock of Springfield, Mass.; Dr. Howard Ayers 
 of Cincinnati, Ohio; Dr. W. M. Wheeler of the American Museum of 
 Natural History, New York City; Dr. W. L. Tower of the University 
 of Chicago; Dr. A. G. Mayer, Director of the Marine Biological Lab- 
 oratory, Tortugas, Fla.; James H. Emerton of Boston, Mass.; Dr. and 
 
 V 
 
VI PREFACE 
 
 Mrs. G. W. Peckham of Milwaukee, Wis.; Dr. William Trelease, 
 Director of the Missouri Botanical Garden; Dr. Henry Skinner, as 
 editor of "Entomological News;" and the editors of "The American 
 Naturalist." 
 
 Acknowledgments are further due to the Boston Society of Natural 
 History, the American Philosophical Society and the Academy of 
 Science of St. Louis. 
 
 Courteous permission to use certain figures was given also by The 
 Macmillan Co.; Henry Holt & Co.; Ginn & Co.; Prof. Carl Chun of 
 Leipzig; F. Diimmler of Berlin, publisher of Kolbe's Einfiihrung; and 
 Gustav Fischer of Jena, publisher of Hertwig's Lehrbuch and Lang's 
 Lehrbuch. 
 
 The first edition, which was translated into Japanese by Professors 
 Miyake and Uchida, has had a large sale in Japan. 
 
 The second edition contained much new matter, particularly a 
 chapter on the transmission of diseases by insects. 
 
 This third edition has been brought up to date by ^he addition of a 
 great deal of new material, including a few new illustrations. Some two 
 hundred and fifty titles have been added to the bibliography but, to 
 accommodate these, it was necessary to discontinue other titles of less 
 importance. 
 
 A new chapter, on insect ecology, is given. This ought to prove 
 useful, as the literature of the subject is scattered, and there has been 
 no similar comprehensive treatment of ecology from the viewpoint of 
 the entomologist. 
 
 In the preparation of this chapter the author has been fortunate in 
 having the expert advice of Professor V. E. Shelford, of the University 
 of Illinois; who is not responsible, however, for any possible short- 
 comings in the chapter. 
 
 The following scientific men also have gladly assisted by giving 
 desired information: — Dr. L. O. Howard, chief of the Bureau of Ento- 
 mology; Mr. A. F. Burgess, of the Bureau of Entomology; Prof. J. H. 
 Comstock, Cornell University; Prof. A. F. Shull, University of Michi- 
 gan; Mr. Nathan Banks, Museum of Comparative Zoology, Cambridge, 
 Mass.; Mr. Charles Macnamara, Arnprior, Ontario, Canada; Professor 
 A. O. Weese, University of New Mexico; Dr. C. P. Alexander, Mr. W. P. 
 Flint and Dr. H. Yuasa, of the Illinois State Natural History Survey; 
 Professor A. D. MacGillivray and Dr. R. D. Glasgow, of the Univer- 
 sity of Illinois. 
 
 Permission to use the map for Plate V. was courteously given by 
 Dr. B. E. Livingston and the Carnegie Institution of Washington. 
 
CONTENTS 
 
 Chapter Page 
 
 I. Classification ' i 
 
 II. Anatomy and Physiology 27 
 
 III. Development 129 
 
 IV. Adaptations of Aquatic Insects 165 
 
 V. Color and Coloration 172 
 
 Vl. Adaptive Coloration 194 
 
 VII. Insects in Relation to Plants 212 
 
 VIII. Insects in Relation to Other Animals 233 
 
 IX. Transmission of Diseases by Insects 248 
 
 X. Interrelations of Insects 270 
 
 XL Insect Behavior 302 
 
 XII. Distribution 322 
 
 XIII. Insect Ecology 348 
 
 XIV. Insects in Relation to Man 410 
 
 Literature 430 
 
 Index 479 
 
ENTOMOLOGY 
 
 CHAPTER I 
 
 CLASSIFICATION 
 
 At tJie outset it is essential to know where insects stand in relation to 
 other animals. 
 
 Arthropoda. — Comparing an insect, a centipede and a crayfish 
 with one another, they are found to have certain fundamental characters 
 in common. All are bilaterally symmetrical, are composed of a linear 
 series of rings, or segments, bearing paired, jointed appendages, and 
 have an external skeleton, consisting largely of a peculiar substance 
 known as chitin. 
 
 If the necessary dissections are made, it can be seen that in each of 
 these types the alimentary canal is axial in position; above it extends 
 
 Fig. 1. — Diagram to express the fundamental structure of an arthropod, a, antenna; 
 al, alimentary canal; b, brain; d, dorsal vessel; ex, exoskeleton; I, limb; n, nerve chain; s, 
 subcesophageal ganglion. — After Schmeil. 
 
 the dorsal blood vessel and below Hes the ventral ladder-like series of 
 segmental ganglia and paired nerve cords, or commissures; between the 
 commissures that connect the brain and the subcesophageal ganglion 
 passes the oesophagus. These relations appear in Figs, i and 165. 
 Furthermore, the sexes are almost invariably separate and the primary 
 sexual organs consist of a single pair. 
 
 No animals but arthropods have all these characters, though the 
 segmented worms, or annelids, have some of them^ — for example the 
 segmentation, dorsal heart and ventral nervous chain. On account of 
 these correspondences and for other weighty reasons it is believed that 
 
 I 
 
ENTOMOLOGY 
 
 arthropods have descended from annelid-Hke ancestors. Annelids, 
 however, as contrasted with arthropods, have segments that are essen- 
 tially ahke, have no external skeleton and never have paired limbs that 
 are jointed. 
 
 Classes of Arthropoda. — Excluding the king-crab, trilobites and a 
 few other forms that have no im- 
 mediate entomological importance, 
 the remaining arthropods fall into nine 
 classes, which are characterized as 
 follows : 
 
 Crustacea. — Aquatic, as a rule. 
 Head and thorax often united into a 
 cephalo thorax. Numerous paired 
 appendages, typically biramous (Y- 
 shaped) ; abdominal limbs often pres- 
 ent. Two pairs of antennae. 
 Respiration branchial (by means of 
 gills) or cutaneous (directly through 
 the skin). The exoskeleton contains 
 carbonate and phosphate of lime in 
 addition to chitin. Example, crayfish. 
 Arachnida. — Terrestrial. Usually 
 two regions, cephalothorax and abdo- 
 men; though various Acarina have but 
 one and Solpugida have all three— head, 
 thorax and abdomen. Cephalothorax 
 unsegmented, bearing two pairs of oral 
 Natural appendages and four pairs of legs. 
 Eyes simple. Abdomen segmented or 
 not, limbless. Respiration tracheal, by means of book-leaf tracheae, 
 tubular tracheae, or both; stigmata almost always abdominal, at 
 most four pairs. Heart abdominal in position. Example, Buthus 
 (Fig. 2). 
 
 Onychophora. — Terrestrial. Vermiform (worm-like), unsegmented 
 externally. One pair of ringed antennae, a pair of jaws and a pair of 
 oral shme papillae. Legs numerous, paired, imperfectly segmented. 
 Respiration by means of short tubular tracheae, the stigmata of which 
 are scattered over the surface of the body, or arranged in rows. Genital 
 opening posterior. Numerous nephridia (excretory) are present, 
 arranged segmentally in pairs. Two separate longitudinal nerve cords. 
 
 -A scorpion, Buthus. 
 size. 
 
CLASSIFICATION 3 
 
 connected by transverse commissures. Integument delicate. Some 
 fifty species are known. Example, Peripatus (Fig. 3). 
 
 Diplopoda. — Terrestrial. Two regions, head and body. Body 
 usually cylindrical, with numerous segments, most of which are double 
 and bear two pairs of short limbs, which are inserted near the median 
 ventral line. Eyes simple, antennae short, usually seven-segmented, 
 
 Fig. 3. — Peripatus capensis. Natural size. — After Moseley. 
 
 mouth parts consisting of a pair of mandibles and a compound plate, 
 or gnathochilarium. Genital openings separate, anterior in position 
 (on the second segment of the body). Example, Spirobolus (Fig. 4).. 
 
 Pauropoda. — Terrestrial. Two regions, head and body. Body 
 elongate, twelve-segmented, with nine pairs of functional legs; each of 
 the first five apparent terga consists morphologically of two united 
 terga. Eyes absent, but a pair of eye-like spots may be present. 
 Antennas characteristic; with four proxi- 
 mal segments and a pair of distal 
 branches bearing three filaments in all. 
 Mouth parts represented by mandibles, 
 maxillae (?) and labium (?). A single 
 genital opening (female) or a pair of 
 openings (male) on the third body 
 segment. Minute arthropods, at most 
 about one millimeter in length. Example, 
 Pauropus. 
 
 Chilopoda. — Terrestrial. Two regions, 
 head and body. Body long and flat- 
 tened, with numerous segments, each of 
 which bears a pair of long six- or seven- 
 segmented limbs, which are not inserted near the median line. Eyes 
 simple and numerous (agglomerate in Scutigera) antennae long, many- 
 segmented. A pair of mandibles and two pairs of maxillae. A single 
 genital opening, on the preanal segment. Example, Scolopendra (Fig. 5) . 
 
 Symphyla. — Terrestrial. Two regions, head and body. Head 
 prognathous, with a Y-shaped epicranial suture. Eyes few. Antennae 
 long, multiarticulate. Four pairs of mouth parts; mandibles two- 
 
 FiG. 4. — A diplopod, Spirobolus 
 marginatus. Natural size. 
 
4 ENTOMOLOGY 
 
 segmented. Body elongate, with fifteen distinct terga, and eleven or 
 twelve pairs of legs. Cerci well developed. Genital opening in the 
 third body segment. One pair of spiracles, opening on the head, under 
 the antennae. Small arthropods not more than five or six millimeters 
 in length. Example, Scolopendrella (Fig. 6). 
 
 Mjrrientomata. — Terrestrial. Three regions: head, thorax and 
 abdomen. Head small, conical, prognathous. One pair of eye-like 
 spots. Antennae absent. Mouth parts suctorial. Mandibles and 
 maxillae attenuate, styliform, protrusible and retractile. Labium 
 attenuate. Body strongly elongate, fusiform, narrowing posteriorly, 
 fifteen-segmented in adults. Thorax distinct from abdomen; prothorax 
 shorter than meso- or metathorax. Three pairs of thoracic legs, and a 
 pair of vestigial legs on each of the first three abdominal segments. 
 Last four abdominal segments more or less retractile. Cerci absent. 
 Genital opening posterior. Male genitalia elongate, retractile, distally 
 bilobed, with a pair of slender, forceps-like appendages. Female appen- 
 dage short, with short forceps. Minute delicate arthropods, seldom 
 more than one millimeter in length. Example, Acerentomon (Fig. 8.) 
 
 A single order, Protura, discovered and named by Silvestri, and 
 consisting of two families: Acerentomidae, without a tracheal system, 
 and Eosentomidae, with simple tracheae and two pairs of thoracic 
 spiracles. Protura, easily overlooked on account of their small size, are 
 doubtless widely distributed. At present twelve species are known from 
 Europe and twelve from the United States, all but one of our species 
 having been described by Dr. H. E. Ewing. 
 
 Insecta (Hexapoda). — Primarily terrestrial. Three distinct regions 
 — head, thorax and abdomen. Head with a pair of compound eyes in 
 most adults, one pair of antennae and typically three pairs of mouth 
 parts — mandibles, maxillae and labium — besides which a hypopharynx, 
 or tongue, is present. In Apterygota a fourth pair of mouth parts is 
 associated with the hypopharynx. Thorax with a pair of legs on each 
 of its three segments and usually a pair of wings on each of the posterior 
 two segments; though there may be only one pair of wings (as in Diptera, 
 male Coccidae and male Strepsiptera) ; the prothorax never bears wings. 
 Abdomen typically with eleven segments and without legs, excepting in 
 some larvae (as those of Lepidoptera, Tenthredinidae and Panorpidae). 
 Stigmata paired and segmentally arranged. A metamorphosis (direct 
 or indirect) occurs except in Thysanura and Collembola. 
 
 Relationships. — The interrelationships of the classes of Arthropoda 
 form an obscure and highly debatable subject. 
 
CLASSIFICATION 
 
 5 
 
 Crustacea and Insecta agree in so many morphological details that 
 their resemblances can no longer be dismissed as results of a vague 
 ''parallelism," or "convergence" of development, but are inexplicable 
 except in terms of community of origin, as Carpenter has insisted. 
 
 Arachnida are extremely unhke other arthropods but find their 
 nearest allies among Crustacea, particu- 
 larly the fossil forms known as trilobites. 
 
 Onychophora, as represented by Peri- 
 patus, are often spoken of as bridging the 
 gulf that separates Insecta, Chilopoda and 
 Diplopoda from Annelida. Peripatus in- 
 deed resembles the cha^topod annelids in 
 its segmentally arranged nephridia, der- 
 momuscular tube, coxal glands and soft 
 integument, and resembles the three other 
 classes in its tracheae, dorsal vessel with 
 paired ostia, lacunar circulation, mouth 
 parts and salivary glands. These resem- 
 blances are by no means close, however, 
 and Peripatus does not form a direct link 
 between the other tracheate arthropods 
 and the annelid stock, but is best regard- 
 ed as an offshoot from the base of the 
 arthropodan stem. 
 
 In speaking of annelid ancestors, none 
 of the recent annelids are meant, of course, 
 but reference is made to the primordial 
 stock from which recent annelids them- 
 selves have been derived. 
 
 Though Diplopoda and Chilopoda have 
 long been grouped together under the name 
 Myriopoda, they really have so little in 
 common, beyond the numerous limb-bearing segments and the charac- 
 ters that are possessed by all tracheate arthropods, that their differences 
 entitle them to rank as separate classes. Chilopoda as a whole are 
 more nearly related to Insecta than are Diplopoda, as regards seg- 
 mentation, mouth parts, tracheae, genital openings and other characters. 
 
 Scolopendrella, now placed in a class by itself, Symphyla, presents a 
 remarkable combination of diplopodan and insectean characters. 
 Scolopendrella (Fig. 6) and the thysanuran Campodea have the same 
 
 Fig. s. — A centipede, Scolopen- 
 dra heros. About two-thirds the 
 maximum length. 
 
ENTOMOLOGY 
 
 kind of head, with long moniliform antennae, and agree in the general 
 structure of the mouth parts; the number of body segments is nearly 
 the same, the legs and claws are essentially alike, and cerci and paired 
 abdominal stylets are present in the two genera, not to mention the 
 
 Fig. 6. — Section of Scolopendrella immaculata, b, brain; c, coxal gland; /, fore intes" 
 tine; h, hind intestine; m, mid-intestine; n, nerve chain; o, opening of silk gland; od, oviduct; 
 ov, ovary; s, silk gland; u, urinary tube. — After Packard. 
 
 correspondences of internal organization. Indeed, it is highly prob- 
 bable, as Packard maintained, that the most primitive insects, Thysa- 
 nura (and consequently all other insects), originated from a form much 
 like Scolopendrella. A singular thysanuran, Anajapyx vesiculosus 
 (Fig. 7) was discovered by Silvestri, who regarded 
 it as being in many respects the most primitive in- 
 sect known, combining as it does characters of 
 Symphyla, Diplopoda and Campodea. 
 
 Silvestri discovered also a peculiar arthropod, 
 Acerentomon doderoi (Fig. 8) for which he made a 
 new order — Protura. Berlese added two genera to 
 this order, namely, Eosentomon and Acerentulus ; and 
 according to good authority Protapteron indicum 
 Schepotieff belongs to the former genus. Silvestri, 
 followed by Borner, put Protura among Aptery- 
 gota; but Berlese, who grouped these forms under 
 the name of Myrientomata, found that they had 
 myriopodan as well as insectean affinities; and 
 Rimsky-Korsakow argued that Myrientomata 
 cannot be rightly regarded as insects, but logically 
 constitute a class by themselves; and that this class 
 does not form a direct link between myriopods and 
 insects, but that all these groups came from the same ancestral 
 stock. Protura have actually little in common with insects; the pecu- 
 liar structure of the mouth parts and genitalia excluding them from 
 the group Apterygota. 
 
 Fig. 7. — Anajapyx 
 vesiculosus. Length, 2 
 mm. — After Silvestri. 
 
CLASSIFICATION 
 
 The following diagram (Fig. 9) expresses very crudely one view as 
 to the annelid origin of the chief classes of Arthropoda. 
 
 The naturalness of the phylum Arthropoda was questioned by 
 Kingsley and Packard. The latter author divided Arthropoda into 
 five independent phyla, holding that "there was no common ancestor 
 of the Arthropoda as a whole, and that the group is a polyphyletic one." 
 This iconoclastic view, however, by emphasizing unduly the structural 
 differences among arthropods, tends to conceal the 
 many deep-seated resemblances that exist between the 
 classes of Arthropoda. 
 
 Carpenter, in a most sagacious summary of the 
 whole subject of arthropod relationships, brought to- 
 gether no little evidence in favor of a revised form of 
 the old Miillerian theory of crustacean origins. He 
 traced all the classes of Arthropoda back to com- 
 mon arthropodan ancestors with a definite number 
 of segments and distinctly crustacean in character; 
 then traced these primitive arthropods back to forms 
 like the nauplius larva of Crustacea, and these in turn 
 to a hypothetical form like the trochosphere larva of 
 recent polychaete annelids. 
 
 Orders of Insects. — Linnaeus arranged insects in 
 seven orders, namely, Coleoptera, Hemiptera, Lepi- 
 doptera, Neuroptera, Hymenoptera, Diptera and 
 Aptera. The wingless insects termed Aptera were 
 soon found to belong to diverse orders and the name 
 has become so ambiguous as to meet with little 
 approval. 
 
 From theLinnsean group Hemiptera, the Or thoptera Length, i.28nim.— 
 
 , , 1 XT 1 After SiLVESTRi. 
 
 were set apart the old order Neuroptera a heteroge- 
 neous and unnatural group, was split into several distinct orders, and 
 many other changes in the classification were necessary. 
 
 Without entering any further into the history of the subject, it is 
 sufficient to say that increasing discrimination on the part of entomolo- 
 gists has been followed by a gradual increase in the number of orders. 
 
 Naturally, the systems of classification have grown and changed 
 considerably, keeping pace with increasing knowledge. 
 
 Brauer (1885) made such important contributions to the subject that 
 his system, modified more or less by Packard, Comstock and others, 
 has been followed for almost forty years. 
 
 Pig. 8. — Aceren- 
 tomon doderoi. 
 
8 ENTOMOLOGY 
 
 Handlirsch has made the most exhaustive investigation of the phylo- 
 geny of the major groups of insects. His revolutionary system, which 
 is based upon fossil as well as recent forms, is of the kind to which one 
 applies the term "epoch-making," but is unfortunately so erratic and 
 fantastic in some respects that it has not been generally adopted. 
 
 As the orders of insects have evolved from one another in many 
 different directions, like the branches of a tree, their natural relation- 
 ships can not be expressed correctly in any linear sequence, like that 
 of this book. Here the orders are listed approximately according to 
 the degree of specialization, beginning with the most primitive insects; 
 
 
 INSECTA 
 
 CRUSTACEA \ .CHILOPODA 
 
 \ symphylaA/^diplopoda 
 arachnidaX / 
 
 ^ 
 
 / 
 
 ^MAUGOPODA 
 
 ARTHR 
 
 jpooj^ ANNELIDA 
 
 Fig. 9. — Diagram to indicate the origin of classes of Arthropoda. 
 
 and the attempt is made to group together orders that are nearly 
 related to one another. 
 
 In the course of the following synopsis of the orders of insects it is 
 necessary to use some terms, as metamorphosis and thysanurijorm, in 
 anticipation of their subsequent definition. 
 
 I. Thysanura. — No metamorphosis. Eyes aggregate, compound 
 or absent. Antennae long, filiform, multiarticulate. Mouth parts 
 mandibulate, either free (ectognathous) or enclosed in the head {ento- 
 gnathous). Wings invariably absent. Thoracic segments simple 
 and similar; prothorax well developed. Abdomen usually elongate, 
 with ten evident segments and often traces of an eleventh segment; 
 with two to eight pairs of rudimentary limbs, or styli, often accompanied 
 by eversible ventral sacs. Cerci usually long, filiform, multiarticulate, 
 with frequently a similar median pseudocercus; but sometimes with 
 
CLASSIFICATION 9 
 
 few segments (Anajapyx) or represented by a pair of forceps (Japyx). 
 Integument thin; scales present or absent. Active and terrestrial, 
 "bristletails." Examples, Campodea (Fig. lo), Japyx, Machilis, 
 Lepisma (Fig. ii), Anajapyx (Fig. 7). Some three hundred species are 
 known. 
 
 2. Collembola. — No metamorphosis. Eyes ocelliform, not more 
 than eight on each side, often fewer in number or absent. Antennae 
 short, of four segments in most genera; five or six in a few genera. 
 Mouth parts entognathous and typically mandibulate, with occasional 
 secondary suctorial modifications. Wings invariably absent. Tho- 
 
 FiG. 10. — Campodea. Length, 3 mm. FiG. 11. — Lepisma. Length, 10 mm. 
 
 racic segments simple and similar, or prothorax reduced. Body cylin- 
 drical or globular. Ventral tube and furcula usually present, sometimes 
 rudimentary. Integument delicate; scales present in some genera. 
 Small or minute terrestrial insects, "springtails. " Examples, Acliorutes 
 (Fig. 12), Sminthurus (Fig. 13). About nine hundred species have 
 been described. 
 
 Under the term Apterygota the Thysanura and Collembola, as primi- 
 tively wingless insects, are conveniently distinguished from all other 
 insects, or Pterygota. 
 
 3. Orthoptera. — Metamorphosis direct. Eyes well developed. 
 Antennae usually filamentous, shorter or much longer than the body, 
 multiarticulate. Mouth parts mandibulate. Pronotum usually large 
 
ENTOMOLOGY 
 
 (small in Phasmidae). Wings two pairs as a rule, though not infre- 
 quently reduced or absent. Fore wings coriaceous (leathery, forming 
 tegmina); hind pair membranous, ample, closely reticulate, plicate 
 along the numerous radiating principal veins. 
 Abdomen with ten evident segments and traces of 
 eleven or twelve. Cerci one- to eight-segmented. 
 Terrestrial and mostly phytophagous. Seven 
 families: Blattidae, Mantidae Gryllidae, Grylloblat- 
 tidae, Tettigoniidae (formerly Locustidae), Locus- 
 tidae (formerly Acridiidae, Fig. 14), Phasmidae (Fig. 
 243). More than ten thousand species are known. 
 4. Dermaptera.— Metamorphosis direct. Eyes 
 facetted, reduced, or absent. Antennae long, filiform, 
 with ten to fifty segments in adults. Mouth parts 
 mandibulate, prognathous; lingua and superlinguae 
 well developed; labium split to the mentum; para- 
 glossa united with glossa of same side. Prothorax 
 large. Thoracic segments distinct. Tarsi three- 
 segmented. Elytra short, 'scale-like, meeting in a 
 straight line. Wings projecting from under the 
 elytra, ear-shaped, with many radiating principal 
 veins, folding plicately, also twice transversely. 
 Abdomen with eleven segments, the tergites and 
 sternites strongly and complexly imbricate laterally, with a terminal 
 pair of forceps (cerci). Wingless species numerous. Some four hun- 
 dred species are at present known. 
 
 Three suborders, each represented by one family : Arixeniidae (one 
 species) ; Hemimeridae, containing 
 a single African species (Fig. 15), 
 which is flattened, eyeless, wing- 
 less, with long unsegmented cerci, 
 viviparous, and parasitic on the rat; 
 and Forficulidae, formerly a family 
 of Orthoptera. 
 
 5. Platyptera. — Metamorphosis 
 direct. Mouth parts mandibulate. 
 Wings, if present, two pairs, delicate, 
 
 membranous, equal or hind pair smaller, and with the principal veins 
 few and simple. Abdomen with usually ten evident segments and 
 often traces of an eleventh. Integument usually thin. Nymphs thy- 
 sanuriform. Five suborders. 
 
 Fig. 12. — The snow 
 &ea, Achorutes nivicola. 
 Length, 2 mm. 
 
 Sminlhiiriis hortensis. Length, 
 1.2 mm. 
 
CLASSIFICATION 
 
 Suborder Isoptera. — Eyes facetted, vestigial or absent. Antennae 
 long and filamentous or short and moniliform, nine- to thirty-one- 
 
 FiG. 14. — Schistocerca americana. Slightly re- 
 duced. 
 
 Fig. 15. — Hemimerus talpoides. Length, 
 1 1.5 mm. — After Hansen. 
 
 segmented. Mouth parts prognathous or hypognathous.^ Thoracic 
 segments simple, similar and equal ; pro thorax large, free. Tarsi four- or 
 five-segmented. Alate or apter- 
 ous. Wings elongate, similar, 
 equal, membranous, dehcate, with 
 few veins, sometimes with an in- 
 deffnite reticulation, with a char- 
 acteristic basal suture a ong which 
 the wing breaks off; hind wings not 
 folded. Abdomen elongate, wieh 
 ten segments and a pair of short 
 two- to six-segmented eerie In- 
 tegument weak. Social in habit 
 and polymorphic; known as white 
 ants. Example, Termes (Fig. 
 28o)Aboutonethousanddescribedspecies. 
 
 Suborder Embioptera. — Eyes facetted. Antennae with fifteen to 
 thirty-one or more segments. Mouth partsprognathous; with a labial 
 
 ^Prognathous, directed forward, hypognatJwus, directed downward. 
 
 Fig. 16. — Oligotoma michaeli. Length 10.5 
 mm. — After McLachlan. 
 
ENTOMOLOGY 
 
 Fig. 
 
 Psocus venosus. Length, 5 mm. 
 
 spinneret. Thorax elongate; pro thorax small. Tarsi three-segmented. 
 Wings (sometimes absent) two pairs, elongate, similar, equal, mem- 
 branous, delicate, with few and feebly developed longitudinal and cross 
 veins; not folded. Abdomen elongate, with ten segments and frequent- 
 ly an eleventh tergite, and a pair of short stout biarticulate cerci. 
 
 Integument delicate. Feeble insects, 
 not social in habit. Examples, 
 Embia, Oligotoma (Fig. i6). Some 
 twenty species, all from warm 
 climates. 
 
 Suborder Zoraptera. — Eyes ves- 
 tigial or absent. Antennse monili- 
 f orm, nine-segmented. Thorax long, 
 as long as the abdomen; prothorax large, larger than the meso- and 
 metathorax combined. Tarsi two-segmented. Apterous, or with two 
 pairs of wings; the fore wings with a few irregular veins and cells. 
 Abdomen with ten evident segments; the tenth and eleventh united 
 dorsally. Cerci short, one -segmented. Minute, active forms (little 
 more than two millimeters in length), terrestrial, 
 predaceous. One genus, Zorotypus, represented 
 by three Oriental species (Africa, Ceylon, Java), 
 one species from Costa Rica and two from the 
 United States. 
 
 These insects are most nearly related to Isop- 
 tera and Corrodentia. 
 
 Suborder Corrodentia.^Eyes facetted. An- 
 tennae filiform, with thirteen to fifty or more 
 segments. Mouth parts hypognathous. Pro- 
 thorax reduced. Tarsi two- or three-segmented. 
 Wings present, rudimentary or absent; fore pair the 
 larger; veins few and irregular. Abdomen short 
 and stout, with nine or ten segments. Cerci absent. 
 Integument delicate. Small terrestrial insects, 
 including the book lice and other psocids. 
 Example, Psocus (Fig. 17). More than two hundred species are 
 known. 
 
 Suborder Mallophaga.^Small wingless flattened insects of parasitic 
 habit. Head large. Eyes of a few isolated ocelli, or vestigial, or 
 absent. Antennae three- to five-segmented. Mouth parts prognathous. 
 Prothorax distinct; mesothorax often, and metathorax usually, trans- 
 
 FiG. 18.— A 
 louse, Menopon. 
 2 mm. 
 
CLASSIFICATION 
 
 13 
 
 ferred to the abdominal region. Tarsi one- or two-segmented. Abdomen 
 usually short and broad, eight- to ten-segmented. Cerci absent. 
 
 A B 
 
 Fig. 19. — Pteronarcys regalis. A, nymph (after Newport); B. imago. Slightly reduced. 
 
 Fig. 20. — Hexagenia variabilis. A, nymph; B, imago. Natural size. 
 
 Biting lice, or bird Hce, parasitic on birds and a few mammals, feeding 
 on feathers, hair or skin. Example, Menopon (Fig. 18). More than 
 fifteen hundred species have been described. 
 
14 
 
 ENTOMOLOGY 
 
 6. Plecoptera. — Metamorphosis direct. Antennae filiform, long, 
 multiarticulate. Mouth parts mandibulate. Prothorax large. Wings 
 
 Fig. 21. — Libellula pulchella. A, last nymphal skin; B, imago. Slightly reduced. 
 
 two pairs, membranous, coarsely and complexly reticulate; equal or 
 else hind wings larger and with an ample plicate anal area. Abdomen 
 
 with ten segments and usually 
 a pair of long multiarticulate 
 cerci. Integument soft. 
 Nymphs thysanuriform, 
 
 aquatic; adults unique in 
 having tracheal gills. The 
 stone-flies. Example, Ptero- 
 narcys (Fig. 19). A single 
 family, Perlidae, comprising 
 two hundred species. 
 
 7. Ephemerida.— Meta- 
 morphosis direct. Antennae 
 bristle-like. Mouth parts 
 mandibulate, but atrophied 
 in the adult. Prothorax 
 small. Wings membranous, minutely reticulate; hind pair much the 
 smaller, rarely absent. Abdomen slender, with ten segments and three 
 or two very long multiarticulate caudal filaments (a pair of cerci, with 
 of ten a median pseudocercus) . Integument delicate. Nymphs thysa- 
 nuriform, aquatic, with lateral gills. May-flies, or sand-flies. Exam- 
 ple, Hexagenia (Fig. 20). Three hundred species. 
 
 8. Odonata. — Metamorphosis direct. Head mobile; eyes large. 
 Antennas inconspicuous, bristle-shaped. Mouth parts mandibulate. 
 Prothorax small, free; meso- and metathorax intimately united. 
 Tarsi three-segmented. Wings four, elongate, subequal, similar, mem- 
 
 FiG. 22. — Euthrips tritici. Length, 1.2 mm. 
 
CLASSIFICATION 
 
 15 
 
 branous, minutely reticulate, with characteristic costal joint (nodus), 
 arculus and triangle. Abdomen slender, with ten segments. Cerci 
 one-segmented. Nymphs aquatic; adults predatory. Dragon-flies 
 
 Fig. 23. — Benacus griseus. Slightly reduced. 
 
 Fig. 24. — Head louse, 
 Pediculus capitis, female. 
 Length, 2 mm. 
 
 and damsel -flies. Example, Lihellula (Fig. 21). About two thousand 
 species have been described. 
 
 Fig. 25. — Hydrophilus triangularis. Natural size. 
 
 9. Thysanoptera. — Metamorphosis direct, but including a subpupal 
 stage. Eyes well developed. Mouth parts suctorial, in part asym- 
 metrical. Prothorax long, free. Tarsus one- or two-segmented, ter- 
 
i6 
 
 ENTOMOLOGY 
 
 Fig. 26.— Chrysopa 
 plorabunda. Slightly 
 
 reudced. 
 
 minating in a bladder -like organ. Wings present, rudimentary or 
 absent, the two pairs narrow, equal, similar, with few or no veins and 
 fringed with long hairs. Abdomen with ten segments. Minute, slender 
 insects, known as "thrips." Example, Euthrips (Fig. 22). About 
 two hundred species have been described. 
 
 10. Hemiptera. — Metamorphosis direct. Antennae usually few- 
 segmented. Mouth parts suctorial. Prothorax usually large. Wings 
 
 usually present, except in the parasitic forms. 
 Eighteen thousand species. Two suborders. 
 
 Suborder Homoptera. — Head deflexed. Wings 
 four, sloping roof -like, similar and membranous 
 or fore pair somewhat coriaceous (leathery) 
 throughout. Wings absent in female Coccidae; in 
 males, fore wings present, hind wings absent, 
 represented by halteres. Phytophagous insects. 
 
 Example, Cicada (Fig. 209). Six thousand species. 
 
 Suborder Heteroptera. — Head free, not deflexed. Antennas often 
 
 long, few-segmented. Prothorax free. Wings four (sometimes reduced 
 
 or absent) folded flat; fore wings thickened basally, membranous 
 
 apically (hemelytra) , overlapping obliquely; hind wings membranous, 
 
 with large anal area. Terrestrial or 
 
 aquatic. The true "bugs." Example, 
 
 Benacus (Fig. 23) . About twelve thousand 
 
 species. 
 
 11. Parasita.^ — Metamorphosis direct. 
 Wingless parasites. Eyes simple or absent. 
 Antennae short, three- to five-segmented. 
 Prognathous. Head with a short tubular 
 beak, crowned with hooks, containing 
 a delicate protrusible sucking tube. Tho- 
 racic segments intimately united. Tarsus 
 with a single claw. Integument thin. The sucking lice, blood-sucking 
 parasites of mammals, represented by the " cooties." Example, Pedicu- 
 lus (Fig. 24). Some fifty species are known. 
 
 12. Coleoptera. — Metamorphosis indirect. Ocelli usually absent. 
 Antennae of various forms, with segments varying in number (two to 
 twenty-seven) but commonly ten or eleven. Mouth parts mandibulate. 
 Prothorax large, free. Two pairs of wings ; fore pair horny or shell-hke as 
 
 1 Various names have been used for this group, but the name which has priority and 
 is sanctioned by longest usage is Farasiia (Latreille, 1796). 
 
 Fig. 27. — Bittacus slrigosus. Nat- 
 ural size. 
 
CLASSIFICATION 
 
 17 
 
 a rule {elytra), meeting in a straight line; hind pair membranous, often 
 folded. Larvae sometimes thysanuriform, often eruciform, mandibulate. 
 Hard-bodied iusects, the beetles. Example, Hydrophiliis (Fig. 25). 
 About one hundred and fifty thousand species. 
 
 13. Strepsiptera. — Hypermetamorphic; first larva hexapodous, with 
 long anal stylets; later larvae apodous, degenerate. Female legless, 
 larviform, larviparous, with no pupal stage; male pupa hymenopteroid, 
 within a puparium. Male with large eyes; antennae seven- to four-seg- 
 mented, flabellately produced; labrum and labium absent; mandibles 
 ensiform; maxillae palpiform, two- or three-segmented. Prothorax and 
 mesothorax greatly reduced; metathorax preponderant. One pair of 
 
 Fig. 28. — Molanna cinerea. A, larva; B, imago. X 4 diameters. — After Felt. 
 
 wings, the metathoracic, membranous, with only radial veins (eight to 
 five), folding longitudinally. Anterior wings reduced to balancers. 
 Abdomen ten-segmented. Integument thin and soft. Parasitic. About 
 two hundred species are known. Found in all regions of the world. 
 
 14. Neuroptera. — Metamorphosis indirect. Antennae conspicuous. 
 Mouth parts mandibulate. Prothorax large. Wings almost always 
 four, membranous, subequal or else hind pair smaller, complexly 
 reticulate, not plicate, without large anal area. Larvae thysanuriform 
 or in some cases eruciform, and aquatic or terrestrial, predaceous. 
 Example, lace-winged fly, Chrysopa (Fig. 26). About six hundred 
 species have been named. 
 
 15. Mecoptera. — Metamorphosis indirect. Antennae long, filiform. 
 Mouth parts mandibulate, at the end of a deflexed rostrum, or beak. 
 Prothorax small. Tarsi five-segmented. Wings four, elongate, mem- 
 
l8 ENTOMOLOGY 
 
 branous, naked, coarsely reticulate, or else rudimentary or absent. 
 Larvae eruciform, caterpillar-like, with three pairs of thoracic legs and 
 often eight pairs of abdominal prolegs, carnivorous. Example, Bittacus 
 (Fig. 27). A single family, Panorpidae, comprising but few known species . 
 
 16. Trichoptera. — Metamorphosis indirect. Eyes prominent. 
 Antennae filiform. Mouth parts of imago rudimentary or imperfectly 
 suctorial; mandibles rudimentary or absent. Prothorax small. Tarsi 
 five-segmented. Wings four, membranous, hairy, veins moderate in 
 number, cross veins few; hind pair almost always the larger, with 
 pHcate anal area. Larvae suberuciform, with three pairs of thoracic 
 legs, aquatic, usually case-forming. Caddis worms and caddis flies. 
 Example, Molanna (Fig. 28). Between five and six hundred species 
 are known. 
 
 17. Lepidoptera. — Metamorphosis indirect. Antennae long, of vari- 
 ous forms, many-segmented. Mouth parts suctorial, mandibles absent 
 or rudimentary (except in a few generahzed species). Eyes well 
 developed. Ocelli sometimes present. Prothorax reduced. Tarsi 
 usually five-segmented. Wings four, large, similar, membranous, with 
 veins moderate in number, and few cross veins. Adults usually clothed 
 throughout with scales. Larvae eruciform (caterpillars), typically with 
 three pairs of thoracic legs and five pairs (sometimes fewer) of abdom- 
 inal prolegs, mandibulate, phytophagous (rarely carnivorous). Butter- 
 flies and moths. Some fifty thousand species have been described. 
 Two suborders, not sharply separated from each other. 
 
 Suborder Heterocera. — Antennae of various forms, but not ter- 
 minating in a distinct knob or club. Frenulum usually present. 
 Chiefly nocturnal in habit. Example, Callosamia (Fig. 239). 
 
 Suborder Rhopalocera.— Antennae simple, terminating in a distinct 
 club and without conspicuous lateral processes. Frenulum absent. 
 Diurnal normally. Examples, Papilio (Fig. 29), Anosia (Fig. 247, A). 
 
 18. Hymenoptera. — Metamorphosis indirect. Mouth parts at the 
 same time mandibulate and suctorial. Prothorax usually small. Tarsi 
 usually five-segmented. Wings two pairs, similar, membranous, trans- 
 parent or translucent, without scales, with a few irregular veins and 
 cells; venation sometimes reduced; hind wings smaller than fore wings; 
 fore and hind wings held together by a series of hooks {hamuli). 
 Abdomen usually with six or seven evident segments. Females with an 
 ovipositor, modified for sawing, boring or stinging. Larvae eruciform, 
 mandibulate; caterpillar-like, with head and legs, or maggot-like and 
 apodous. Twenty-five or thirty thousand species. Two suborders. 
 
CLASSIFICATION 
 
 19 
 
 Suborder Terebrantia (Phytophaga, Sessiliventres). — Abdomen 
 broadly attached to the thorax (sessile). Trochanters of posterior 
 legs two-segmented. Ovipositor modified for boring, sawing or cutting. 
 Larvae with complex mouth parts, frequently caterpillar-like, with three 
 
 Pig. 29. — Papilio troilus. A, larva; B, larva suspended for pupation; C, chrysalis. Nat- 
 ural size. 
 
 pairs of thoracic legs and seven or eight pairs of abdominal prolegs. 
 Phytophagous or parasitic. Saw-flies, gall-flies, ichneumon-flies, etc. 
 Example, the pigeon horn-tail, Tremex (Fig. 30). 
 
 Suborder Aculeata (Heterophaga, 
 Petiolata.) — Abdomen petiolate or 
 subpetiolate (with a deep constriction 
 between the thoracic and abdominal 
 regions). First abdominal segment 
 (propodeum) transferred to the tho- 
 racic region. Trochanters of posterior 
 legs one-segmented. Ovipositor often 
 modified to form a sting. Larvae 
 apodous. Ants, bees, wasps, etc. Ex- 
 ample, the honey bee, Apis (Fig. 284). 
 
 19. Diptera. — Metamorphosis indi- 
 rect. Mouth parts typically sectorial, 
 but modified for piercing, lapping, 
 rasping, etc. Prothorax and meta- 
 
 thorax small, mesothorax predominant. Tarsi usually five-segmented. 
 One pair of wings (mesothoracic) , membranous, transparent, with 
 few veins; wings rudimentary or absent, however, in most of the 
 
 Pig. 30. — Tremex columba. /I, imago; 
 B, larva (with parasitic larva of Thalessa 
 attached). Natural size. — After Riley. 
 
20 ENTOMOLOGY 
 
 parasitic species; hind wings represented by a pair of knobbed 
 threads, or balancers. Larvae usually eruciform, with the head fre- 
 quently reduced to a mere vestige with or without a pair of mandibles, 
 and usually without true legs, though pseudopods may be present. 
 Pupa naked, or enclosed in a puparium. The flies. Example, crane- 
 fly, Tipula (Fig. 31). About forty thousand described species. 
 
 Fig. 31. — Tipula. A, larva; B, cast pupal skin; C, imago. Slightly reduced. 
 
 20. Siphonaptera. — Metamorphosis indirect. Head small, not 
 sharply separated from the thorax. Eyes minute and simple, or 
 
 absent. Antennae short and 
 stout, situated in depressions. 
 Mouth parts suctorial. Body 
 laterally compressed. Tho- 
 racic segments subequal, free; 
 coxae large; tarsi five-segment- 
 ed. Wings absent or at most 
 quite rudimentary. Larva 
 with a head, mandibulate, 
 apodous, vermiform. Adults 
 saltatorial, parasitic on warm- 
 blooded animals. The well 
 (Fig. 32). One hundred and 
 
 Fig. 32. — Cat and dog flea, Ctenocephalus canis. 
 A, larva (after Kunckel d'Herculais); B, advdt. 
 Length of adult, 2 mm. 
 
 Example, Ctenocephalus 
 
 known fleas, 
 fifty species. 
 
 Interrelations of the Orders. — The modern classification aims to 
 express relationships, and these are most clearly to be ascertained by a 
 comparative study of the facts of anatomy and development. 
 
 The most generahzed, or primitive, insects are the Thysanura. Sub- 
 tracting their special, or adaptive, pecuHarities, their remaining charac- 
 ters may properly be regarded as inheritances from some vanished 
 
CLASSIFICATION 2 1 
 
 ancestral type of arthropod. This primordial type, then, probably had 
 three simple and equal thoracic segments differing but slightly from 
 the ten abdominal segments; three pairs of legs and no wings; three pairs 
 of exposed biting mouth parts; a pair of long, many- jointed antennas 
 and a pair of cerci of the same description; a thin naked integument; a 
 simple straight alimentary canal distinctly divided into three primary 
 regions; a ganglion and a pair of spiracles for each of the three thoracic 
 and the first eight abdominal segments, if not all the latter; no meta- 
 morphosis; functional abdominal legs and active terrestrial habits. 
 
 The existing form that best meets these requirements is Scolopen- 
 drella, which is not an insect, however, but belongs in the class Sym- 
 phyla. The most primitive of known insects are Anajapyx and Campo- 
 dea, through which other insects trace their origin to the stock from 
 which Symphyla and Diplopoda arose. 
 
 There is not the slightest evidence to support the assumption by 
 Handlirsch that Thysanura and Collembola are degenerate descendants 
 of winged ancestors. They are primitively wingless insects (Aptery- 
 gota) ; in other words, they originated before insects acquired wings. 
 
 Among Thysanura, the genera Machilis and Lepisma show decided 
 orthopteran affinities; thus their eyes are compound and their mouth 
 parts strongly orthopteran; indeed, the likeness of Lepisma to a young 
 cockroach is striking. According to Crampton, Lepisma leads to 
 Plecoptera and Ephemerida; while Machilis has suggestions of affinities 
 with Crustacea. 
 
 "The generalized form of Thysanura, and the manner in which 
 it reappears in the larvae of other insects, is the natural key of the clas- 
 sification" (Hyatt and Arms). 
 
 Collembola, though specialized in several important ways, all 
 have the same peculiar kind of entognathous mouth parts as Campodea 
 and Japyx, for which reason and many others it is believed that Col- 
 lembola are an offshoot from the thysanuran stem. Collembola are 
 not nearly so primitive as Thysanura, however, for they have fewer 
 abdominal segments than the latter, exhibit much greater concentra- 
 tion of the nervous system, and are uniquely specialized in several 
 respects, notably as regards the ventral tube and the furcula, or spring- 
 ing organ. 
 
 Collembola are no longer regarded as a suborder of Thysanura by 
 those who are familiar with the morphology of the two groups. All the 
 specialists in Thysanura and Collembola agree in regarding them as 
 two distinct orders. 
 
2 2 ENTOMOLOGY 
 
 Orthoptera probably arose directly from the original thysanuri- 
 form stem. Of Orthoptera, Blattidae are the most primitive, with 
 Mantidae closely allied to them. In a linear arrangement, Gryllidae 
 may follow, though not closely related to Mantidae. Between Gryl- 
 lidae and Tettigoniidae (formerly Locustidae) comes Walker's new family 
 Grylloblattidae, which a few authors prefer to regard as a new order. 
 Tettigoniidas and Locustidae (formerly Acridiidae) belong together. 
 Phasmidae have some affinities with Locustidae, but show the greatest 
 departure from the primitive orthopteran type. 
 
 Dermaptera, represented almost entirely by the family Forficulidae, 
 which some authorities still retain in the order Orthoptera, must have 
 come from the same ancestors as Orthoptera, needless to say. In 
 some respects they are more primitive than Orthoptera; in others, more 
 specialized. Though the order shows some thysanuran characters, 
 the resemblance between a young earwig and the thysanuran Japyx 
 (both having forceps, for example) is on the whole superficial; the mouth 
 parts of the two agreeing only in the broadest way. On the other hand, 
 the resemblances in structure between Dermaptera and Coleoptera 
 are deep-seated. The dermapteran genus Hemimerus has strong 
 affinities with the orthopteran family Blattidae. 
 
 The suborders of Platyptera are by some raised to the rank of 
 orders. They are so closely related, however, that it seems preferable 
 to the writer to express their resemblances by keeping them together, 
 rather than to emphasize their differences by separating them. 
 
 Platyptera, as a whole, are most nearly related to Orthoptera on the 
 one hand and to Plecoptera on the other; Isoptera and Embioptera in 
 particular being strongly orthopteran. Mallophaga, aside from their 
 parasitic characters, agree closely with Corrodentia, especially as 
 regards the structure of the head and mouth parts. The bird lice are 
 essentially degenerate descendants of psocid-hke ancestors (Snodgrass). 
 
 Zoraptera, represented by six species of the genus Zorotypus, is 
 held to be a distinct order by some authors. A few years ago, Zoro- 
 typus would have been placed without hesitation among the termites. 
 The species of the genus are essentially termites, with a wing venation 
 suggesting that of psocids. 
 
 Plecoptera, which Packard placed in his order Platyptera, show 
 many primitive characters, including thysanuriform nymphs. 
 
 The more generalized winged insects fall naturally into two 
 groups, which are not sharply separated, however: orthopteroid and 
 plecopteroid. The latter group consists of the aquatic orders Plecop- 
 
CLASSIFICATION 23 
 
 tera, Ephemerida and Odonata. Of these, Plecoptera is probably the 
 most generalized order; though Ephemerida has retained some very- 
 primitive structures, notably the paired genital openings and ducts. 
 
 It is often stated that Plecoptera are the most primitive of winged 
 insec.ts. According to this view, then, Orthoptera have arisen from 
 the plecopteran stem. They show, however, no evidence of an aquatic 
 ancestry; and everything indicates that terrestrial insects preceded 
 aquatic. Doubtless plecopteroid and orthopteroid insects both arose 
 from a type that was winged, with many wing veins, mandibulate, and 
 terrestrial — a form like a thysanuran but with wings. 
 
 On the basis of metamorphosis, Plecoptera, Ephemerida and Odo- 
 nata form a natural group, Hemimetabola, in which the changes in 
 form during development are greater than in other Heterometabola, 
 the aquatic nymphs of these three orders being termed naiads by 
 Comstock. 
 
 Odonata are naturally placed next to Ephemerida but are strongly 
 aberrant forms with a unique kind of specialization. 
 
 Thysanoptera form a distinct order which is usually placed next to 
 Hemiptera, chiefly on account of the suctorial mouth parts, though 
 even in this respect there is no close agreement between the two orders. 
 They are aberrant and hard to place. Borner and Crampton find 
 resemblances between Thysanoptera and Corrodentia. 
 
 Hemiptera form a homogeneous and monophyletic order, charac- 
 terized by the unique shape and arrangement of the mouth parts, 
 which are always of the same type (Muir). Hemiptera are somewhat 
 like Orthoptera and possibly originated with Thysanoptera from some 
 mandibulate and winged form. The conversion of mandibulate into 
 suctorial organs may be seen within the order Collembola, though it is 
 improbable that Hemiptera arose from forms like Collembola. Hemip- 
 tera are exceptional among insects with a direct metamorphosis in 
 their highly developed type of suctorial mouth parts. Homoptera 
 are on the whole more primitive than Heteroptera. 
 
 Parasita, long a suborder of Hemiptera, should rank as an order, 
 apparently; though opinions differ in regard to this. 
 
 In the early days of the classification, the sucking lice and the biting 
 lice were always grouped together, on account of their resemblances. 
 Then it was found that these similarities, correlated with parasitic 
 existence, were only superficial; and the two groups were separated. 
 Some recent authors have, however, followed one another in the opinion 
 that the two kinds of lice are closely related to each other — an opinion 
 
24 ENTOMOLOGY 
 
 that is surprising in view of the many strong differences of structure 
 between the two groups, particularly as regards the mouth parts. 
 Though investigators have not agreed as to the morphology of the 
 mouth parts of the sucking lice, a study of cross sections of the mouth 
 parts leads to the conclusion that they conform fundamentally to the 
 hemipteran type. 
 
 Metamorphosis offers the broadest criteria for the separation of 
 insects into primary groups. All the orders considered thus far are 
 characterized either by no metamorphosis or by a relatively slight, or 
 so-called direct, or incomplete, transformation. The following orders, 
 on the contrary, are distinguished by an indirect, or complete, metamor- 
 phosis, which appears in Coleoptera and attains its maximum develop- 
 ment in Hymenoptera and Diptera. 
 
 With Coleoptera the cruciform type of larva appears, as a derivative 
 of the earlier thysanuriform type. The larvae of Meloe, Epicauta (Fig. 
 220) and other genera pass from a thysanuriform stage to an cruciform 
 condition during their development. 
 
 It was formerly thought that the resemblances between Coleoptera 
 and Dermaptera were superficial, but at present there is reason to 
 believe that these two orders are related. They agree rather closely 
 in structure, especially as regards the structure of the head (Crampton) 
 and the thoracic sclerites (Snodgrass). Coleoptera have affinities 
 with Neuroptera also, that appear in some of the larvae as well as in the 
 adult forms. Coleoptera are, however, more primitive than Neurop- 
 tera, and are placed here at the beginning of the holometabolous series. 
 
 Strepsiptera should be separated from Coleoptera as a distinct 
 order, accepting the opinion of Dr. W. D. Pierce, who has studied the 
 group thoroughly. Strepsiptera are aberrant, peculiarly specialized 
 forms. The fact that the male strepsipteran pupa has the form of a 
 hymenopterous pupa may or may not be significant. 
 
 In Neuroptera, as in Coleoptera, the transition from the thysanu- 
 riform to the cruciform type of larva may take place during the develop- 
 ment of the individual, as in the larva of Mantispa. 
 
 Neuroptera have kinship with Coleoptera; the structure of the head, 
 for one thing, being essentially the same in the two groups. They 
 resemble Plecoptera also; thus a form like Sialis may have come from 
 ancestors like perlids. 
 
 All the orders that follow are derived from the neuropteran stem, 
 in the opinion of many authorities. 
 
 Mecoptera form an isolated order, though their caterpillar-like 
 
CLASSIFICATION 
 
 25 
 
 larvae, with eleven or twelve pairs of legs, suggest affinities with Lepidop- 
 tera and, more remotely, with the tenthredinid Hymenoptera. Mecop- 
 tera are most nearly related to Neuroptera (through the genus Nemop- 
 tera) and have also certain affinities with Diptera (Cramp ton). 
 
 Trichoptera, while much like Mecoptera in structure and meta- 
 morphosis, are jindoubtedly closely related to Lepidoptera; in view of 
 the extensive and deep-seated resemblances between caddis flies and 
 the most generalized moths (Micropterygidaj) it must be concluded that 
 Trichoptera and Lepidoptera originated from the same stock, which 
 was doubtless neuropteroid. 
 
 
 %*»> 
 
 # .^^ 
 
 DIPTERA 
 
 PLECOPTERA 
 PLATYPTERA 
 
 ORTHOPTERA 
 
 HEMIPTERA 
 
 THYSANURA 
 
 CQLEOPTERA 
 
 Fig. 33. — Genealogical diagram of the orders of insects. 
 
 Hymenoptera also trace their ancestry back to neuropteroid forms. 
 The most generalized hymenopterous larvae, those of saw-flies, are 
 caterpillar-like; but the most specialized larvae, as those of ants, bees, 
 wasps, and parasitic Hymenoptera, are more like maggots, in correlation 
 with their sedentary mode of life. 
 
 Hymenoptera are often called the "highest" insects, chiefly on 
 account of their highly developed instincts and social life. From this 
 point of view, however, the termites also would rank high, though 
 structurally they belong among the more generalized insects. As a 
 matter of fact, the system of classification is based necessarily on 
 structure, and not on psychology; and structurally Hymenoptera are, 
 taking everything into consideration, less specialized than Diptera. 
 
 In Diptera the eruciform type of larva attains its extreme degree of 
 
26 ENTOMOLOGY 
 
 specialization, as in the family Muscidae. Such larvae as those of 
 mosquitoes are comparatively primitive. 
 
 The relationships of Diptera to other orders are not evident, but 
 the order is in some respects like Mecoptera. Diptera possibly came 
 from forms like Mecoptera, or both orders may have arisen from neu- 
 ropteroid ancestors. 
 
 The fleas, Siphonaptera, are usually placed next to Diptera, being 
 regarded as degenerate flies. 
 
 The preceding diagram (Fig. 33) is a graphic summary of the gen- 
 ealogy of some of the orders of insects. The central group (T) is the 
 hypothetical thysanuroid source of all insects, including Thysanura 
 themselves. Though Thysanura and Collembola show no traces of 
 wings, even in the embryo, it should be borne in mind that all the other 
 insects probably had winged ancestors and that it is more reasonable to 
 assume a single winged group as a starting point than to suppose that 
 wings originated independently in several different groups of insects. 
 
CHAPTER II 
 
 ANATOMY AND PHYSIOLOGY 
 
 I. Skeleton 
 
 Number and Size of Insects. — The number of insect species al- 
 ready known is about 400,000 and it is safe to estimate the total number 
 of existing species as at least one million. 
 
 Among the largest living species are the Venezuelan beetle, Dynastes 
 hercules, which is 155 mm. long, and the Venezuelan grasshopper, 
 Tropidacris latreillei, which has a length of 166 mm. and an alar expanse 
 of 240 mm. Among Lepidoptera, Attacus atlas of Indo-China spreads 
 240 mm.; Attacus casar oi the Philippines, 255 mm.; and the Brazilian 
 noctuid Erebus agrippina, 280 mm. Some of the exotic wood-boring 
 larvae attain a length of 150 mm. 
 
 The giants among insects have been found in the Carboniferous, 
 from which Brongniart described a phasmid (Titanophasma) as being 
 one-fourth of a meter long, and a huge dragon fly {Meganeura) with 
 a spread of more than two feet. 
 
 At the other extreme are beetles of the family Trichopterygidae, 
 some of which are only 0.25 mm. in length, as are also certain hymenop- 
 terous egg-parasites of the families Chalcididse and Proctotrypidae. 
 
 Thus, as regards size, insects occupy an intermediate place among 
 animals; though some insects are smaller than the largest protozoans 
 and others are larger than the smallest vertebrates. 
 
 Segmentation. — One of the fundamental characteristics of arthro- 
 pods is their linear segmentation. The subject of the origin of this seg- 
 mentation is far from simple, as it involves some of the most difficult 
 questions of heredity and variation. As arthropod segmentation is 
 usually regarded as an inheritance from annelid-like ancestors, the sub- 
 ject resolves itself into the question of the origin of the segmented 
 from the unsegmented "worms." Cope, Packard and others give the 
 mechanical explanation which is here summarized. In a thin-skinned, 
 unsegmented worm, the flexures of the body initiated by the muscular 
 system would throw the integument into folds, much as in the leech, 
 and with the thickening of the integument, segmentation would appear 
 from the fact that the deposit of chitin would be least at the places of 
 
 27 
 
28 ENTOMOLOGY 
 
 greatest flexure, i. e., the valleys of the folds, and greatest at the places 
 of least flexure, i. e., the crests of the folds. This explanation, which 
 has been elaborated in some detail by the Neo-Lamarckians, applies 
 also to the segmentation of the limbs, as well as the body. 
 
 Head. — In an insect several of the most anterior pairs of primary 
 appendages have been brought together to co-operate as mouth parts 
 and sense organs, and the segments to which they belong have become 
 compacted into a single mass — the head^- in which the original seg- 
 mentation is difficult to trace. The thickened cuticula of the head forms 
 a skull, which serves as a fulcrum for the mouth parts, furnishes a base 
 of attachment for muscles and protects the brain and other organs. 
 
 While the jaws of most insects can only open and shut, transversely, 
 their range of action is enlarged by movements of the entire head, which 
 are permitted by the articulation between the head and thorax. 
 
 As a rule, one segment overlaps the one next behind; but the head, 
 though not a single segment of course, never overlaps the prothorax in 
 the typical manner, but is usually received into that segment. This 
 condition, which may possibly have been brought about simply by the 
 backward pull of the muscles that move the head, has certain 
 mechanical advantages over the alternative condition, in securing, 
 most economically, freedom of movement of the head and protection 
 for the articulation itself. 
 
 The size and strength of the skull are usually proportionate to the 
 size and power of the mouth parts. In some insects almost the entire 
 surface of the head is occupied by the eyes, as in Odonata (Fig. 21, B) 
 and Diptera (Fig. 40). In muscid and many other dipterous larvae, or 
 "maggots," the head is reduced to the merest rudiment. 
 
 Though commonly more or less globose or ovate, the head presents 
 innumerable forms; it often bears unarticulated outgrowths of various 
 kinds, some of which are plainly adaptive, while others are apparently 
 purposeless and often fantastic. 
 
 Sclerites and Regions of the Skull. — The dorsal part of the skull 
 (Fig. 34) consists almost entirely of the epicranium, which bears the 
 compound eyes; it is usually a single piece, or sclerite, though in some 
 of the simpler insects it is divided by a Y-shaped suture, the epicranial 
 suture. The middle of the face, where the median ocellus often occurs, 
 is termed the front; ordinarily this is simply a region, though a frontal 
 sclerite exists in some insects between the branches of the epicranial 
 suture. Just above the front, and forming the summit of the head, is 
 the region known as the vertex; it often bears ocelli. The clypeus is 
 
ANATOMY AND PHYSIOLOGY 
 
 29 
 
 easily recognized as being the sclerite to which the upper Hp, or lahrum, 
 is hinged, though the clypeus is not invariably delimited as a distinct 
 sclerite. In certain insects a transverse suture divides the clypeus 
 into an anteclypeus and a postdypeus. The cheeks of an insect are 
 known as the gencB, and post-gence sometimes occur. On the under side 
 of the head is the gula, which bears the under lip, or labium. That part 
 of the skull nearest the pro thorax is termed the occiput; usually it is not 
 delimited from the epicranium, though in some insects it is continuous 
 with the post-genai to form a distinct sclerite. The occiput surrounds 
 the opening known as the occipital foramen, through which the oesopha- 
 
 FiG. 34. — Skull of a grasshopper, Melanoplus differenlialis. a, antenna; c, clypeus; e, 
 compound eye; /, front; g, gena; I, labrum; i^, labial palpus; m, mandible; mp, maxillary 
 palpus; o, ocelli; oc, occiput; pg, post-gena; v, vertex. 
 
 gus and other organs pass into the thorax. The membrane of the 
 neck in Orthoptera and some other insects contains small cervical 
 sclerites, dorsal, lateral or ventral in position; these, in the opinion of 
 Comstock, pertain to the last segment of the head. Besides those 
 described, a few other cephalic sclerites may occur, small and incon- 
 spicuous, but nevertheless of morphological importance; for example, 
 ocular or antennal sclerites, bearing the eyes or the antennas, respec- 
 tively; and the trochantin of the mandible, situated between the mandi- 
 ble and gena. 
 
 Tentorium. — In the head is a chitinous supporting structure known 
 as the tentorium. This consists of a central plate from which diverge 
 either two or three pairs of arms {anterior, posterior and dorsal) extending 
 
so 
 
 ENTOMOLOGY 
 
 to the skull (Fig. 35). The central plate, or body, lies between the 
 brain and the suboesophageal ganghon and under the oesophagus, which 
 passes between the anterior pair of arms. The tentorium braces the 
 skull, affords muscular attachments and holds the cephalic ganglia and 
 the oesophagus in place. It is not a true internal skeleton, but arises 
 
 Fig. 35. — Skull of a grasshopper, Dissos 
 teira Carolina, o, occipital foramen; t, t, 
 anterior arms of tentorium. 
 
 Fig. 36. 
 
 -Head of a gyrinid beetle, Dineutus, 
 to show divided eye. 
 
 from the same ectodermal layer which produces the external cuticula; 
 though authors are not agreed as to the details of the development. 
 
 Eyes. — The eyes are of two kinds — simple and compound. The 
 latter, or eyes proper, conspicuous on each side of the head, are of com- 
 
 FiG. 37. — Agglomerate eyes of a male coccid, 
 Leachia fuscipennis. — After Signoret. 
 
 Fig. 38. — FacuU '^^i a compound eye of 
 Melanoplus. Highly magnified. 
 
 mon occurrence except in the larvae of most holometabolous insects, in 
 some generalized forms (as Collembola) and in parasitic insects. The 
 compound eyes (Fig. 41) are convex and often hemispherical, though 
 their outline varies greatly; thus it may be oval (Orthoptera) or triangu- 
 lar (Notonecta), while in the aquatic beetles of the family Gyrinidae 
 (Fig. 36) each eye has a dorsal and a ventral lobe, enabhng the insect 
 to see upward and downward at the same time ; so also in Oberea and 
 
ANATOMY AND PHYSIOLOGY 
 
 31 
 
 other terrestrial beetles of the same family. Superficially, a compound 
 eye is divided into minute areas, or facets, which though circular in the 
 agglomerate type of eye (Fig. 37) are commonly more or less hexagonal 
 (Fig. 38), as the result of mutual pressure. These facets are not 
 necessarily equal in size, for in dragon flies the dorsal facets are fre- 
 quently larger than the ventral. In diame- 
 ter the facets range from .016 mm. {Lycana) 
 to .094 mm. {Ceramhyx). Their number is 
 often enormous; thus the house fly {Musca 
 domestica) has 4,000 to each eye, a butterfly 
 {Papilio) 17,000, a beetle (Mordella) 25,000 
 and a sphingidmoth 27,000; on the other hand, 
 ants have from 400 down, the worker ant of 
 Eciton having at most a single facet on each 
 side of the head. 
 
 Ocelli. — The simple eyes, or ocelli, appear 
 as small polished lenses, either lateral or dor- 
 sal in position. Lateral ocelli (Fig. 39) occur 
 
 Fig. 
 
 39- 
 
 ^^ -Head of a cater- 
 in the larvae of most holometaboloUS insects pillar Samia cecropia, to show 
 
 and in parasitic forms. Dorsal ocelli, sup- ^^'''^^ °'^""^- 
 plementary to the compound eyes, occur on or near the vertex, and 
 are more commonly three in number, arranged in a triangle, as in 
 Odonata, Diptera (Fig. 40) and Hymenoptera (Fig. 41) as well as many 
 Orthoptera and Hemiptera. Few beetles have ocelli and almost no 
 
 ^ A 
 
 ^-r-^^y- 
 
 Fig. 40.^ — Ocelli and compound eyes of a fly, Phormia regina. A, male; B, female. 
 
 butterflies (Lerema accius with its one ocellus being the only exception 
 known), though not a few moths have two ocelli. 
 
 As explained beyond, the compound eyes are adapted to perceive 
 form and movements and the ocelli to form images of objects at close 
 range or simply to distinguish between Hght and darkness. 
 
 Sexual Differences in Eyes. — In most Diptera (Fig. 40) and in 
 Hymenoptera (Fig. 41) and Ephemeridas as well, the eyes of the male are 
 
32 
 
 ENTOMOLOGY 
 
 larger and closer together (holoptic) than those of the female (dichoptic). 
 This difference is attributed to the fact that the male is more active 
 
 Fig. 41.— Ocelli and compound eyes of the honey bee. Apis mellifera. A. queen; B, 
 drone. — After Cheshire. 
 
 Fig. 42. — Various forms of antennae. A, fiUform, Eiischistus; B, setaceous, Plathemis; 
 C, moniliform, Catogenus; D, geniculate, Bombus; f, flagellum; ^.pedicel; 5, scape; E, irreg- 
 ular, Phormia; a, arista; F, setaceous, Galerita; G, clavate, Anosia; H, pectinate, male 
 Ptilodaclyla; I, lamellate, Lachnosterna; J, capitate, Megalodacne; K, irregular, DinetUus. 
 
 than the female, especially in the matter of seeking out the opposite sex. 
 
ANATOMY AND PHYSIOLOGY 33 
 
 Among ants of the same species the different forms may differ greatly 
 in the number of lateral facets. Thus in Formica pratensis, according to 
 Forel, the worker has about 600 facets in each eye, the queen 800-900 
 and the male 1,200. 
 
 Blind Insects. — Many larva?, surrounded by an abundance of food 
 and living often in darkness, need no eyes and have none; this is true of 
 the dipterous "maggots" and many other sedentary larvas, particularly 
 such as are internal parasites (Tachinidge, Ichneumonidae), or such as 
 feed within the tissues of plants (many Buprestidae, Cerambycidae and 
 CurcuHonidcE). Subterranean or cavernicolous insects are either 
 eyeless or else their eyes are more or less degenerate, according to the 
 amount of light to which they have 
 access. The statement is made that 
 blind insects never have functional 
 wings. 
 
 Antennae. — The antennae, never 
 more than a single pair (though 
 embryonic "second antennae " occur 
 in Thysanura and Collembola), are 
 situated near the compound eyes and 
 frequently between them. With rare 
 exceptions the antennae have always 
 several and usually many segments. 
 In form these organs are exceedingly 
 varied, though many of them may 
 be referred to the types represented Fi^. 43.— Antennje of a moth. Samia 
 
 cecropia. A, male; B, female. 
 
 in Figs. 42-44. 
 
 Though homologous in all insects, the antennae are by no means equiv- 
 alent in function. They are commonly tactile (grasshoppers, etc.) or 
 olfactory (beetles, moths) and occasionally auditory (mosquito), as 
 described beyond, but may be adapted for other than sensory functions. 
 Thus the antennae of the aquatic beetle Hydrophilus are used in connec- 
 tion with respiration and those of the male Meloe to hold the female. 
 
 Sexual Differences in Antennae. — In moths of the family Saturniidee 
 [S. cecropia, C. promethea, etc.) the pectinate antennae of the male are 
 larger and more feathered than those of the female, and differ also in 
 having more segments (Fig. 43). Here the antennae are chiefly olfac- 
 tory, and the reason for their greater development in the male appears 
 from the fact that the male seeks out the female by means of the sense 
 of smell and depends upon his antennae to perceive the odor emanating 
 from the opposite sex. 
 
34 
 
 ENTOMOLOGY 
 
 The plumose antennae of the male mosquito (Fig. 44) are highly de- 
 veloped organs of hearing, and are used to locate the female ; they have 
 delicate fibrillae of various lengths, some of which are thrown into sym- 
 pathetic vibration by the note of the female (p. 94). 
 
 Meloe has just been mentioned. In Sminthurus malmgrenii (Collem- 
 bola) the antennae of the male are provided with hooks and otherwise 
 adapted to grasp those of the female at copulation. 
 
 Though systematists have recorded many instances of antennal 
 antigeny, the interpretation of these sexual differences has received very 
 little attention; a beginning in the subject has been made by Schenk, 
 whose results will be referred to in connection with the sense organs. 
 
 Fig. 44. — Antennae of mosquito, Culex pipiens. A, male; B, female. The antenna has a 
 short basal segment, not shown in the figure. 
 
 Mouth Parts. — On account of their great range of differentiation, 
 the mouth parts are of fundamental importance to the systematist, par- 
 ticularly for the separation of insects into orders. Most of the orders 
 fall into two groups according as the mouth parts are either biting 
 (mandibulate) or sucking {suctorial). Collembola and Hymenoptera, 
 however, combine both functions; Diptera, though suctorial, exhibit 
 various modifications for piercing, lapping or rasping; Thysanoptera 
 are partly mandibulate but chiefly suctorial; and adult Ephemerida 
 and Trichoptera have but rudimentary mouth parts. 
 
 The mandibulate orders are Thysanura, Collembola (primarily), 
 Orthoptera, Dermaptera, Isoptera, Embioptera, Corrodentia, Mal- 
 lophaga, Plecoptera, Ephemerida (rudimentarily in adult), Odonata, 
 Coleoptera, Strepsiptera, Neuroptera and Mecoptera. 
 
ANATOMY AND PHYSIOLOGY 
 
 35 
 
 The usual statement is that there are three pairs of mouth parts, 
 namely, mandibles, maxillcB and labium. As a matter of fact, there are 
 four pairs, counting the superlingucB, which are evident in Thysanura 
 and Collembola, become vestigial in Heterometabola, and disappear in 
 the most specialized Holometabola. The mandibulate, or primary 
 type (Fig. 45), from which the suctorial, or secondary type, has been 
 derived, will be considered first. 
 
 Mandibulate Type. — The labrum, or upper lip, in biting insects is a 
 simple plate, hinged to the clypeus and moving up and down; though 
 capable of protrusion and retraction to some extent. It covers the man- 
 
 FiG. 45. — Mouth parts of a cockroach, Parcoblatta pennsylvanica. A, labrum; B, 
 mandible; C, hypopharynx; D, maxilla; E, labium; c, cardo; g (of maxilla), galea; g (of 
 labium), glossa; /, lacinia; /^, labial palpus; m, mentum; mp, maxillary palpus; p, paraglossa; 
 pf, palpifer; pg, palpiger; s, stipes; sm, submentum. B, D, and E are in ventral aspect. 
 
 dibles in front and pulls food back to these organs. On the roof of the 
 pharynx, under the labrum and clypeus, is the epipharynx; this consists 
 of teeth, tubercles or bristles, which serve in some insects merely to hold 
 food, though as a rule the epipharynx in mandibulate insects bears end- 
 organs of taste (Packard). The labrum does not represent a pair of 
 primary appendages. 
 
 The mandibles, or jaws proper, move in a transverse plane, being 
 closed by a pair of strong adductor muscles and opened by a pair of 
 weaker abductors. The mandible is almost always a single solid piece. 
 In herbivorous insects (Fig. 46, A) it is compact, bluntly toothed, and 
 
36 
 
 ENTOMOLOGY 
 
 often bears a molar, or crushing, surface behind the incisive teeth. In 
 carnivorous species (B) the mandible is usually long, slender and sharply 
 toothed, without a molar surface. Often, as in soldier ants, the man- 
 dibles are used as piercing weapons; in bees (C) they are used for various 
 industrial purposes; in some beetles they are large, grotesque in form and 
 apparently purposeless. The mandibles of Onthophagus (D) and many 
 other dung beetles consist chiefly of a flexible lamella, admirably adapted 
 for its special purpose. In Euphoria (Fig. 265), which feeds on pollen 
 and the juices of fruits, the mandibles, and the other mouth parts as 
 well, are densely clothed with hairs. In the larva of Chrysopa, the 
 inner face of the mandible (Fig. 46, E) has a longitudinal groove against 
 which the maxilla fits to form a canal, through which the blood of 
 
 Pig. 46. — Various forms of mandibles. A, Melanoplus; B, Cicindela; C, Apis; D, Onthoph- 
 agus; E, Chrysopa; F-I, soldier termites (after Hagen). 
 
 plant lice is sucked into the oesophagus. In termites (F-I) the mandi- 
 bles assume curious and often inexplicable forms. 
 
 Next in order are the superlingua {maxillulcB) , which have been 
 overlooked or disregarded by most entomologists. The superlinguas 
 are well developed in Thysanura and Collembola, particularly the 
 former order. In Machilis, for example, the superlingua has essentially 
 the same structure as a maxilla, as appears in Fig. 47; in Japyx the 
 palpus is three-segmented (Hansen). The superlinguae, arising in the 
 embryo as a separate pair of appendages (Fig. 198, si), always become 
 united by their bases with the lingua (Fig. 198, In), forming a pair of 
 wing-like appendages on the dorsal side of the lingua (Figs. 50, 51). 
 
 Among insects, superlinguae are best developed in Thysanura and 
 Collembola, and are known to occur also in Orthoptera, Dermaptera, 
 Isoptera, Corrodentia, nymphs of Ephemerida and larvae of some 
 Coleoptera. 
 
 Hansen ('93) termed these appendages "maxillulae," regarding 
 them as homologous with the first maxillae of Crustacea; and in this 
 
ANATOMY AND PHYSIOLOGY 
 
 37 
 
 interpretation he was followed by others, including the writer, who 
 (Folsom, 'go) termed them "superlinguai." The writer at present 
 agrees with Crampton, however, that these appendages are homologous 
 with the paragnaths of Crustacea. If they are not equivalent to the 
 first maxillae of Crustacea, the term "maxillulae" should not be applied 
 to them; they may be termed " superlinguse " or "paragnaths," as one 
 prefers. 
 
 Following the superlinguae are the maxillcB, or under jaws, which are 
 less powerful than the mandibles and more complex, consisting as they 
 do of several sclerites (Figs. 45, 48). Essen- 
 tially, the maxilla consists of three lobes, 
 namely, palpus, galea and lacinia, which are 
 borne by a stipes, and hinged to the skull by 
 means of a cardo. The palpus, always lateral 
 in position, is usually four- or five-segmented 
 and is tactile, olfactory or gustatory in function. 
 The lacinia is commonly provided with teeth or 
 spines. The maxillae supplement the mandi- 
 bles by holding the food when the latter open, 
 and help to comminute the food. Additional 
 maxillary sclerites, of minor importance, often 
 occur. 
 
 The labium, or under lip, may properly be 
 likened to a united pair of maxillae, for both 
 are formed on the same three-lobed plan. 
 This correspondence is evident in the cock- 
 roach, among other generalized insects. Thus, in this insect (Fig. 45) : 
 
 Labium = Maxilla 
 palpus = palpus 
 paraglossa = galea 
 glossa = lacinia 
 palpiger = palpifer 
 menium = stipites 
 suhmentum with gula = cardines 
 
 In most mandibulate orders the glossae unite to form a single me- 
 dian organ, as in Harpalus (Fig. 49, g). The labium forms the floor of 
 the pharynx and assists in carrying food to the mandibles and maxillae. 
 
 The tongue, or hypopharynx, is a median fleshy organ (Fig. 45) 
 which is usually united more or less with the base of the labium. In 
 
 Fig. 47. — Left superlingua 
 of Machilis variabilis. g, 
 galea; /, lacinia; p, palpus. 
 
38 
 
 ENTOMOLOGY 
 
 insects in general, the salivary glands open at the base of the hypo- 
 pharynx. In the most generalized insects, Thysanura and Collembola. 
 the hypopharynx is a compound organ, consisting of a median ventral 
 lobe, or lingua, and two dorsolateral lobes, termed superlingucs by the 
 
 Fig. 48. — Maxilla of Har pains caliginosus, 
 ventral aspect, c, cardo; g, galea; /, lacinia; 
 p, palpus; pf, palpifer; s, stipes; sg, subgalea. 
 
 Pig. 49. — Labium of Harpalus caliginosus, 
 ventral aspect, g, united glossae, termed 
 the glossa; m, mentum; p. palpus; pg, palpi- 
 ger; pr, paraglossa; sm, submentum. The 
 median portion of the labium beyond the 
 mentum (excepting the palpi) is termed the 
 ligula. 
 
 author. Superlinguse occur in other mandibulate orders just mentioned, 
 but have not yet been recognized in the most specialized orders of 
 insects. 
 
 Fig. 50. — Hypopharynx of Hemitnerus 
 talpoides. I, lingua; s, superlingua. — After 
 Hansen. 
 
 Fig. s i .• — Hypopharynx of an ephemerid, 
 Heptagenia. I, lingua; si, si, superlingua5. — 
 After Vayssiere. 
 
 Suctorial Types. — The mandibulate type of mouth parts is the 
 primitive type, from which the suctorial types have been derived. 
 Though the latter have evolved in several directions, they may all 
 be homologized with the former. 
 
ANATOMY AND PHYSIOLOGY 
 
 39 
 
 The suctorial, or haustellate, orders, are CoUembola (in part), 
 -Thysanoptera (in part), Hemiptera, Parasita, Trichoptera (imper- 
 fectly), Lepidoptera, Diptera, Siphonaptera and Hymenoptera (which 
 have functional mandibles, however). 
 
 Hemiptera. — The beak, or rostrum, in Hemiptera consists (Fig. 52) 
 of a conspicuous, one- to four-segmented labium, which ensheathes hair- 
 like mandibles and maxillae and is covered above at its base by a short 
 
 Fig. 52. — Mouth parts of a hemipteron, Benacus grisens. A, dorsal aspect; B, trans- 
 verse section; C, extremity of mandible; D, transverse section of mandibles and maxillae 
 c, suction canal; I, labrum; li, labium; m, mandible; mx, maxillae. 
 
 labrum. The mandibles and maxillae are sharply-pointed, piercing 
 organs and the former frequently bear retrorse barbs just behind the 
 tip ; the two maxillae lock together to form a sucking tube with two 
 canals: an upper, suction canal and a lower, salivary canal. Though 
 primarily a sheath, the labium bears at its extremity sensory hairs, 
 which are doubtless used to test the food. This general description 
 appUes to all Hemiptera except the parasitic forms, which present 
 special modifications. A pharyngeal pumping apparatus is present, 
 which is similar in its general plan to that of Lepidoptera and Diptera, 
 
40 
 
 ENTOMOLOGY 
 
 as presently described, though it differs as regards the smaller details of 
 construction. 
 
 Lepidoptera.— In Lepidoptera, excepting Eriocephala, the labrum is 
 reduced (Fig. 53) and the mandibles are either rudimentary or absent 
 (Rhopolscera). The two maxillae are represented by their galeae, 
 which form a conspicuous proboscis; the grooved inner faces of the galeae 
 (or laciniae, according to Kellogg) form the sucking tube, which opens 
 into the oesophagus. The labium is reduced, though the labial palpi 
 (Fig. 54) are well developed. The so- 
 called rudimentary mandibles of Anosia 
 and other forms have been shown by 
 Kellogg to be lateral projections of the la- 
 brum (Fig. 53) and are ^rvovfn 2i^ pilifers . 
 
 Fig. 53. — Head of a sphingid moth, Pro- 
 toparce sexla. a, antenna; c, clypeus; e, eye; 
 I, labrum; m, mandible; ^, pilifer; />r, proboscis. 
 
 Fig. 54. — Head of a butter- 
 fly, Vanessa, a, antennae; I, 
 labial palpus; p, proboscis. 
 
 The exceptional structure of the mouth parts in the generalized 
 genus Eriocephala (Micropteryx) sheds much light on the morphology 
 of these organs in other Lepidoptera, as Walter and Kellogg have shown. 
 In this genus there are functional mandibles; the maxilla presents 
 palpus, galea, lacinia, stipes and cardo, though there is no proboscis; 
 the labium has well developed submentum, mentum and palpi; a 
 hypopharynx is present. 
 
 The sucking apparatus, as described by Burgess, is essentially like 
 that of Diptera. Five muscles, originating at the skull and inserted 
 on the wall of a pharyngeal bulb, serve to dilate the bulb that it may 
 suck in fluids, while numerous circular muscles serve by contracting 
 successively to squeeze the contents of the bulb back into the stomach ; 
 a hypopharyngeal valve prevents their return forward. 
 
ANATOMY AND PHYSIOLOGY 
 
 41 
 
 Diptera. — In the female mosquito the mouth parts (Fig. 55) are 
 long and slender. As Dimmock found, the labrum and epipharynx 
 combine^ to form a sucking tube; the mandibles and maxillai are delicate, 
 linear, piercing organs, the latter being barbed distally; maxillary 
 palpi are present ; the hypopharynx is linear also and serves to conduct 
 saliva; the labium forms a sheath, enclosing the other mouth parts 
 when they are not in use; a pair of sensory lobes, termed labella, occur 
 at the extremity of the labium. 
 
 
 Fig. 55. — Mouth parts of female mosquito, Culex pipiens. A, dorsal aspect; B, trans- 
 verse section; C, extremity of maxilla; D, extremity of labrum-epipharynx; a, antenna; e, 
 compound eye; h, hypopharynx; /, labrum-epipharynx; li, labium; tn, mandible; mx, 
 maxilla; p, maxillary palpus. — B, after Dimmock. 
 
 The oesophagus is dilated to form a bulb, or sucking organ, from 
 which muscles pass outward to the skull; when these contract, the 
 bulb dilates and can suck in fluids, as blood or water, which are forced 
 back into the stomach by the elasticity of the bulb itself, according to 
 Dimmock; the regurgitation of the food is prevented by a valve. 
 
 The male mosquito rarely if ever sucks blood, and its mouth parts 
 differ from those of the female in having the mandibles aborted and the 
 maxillae slightly developed, but with long palpi, while the hypopharynx 
 coalesces with the labium and there is no oesophageal bulb. 
 1 Kulagin, however, described them as remaining separate. 
 
42 
 
 ENTOMOLOGY 
 
 Hymenoptera. — In the honey bee, which will serve as a type, the 
 labrum is simple; the mandibles are well developed instruments for 
 cutting and other purposes (Fig. 56) and the remaining mouth parts 
 form a highly complex suctorial apparatus, as follows. The "tongue'' 
 (glossa) is a long flexible organ, terminating in a "spoon" {labellum, 
 Figs. 56, 129) and clothed with hairs of various kinds, for gathering 
 
 Fig. 56. — Mouth parts of the honey bee, Apis mellifera, ventral aspect, c, cardo; g, 
 ssa (united glossae); I, lorum; lb, labellum; Ip, labial palpus; m, mentum; md, mandible; 
 mp. maxillary palpus; mx, maxilla; p, paraglossa; pg, palpiger; s, stipes (plus subgalea and 
 palpifer) ; sm, submentum. The blade of the maxilla is the galea, and the rounded lobe 
 opposite the palpus is the lacinia. 
 
 nectar or for sensory or mechanical purposes. The maxillae and labial 
 palpi form a tube embracing the tongue, while the epipharynx fits into 
 the space between the bases of the maxillae to complete this tube. 
 Through this canal nectar is driven, by the expansion and contraction 
 of the tube itself, according to Cheshire, except that when only a small 
 quantity of nectar is taken, this passes from the spoon into a fine "cen- 
 
ANATOMY AND PHYSIOLOGY 
 
 43 
 
 tral duct," or also into the "side ducts," which are specially fitted to 
 convey quantities of fluid too small for the main tube. For a detailed 
 account of the highly complex and exquisitely adapted mouth parts of 
 the honey bee, the reader is referred to Cheshire's admirable work, 
 Packard's Text-Book, or Snodgrass' The Anatomy of the Honey Bee. 
 
 Segmentation of the Head. — The determination of the number of 
 segments entering into the composition of the insect head has been a 
 difficult problem. As no segment bears more than one pair of primary 
 appendages, there are at least as many segments in the head as there are 
 
 fBr.°° o^»aj3 "aSi 
 
 Fig. 57. — Paramedian section of an embryo of the coUemboIan Anurida marilima; to 
 show the primitive cephalic ganglia, i, ocular neuromere; 2, antennal; 3, intercalary; 
 4, mandibular; 5, superlingual; 6, maxillary; 7, labial; 8, prothoracic; 9, mesothoracic; a; 
 antenna; /, labnim; Zt, labium; U, I'', P, thoracic legs; tn, mandible; mx, maxilla.- — After 
 
 FOLSOM. 
 
 pairs of primary appendages. On this basis, then, the antennae, man- 
 dibles, maxillae and labium may be taken to indicate so many segments; 
 but in order to decide whether the eyes, labrum and hypopharynx repre- 
 sent segments, other than purely anatomical evidence is necessary. The 
 key to the subject is furnished by embryology. At an early stage of 
 development the future segments are marked off by transverse grooves 
 on the ventral surface of the embryo, and the pairs of segmental appen- 
 dages are all alike (Fig. 197), or equivalent, though later they differen- 
 tiate into antennae, mouth parts, legs, etc. Moreover, the nervous 
 
44 ENTOMOLOGY 
 
 system exhibits a segmentation which corresponds to that of the entire 
 insect; in other words, each pair of primitive gangha, constituting a 
 neuromere, indicates a segment. Now in front of the oesophagus three 
 primitive segments appear, each with its neuromere (Fig. 57): first in 
 position, an ocular segment, destined to bear the compound eyes; 
 second, an antennal segment; third, an intercalary (premandibular) 
 segment, which in the generalized orders Thysanura and Collembola 
 bears a transient pair of appendages that are probably homologous with 
 the second antennae of Crustacea. In the adult, the ganglia of these 
 three segments have united to form the brain, and the original simpli- 
 city and distinctness have been lost. The labrum, by the way, does 
 not represent a pair of appendages, but arises as a single median lobe. 
 Behind the oesophagus, three embryonic segments are clearly distin- 
 guishable, each with its pair of appendages, namely, mandibular, 
 maxillary and labial. Finally, the hypopharynx, or rather a part of 
 it, claims a place in the series of segmental appendages, as the author 
 has maintained; for in Collembola its two dorsal constituents, or super- 
 lingucB, develop essentially as do the other paired appendages and, more- 
 over, a superlingual neuromere (Fig. 57) exists (even though Philip- 
 tschenko failed to find it). The four primitive ganglia immediately 
 behind the mouth eventually combine to form the suboesophageal 
 ganglion. 
 
 To summarize — the head of an insect is composed of at least six seg- 
 ments, namely, ocular, antennal, intercalary, mandibular, maxillary 
 and labial; and at most seven, since a superHngual segment occurs 
 between the mandibular and maxillary segments in Collembola and 
 Thysanura. 
 
 Thorax. — The thorax, or middle region, comprises the three segments 
 next behind the head, which are termed, respectively, pro-, meso- and 
 metathorax. In aculeate Hymenoptera, however, the thoracic mass in- 
 cludes also the first abdominal segment, then known as the propodeum, 
 or median segment. Each of the three thoracic segments bears a pair 
 of legs in almost all adult insects, but only the meso- and metathorax 
 may bear wings. 
 
 The dift"erentiation of the thorax as a distinct region is an incidental 
 result of the development of the organs of locomotion, particularly the 
 wings. Thus in legless (apodous) larvae the thoracic and abdominal 
 segments are alike; when legs are present, but no wings, the thoracic 
 segments are somewhat enlarged; and when wings occur, the size of a 
 wing-bearing segment depends on the volume of the wing muscles. 
 
ANATOMY AND PHYSIOLOGY 45 
 
 which in turn is proportionate to the size of the wings. When wings 
 are absent (as in Thysanura and CoUembola) or the two pairs equal 
 in area (as in Termitidae, Odonata, Trichoptera and most Lepidoptera) 
 the meso- and metathorax are equal. If the fore wings exceed the 
 hind ones (Ephemeridae, Hymenoptera) the mesothorax is proportion- 
 ately larger than the metathorax; as also in Diptera, where no hind 
 wings occur. If the fore wings are small (Coleoptera) or almost 
 absent (Stylopidae) the mesothorax is correspondingly smaller than the 
 metathorax. The prothorax, which never bears wings, may be enlarged 
 dorsally to form a protective shield, as in Orthoptera, Hemiptera and 
 Coleoptera; or, on the contrary, may be greatly Pes/ 
 
 reduced, as in Ephemerida, Odonata, Lepi- 
 doptera and Hymenoptera. In the primitive V— 7t- 
 Apterygota the prothorax may become re- 
 duced (many Collembola) or slightly enlarged P^'' 
 {Lepisma) . 
 
 The dorsal wall of a thoracic segment is 
 termed the notum, or tergum; the ventral wall, Pig. 58.— Diagram of the 
 the stermmi; and each lateral wall, a pleuron; p"':^^^?^! ^^Y"'^^ °^-^ *^°' 
 
 ' ' J: ' racic segment, ew.epimeron; 
 
 the restriction of these terms to particular es, epistemum; p, prsscutum; 
 segments of the thorax being indicated by the iCmr^'^^^Sum;?/. sSSuim- 
 prefixes pro-, meso- or meta-. These parts are -s^ sternum.— After Comstock. 
 usually divided by sutures into distinct pieces, or sclerites, as represented 
 diagrammatically in Fig. 58. Thus the tergum of a wing-bearing 
 segment is regarded as being composed of four sclerites {tergites, Fig. 
 59), namely and in order, prcescutum, scutum, scutellum and postscu- 
 tellum. The scutum and scuteUum are commonly evident, but the 
 two other sclerites are usually small and may be absent. According 
 to Snodgrass, the tergum consists primitively of a single sclerite, the 
 notum; the four sclerites having arisen as specializations; being not 
 always homologous in different orders of insects. Each pleuron con- 
 sists chiefly of two sclerites {pleurites, Figs. 58 and 60), separated from 
 each other by a more or less oblique suture. The anterior of these 
 two, which joins the sternum, is termed the epistemum; the other, the 
 epimeron. The former is divided into two sclerites in Odonata and 
 both are so divided in Neuroptera. 
 
 The sternum, though usually a single plate, is in some instances 
 divided into halves, as in the cockroach, or even into five sclerites 
 (Forficulidae) . 
 
 To these should be added the patagia of Lepidoptera — a pair of 
 
46 
 
 ENTOMOLOGY 
 
 erectile appendages of the prothorax; and the tegulce (paraptera) of 
 
 Lepidoptera, Diptera and Hymenoptera — a pair of small sclerites at 
 
 the bases of the front wings. 
 
 The thorax has also several small sclerites which are not described 
 
 here, though they are of interest to the morphologist. 
 
 Each of the three thoracic segments bears a pair of spiracles in 
 
 the embryo, but in most imagines there are only two pairs of thoracic 
 
 spiracles, the suppressed pair being the prothoracic. 
 
 The sclerites of the thorax owe their origin probably to local strains 
 
 on the integument, brought about by the muscles of the thorax. Thus 
 
 the primitively wingless Thysanura and 
 CoUembola have no hard thoracic 
 sclerites, though certain creases about 
 the bases of the legs may be regarded 
 as incipient sutures, produced mechan- 
 ically by the movements of the legs. 
 In soft njrmphs and larvae, the sclerites 
 ■0 do not form until the wings develop; 
 and in forms that have nearly or quite 
 lost their wings, as Pedicuhdae, Mallo- 
 phaga, Siphonaptera and some para- 
 sitic Diptera, the sclerites of the thorax 
 tend to disappear. Furthermore, the 
 absence of sclerites in the prothorax is 
 
 Fig. 59.— Dorsal aspect of the tho- probably duc to the lack of prothoracic 
 
 rax of a beetle, Hydrous piceus. 1, 
 pronotum; 2, mesopraescutum; 3, WingS 
 
 mesoscutum; 4. mesoscutellum; 5. obsolete SUturCS of the 
 mesopostscutellum; 6, metapraescu- 
 tum; 7, metascutum; 8, metascutellum; graSshoppcrs. 
 9, metapostscutellum. — After New- 
 port. 
 
 not withstanding the so-called 
 pronotum in 
 
 Endoskeleton. — An insect has no 
 internal skeleton, strictly speaking, 
 though the term endoskeleton is used in reference to certain ingrowths of 
 the external cuticula which serve as mechanical supports or as protec- 
 tions for some of the internal organs. The tentorium of the head has 
 already been referred to. In the thorax three kinds of chitinous in- 
 growths may be distinguished according to their positions: (i) phrag- 
 mas, or dorsal projections; (2) apodemes, lateral; (3) furcce, or apo- 
 physes, ventral. The phragmas (Fig. 61) are commonly three large 
 plates, pertaining to the meso- and metathorax, and serving for the 
 origin of indirect muscles of flight in Lepidoptera, Diptera, Hymenop- 
 tera and other strong-winged orders. The apodemes are comparatively 
 
ANATOMY AND PHYSIOLOGY 
 
 47 
 
 small ingrowths, occurring sometimes in all three thoracic segments, 
 though usually absent in the prothorax. The furcae occur in each 
 thoracic segment as a pair of conspicuous processes, which either 
 remain separate or else unite more or less; leaving, however, a passage 
 for the ventral nerve cord. 
 
 - 
 
 ' w 
 
 m::.L 
 
 / ^ J 
 
 t 
 
 a 
 a 
 
 : 
 
 
 
 Fig. 6o. — Ventral aspect of a carabid beetle, Galerita janus. i, prosternum ; 2, proepi- 
 sternum; 3, proepimeron; 4. coxal cavity; 5. inflexed side of pronotum; 6. mesosternum; 7. 
 mesoepis'ternum; 8, mesoepimeron ; 9. metasternum; 10, antecoxal piece; 11, metaepi- 
 sternum- 12, metaepimeron; 13. inflexed side of elytron; a. sternum of an abdominal seg- 
 ment; an. antenna; c, coxa; /, femur; Ip, labial palpus; md. mandible; mp, maxillary pal- 
 pus; /, trochanter; tb, tibia; ts, tarsus. 
 
 These endoskeletal processes serve chiefly for the origin of muscles 
 concerned with the wings or legs, and are absent in such wingless forms 
 as Thysanura, Pediculidae and Mallophaga. 
 
 Some ambiguity attends the use of these terms. Thus some writers 
 
48 
 
 ENTOMOLOGY 
 
 use the term apodemes for furcse and others apply the term apodeme 
 to any of the three kinds of ingrowths. 
 
 Legs. — In almost all adult insects and in most larvae each of the 
 three thoracic segments bears a pair of legs. The leg is articulated to 
 the sternum, episternum and epimeron, partly by means of small 
 articular sclerites (one of which, the trochantin, is shown in Fig. 63) 
 and consists of five segments (Fig. 62), in the 
 following order: coxa, trochanter, femur, tibia, 
 tarsus. The coxa is the basal segment. The 
 trochanter is small and in parasitic Hymenop- 
 tera consists of two subsegments. The femur 
 is usually stout and conspicuous, the tibia 
 commonly slender. The tarsus, rarely single- 
 jointed, consists usually of five segments, the 
 last of which bears a pair of claws in the adults 
 of most orders of insects and a single claw in 
 larvae; between the claws in most imagines is a 
 pad, usually termed the pulvillus, or empodium. 
 Adaptations of Legs. — The legs exhibit a 
 great variety of adaptive modifications. A 
 walking ' or running insect, as a carabid or 
 cicindelid beetle (Fig. 64, A) presents an aver- 
 FiG. 61. -Transverse sec- ^ge Condition as regards the legs. In leaping 
 tions of the thoracic segments insccts (grasshoppers, crickcts, Haltica) the 
 
 of a beetle, Co/Ja</z!i5, to show , . , . ^ ^ / ■n\ 
 
 the endoskeietai processes, hmd fcmora are enlarged {B) to accommodate 
 A, prothorax; 5. mesotho- ^j^^ powerful cxtcusor musclcs. In insccts that 
 
 rax; C, metathorax; a, a, ^ 
 
 furcae; ad, apodeme; p, make little use of their legs, as May flies and 
 p ragma. ter olbe. xipulidse, these appendages are but weakly 
 developed. The spinous legs of dragon flies form a basket for catching 
 the prey on the wing. Modifications of the front legs for the 
 purpose of grasping occur in many insects, as the terrestrial 
 families Mantidae (C) and Reduviidae and the aquatic famihes 
 Belostomidae and Naucoridae (D). Swimming species present special 
 adaptations of the legs (Fig. 231), as described in the chapter 
 on aquatic insects. In digging insects, the fore legs are expanded to 
 form shovel-like organs, notably in the mole-cricket (Fig. 64, E), in 
 which the fore tibia has some resemblance to the human hand, while 
 the tarsus and tibia are remarkably adapted for cutting roots, after 
 the manner of shears. The Scarabaeidae have fossorial legs, the anterior 
 tarsi of which are in some genera reduced {F) or absent; they are rudi- 
 
ANATOMY AND PHYSIOLOGY 
 
 49 
 
 -tr 
 
 mentary in the female (G) of Phanceus carnifex and absent in the male 
 {H), and absent in both sexes of Deltochilum. Though females of 
 PhancBus lose their front tarsi by digging, the degenerate condition of 
 these organs cannot be attributed to the inheritance of a mutilation, 
 but may have been brought about by disuse; though no one has ex- 
 plained why the two sexes should differ in this 
 respect. Many insects use the legs to clean the 
 antennae, head, mouth parts, wings or legs; the 
 honey bee (with other bees, also ants, Carabidae, 
 etc.) has a special antenna cleaner on the front legs 
 (Fig. 267, D), which is described, with other inter- 
 esting modifications of the legs, on page 229. 
 
 Indeed, the legs serve many such minor pur- 
 poses in addition to locomotion. They are com- 
 monly used to hold the female during coition, 
 and in several genera of Dytiscidae (Dytiscus, 
 Cyhister) the male (Fig. 64, /) has tarsal disks and 
 cupules chiefly on the front tarsi, for this purpose. 
 
 tb 
 
 Fig. 62. — Leg of a beetle, Calo- 
 soma calidutn. c, coxa; cl, claws; 
 /, femur; s, spur; t^-t^, tarsal seg- 
 ments; tb, tibia; tr, trochanter. 
 
 Fig. 63. — Left hind leg of Bittacus. 
 c, coxa genuina; cm, epimeron; es, 
 episternum; /, femur; m, trochantin; t; 
 trochanter. 
 
 Among other secondary sexual peculiarities of the legs may be men- 
 tioned the tibial brushes of the male Catocala concumbens, regarded as 
 scent organs, and the queer appendages of male Dolichopodid^E that 
 dangle in the air as these flies perform their dances. 
 
 The pulvillus is commonly an adhesive organ. In flies it has glandu- 
 lar hairs that enable the insects to walk on smooth surfaces and to walk 
 upside down; so also in many beetles and notably in the honey bee (Fig. 
 65) ; in this insect the pulvillus is released rapidly from the surface to 
 which it has been applied, by rolling up from the edges inward. 
 
 Sense organs occur on the legs. Thus tactile hairs are almost 
 always present on these appendages, while auditory organs occur on 
 the front tibiae of Tettigoniidae, Grylhdae and some ants. Finally, the 
 
so 
 
 ENTOMOLOGi' 
 
 legs may be used to produce sound, as in Stenohothrus and such other 
 Locustidae as stridulate by rubbing the femora against the tegmina. 
 
 Legs of Larvae.— Thoracic legs, terminating in a single claw, are 
 present in most larvae. Caterpillars have, in addition, fleshy abdominal 
 
 Fig. 64. — Adaptive modifications of the legs. A, Cicindela sexguttala; B, Nemobius 
 vittatus, hind leg; C, Stagmomantis Carolina, left fore leg; D, Pelocoris femoratus, right fore 
 leg; E, Gryllotalpa borealis, left fore leg; F, Canlhon lavis, right fore leg; G, PhancEus carnifex, 
 fore tibia and tarsus of female; H, P. carnifex, fore tibia of male; /, Dytiscus fascivenlris, 
 right fore leg of male; c, coxa;/, femur; s, spur; t, trochanter; tb, tibia; ts, tarsus. 
 
 legs (Fig. 64) ending in a circlet of hooks. Most caterpillars have five 
 pairs of these legs (on abdominal segments 3, 4, 5, 6, and 10), but the 
 
ANATOMY AND PHYSIOLOGY 
 
 51 
 
 rest vary in this respect. Thus Lagoa has seven pairs (segments 2-7 and 
 10) and Geometridae two (segments 6 and 10), while a few caterpillars 
 {Tischeria, Limacodes) have none. Larvae of 
 saw flies (Tenthredinidae) have seven or eight 
 pairs of abdominal legs and larvae of most 
 Panorpidas, eight pairs. Not a few coleopter- 
 ous larvae (some Cerambycidac, Hypera) also 
 have abdominal tubercles that represent legs, 
 but are incompletely developed as compared 
 with those of Lepidoptera. 
 
 The legless, or apodous, condition occurs 
 frequently among larvae and always in correla- 
 tion with a sedentary mode of life; as in the 
 larvae of many Cerambycidae, almost all Rhyn- 
 chophora, a few Lepidoptera, all Diptera, and Fig. 65.— Foot of honey bee. 
 
 ,, TT , 4-rr 4.U ^- -^ c- • ■ ^P^^ ■inellifera. c, c. claws; /.. 
 
 all Hymenoptera except Ten thredmidae, Sirici- puiviiius; t^-t\ tarsal seg- 
 
 d«, and other Terebrantia. ments.-After Cheshire. 
 
 Among adult insects, female scale insects are exceptional in being 
 legless. 
 
 Walking. — An adult insect, when walking, normally uses its legs in 
 two sets of three each; thus the front and hind legs of one side and the 
 
 Fig. 66. — Caterpillar of Protoparce sexta. Natural size. 
 
 middle leg of the other move forward almost simultaneously — though 
 not quite, for the front leg moves a Httle before the middle one, which, 
 in turn, precedes the hind leg. During these movements the body is 
 supported by the other three legs, as on a tripod. The front leg, 
 having been extended and its claws fixed, pulls the body forward by 
 
52 
 
 ENTOMOLOGY 
 
 means of the contraction of the tibial flexors; the hind leg, on the con- 
 trary, pushes the body, by the shortening of the tibial extensors, 
 against the resistance afforded by the tibial spurs; the middle leg acts 
 much like the hind one, but helps mainly to steady the body. Different 
 species * show different peculiarities of gait. In its analysis, the 
 walking of an insect is rather intricate, as Graber and Marey have shown. 
 The mode of action of the principal leg muscles may be gathered 
 from Fig. 67, Here the flexion of the tibia would cause the tibial spur 
 (s) to describe the line 51 ; and the backward movement of the leg due 
 to the upper coxal rotator r would cause the spur to follow the arc 
 53. As the resultant of both these movements, the path actually 
 
 ec // 
 
 Fig. 67. — Mechanics of an insect's leg. a, axis of coxa; c, coxa; cl, claw; e, extensor of 
 tibia; ec, extensor of claw; et, extensor of tarsus ;/, flexor of tibia ;/c, flexor of claw;//, flexor 
 of tarsus; r, r, rotators of coxa; 5, spur; t, trochanter muscle (elevator of femur) ; ti, tibia. — 
 After Graber. 
 
 described by the tibial spur is 5 2 ; then, as the leg moves forward, the 
 curve is continued into a loop. 
 
 Caterpillars use their legs successively in pairs, and when the pairs 
 of legs are few and widely separated, as in Geometridae, a curious looping 
 gait results. 
 
 The leg muscles of a cockroach are shown in Fig. 68. 
 
 Leaping. — The hind legs, inserted nearest the center of gravity, are 
 the ones employed in leaping, and they act together. A grasshopper 
 prepares to jump by bending the femur back against the tibia; to make 
 the jump, the tibia is jerked back against the ground, into which the 
 tibial spurs are driven, and the straightening of the leg by means of the 
 powerful extensors throws the insect into the air. At the distal end of 
 the femur are two lobes, one on each side of the tibia, which prevent 
 wobbling movements of the tibia. 
 
ANATOMY AND PHYSIOLOGY 
 
 53 
 
 Wings. — The success of insects as a class is to be attributed largely 
 to their possession of wings. These and the mouth parts, surpassing all 
 the other organs as regards range of differentiation, have furnished the 
 best criteria for the purposes of classification. The wings of insects 
 present such countless differences that an expert can usually refer a 
 detached wing to its proper genus and often to its species, though no 
 fewer than four hundred thousand species of insects are already known. 
 
 Typically, there are two pairs of wings, at- 
 tached respectively to the mesothorax and the 
 metathorax, the prothorax never bearing wings, 
 as was said. When only one pair is present it is 
 almost invariably the anterior pair, as in Diptera 
 and male Coccidae, though in male Strepsiptera it 
 is the posterior pair, the fore wings being 
 rudimentary. 
 
 In bird lice, fleas and most other parasitic in- 
 sects, the wings have degenerated through disuse. 
 In Thysanura and Collembola there are no traces 
 of wings even in the embryo; whence it is inferred 
 that wings originated later than these orders of 
 insects. 
 
 M tiller and Packard have regarded the wings 
 
 as tergal outgrowths; Tower, however, has shown 
 
 that the wings of Coleoptera, Orthoptera and 
 
 Lepidoptera are pleural in origin, arising just below _ 
 
 the line where later the suture between the pleuron left mid leg of a cock- 
 roach, posterior aspect. 
 abc, abductor of coxa; 
 adc, adductor of coxa; ef, 
 extensor of tibia; et, ex- 
 tensor of femur; /^ flexor 
 of tibia.; fta, flexor of tar- 
 sus; rl, retractor of tar- 
 sus. — After MiALL and 
 Denny. 
 
 and tergum will originate, though the wings may 
 subsequently shift to a more dorsal position. 
 
 Modifications of Wings. — Being commonly 
 more or less triangular, a wing presents three mar- 
 gins: front (costal), outer (apical) and inner (anal) ; 
 and three angles: humeral (at the base of the casta), 
 apical (at the apex of the wing) and anal (between outer and inner 
 margins). Various modifications occur in the front wings, which are 
 in many orders more useful for protection than for flight. Thus, in 
 Orthoptera, they are leathery, and are known as tegmina; in Coleoptera 
 they are usually horny, and are termed elytra; in Heteroptera, the base 
 of the front wing is thickened and the apex remains membranous, 
 forming a hemelytron. Diptera have, in place of the hind wings, a 
 pair of clubbed threads, known as balancers, or halteres, and male 
 
54 
 
 ENTOMOLOGY 
 
 Scl 
 
 Coccidae have on each side a bristle that hooks into a pocket on the 
 wing and serves to support the latter. In many muscid flies a doubly 
 lobed membranous squama occurs at the base of the wing. 
 
 In Hymenoptera the front and hind wings of the same side are held 
 together by a row of hooks {hamuli); these are situated on the costal 
 margin of the hind wing and clutch a rod-like fold of the fore wing. 
 In very many moths, the two wings are enabled to act as one by means 
 of a frenulum, consisting of a spine or a bunch of bristles near the base 
 of the hind wing, which, in some forms, engages a membranous loop on 
 the fore wing. 
 
 In the generalized moths of the family Hepialidae, the overlapping 
 fore and hind wings are held together by SLJugum, projecting backward 
 from the base of the fore wing. 
 
 Venation, or Neuration. — A wing is divided by its veins, or nervures, 
 
 into spaces, or cells. 
 Sc2 „ . The distribution of the 
 
 veins is of great sys- 
 tematic importance, 
 but formerly, the ho- 
 mologies of the veins in 
 the different orders of 
 insects were not fixed, 
 so that no little con- 
 fusion resulted. For 
 example, the term dis- 
 cal cell, used in descriptions of Lepidoptera, Diptera, Trichoptera and 
 Psocidae, was in no two of these groups appHed to the same cell. The 
 admirable work of Comstock and Needham, however, seems to settle 
 this disputed subject. By a study of the tracheae which precede and, 
 in a broad way, determine the positions of the veins, these authors have 
 arrived at a primitive type of tracheation (Fig. 69) to which the more 
 complex types of tracheation and venation may be referred. 
 
 In general, the following principal longitudinal veins may be distin- 
 guished, in the following order: costa, suhcosta, radius, media, cubitus, 
 and anal (Figs. 69-73). 
 
 The costa (C) strengthens the front margin of the wing and is essen- 
 tially unbranched. 
 
 The subcosta {Sc) is close behind the costa and is unbranched in the 
 imagines of many orders in which there are few wing veins, though it is 
 typically a forked vein. 
 
 3dA 2dA 
 
 IstA 
 
 Cu2 
 
 Pig. 69. — Hypothetical type of venation. A, anal vein; 
 C, costa; Cu, cubitus; M, media; R, radius; Sc, subcosta. — 
 Figs. 69-73 after Comstock and Needham. 
 
ANATOMY AND PHYSIOLOGY 
 
 55 
 
 The radius (R), though subject to much modification, is typically 
 five-branched, as in Fig. 69. The second principal branch of the 
 radius is termed the radial sector (Rs) . 
 
 The media (M) is often three-branched and is typically four- 
 branched, according to Comstock and Needham. 
 
 The cubitus (Cw) has two branches. 
 
 Fig. 70. — Wing of a fly, Rhyphus. Lettering as before. 
 
 The anal veins {A) are typically three, of which the first is usually 
 simple, while the second and third are many-branched in wings that 
 have an expanded anal area. 
 
 The Plecoptera, as a whole, show the least departure from the 
 primitive type of venation; which is well preserved, also, in the more 
 generalized genera of the Trichoptera. 
 
 Starting from the primitive type, specialization has occurred in two 
 ways: by reduction and by 
 addition. Reduction occurs £ 
 
 either by the atrophy of veins 
 or by the coalescence of two 
 or more adjacent veins. 
 Atrophy explains the lack of 
 all but one anal vein in 
 Rhyphus (Fig. 70) and other 
 Diptera, and the absence of 
 the base of the media in vl wo- ^^^- ''^ 
 sia (Fig. 71) and many other 
 Lepidoptera; in the pupa of Anosia, the media may be found com- 
 plete. Coalescence "takes places in two ways: first, the point at 
 which two veins separate occurs nearer and nearer the margin of the 
 wing, until finally, when the margin is reached, a single vein remains 
 where there were two before ; second, the tips of two veins may approach 
 each other on the margin of the wing until they unite, and then the 
 coalescence proceeds towards the base of the wing." (Comstock and 
 
 2dA 
 
 -Wing of a butterfly, 
 as before. 
 
 A nosia . Lettering 
 
56 
 
 ENTOMOLOGY 
 
 Needham.) The former, or outward, kind of coalescence is common 
 in most orders of insects; the latter, or inward, kind is especially 
 prevalent in Diptera. 
 
 Speciahzation by addition occurs by a multiplication of the branches 
 of the principal veins, or by the development of secondary longitudinal 
 veins between these branches. 
 
 Comstock and Needham have succeeded in homologizing practically 
 
 all the types of neuration, 
 including such perplexing 
 types as those of Ephemerida 
 (Fig. 72), Odonata (Fig. 21, 
 B) and Hymenoptera (Fig. 
 73), and have established a 
 uniform terminology of the 
 wing veins. The system built 
 up during some twenty-five 
 years by Comstock and his fol- 
 lowers is embodied in his great 
 volume. The Wings of Insects. 
 A student of the subject of venation should consult the many articles 
 by Tillyard, a keen investigator, whose point of view is in some respects 
 different from that of Comstock and Needham. He holds, for example, 
 that the primitive type of wing had many veins instead of few, and 
 that the evolutionary tendency has been, generally speaking, toward a 
 reduction in the number of veins. 
 
 Fig. 72. — Wings of a May fly. Lettering as before. 
 
 Fig. 73. — A typical hymenopterous wing. Lettering 
 
 Folding of Wing. — In some beetles (as Chrysohothris) the wings are 
 no larger than the elytra and are not folded; in others the wings exceed 
 the elytra in size, and when not in use are folded under the elytra in 
 ways that are simple but efficient, as described by Kolbe and by Tower. 
 To be understood, the process of folding should be observed in the 
 living insect. As described by Tower for the Colorado potato beetle, 
 
ANATOMY AND PHYSIOLOGY 
 
 57 
 
 the folded wing (Fig. 74, B) exhibits a costal joint (a), a fold parallel 
 to the transverse vein (b) , and a complex joint at d. The wing rotates 
 upon the articular head (ah) and when folded back beneath the wing- 
 covers the inner end of the cotyla (c) is brought into contact with a 
 chitinous sclerite of the thorax, which stops the further movement 
 of the cotyla medianward, and as the wing swings farther back the 
 middle system of veins (m) is pushed outward and anteriorly. This 
 motion, combined with the backward movement of the wing as a whole, 
 produces the folding of the 
 distal end of the wing. There 
 are no traces of muscles or 
 elastic ligaments in the wing 
 which could aid in the folding. 
 Mechanics of Flight. — The 
 mechanism of insect flight is 
 much less complex than one 
 might anticipate. Indeed, 
 owing to the structure of the 
 wing itself, simple up and 
 down movements are suffi- 
 cient for the simplest kind of 
 flight. During oscillation, 
 the plane of the wing changes, 
 as may be demonstrated by 
 holding a detached wing by 
 its base and blowing at right 
 angles to its surface ; the mem- 
 brane of the wing then yields 
 to the pressure of the air while 
 
 the rigid anterior margin does not, to any great extent. Similarly, 
 as the wing moves downward the membrane is inclined upward by the 
 resistance of the air, and as the wing moves upward the membrane 
 bends downward. Therefore, by becoming deflected, the wing encoun- 
 ters a certain amount of resistance from behind, which is sufficient to 
 propel the insect. The faster the wings vibrate, the greater the deflec- 
 tion, the greater the resistance from behind, and the faster the flight 
 of the insect. 
 
 The path traced in the air by a rapidly vibrating wing may be deter- 
 mined by fastening a bit of gold leaf to the tip of the wing and allowing 
 the insect — a wasp, for example — to vibrate its wings in the sunlight, 
 
 Fig. 74. — Wing of Leptinotarsa decemlineata. A, 
 spread; B, folded; a, costal joint; ah, articular head; 
 an, anterior system of veins; b, transverse vein; c, 
 cotyla; d, joint; in, middle system of veins; p, poste- 
 rior system of veins. — After Tower. 
 
58 
 
 ENTOMOLOGY 
 
 against a dark background. Under these conditions, the trajectory 
 of the wing appears as a luminous elongate figure 8. During flight, 
 the trajectory consists of a continuous series of these figures, as in Fig. 
 
 75- 
 
 Marey, an authority on animal locomotion, used chronophotography, 
 
 among other methods, in studying the proc- 
 ess of flight, and obtained at first twenty, 
 and later one hundred and ten, successive 
 photographs per second of a bee in flight. 
 As the wings were vibrating 190 times per 
 second, however, the images evidently 
 -Trajectory of the wing represented isolated and not consecutive 
 
 of an insect. ^ 
 
 phases of wing movement. Nevertheless, 
 the images could be interpreted without difficulty, in the light of 
 the results obtained by other methods. At length he obtained sharp 
 
 Fig. 
 
 of a second. 
 
 The frequency of wing vibration may be ascertained from the note 
 made by the wing— if it vibrates rapidly enough to make one; and, in 
 
 Pig. 76. — Records of wing vibration. A, mosquito. Anopheles. Above is the wing 
 record and below is the record of a tuning-fork which vibrated 264.6 times per second. B, 
 wasp, Polistes. The tuning-fork in this instance had a vibration frequency of 97.6. 
 
 any case, may be determined graphically by means of a kymograph, 
 which, in one of its forms, consists of a cylinder covered with smoked 
 paper and revolved by clockwork at a uniform rate. The insect is 
 held in such a position that each stroke of the wing makes a record on 
 the smoked paper, as in Fig. 76, A. Comparing this record with one 
 made on the same paper by a tuning-fork of known vibration period, 
 the frequency of wing vibration can be determined with great accuracy. 
 
ANATOMY AND PHYSIOLOGY 
 
 59 
 
 As the wing moves in the arc of a circle, the radius of which is the length 
 of the wing, the extreme tip of the wing records only a short mark; if, 
 however, the wing is pressed against the smoked cylinder, a large part 
 of the figure-8 trajectory may be obtained, as in Fig. 76, B. The wings 
 of the two sides move synchronously, as Marey found. 
 
 The smaller the wings are, the more rapidly they vibrate. Thus a 
 butterfly {P. rapce) makes 9 
 strokes per second, a dragon 
 fly 28, a sphingid moth 72, a 
 bee 190 and a house fly 330. 
 
 Wing Muscles. — The base 
 of a wing projects into the 
 thoracic cavity and serves for 
 the insertion of the direct 
 muscles of flight. Regarding 
 the wing as a lever (Fig. 77, 
 A) with the fulcrum at p, it 
 is easy to understand how the 
 contraction of muscle e raises 
 the wing and that of muscle d 
 lowers it. These muscles are 
 shown diagrammatically in Fig. 
 77, B. Besides these, there 
 are certain muscles of flight 
 
 which act indirectly upon the ,^'^- 'Z--^- ^fSra^a to illustrate the action 
 
 J ^ of the wing muscles of an insect. B, diagram of 
 
 wings, by altering the form of wing muscles, a, alimentary canal; cm. muscle 
 
 11 . ,, rpi ,1 for contracting the thorax, to depress the wings; 
 
 tne tnOraClC wall. inUS trie ^^ depressor of wing; e, elevator of wing; ex, 
 
 muscle id (Fis 77 B) elevates ^^^cle for expanding the thorax, to elevate the 
 
 wings; id, indirect depressor; ie, indirect elevator; 
 
 the wing by pulling the tergum /. leg muscle; p, pivot, or fulcrum; s. sternum; t, 
 
 toward the sternum; and the tergum; ^g. wing.-After Graber. 
 longitudinal muscle id depresses the wing indirectly by arching the ter- 
 gum of the thorax. 
 
 Though up and down movements are all that are necessary for the 
 simplest kind of insect flight, the process becomes complex in proportion 
 to the efl&ciency of the flight. Thus in dragon flies there are nine 
 muscles to each wing: five depressors, three elevators and one adductor. 
 The earlier accounts of the mechanics of flight by Marey and others 
 have been modified and improved upon by Stellwaag and by Ritter, 
 whose modern methods of investigation have added considerably to our 
 knowledge of the subject. These later authors have shown, particu- 
 larly, the parts played by the thoracic sclerites during flight. 
 
6o ENTOMOLOGY 
 
 The development of aviation was due largely to thorough studies 
 of the flight of birds and insects. 
 
 Abdomen. — The chief functions of the abdomen are respiration and 
 reproduction, to which should be added digestion. The abdomen as a 
 whole has undergone less differentiation than the thorax and presents a 
 simpler and more primitive segmentation. 
 
 Segments. — A typical abdominal segment bears a dorsal plate, or 
 tergum (notum) and a ventral plate, or sternum, the two being connected 
 by a pair of pleural membranes, which facilitate the respiratory move- 
 ments of the tergum and sternum. Abdominal tergites and sternites 
 are often termed urotergites and urosternites, respectively. Most of 
 the abdominal segments have spiracles, one on each side, situated in or 
 near the pleural membranes of the first seven or eight segments. The 
 total number of pairs of spiracles is as follows: 
 
 Thoracic Abdominal Total 
 
 Campodea 2 i 3 
 
 Japyx^ 4 7 II 
 
 Machilis 2 7 9 
 
 Lepisma 2 8 10 
 
 Nicoletia. • 2 8 10 
 
 Orthoptera 2 8 10 
 
 Odonata 2 8 10 
 
 Heteroptera 2 6(7) 8(9) 
 
 Lepidoptera 2 7 9 
 
 Diptera 2 7 9 
 
 1 Japyx actually has four thoracic and seven abdominal spiracles, as described and 
 illustrated by Grassi (1888), Willem (1900) and Verhoeff (1904); a study of their figures 
 indicates, however, that the spiracles may have migrated forward, and that the fourth 
 thoracic pair (there being two pairs in the metathorax) belongs morphologically to the 
 first abdominal segment. 
 
 Number of Abdominal Segments. — Though only ten abdominal 
 segments are evident in many adult insects and many larvae as well, 
 the typical number is eleven, and the maximum twelve. In embryos of 
 Thysanura, Orthoptera, Ephemerida, Odonata, Coleoptera and Hy- 
 menoptera, eleven abdominal neuromeres (primitive ganglia) have been 
 found by Heymons and others; each neuromere representing a segment; 
 and the twelfth segment is present as a telson, a terminal, segment con- 
 taining the anus, but without a neuromere and never bearing a pair of 
 appendages. This telson is present also in the adults of some generalized 
 insects, as Orthoptera. In the more specialized orders, ten may usually 
 be distinguished, with more or less difiiculty, though the number is 
 apparently, and in some cases actually, less owing to modifications of 
 
ANATOMY AND PHYSIOLOGY 
 
 6l 
 
 the base of the abdomen in relation to the thorax, but especially to 
 modifications of the extremity of the abdomen, for sexual purposes. 
 
 Modifications. — In aculeate Hymenoptera the first segment of the 
 abdomen has been transferred to the thorax, where it is known as the 
 propodeiim, or median segment; in other words, what appears to be the 
 first abdominal segment is actually the second; this, as in bees and 
 wasps, often forms a petiole, which enables 
 the sting to be applied in almost any direc- 
 tion. In Cynipidae the tergum of segment 
 two or three occupies most of the abdom- 
 inal mass, the remaining segments being 
 reduced and inconspicuous. The terminal 
 segments of the abdomen often telescope 
 into one another, as in many Coleoptera and 
 Hymenoptera (Chrysididae), or undergo 
 other modifications of form and position 
 which obscure the segmentation. As to 
 the number of evident (not actual) abdom- 
 inal segments, Coleoptera show five or six 
 ventrally and seven or eight dorsally; 
 Lepidoptera, seven in the female and eight 
 in the male; Diptera, nine (male Tipulidae) 
 or only four or five; and Hymenoptera, nine 
 (Tenthredinidas) or as few as three (Chry- 
 sididae). In the larvae of these insects, 
 nine or ten abdominal segments are usually 
 distinguishable, though the tenth is fre- 
 quently modified, being in caterpillars 
 
 united with the ninth. Fig. 78.— Ventral aspect of the 
 
 . J -nv !• 1 1 • 1 abdomen of a female Machilis 
 
 Appendages.— Rudimentary abdommal maritima, to show rudimentary 
 limbs occur in Thysanura {Machilis, Fig. (^h^e^SJ apSSeVf'^tL*^^^^^^ 
 
 78). Functional abdominallegS do not occur segment is omitted.) c, c, c, lateral 
 11, • iT_j.*i ^1. 1.J cerci and median pseudocercus. — 
 
 m adult msects, but m larvae the abdom- p^^^^ qudemans. 
 inal rolegs (Fig. 66) are homologous 
 
 with the thoracic legs and the other paired segmental appendages, as 
 the embryology shows. The embryo of (Ecanthus, according to Ayers, 
 has ten pairs of abdominal appendages (Fig. 199), equivalent to the 
 thoracic legs. Most of these embryonic abdominal appendages are 
 only transitory, but the last three pairs frequently persist to form the 
 genitalia, as in Orthoptera (to which order (Ecanthus belongs). In 
 
62 ENTOMOLOGY 
 
 Collembola, the embryo has paired abdominal limbs, and those of the 
 first abdominal segment eventually unite to form the peculiar ventral 
 tube (Fig. 13) of these insects, while those of the fourth segment form 
 the characteristic leaping organ, or fur cula, and those of the third, the 
 tenaculum. 
 
 Cerci. — In many of the more generalized insects the abdomen bears 
 at its extremity a pair of appendages termed cerci. These occur in 
 both sexes and are frequently long and multiarticulate, as in Thysanura 
 (Figs. 78, 10, 11), Plecoptera (Fig. 19) and Ephemerida (Figs. 20, B;S6) 
 though shorter in cockroaches and reduced to a single sclerite in Locus- 
 tidae (Fig. 89). The paired cerci, or cercopoda of Packard, are usually 
 though not always associated with the eleventh abdominal segment and 
 are homologous with legs, as Ayers has found in (Ecanthus and Wheeler 
 in Xiphidium. As to their function, the cerci of Thysanura are tactile, 
 and those of the cockroach olfactory, while the cerci of male Locustidae 
 often serve to hold the female during copulation. 
 
 The so-called "median cercus" or "filum terminale" of Thysanura 
 (Figs. II, 78) and Ephemerida (Fig. 86) resembles the true cerci of 
 these insects in being multiarticulate and usually long, and in having the 
 same function; but differs from these morphologically in arising as a 
 median dorsal prolongation of the eleventh abdominal segment; being 
 therefore not equivalent to one of the paired segmental appendages. 
 For this median filament the term pseudocercus is appropriate. 
 
 Extremity of Abdomen. — Various modifications of the terminal 
 segments of the abdomen occur for the purposes of defecation and 
 especially reproduction. The anus, dorsal in position, opens always 
 through the last segment and is often shielded above by a suranal plate 
 and on each side by a lateral plate. The genital orifice is always ventral 
 in position and occurs commonly on the ninth abdominal segment, 
 though there is some variation in this respect. The external, or 
 accessory, organs of reproduction are termed the genitalia. 
 
 Female Genitalia. — In Neuroptera, Coleoptera, Lepidoptera and 
 Diptera the vagina simply opens to the exterior or else with the anus 
 into a common chamber, or cloaca. Often, as in Cerambyx (Fig. 79) 
 and Dasyneura (Fig. 80) the attenuated distal segments of the abdomen 
 serve the purpose of an ovipositor; thus in Itonididae, the terminal 
 segments, telescoped into one another when not in use, form when 
 extruded a lash-like organ exceeding frequently the remainder of the 
 body in length. 
 
 A true ovipositor occurs in Thysanura, Orthoptera, Odonata, Hemip- 
 
ANATOMY AND PHYSIOLOGY 
 
 63 
 
 tera, Hymenoptera and some other orders of insects. The ovipositor 
 consists essentially of three pairs of valves, or gonapophyses — a dorsal, a 
 ventral and an inner pair. The two inner valves form a channel through 
 which the eggs are conveyed. In Tettigoniidai (Fig. 81) the three 
 J ^ 5 ^ valves of each side are held to- 
 
 gether by tongues and grooves, 
 which, however, permit sliding 
 
 Fig. 79. — Abdomen of female beetle, Cer- 
 ambyx, in which the last three segments are 
 used as an ovipositor. — After Kolbe. 
 
 Fig. 80. — Abdomen of a female midge, 
 Dasyneura leguminicola, to show the 
 pseudo -ovipositor. 
 
 movements to take place. Most authorities have found that the 
 gonapophyses belong to the segmental series of paired appendages — 
 are homodynamous with limbs — and pertain commonly to abdominal 
 
 Fig. 81. — Ovipositor of Phasgonura. — A, lateral aspect; B, ventral aspect; C, transverse 
 section; c, cerci; d, dorsal valve; i, inner valve; v, ventral valve. The numbers refer to ab- 
 dominal segments. — After Kolbe and Dewitz. 
 
 segments eight, nine and ten; though there are different views in 
 regard to this. 
 
 The ovipositor attains its greatest complexity in Hymenoptera, in 
 which it becomes modified for sawing, boring or stinging. In Sirex (Fig. 
 
64 
 
 ENTOMOLOGY 
 
 82) the inner valves are united; in Apis the dorsal valves are represented 
 by a pair of palpi, the inner valves unite to form the sheath (Fig. 83, B), 
 and the ventral two form the darts, each of which has ten barbed teeth 
 behind its apex, which tend to prevent the with- 
 drawal of the sting from a wound. The action of 
 the sting, as described by Cheshire, is rather com- 
 plex. Briefly, the sheath serves to open a wound 
 and to guide the darts; these strike in alternately, 
 interrupted at intervals by the deeper plunging of 
 the sheath (Fig. 83, A). The poison of the honey 
 bee is secreted by two glands, one acid and the 
 other alkaline. The former (Fig. 84) consists of a 
 glandular region which secretes formic acid, of a 
 reservoir, and a duct that empties its contents into 
 the channel of the sheath. The alkaline gland also opens into the reser- 
 voir. It is said that both fluids are necessary for a deadly effect; and 
 that in insects which simply paralyze their 
 prey, as the solitary wasps, the alkaline 
 glands are functionless. 
 
 Fig. 82. — Cross-sec- 
 tion of the ovipositor of 
 Sir ex. c, channel; d, 
 d, dorsal valves; i, 
 united inner valves; v, 
 V, ventral valves.— After 
 Taschenberg 
 
 Fig. 83. — Sting of honey bee. A, i, 2, 3, posi- 
 tions in three successive thrusts; s, sheath. B, 
 cross-section; c, channel; i, united inner valves, 
 forming the sheath; v, v, ventral valves, or darts. — 
 A, after Cheshire; B, after Penger. 
 
 Fig. 84. — Sting and poison appara- 
 tus of honey bee. ag, accessory gland ; 
 p, palpus; pg, poison gland (formic 
 acid); r. reservoir; s, sting. — After 
 Kraepelin. 
 
 Male Genitalia. — The penis may be hollow or else solid, and in the 
 latter case the contents of the ejaculatory duct are spread upon its 
 surface. Morphologically, the male gonapophyses correspond to those 
 of the female. The penis (Fig. 85) represents the two inner valves of 
 the ovipositor and is frequently enclosed by one or two pairs of valves. 
 
ANATOMY AND PHYSIOLOGY 
 
 6S 
 
 In Ephemerida the two inner valves are partly or entirely separate 
 from each other, forming two intromittent organs (Fig. 86) . 
 
 In male Odonata, the ejaculatory duct opens on the ninth abdominal 
 segment, but the copulatory organ is placed on the under side of the sec- 
 ond segment, to which the spermatozoa are transferred by the bending 
 of the abdomen. At copulation, the abdominal claspers of the male 
 grasp the neck of the female, and the latter bends her abdomen forward 
 until the tip reaches the pecuHar copulatory apparatus of the male. 
 
 The claspers of the male consist of a single pair, variously formed. 
 They are present in Ephemerida, Neuroptera, Trichoptera, Lepidoptera 
 (Fig. 87), Diptera and some Hymenoptera, though not in Coleoptera, 
 and often afford good specific characters, as in Odonata. In butterflies 
 of the genus Thanaos, the claspers are pecuHar in being strongly 
 asymmetrical. In Odonata (Fig. 88, A) and Orthoptera (Fig. 89, A) 
 the superior appendages of the male often serve as claspers. 
 
 In many insects the tergum of the last abdominal segment forms a 
 small suranal plate (Fig. 89, B, sp); this sometimes supplements the 
 claspers of the male in their function, as in Lepidoptera (Fig. 87, A, s). 
 
 2. Integument 
 
 Insects excel all other animals in respect to adaptive modifications of 
 the integument. No longer a simple limiting membrane, the integu- 
 
 FiG. 85. — Extremity of abdomen of a 
 male beetle, Hydrophilus, ventral aspect, g, 
 genitalia; p, penis; v^, v', pairs of valves 
 enclosing the penis; 6-9, sterna of abdominal 
 segments. — Aiter Kolbe. 
 
 '■■-.A^ 
 
 
 1: 
 
 
 H 
 
 1 
 
 c 
 
 \ 
 
 c M 
 
 
 \\ ^ 
 
 m 
 
 
 B 
 
 Fig. 86. — Extremity of abdomen of a 
 male May fly, Hexagenia variabilis, ventral 
 aspect, c, c, c, cerci and pseudocercus (medi- 
 an); cl, cl, claspers; i, i, intromittent organs. 
 
 ment has become hardened into an external skeleton, evaginated to 
 form manifold adaptive structures, such as hairs and scales, and 
 
66 
 
 ENTOMOLOGY 
 
 invaginated, along with the underlying cellular layer, to make glands of 
 various kinds. 
 
 Chitin. — The skin, or cuticula,^ of an insect differs from that of a 
 worm, for example, in being thoroughly permeated with a pecuHar sub- 
 stance known as chitin — the basis of the arthropod skeleton. This is a 
 
 Fig. 87. — Genitalia of a moth, Samia cecropia. A, male; B, female; a, anus; c, c, 
 claspers; o, opening of common oviduct; p, penis; 5, uncus (the doubly hooked organ); 
 V, vestibule, into which the vagina opens. The numbers refer to abdominal segments. 
 
 substance of remarkable stability, for it is unaffected by almost all ordi- 
 nary acids and alkalies, though it is soluble in sodic or potassic hypo- 
 chlorite (respectively, Eau de Labarraque and Eau de Javelle) and 
 yields to boihng sulphuric acid. If kept for a year or so under water, 
 
 Pig. 88. — Terminal abdominal appendages of a dragon fly, Plathemis tri?naculala. A, 
 male; B. female, i, inferior appendage; 5, s, superior appendages. The numbers refer to 
 abdominal segments. 
 
 however, chitin undergoes a slow dissolution, possibly a putrefaction, 
 which accounts in a measure for the rapid disappearance of insect 
 skeletons in the soil (Miall and Denny). By boiling the skin of an 
 insect in potassic hydroxide it is possible to dissolve away the cuticular 
 framework, leaving fairly pure chitin, without destroying the organized 
 
 1 The cuticula of an insect should be distinguished from the cuticle of a vertebrate, the 
 former being a hardened fluid, while the latter consists of cells themselves, in a dead and 
 flattened condition. 
 
ANATOMY AND PHYSIOLOGY 
 
 67 
 
 form of the integument, though less than half the weight of the integu- 
 ment is due to chitin. The formula of chitin is given as CgHuNOa or 
 C18H15NO12 by Krukenberg, and many adopt the formula C15H26N2O10; 
 though no two chemists agree as to the exact proportions of these 
 elements, owing probably to variations in the substance itself in differ- 
 
 89 10 11 
 
 Fig. 89. — Extremity of the abdomen of a grasshopper, Melanoplns differenlialis. A, 
 male- B, female. The terga and sterna are numbered, c, cercus; d, dorsal valves of ovi- 
 positor; e, egg guide; p, podical plate; s, spiracle; sp, suranal plate; v. ventral valves of 
 ovipositor. 
 
 ent insects or even in the same species of insect. Iron, manganese and 
 certain pigments also enter into the composition of the integument. 
 
 Chitin is not peculiar to arthropods, for it has been detected in the 
 set£e and pharyngeal teeth of annelid worms, the shell of Lingula and the 
 pen of the cuttle fish (Krukenberg) . 
 
 The chitinous integument (Fig. 90) of most insects consists of two 
 layers: (i) an outer layer, homogeneous, dense, 
 without lamellae or pore canals, and being the 
 seat of the cuticular colors; (2) an inner layer, 
 "thickly pierced with pore canals, and always 
 in layers of different refractive indices and differ- 
 ent stainability." (Tower.) These two layers, 
 respectively primary and secondary cuticula, are 
 radically different in chemical and physical prop- 
 erties. 
 
 from the hypodermis cells, the primary cuticula ^X^cutic™!!'*:^":: 
 being the first to form and harden. dermis cell; n, nucleus.' — 
 
 The fluid that separates the old from the new ^^*" Tower. 
 cuticula at ecdysis is poured over the hypodermis by certain large special 
 cells, which, according to Tower, "are not true glands, but the setiger- 
 ous cells which, in early Hfe, are chiefly concerned with the formation 
 of the hairs upon the body; but upon the loss of these, the cell takes 
 on the function of secreting the exuvial fluid, which is most copious at 
 
 Fig. 90. — Section 
 through integument of a 
 ^ , , . n •! -• beetle, Chrysobothris. b. 
 
 Each layer arises as a fluid secretion basement membrane; cK 
 
68 
 
 ENTOMOLOGY 
 
 pupation. These cells degenerate in the pupa, and take no part in the 
 formation of the imaginal ornamentation." 
 
 \ 
 
 Fig. 91. — Modifications of the hairs of bees. A, B, Megachile; C, E, F, Colletes; D, Chelos' 
 
 toma. — After Saunders. 
 I 
 
 Histology. — The chitinous cuticula owes its existence to the activity 
 of the underlying layer of hypodermis cells (Fig. 90), a single layer, 
 
 Pig. 92. — Section of antenna of a moth, 
 Salurnia, to show developing hairs, c, cutic- 
 ula; /, formative cell, or trichogen, of hair; 
 h, hypodermis; t, trachea. — After Semper. 
 
 Fig. 93. — Radial section through the 
 base of a hair of a caterpillar, Pieris rapce. 
 c, cuticula; /, formative cell, or trichogen; 
 h, hair; hy, hypodermis. 
 
 Ectodermal in origin. These cells, distinct in embryonic and often in 
 early larval life, subsequently become confluent by the disappearance 
 6i the intervening cell walls, though each cell is still indicated by its 
 
ANATOMY AND PHYSIOLOGY 
 
 69C 
 
 nucleus. The cells are limited outwardly by the cuticula and inwardly, 
 by a delicate, hyaline basement membrane; they contain pigment granules,' 
 fat-drops, etc. 
 
 Externally the cuticula may be smooth, wrinkled, striate, granulate,: 
 tuberculate, or sculptured in numberless other ways; it may be shaped 
 into all manner of structures, some of which are clearly adaptive, while 
 others are unintelligible. 
 
 Hairs, Setae and Spines. — These occur universally, serving a great 
 variety of purposes; they are not always simple in form, but are often 
 toothed, branched or otherwise modified 
 (Fig. 91) . Hairs and bristles are frequently 
 tactile in function, over the general integu- 
 ment or else locally; or olfactory, as on the 
 antennae of moths; or occasionally auditory, 
 as on the antennae of the male mosquito; 
 these and other sensory modifications are 
 described beyond. The hairy clothing of 
 some hibernating caterpillars (as Isia isa- 
 bella) probably protects them from sudden 
 changes of temperature. Hairs and spines 
 frequently protect an insect from its enemies, 
 especially when these structures are glandu- 
 lar and emit a malodorous, nauseous or 
 irritant fluid. Glandular hairs on the pul- 
 villi of many flies, beetles, etc., enable these 
 insects to walk on slippery surfaces. The 
 twisted or branched hairs of bees serve to 
 
 . 1111 11 • • 1 ^ ^J^- 94-— Vanous forms of 
 
 gather and hold pollen grams; m short, scales. A,E,thysa.nnTan,Machi- 
 these simple structures exhibit a surprising ^;^:^SJ::^X:SXi^c^S. 
 variety of adaptive modifications, many of 
 which will be described in connection with other subjects. 
 
 A hair arises from a modified hypodermis cell, formative cell or 
 trichogen (Fig. 92), the contents of which extend through a pore canal 
 into the interior of the hair (Fig. 93) ; sometimes, to be sure, as in 
 glandular or sensory hairs, the hair cell is multinucleate, representing, 
 therefore, as many cells as there are nuclei. The wall of a hair is 
 continuous with the general cuticula and at moulting each hair is 
 stripped off with the rest of the cuticula, leaving in its place a new hair, 
 which has been forming inside the old one. 
 
 Scales. — Besides occurring throughout the order Lepidoptera and 
 in numerous Trichoptera, scales are found in many Thysanura and 
 
70 
 
 ENTOMOLOGY 
 
 Fig. 95. — Cross-section of scale 
 Anosia. — After Mayer. 
 
 Collembola, several families of Coleoptera (including Dermestidae, 
 Cerambycidae and Curculionidae) , a few Diptera and a few Psocidae. 
 
 Though diverse in form (Fig. 94) , scales are essentially flattened sacs 
 having at one end a short pedicel for attachment to the integument. 
 The scales usually bear markings, which are more or less characteristic 
 
 of the species; these markings, always 
 minute, are in some species so exqui- 
 sitely fine as to test the highest powers 
 of the microscope; the scales of certain 
 Collembola {Lepidocyrtus, etc.) have long 
 been used, under the name of " Podura " scales, to test the resolving power 
 of objectives, for which purpose they are excelled only by some of the 
 diatoms. Butterfly scales are marked with parallel longitudinal 
 ridges (Fig. 94, C), which are confined almost entirely to the upper, or 
 exposed, surface of the scale (Fig. 95) and number from 33 or less 
 (Anosia) to 1,400 {Morpho) to each scale, the striae being in the latter 
 genus from .002 mm. to .0007 mm. 
 
 apart (Kellogg) ; between these longi- ^ ^ ^ ( 
 
 tudinal ridges may be discerned 
 delicate transverse markings. Inter- 
 nally, scales are hollow and often 
 contain pigments derived from the 
 blood. 
 
 On the wing of a butterfly the 
 scales are arranged in regular rows and 
 overlap one another, as in Fig. 96 ; in 
 the more primitive moths and in Tri- 
 choptera, however, their distribution 
 is rather irregular. 
 
 A scale is the equivalent of a hair, 
 
 for (l) a complete series of transitions ^^^- 96.— Arrangement of scales on the 
 - , . , , wing of a butterfly, Papilio. 
 
 from hairs to scales may be found on 
 
 a single individual (Fig. 97) ; and (2) hairs and scales agree in their man- 
 ner of development, as shown by Semper, Schaffer, Spuler, Mayer and 
 others. Both hairs and scales arise as processes from enlarged hypo- 
 dermis cells, or formative cells (Fig. 98). The scale at first contains 
 protoplasm, which gradually withdraws, leaving short chitinous strands 
 to hold the two membranes of the scale together. 
 
 Uses of Scales. — Among Thysanura and Collembola, scales occur 
 only on such species as live in comparatively dry situations, from which 
 
ANATOMY AND PHYSIOLOGY 
 
 71 
 
 it may be inferred that the scales serve to retard the evaporation of mois- 
 ture through the delicate integument of these insects. This inference is 
 
 Fig. 97. — Hairs and scales of a moth, Samia cecropia. 
 
 supported by the fact that none of the scaleless Collembola can live long 
 in a dry atmosphere; they soon shrivel and die even under conditions 
 
 Fig. 98. — Development of butterfly scales. FiG. 99. — Androconia of butterflies. A, 
 A. Vanessa; B, Anosia. 6, basement mem- Pieris rapm; B, Everes comyntas. 
 
 brane; /, formative cell; h, hypodermis; s, 
 scale. — After Mayer. 
 
 of dryness which the scaled species are able to withstand. In Lepidop- 
 tera the scales are possibly of some value as a mechanical protection; 
 
72 
 
 ENTOMOLOGY 
 
 they have no injfluence upon flight, as Mayer has proved, and appear to 
 be useful chiefly as a basis for the development of color and color 
 patterns — which are not infrequently adaptive. 
 
 Androconia. — The males of many butterflies, and the males only, 
 have peculiarly shaped scales known as androconia (Fig. 99) ; these are 
 commonly confined to the upper surfaces of the front wings, where they 
 are mingled with the ordinary scales or else are disposed in special 
 patches or under a fold of the costal margin of the wing (Thanaos). 
 The characteristic odors of male butterflies have long been attributed 
 to these androconia, and M. B. Thomas has found that the scales arise 
 
 Fig. 100. — Section across tarsus of a beetle, 
 Hylobius, to show bulbous glandular hairs. — 
 
 After SiMMERMACHER. 
 
 Fig. ioi. — Stinging hair of a caterpillar, 
 Gaslropacha. c, cuticula; g, gland cell; h, 
 hair; hy, hypodermis. — After Claus. 
 
 from glandular cells, which doubtless secrete a fluid that emanates 
 from the scale as an odorous vapor, the evaporation of the fluid being 
 facilitated by the spreading or branching form of the androconium. 
 Similar scales occur also on the wings of various moths and some 
 Trichoptera {Mystacides) . 
 
 Glands. — A great many glands of various form and function have 
 been found in insects. Most of these, being formed from the hypoder- 
 mis, may logically be considered here, excepting some which are inti- 
 mately concerned with digestion or reproduction. 
 
 Glandular Hairs and Spines. — The presence of adhesive hairs on 
 the empodium of the foot of a fly enables the insect to walk on a smooth 
 surface and to walk upside down; these tenent hairs emit a transparent 
 sticky fluid through minute pore canals in their apices. The tenent 
 hairs of Hylobius (Fig. 100) are each supplied with a flask-shaped unicel- 
 lular gland, the glutinous secretion of which issues from the bulbous 
 
ANATOMY AND PHYSIOLOGY 73 
 
 extremity of the hair. Bulbous tenent hairs occur also on the tarsi of 
 Collembola, Aphididas and other insects. 
 
 Nettling hairs or spines clothe the caterpillars of certain Saturniida) 
 {Automeris), Liparidae, etc. These spines (Fig. loi), which are sharp, 
 brittle and filled with poison, break to pieces when the insect is handled 
 and cause a cutaneous irritation much like that made by nettles. In 
 Lagoa crispata (Fig. 102) the irritating fluid 'is secreted, as is usual, by 
 several large hypodermal cells at the base of each spine. These irritating 
 hairs protect their possessors from almost all birds except cuckoos. 
 
 Repellent Glands. — The various offensive fluids emitted by insects 
 are also a highly effective means of defense against birds and other in- 
 sectivorous vertebrates as well as against predace- 
 ous insects. The blood itself serves as a repellent 
 fluid in the oil-beetles (Meloidae) and Coccinellidae, 
 issuing as a yellow fluid from a pore at the end of 
 the femur. The blood of Meloidae (one species of 
 which is still used medicinally under the name of 
 ''Spanish Fly") contains cantharidine, an extremely 
 caustic substance, which is an almost perfect pro- 
 tection against birds, reptiles and predaceous insects. 
 Coccinellidae and Lampyridae are similarly exempt from 
 attack. Larvae of Cimbex when disturbed squirt 
 jets of a watery fluid from glands opening above the Fig. 102.— sting- 
 spiracles. Many Carabid^ eject a pungent and often ':^:!Z^:S^_ 
 corrosive fluid from a pair of anal glands (Fig. —After Packard. 
 148); this fluid in Brachinus, and occasionally 
 in Galerita janus and a few other carabids, volatilizes explosively 
 upon contact with the air. When one of these ''bombardier-beetles" 
 is molested it discharges a puff of vapor, accompanied by a distinct 
 report, reminding one of a miniature cannon, and this performance 
 may be repeated several times in rapid succession; the vapor is acid and 
 corrosive, staining the human skin a rust-red color. Individuals of a 
 large South American Brachinus when seized "immediately began to 
 play off their artillery, burning and staining the flesh to such a degree 
 that only a few specimens could be captured with the naked hand, 
 leaving a mark which remained for a considerable time." (Westwood.) 
 
 As malodorous insects, Hemiptera are notorious, though not a few 
 hemipterous odors are (apart from their associations) rather agreeable 
 to the human olfactory sense. Commonly the odor is due to a fluid 
 frorfi a mesothoracic gland or glands, opening between the hind coxae. 
 
74 
 
 ENTOMOLOGY 
 
 Eversible hypodermal glands of many kinds are common in larvae of 
 Coleoptera and Lepidoptera. The larvae of Lina lap_ponica, among 
 other Chrysomelidae, evert numerous paired vesicles which emit a 
 peculiar odor. The caterpillars of our Papilio butterflies, upon being 
 irritated, evert from the prothorax a yellow Y-shaped osmeterium (Fig. 
 
 <■: 
 
 Pig. 103. — Osmeterium of Papilio Pig. 104.— Ventralaspectofworke^honeybee,show- 
 /)oZy«:en«. ing the four pairs of wax scales. — After Cheshire. 
 
 103) which diffuses a characteristic but indescribable odor that is 
 probably repellent. The larva of Cerura everts from the under side of 
 the neck a curious spraying apparatus which discharges formic acid. 
 
 ^ Alluring Glands.^Odors are 
 
 '■• ' largely used among insects to 
 
 attract the opposite sex. The 
 androconia of male butterflies 
 have already been spoken of. 
 Males of Catocala concumhens dis- 
 seminate an alluring odor from 
 scent tufts on the middle legs. 
 Female saturniid moths (as cecro- 
 pia and promethea) entice the 
 males by means of a characteris- 
 tic odor emanating from the ex- 
 tremity of the abdomen. In 
 lycaenid caterpillars, an eversible 
 sac on the dorsum of the seventh abdominal segment secretes a sweet 
 fluid, for the sake of which these larvae are sought out by ants. 
 
 Wax Glands. — Wax is secreted by insects of several orders, but es- 
 pecially Hymenoptera and Hemiptera. In the worker honey bee the 
 wax exudes from unicellular hypodermal glands and appears on the 
 
 Fig. 105. — Head of caterpillar of Samia 
 cecropia. a, antenna; c, clypeus; I, labrum; 
 Ip, labial palpus; m, mandible; mp, maxillary 
 palpi; o, ocelli; s, spinneret. 
 
ANATOMY AND PHYSIOLOGY 75 
 
 under side of the abdomen as four pairs of wax scales (Fig. 104), on 
 the last four of the six evident segments of the abdomen (Dreyling). 
 Plant lice of the genus Schizoneura owe their woolly appearance to dense 
 white filaments of wax, which arise from glandular hypodermal cells. 
 In scale insects, waxen threads, emerging from cuticular pores, become 
 matted together to form a continuous shield over and often under the 
 insect itself, the cast skins often being incorporated into this waxen 
 scale. The wax glands in Coccidae are simply enlarged hypodermis 
 cells. 
 
 Some coccids produce wax in quantities sufficient for commercial 
 use. Thus species of Ceroplastes (and certain fulgorids as well) in 
 India and China yield a white wax that is used for making candles and 
 for other purposes. 
 
 The lac-insect, Tachardia lacca, of India, a scale insect Uving on 
 more than ninety species of trees and shrubs {Acacia, Ficus, Zizyphus, 
 etc.), furnishes the lac from which shellac, lacquer and other varnishes 
 are made. The raw lac is the scale, or shell, of the female insect (the 
 male producing scarcely any lac) and consists of a yellow to reddish 
 brown resinous exudation containing considerable wax, along with the 
 cast skins of the insect. From this material the commercial products 
 are extracted. 
 
 Silk Glands.^Larvae of very diverse orders spin silk, for the purpose 
 of making cocoons, webs, cases, and supports of one kind or another. 
 Silk glands, though most characteristic of Lepidoptera and Trichoptera, 
 oceur also in the cocoon-spinning larvae of not a few Hymenoptera 
 (saw flies, ichneumons, wasps, bees, etc.), in Diptera (Itonididae), 
 Siphonaptera, Neuroptera (Chrysopidae, Myrmeleonidae) , and in 
 various larvae whose pupae are suspended from a silken support, as in 
 the coleopterous families Coccinelhdae and Chrysomelidae (in part) 
 and the dipterous family Syrphidae, as well as most diurnal Lepidoptera. 
 
 The silk glands of caterpillars are homologous with the true saHvary 
 glands of other insects, opening as usual through the hypopharynx, 
 which is modified to form a spinning organ, or spinneret (Fig. 105). 
 The silk glands of Lepidoptera are a pair of long tubes, one on each side 
 of the body, but often much longer than the body and consequently 
 convoluted. Thus in the silk worm {Bomhyx mori) they are from four 
 to five times as long as the body and in Telea polyphemus, seven times 
 as long. In the silk worm the convoluted glandular portion of each 
 tube (Fig. 106) opens into a dilatation, or silk reservoir, which in turn 
 empties into a slender duct, and the two ducts join into a short common 
 
7-6 
 
 ENTOMOLOGY 
 
 duct, which passes through the tubular spinneret. Two divisions of 
 the spinning tube are distinguished: (i) a posterior muscular portion, or 
 thread-press and (2) an anterior directing tube. The thread-press com- 
 bines the two streams of silk fluid into one, determines the form of the 
 silken thread and arrests the emission of the thread at times, besides 
 having other functions. The silk fluid hardens rapidly upon exposure 
 to the air; about fifty per cent, of the fluid 
 is actual silk substance and the remainder 
 consists of protoplasm and gum, with traces 
 of wax, pigment, fat and resin. 
 
 ( Fig. 106. — Silk glands of the 
 silk worm, Bombyx mori. cd, 
 common duct; d, one of the 
 paired ducts; g, g, Filippi's 
 glands; gl, gland proper; p, 
 thread press; r, reservoir. 
 
 Fig. 107. — Sections of silk gland of the silk worm. 
 A, radial; B, transverse, b, basement membrane; i, 
 intima; 5, glandular cell with branched nucleus. — 
 After Helm. 
 
 A transverse or radial section of a silk gland shows a layer of glandu- 
 lar epithehal cells, with the usual intima and basement membrane (Fig. 
 107) ; the cells are remarkably large and their nuclei are often branched; 
 the intima is distinctly striated, from the presence of pore-canals. The 
 glands arise as evaginations of the pharynx (ectodermal) and the chi- 
 tinous intima of each gland is cast at each moult, along with the general 
 integument. 
 
ANATOMY AND PHYSIOLOGY 
 
 7.7 
 
 The silk glands of caddis worms (Trichoptera) are essentially like 
 those of caterpillars (Lepidoptera) but the glands of Neuroptera 
 {Chrysopa, Myrmeleon, etc.) Coccinellidae, Chrysomelidae and Syrphidae, 
 which open into the rectum, are morphologically quite different frorti 
 those of Lepidoptera. 
 
 3. Muscular System 
 
 The number of muscles possessed by an insect is surprisingly large. 
 A caterpillar, for example, has about two thousand. 
 
 The muscles of the trunk are segmentally arranged — most evidently 
 
 abc 
 
 Fig. 108. Fig. 109. Fig. iio. 
 
 Muscles of cockroach; of ventral, dorsal and lateral walls, respectively, a, alary muscle; 
 abc, abductor of coxa; adc, adductor of coxa; ef, extensor of femur; h, head muscles; Is, 
 longitudinal sternal; It, longitudinal tergal; Ith, lateral thoracic; os, oblique sternal; ot, 
 oblique tergal; ts, tergo-stemal; ts^, first tergo-sternal. After Miall and Denny. 
 
 SO in the body of a larva or the abdomen of an imago, where the muscu- 
 lature is essentially the same in several successive segments. In the 
 thoracic segments of an imago, however, the musculature is, at first 
 sight, unlike that of the abdomen, and in the head it is decidedly- 
 different; though future studies will doubtless show that the thoracit 
 and cephalic kinds of musculature are only modifications of the simplet 
 abdominal type — modifications brought about in relation to the needs 
 of the legs, wings, mouth parts, antennse and other movable structures. 
 The muscular system has been generally neglected by students of 
 insect anatomy; the only comprehensive studies upon the subject being 
 
78 
 
 ENTOMOLOGY 
 
 ^ii 
 
 m 
 
 ^^ 
 
 
 Striated muscle chitinous tendons 
 
 fiber of an insect. 
 
 each of which has 
 
 those of Straus-Diirckheim (1828) on the beetle Melolontha; Lyonet 
 (1762), Newport (1834) and Lubbock (1859) on caterpillars; Lubbock 
 and Janet on Hymenoptera; Bauer (1910) on Dytiscus; and Berlese 
 (1909-13) on various insects. 
 
 The more important muscles in the body of a cockroach 
 are represented in Figs. 108-110, from Miall and Denny. 
 The longitudinal sternals with the longitudinal tergals act 
 to telescope the abdominal segments; the oblique ster- 
 nals bend the abdomen laterally; the ter go sternals, or 
 vertical expiratory muscles, draw the tergum and sternum 
 together. The muscles of the legs and the wings have 
 already been referred to. 
 
 Structure of Muscles. — The muscles of insects differ 
 greatly in form and are inserted frequently by means of 
 A muscle is a bundle of long fibers, 
 an outer elastic membrane, or 
 sarcolemma, within which are several nuclei; thus the fiber represents 
 several cells, which have become confluent. With rare exceptions 
 ("alary" muscles and possibly a few thoracic muscles) the muscle fibers 
 of an insect present a striated appear- 
 ance, owing to alternate light and dark 
 bands (Fig. 1 1 1) , the former being singly 
 refracting, or isotropic, and the latter 
 doubly refracting, or anisotropic. 
 
 The minute structure of these fibers, 
 being extremely difficult of interpreta- 
 tion, has given rise to much difference of 
 opinion. The most plausible view is 
 that of van Gehuchten, Janet and others, 
 who hold that both kinds of dark bands 
 (Fig. 112) consist of highly elastic threads 
 of spongioplasm (anisotropic) embedded 
 in a matrix of clear, semi-fluid, nutritive 
 hyaloplasm (isotropic). The spongio- 
 plasmic threads of the long bands extend 
 
 longitudinally and those of the short bands {"Krause's membrane'') 
 radially, in respect to the form of the fiber. Moreover, the attenuated 
 extremities of the longitudinal fibrillae connect with the radial fibrill^, 
 the points of connection being marked by sHght thickenings, or nodes, 
 which go to make up Krause's membrane. 
 
 Fig. 112. — Minute structure of a 
 striated muscle fiber. A , longitudinal 
 section; B, transverse section in the 
 region of I; C, transverse section in the 
 region of n. I, longitudinal fibrillas; 
 n, Krause's membrane; nl, nucleus; 
 r, radial fibrillae; 5, sarcolemma. — After 
 Janet. 
 
ANATOMY AND PHYSIOLOGY 79 
 
 Under nervous stimulus a muscle shortens and thickens because its 
 component fibers do, and this in turn is attributed to the shortening and 
 thickening of the longitudinal fibrillar. When the stimulus ceases, the 
 radial fibrillae, by their elasticity, possibly pull the longitudinal ones 
 back into place. The last word has not been said, however, upon this 
 perplexing subject. 
 
 Muscular Power. — The muscular exploits of insects appear to be 
 marvellous beside those of larger animals, though they are often exag- 
 gerated in popular writings. The weakest insects, according to Plateau, 
 can pull five times their own weight and the average insect, over twenty 
 times its weight, while Donacia (ChrysomeHdae) can pull 42.7 times its^ 
 weight. As contrasted with these feats, a man can pull in the same 
 fashion but 0.86 of his weight and a horse from 0.5 to 0.83. How are 
 these differences explained? 
 
 It is incorrect to say that the muscles of insects are stronger than 
 those of vertebrates, for, as a matter of fact, the contractile force of a 
 vertebrate muscle is greater than that of an insect muscle, other things 
 being equal. The apparently greater strength of an insect in propor- 
 tion to its weight is accounted for in several ways. The specific gravity 
 of chitin is less than that of bone, though it varies greatly in both sub- 
 stances. Furthermore, the external skeleton permits muscular attach- 
 ments of the most advantageous kind as compared with the internal 
 skeleton, so that the muscles of insects surpass those of vertebrates as 
 regards leverage. These reasons are only of minor importance, how- 
 ever. Small animals in general appear to be stronger than larger 
 animals (allowing for the differences in weight) for the same reason that 
 a smaller insect has more conspicuous strength than a larger one, when 
 the two are similar in everything except weight. For example : where 
 a bumblebee can pull 16.1 times its own weight, a honey bee can pull 
 20.2; and where the same bumblebee can carry while flying a load 
 0.63 of its own weight, the honey bee can carry 0.78. Always, as 
 Plateau has shown, the lighter of two insects is the stronger in respect 
 to external manifestations of muscular force — in the ratio of this muscu- 
 lar strength to its own weight. 
 
 To understand this, let us assume that a beetle continues to grow (as 
 never happens, of course). As its weight is increasing so is its strength 
 — but not in the same proportion. For while the weight — say that of a 
 muscle — increases as the cube of a single dimension, the strength of the 
 muscle (depending solely upon the area of its cross-section) is increasing 
 only as the square of one dimension — its diameter. Therefore the 
 
8o ENTOMOLOGY 
 
 increase in strength lags behind that of weight more and more; conse- 
 quently more and more strength is required simply to move the insect 
 itself, and less and less surplus strength remains for carrying additional 
 weight. Thus the larger insect is apparently the weaker, though 
 it is actually the stronger, in that its total muscular force is greater. 
 
 The writer uses this explanation to account also for the inability of 
 certain large beetles and other insects to use their wings, though these 
 organs are well developed. Increasing weight (due to a larger supply 
 of reserve food accumulated by the larva) has made such demands upon 
 the muscular power that insufhcient strength remains for the purpose of 
 flight. 
 
 Statements such as this are often seen — a flea can jump a meter, or 
 six hundred times its own length. Almost needless to say, the length of 
 the body is no criterion of the muscular power of an animal. 
 
 4. Nervous System 
 
 The central nervous system extends along the median line of the floor 
 of the body as a series of ganglia connected by nerve cords. Typically, 
 there is a ganglion (double in origin) for each primary segment, and the 
 connecting cords, or commissures, are paired; these conditions are most 
 nearly realized in embryos and in the most generalized insects — Thysa- 
 nura (Fig. 113). In all adult insects, however, the originally separate 
 gangha consolidate more or less (Fig. 114) and the commissures fre- 
 quently unite to form single cords. Thus in Tabanus (Fig. 1 14, C) the 
 three thoracic gangha have united into a single compound ganglion 
 and the abdominal ganglia are concentrated in the anterior part of the 
 abdomen; in the grasshopper, the nerve cord, double in the thorax, is 
 single in the abdomen. Various other modifications of the same nature 
 occur. 
 
 Cephalic Ganglia. — In the head the primitive .ganglia always unite 
 to form two compound ganglia, namely, the brain and the sub (esophageal 
 ganglion (disregarding a few anomalous cases in which the latter is said 
 to be absent). 
 
 The brain, or supra oesophageal ganglion (Fig. 115), is formed by the 
 union of three primitive ganglia, or neuromeres (Fig. 57), namely, (i) 
 the protocerebrum, which gives off the pair of optic nerves; (2) the deuto- 
 cerebrum, which innervates the antennae; and (3) the tritocerebrum, 
 which in Apterygota bears a pair of rudimentary appendages that are 
 regarded as traces of a second pair of antennae. 
 
ANATOMY AND PHYSIOLOGY 
 
 The suboesophageal ganglion (Fig. 115) is al- 
 ways connected with the brain by a pair of nerve 
 cords {cesephageal commissures) between which 
 the oesophagus passes. This ompound ganglion 
 represents at most four neuromeres: (i) mandi- 
 bular, innervating the mandibles; (2) superlin- 
 gual, found by the author in Collembola, but not 
 yet reported in the less generahzed insects; (3) 
 maxillary, innervating the maxilte; (4) labial, 
 which sends a pair of nerves to the labium. 
 
 The minute structure of the brain, thgouh 
 highly complex, has received considerable study, 
 but will not be described here for the reason that 
 the anatomical facts are of no general interest 
 so long as their physiological interpretation re- 
 mains obscure. 
 
 Sympathetic System. — ^Lying along the 
 median dorsal line of the oesophagus is a recurrent, 
 or stomato gastric, nerve Fig. 116), which arises 
 anteriorly in a frontal ganglion and terminates 
 posteriorly in a stomachic ganglion situated at 
 the anterior end of the mid intestine. Con- 
 nected with the recurrent nerve are two pairs of 
 lateral gangha, the anterior of which innervate 
 the dorsal vessel and the posterior, the tracheae 
 of the head. The ventral nerve cord may include 
 also a median nerve thread (Fig. 113) which gives 
 oft" paired transverse nerves to the muscles of 
 the spiracles. 
 
 Structure of Ganglia and Nerves. — A gang- 
 lion consists of (i) a dense cortex, composed of 
 ganglion cells (Fig. 117), each of which has a large 
 rounded nucleus and gives off usually a single 
 nerve fiber; and (2) a clear medullary portion 
 (Punktsubstanz) derived from the processes of the 
 cortical ganglion cells and serving as the place 
 of origin of nerve fibrillas. There are, however, 
 ganglion cells from which processes may pass 
 directly into nerve fibrillae. 
 
 A nerve fiber, in an insect, consists of an axis- 
 cylinder, composed of fibrillae, and an enveloping 
 membrane, or sheath. The axis-cylinder is the 
 transmitting portion and the ganglia are the 
 
 b-W- 
 
 S"' 
 
 ■sy 
 
 III 
 
 Fig. 113. — Central nerv- 
 ous system of a thysanu- 
 ran, Machilis. The 
 
 thoracic and abdominal 
 ganglia are numbered in 
 succession. a, antennal 
 nerve; b, brain; e, com- 
 pound eye; /, labial nerve; 
 m, mandibular nerve;- mx, 
 maxillary nerve; o, ceso- 
 phagus; ol, optic lobe; s, 
 suboesophageal ganglion; 
 sy, sympathetic nerve. — 
 After GuDEMANS. 
 
82 
 
 ENTOMOLOGY 
 
 trophic centers, i. e., they regulate nutrition. A nerve is always 
 either sensory, transmitting impulses inward from a sense organ; or 
 
 Fig. 114. — Successive stages in the concentration of the central nervous system of Diptera. 
 A, Chironomus; B, Empis; C, Tabanus; D, Sarcophaga. — After Brandt. 
 
 else motor, conveying stimuli from the central nervous system outward 
 to muscles, glands, or other organs. 
 
 Functions." — The brain innervates the chief sensory organs (eyes and 
 antennae) and converts the sensory stimuli that it receives into motor 
 
 Pig. 115. — Nervous system of the head of a cockroach, a, antennal nerve; ag, anterior 
 lateral ganglion of sympathetic system; b, brain; d, salivary duct; /, frontal ganglion; h, 
 hypopharynx; I, labrum; li, labium; m, mandibular nerve; mx, maxillary nerve; nl, nerve to 
 labrum; nli, nerve to labium; o, optic nerve; oc, oesophageal commissure; oe, oesophagus; 
 pg, posterior lateral ganglion of sympathetic system; r, recurrent nerve of sympathetic 
 system; s, suboesophageal ganglion. — After Hofer. 
 
 stimuli, which effect co-ordinated muscular or other movements in 
 response to particular sensations from the environment. The brain 
 is the seat of the will, using the term "will" in a loose sense; it directs 
 locomotor movements of the legs and wings. An insect deprived of its 
 
ANATOMY AND PHYSIOLOGY 
 
 83 
 
 brain cannot go to its food, though it is able to eat if food be placed in 
 contact with the end-organs of taste, as those ^^ ^ 
 
 of the palpi ; furthermore, it walks or flies in an 
 erratic manner, indicating a lack of co-ordina- 
 tion of muscular action. 
 
 The suboesophageal ganglion controls the 
 mouth parts, co-ordinating their movements as 
 well as some of the bodily movements. 
 
 The thoracic ganglia govern the appendages 
 of their respective segments. These ganglia 
 and those of the abdomen are to a great extent 
 independent of brain control, each of these 
 ganglia being an individual motor center for 
 its particular segment. Thus decapitated in- 
 sects are still able to breathe, walk or fly, and 
 often retain for several days some power of 
 movement. 
 
 In regard to the sympathetic system, it 
 has been shown experimentally that the fron- 
 tal ganglion controls the swallowing movements 
 and exerts through the stomatogastric nerve 
 a regulative action upon digestion. The dor- 
 sal sympathetic system controls the dorsal 
 vessel and the salivary glands, while the 
 ventral sympathetic system is concerned with 
 the spiracular muscles. 
 
 5. Sense Organs 
 For the reception of sensory impressions 
 from the external world, the armor-Hke integu- 
 ment of insects is modified in a great variety of ways. Though sense 
 
 Fig. 116.— Sympathetic nerv- 
 ous system of an insect, 
 diagrammatically represented. 
 a, antennal nerve; b, brain; /,■ 
 frontal ganglion; I, I, paired 
 lateral ganglia; m, nerves to 
 upper mouth parts; o, op- 
 tic nerve; r, recurrent 
 nerve; 5, nerve to saUvary 
 glands; st, stomachic ganglion. 
 — After KoLBE. 
 
 Fig. 117.— Transverse section of an abdominal gangUon of a caterpillar. /, nerve fibers; g, 
 gangUon cells; w, nerve sheath; p, Punktsubstanz. 
 
84 ENTOMOLOGY 
 
 organs of one kind or another may occur on almost any part of an 
 insect, they are most numerous and varied upon the head and its appen- 
 dages, particularly the antennae. 
 
 Anteimal Sensilla. — Some idea of the diversity of form in antennal 
 sense organs may be obtained from Figs. 1 18-127, taken from a paper 
 by Schenk, whose useful classification of antennal sensilla, or sense 
 organs, is here outlined: 
 
 1. Sensillum cceloconicum — a conical or peg-like projection immersed 
 in a pit (Figs. 118, 119). In all probability olfactory. 
 
 2. S. hasiconicum — a cone projecting above the general surface (Fig. 
 120). Probably olfactory. 
 
 3. S. styloconicum — a terminal tooth or peg seated upon a more or 
 less conical base (Fig. 121). Olfactory. 
 
 4. S. chaticum — a bristle-like sense organ (Fig. 122). Tactile. 
 
 5. S. trichodeum — a hair-hke sense organ (Figs. 123, 124). Tactile. 
 
 6. S. placodeum — a membranous plate, its outer surface continuous 
 with the general integument (Fig. 125). Function doubtful; not audi- 
 tory and probably not olfactory, though the function is doubtless a 
 mechanical one; Schenk suggests that this organ is affected by air 
 pressure, as when a bee or wasp is moving about in a confined space. 
 
 7. S. ampullaceum — a more or less flask-shaped cavity with an 
 axial rod (Figs. 126, 127). Probably auditory. 
 
 These types of sensilla will be referred to in physiological order. 
 
 Touch.^The tactile sense is highly developed in insects, and end- 
 organs of touch, unlike those of other senses, are commonly distributed 
 over the entire integument, though the antennae, palpi and cerci are 
 especially sensitive to tactile impressions. 
 
 The end-organs of touch are bristles (sensilla chastica) or hairs 
 (sensilla trichodea), each arising from a special hypodermis ceU and 
 having connection with a nerve. SensiUa chsetica doubtless receive 
 impressions from foreign bodies, while sensilla trichodea, being best 
 developed in the swiftest flying insects and least so in the sedentary 
 forms, may be affected by the resistance of the air, when the insect or 
 the air itself is in motion. 
 
 Not all the hairs of an insect are sensory, however, for many of them 
 have no nerve connections. 
 
 In blind cave insects the antennae are very long and are exquisitely 
 sensitive to tactile impressions. 
 
 Taste. — The gustatory sense is unquestionably present in insects, as 
 is shown both, by common observation and by precise experimentation. 
 
ANATOMY AND PHYSIOLOGY 
 
 85 
 
 Will fed wasps with sugar and then replaced it with powdered alum, 
 which the wasps unsuspectingly tried but soon rejected, cleaning the 
 tongue with the fore feet in a comical manner and manifesting other 
 
 Figs, i 18-12 7. — Types of antennal sensilla, in longitudinal section (excepting Figs. 121 
 and 122). Fig. 118, sensillum coeloconicum ; 119, coeloconiciim; 120, basiconicum; 121, 
 styloconicum; 122, chaeticum; 123, trichodeum; 124, trichodeum; 125, placodeum; 126, 
 ampuUaceum; 127, ampullaceum; c, cuticula; h, hypodermis; n, nerve; 5. sensory cell. 
 Figs. 118, 120, 123, 125, 126, honey bee, Apis mellifera; 119, 121, 124, Fidonia piniaria; 
 122, moth, Ino pruni; 127 wasp, Vespa crabro. — After Schenk. 
 
 signs of what we may call disgust. Forel offered ants honey mixed with 
 morphine or strychnine; the ants began to feed but at once rejected the 
 mixture. In its range, however, the gustatory sense of insects differs 
 often from that of man. Thus Will found that Hymenoptera refused 
 
86 ENTOMOLOGY 
 
 honey with which a very httle glycerine had been mixed (though Musci- 
 dse did not object to the glycerine) and Forel found that ants ate un- 
 suspectingly a mixture of honey and phosphorus until some of them 
 were killed by it. Under the same circumstances, man would be able 
 to detect the phosphorus but not the glycerine. 
 
 Location of Gustatory Organs. — As would be expected, the end- 
 organs of taste are situated near the mouth, commonly on the hypo- 
 pharynx (Fig. 128), epipharynx and maxillary palpi. On the tongue of 
 the honey bee the taste organs appear externally as short setae (Fig. 129) 
 and on the maxillae of a wasp as pits, each with a cone, or peg, project- 
 ing from its base (Figs. 130, 131). Similar taste pits and pegs were 
 
 Pig. 128. — -Section through tongue of wasp, Vespa vul- Fig. 129. — Tongue of honey 
 
 garis. c, cuticula; g, gland cell; h, hypodermis; «, nerve; hee, Apis mellifera. /», protect- 
 
 ob, gustatory bristle; ph, protecting hair; sc, sensory cell; ing bristles; s, terminal spoon; 
 
 tb, tactile bristle. — After Will. /, taste setae. — After "Will. 
 
 found by Packard on the epipharynx in most of the mandibulate orders 
 of insects. 
 
 Histology. — The end-organs of taste arise from special hypodermis 
 cells, as minute setae or, more commonly, pegs, each seated in a pit, or 
 cup, and connected with a nerve fiber (Figs. 131, 132). In some cases, 
 however, it is difficult to decide whether a given organ is gustatory or 
 olfactory, owing to the similarity between these two kinds of structures. 
 In aquatic insects, indeed, the senses of taste and smell are not differen- 
 tiated, these forms having with other of the lower animals simply a 
 "chemical" sense. 
 
 Smell. — In most insects the sense of smell is highly efficient and in 
 many species it is inconceivably acute. Hosts of insects depend chiefly 
 on their olfactory powers to find food, for example many beetles, the 
 flesh flies and the flower-visiting moths; or else to discover the opposite 
 
ANATOMY AND PHYSIOLOGY 
 
 87 
 
 sex, as is notably the case in saturniid moths. In dragon flies, however, 
 this sense is reHed upon far less than that of sight. 
 
 Organs of Smell.^By means of simple but conclusive experiments, 
 Hauser and others have shown that the antennae are frequently olfactory 
 — though not to the exclusion of tactile or auditory functions, of course. 
 Hauser found that ants, wasps, various flies, moths, beetles and larvae, 
 which react violently toward the vapor of turpfentine, acetic acid and 
 other pungent fluids, no longer respond to the same stimuli after their 
 antennae have been amputated or else covered with paraffine to exclude 
 
 the air. His experiments were con- 
 ducted under conditions such that the 
 results could not be ascribed to the shock 
 of the operation or to effects upon the 
 gustatory or respiratory systems; except 
 for having lost the sense of smell, the 
 insects experimented upon behaved in 
 , _ __ a normal manner. It should be said, 
 
 Fig. 130. — Under side of left maxilla 
 of wasp, Vespa vulgaris, p, palpus; 
 pr, protecting hairs; tc, taste cup; th, 
 tactile hair. — After Will. 
 
 Fig. 131. — Longitudinal section of gustatory 
 end-organ (tc, of Pig. 130). c, cuticula; k, hypo- 
 dermis; sc, sensory cell; tc, taste cup. — After 
 Will. 
 
 however, that Carabus, Melolontha and Silpha still reacted to some 
 extent toward strong vapors even after the extirpation of the antennae; 
 while in Hemiptera the loss of the antennae did not lessen the response 
 to the odors used. These facts indicate that the sense of smell is not 
 always confined to the antennae; indeed the maxillary palpi are frequently 
 olfactory, as in Silpha and Hydaticus; also the cerci, as in the cock- 
 roach and other Orthoptera. Experiments indicate that an insect per- 
 ceives some odors by means of the antennae and others by the palpi 
 or other organs. Hauser found that the flies Sarcophaga and Calli- 
 phora, after the amputation of their antennae, became quite indifferent 
 toward decayed meat, to which they had previously swarmed with 
 
88 ENTOMOLOGY 
 
 great persistence, though their actions in all other respects remained 
 normal. Males of many moths and a few beetles are unable to find 
 the females (see beyond) when the former are deprived of the use of 
 their antennae. 
 
 Fig. 132. — Taste cup from maxilla of 
 Bombus. sc, sensory cell; n, nerve. — After 
 Will. 
 
 Fig. 133. — Section of antennal olfactory 
 organ of grasshopper, Caloptenus. c, cutic- 
 ula; m, membrane; n, nucleus of sensory 
 cell; nv, nerve; p, pit with olfactory peg, 
 pg, pigment. — After Hauser. 
 
 End-Organs. — Structures which are . regarded as olfactory end- 
 organs occur commonly on the antennae, often on the maxillary and 
 labial palpi and sometimes on the cerci. These end-organs are hypo- 
 dermal in origin and consist, generally speaking, of a multinucleate 
 cell (Fig. 133) penetrated by a nerve and prolonged into a chitinous 
 bristle or peg, which is more or less enclosed in a pit, as in Tahanus 
 (Fig. 134). In many instances, however, the end-organs take the 
 form of teeth or cones projecting from the general surface of the antenna, 
 as in Vespa (Fig. 135). These cones are usually less numerous than 
 the pits; in Vespa crahro, for example, the teeth number 700 and the 
 pits from 13,000 to 14,000 on each antenna. The pits are even more 
 numerous in some other insects; thus there are as many as 17,000 on 
 each antenna of a blow fly (Hicks). The male of Melolontha vulgaris, 
 which seeks out the female by the sense of smell, has according to 
 Hauser 39,000 pits on each antenna, and the female only 35,000. Pits 
 presumably olfactory in function have been found by Packard on the 
 maxillary and labial palpi of Perla and on the cerci of the cockroach, 
 Periplaneta atnericana. Vom Rath has described four kinds of sense 
 
ANATOMY AND PHYSIOLOGY 
 
 89 
 
 hairs from the two larger of the four caudal appendages of a cricket, 
 Gryllus; some of these (Fig. 136) may be olfactory, though possibly 
 tactile. The same author found on the terminal palpal segment in 
 various Lepidoptera a large flask-shaped invagination (Fig. 137) into 
 which project numerous chitinous rods, each a process of a sensory 
 cell, which is supplied by a branch of the principal palpal nerve; these 
 peculiar organs are inferred to be olfactory. 
 
 The chief reason for regarding these various end-organs as olfactory 
 is that they appear from their structure to be better adapted to receive 
 that kind of an impression than any 
 other, so far as we can judge from our 
 own experience. Though it is easy to 
 demonstrate that the antennae, for ex- 
 ample, are olfactory, it frequently hap- 
 
 FiG. 134. — Section through antennal olfactory 
 pit of fly, Tabanus. c, cuticula; p, pit with peg; 
 pb, protecting bristles; s, sensory cell. — After 
 Hauser. 
 
 Fig. 135. — Longitudinal section of 
 antennal olfactory organ of wasp, 
 Vespa. c, olfactory cell; en, olfactory 
 cone; ct, cuticula; h, hypodermis cells; 
 n, nerve; r, rod. — After Hauser. 
 
 pens that the antennae bear several distinct forms of sensory end-organs, so 
 minute and intermingled that their physiological differences can scarcely 
 be ascertained by experiment but must be inferred from their peculiarities 
 of structure. Schenk, however, has arrived at precise results by compar- 
 ing the an.tennal sensilla in the two sexes, selecting species in which the 
 antennae exhibit a pronounced sexual dimorphism, in correlation with sex- 
 ual differences of behavior. Taking Notolophus aniiqua, in which the 
 male seeks out the female by means of antennal organs of smell, he 
 finds that the male has on each antenna about 600 sensilla cceloconica 
 and the female only 75; similarly in the geometrid Fidonia, in which 
 the ratio is 350 to 100. The sensilla styloconica also, of these two 
 genera, are regarded as olfactory organs. These two kinds of end- 
 
90 
 
 ENTOMOLOGY 
 
 organs are not only structurally adapted for the reception of olfactory 
 stimuli, but their numerical differences accord with the observed differ- 
 ences in the olfactory powers of the two sexes, there being no other 
 antennal end-organs to enter into the consideration. 
 
 Dr. N. E. Mclndoo has denied that the antennae are olfactory 
 organs. He finds, in all the large orders of insects, and on almost all 
 parts of the body and legs, on the bases of the wings, and in other situa- 
 tions, the structures that he terms olfactory pores, to which he has 
 devoted an immense amount of study. 
 
 Assembling. — It is a fact, well known to entomologists, that the 
 females of many moths and some beetles are able by emitting an odor to 
 
 Fig. 136. — Longitudinal section of a por- 
 tion of a caudal appendage of a cricket, 
 Gryllus domeslicus. b, bladderlike hair; c, 
 cuticula; h, hypodermis; n, nerve; ns, non- 
 sensory setae; sc, sense cell; sh, sensory hair. 
 — After VOM Rath. 
 
 Fig. 137. — Longitudinal section of apex 
 of palpus of Pier is. c, cuticula; h, hypo- 
 dermis; «, nerve; s, scales; 5C, sense cells. — 
 After VOM Rath. 
 
 attract the opposite sex, often in considerable numbers. Under favor- 
 able conditions, a freshly emerged female of the promethea moth, exposed 
 out of doors in the latter part of the afternoon, will attract scores of the 
 males. A breeze is essential and the males come up against the wind; 
 if they pass the female, they turn back and try again until she is located, 
 vibrating the antennas rapidly as they near her. The female, mean- 
 while, exhales an appreciable odor, chiefly from the region of the ovi- 
 positor, and males will congregate on the ground at a spot where a 
 female has been. If one of these males is deprived of the use of his 
 antennae, however, he flutters about in an aimless way and is no longer 
 able to find the female. 
 
 Among beetles, males of Polyphylla gather and scratch at places 
 
ANATOMY AND PHYSIOLOGY 9 1 
 
 where females are about to emerge from the ground. Prionus also 
 assembles, as Mrs. Dimmock observed in Massachusetts. In this 
 instance many males, with palpitating antennae, ran and flew to the 
 female; moreover, a number oi females were attracted to the scene. 
 
 Sounds of Insects. — Before considering the sense of hearing, some 
 account of the sounds of insects is desirable. Most of these are made by 
 the vibrations of a membrane or by the friction of one part against 
 another. 
 
 The wings of many Diptera and Hymenoptera vibrate with sufficient 
 speed and regularity to give a definite note. The wing tone of a honey 
 bee is A' and that of a common house fly is F'. From the pitch the 
 number of vibrations may be determined; thus ^' means 440^ vibrations 
 per second and F', 352. The numbers thus ascertained may be verified 
 by Marey's graphic method (Fig. 76) ; he found that the fly referred to 
 actually made 330 strokes per second against the smoked surface of a 
 revolving cylinder. 
 
 Flies, bees, dragon flies and some beetles make buzzing or humming 
 sounds by means of the spiracles, there being behind each spiracle a 
 membrane or chitinous projection which vibrates during respiration. 
 This "voice" should be distinguished from the wing tone when both 
 are present, as in bees and flies. A fly will buzz when held by the 
 wings, and some gnats continue to buzz after losing wings, legs and 
 head. The wing tone is the more constant of the two; in the honey bee 
 it is ^', falling to E' if the insect is tired, while the spiracular tone of the 
 same insect is at least an octave higher {A") and often rises to B" or 
 C", according to the state of the nervous system; in fact, it is possible 
 and even probable that various spiracular tones express different 
 emotions, as is indicated by the effects produced by the voice of the old 
 queen bee upon the young queens and the males. 
 
 The well-known ''shrilling" of the male cicada is produced by the 
 rapid vibration of a pair of membranes, or drums, situated on the basal 
 abdominal segment, and vibrated each by means of a special muscle. 
 
 Frictional sounds are made by beetles in a great variety of ways : by 
 the rubbing of the pronotum against the mesonotum (many Cerambyci- 
 dae) ; or of abdominal ridges against elytral rasps {Elaphrus, Cychrus) ; 
 or two dorsal abdominal rasps against specialized portions of the wing 
 folds (Passalus cornutus), not to mention other methods. In most cases 
 one part forms a rasp and the other a scraper, for the production of 
 sound. 
 
 ^ Upon the basis of C as 264 vibrations per second. The C of the physicist has 256 as 
 its frequency of vibration. 
 
92 ENTOMOLOGY 
 
 In many of these instances the sound serves to bring the two sexes 
 together and is not necessarily confined to one sex; thus in Passalus cor- 
 nutus both sexes stridulate, and the larva as well. 
 
 A few moths (Sphingidae) and a few butterflies make sounds; the 
 South American butterfly Ageronia feronia emits a sharp crackling 
 noise as it flies. A rasp and a scraper have been found in several ants, 
 though ants very seldom make any sounds that can be distinguished 
 by the human ear; Mutilla, however, makes a distinct squeaking sound 
 by means of a stridulating organ similar to those of ants. 
 
 Stridulating organs attain their best development in Orthoptera, in 
 which group the abihty to stridulate is often restricted to the male, 
 though not so often as is commonly supposed. Among Locustidae, 
 Stenohothrus rubs the hind femora against the tegmina to make a 
 sound, the femur bearing a series of teeth, which scrape across the 
 elevated veins of the wing-cover; while the male of Dissosteira makes a 
 crackling sound during flight or while poising, by means of friction 
 between the front and hind wings, where the two overlap. 
 
 Tettigoniidae and Gryllidae stridulate by rubbing the bases of the teg- 
 mina against each other. Thus in the male Microcentrum laurifolium 
 the left tegmen, which overlaps the right, bears a file-like organ of about 
 fifty-five teeth (Fig. 138), while the opposite tegmen bears a scraper, at 
 right angles to the file. The tegmina are first spread a little; then, as 
 they close gradually, the scraper clicks across the teeth, making from 
 twenty to thirty sharp "tic"- like sounds in rapid succession. This 
 call guides the female to the male and when they are a few inches apart 
 she makes now and then a short, soft chirp, to which he responds with a 
 similar chirp, which is quite unlike the first call and, moreover, is 
 made by the opening of the tegmina. These and other details of the 
 courtship may readily be observed in twilight and even under artificial 
 light, as the latter, if not too strong, does not disturb the pair. Some- 
 thing similar may be observed in the daytime in Orchelimum, Xiphidium 
 and the tree crickets, (Ecanthus. The stridulating areas are usually 
 membranous and. the rasping organs are modified veins. Frequently 
 the wing-covers bulge out to form a resonant chamber that reinforces 
 the sound, as in the katydid. 
 
 The naturalist can recognize many a species of grasshopper by its 
 song; Scudder has expressed some of these songs in musical notation. 
 The usual song of the common meadow-grasshopper, Orchelimum vul- 
 gare, may be represented by a prolonged zr . . . sound, followed by 
 a staccato jip-jip-jip-jip. . . . 
 
ANATOMY AND PHYSIOLOGY 
 
 93 
 
 In Orthoptera, the frequency of stridulation increases with the tem- 
 perature; and the correlation between the two is so close that it is easy 
 
 Fig. 138. — Stridulating organs of Microcentrum laurifolium. A, dorsal aspect of 
 file (st) when the tegmina are closed; B, ventral aspect of left tegmen to show file; C, dorsal 
 aspect of right tegmen to show scraper (s). 
 
 to compute the temperature from the number of calls per minute, by 
 means of formulae. The formula for a common cricket [probably a 
 tree-cricket, CEcanthus niveus], as given by Professor Dolbear, is 
 
 r = 50 H , which simplified is T = 40 H 
 
 4 4 
 
 Here T stands for temperature and N, the rate per minute. 
 
 A similar formula for the katydid {Cyrtophyllus perspicillatus) , 
 based upon observations made by R. Hayward, would be 
 
 r = 60 + 
 
 N- ig 
 
 Here, in computing N, either the "katy-did" or the "she-did" is taken 
 as a single call. 
 
94 ENTOMOLOGY 
 
 Professor A. F. Shull, who has made precise observations on the 
 stridulation of (Ecanthus, finds that there are numerous variations of. 
 rate that cannot be accounted for by differences of temperature; that 
 Dolbear's formula cannot be appHed without a possible error of 6.65° 
 F.; that humidity seems to affect the rate of chirping and that crickets 
 show a certain individuality in their manner of chirping under the same 
 external conditions. 
 
 Hearing. — There is no doubt that insects can hear. The presence 
 of sound-making organs is strong presumptive evidence that the sense of 
 hearing is present. Female grasshoppers and beetles make locomotor 
 and other responses to the sounds of the males, and male grasshoppers 
 will answer the counterfeit chirping made with a quill and a file. 
 
 Auditory organs are not restricted to any one region of an insect, but 
 occur,. according to the species, on antennae, abdomen, legs, or elsewhere. 
 
 The antennae of some insects are evidently stimulated by certain 
 notes, particularly those made by their own kind. Thus the antennae 
 of the male mosquito are auditory, as proved by the well-known experi- 
 ments of Mayer. He fastened a male Culex to a microscope slide and 
 sounded various tuning forks. Certain tones caused certain of the 
 antennal hairs to vibrate sympathetically, and the greatest amount of 
 vibration occurred in response to 512 vibrations per second, or the note 
 C", which is approximately the note upon which the female hums. 
 The male probably turns his head until the two antennae are equally 
 affected by the note of the female, when, by going straight ahead, he is 
 able to locate her with great precision. 
 
 In the lack of experimental evidence, other organs are inferred to be 
 auditory on account of their structure. Locustidae bear on each side of 
 the first abdominal segment a tympanal sense organ — the subject of 
 Graber's well-known figure (Fig. 139) . This organ is admirably adapted 
 to receive and transmit sound-waves. The tympanum, or membrane, 
 is tense, and can vibrate freely, as the air pressure against the two sur- 
 faces of the membrane is equalized by means of an adjacent spiracle, 
 which admits air to the inner surface. Resting against the inner face 
 of the tympanum are two processes (Fig. 139, p, p), which serve proba- 
 bly to transfer the vibrations, and there is also a delicate vesicle con- 
 nected by means of an intervening ganglion with the auditory nerve, 
 which in this case comes from the metathoracic ganghon. The nerve 
 terminations consist of delicate bristle-like processes which are probably 
 affected by the oscillations of the fluid contained in the vesicle just 
 referred to. 
 
ANATOMY AND PHYSIOLOGY 
 
 95 
 
 Other tympanal organs, doubtless auditory, are found on the fore 
 tibiae of Tettigoniidas, ants, termites and PerHda), on the femora of Pedicu- 
 hdae and the tarsi of some Coleoptera. 
 
 Several types of diordotonal organs have been described, of which 
 those of the transparent Core/Ara larva may serve as an example. These 
 organs, situated on each side of abdominal segments 4-10, inclusive, 
 consist each (Fig. 140) of a tense cord, probably capable of vibration, 
 which is attached at its posterior end to the integument and at its 
 
 -i^ 
 
 Fig. 139. — Inner aspect of right tympanal sense 
 organ of a grasshopper, Caloplenus italicus. b. chitin- 
 ous border; c, closing muscle of spiracle; gn, gan- 
 glion; m, tympanum; n, nerve; o, opening muscle 
 of spiracle; p, p, processes resting against tympan- 
 um; s, spiracle; tm, tensor muscle of tympanum; v, 
 vesicle. After Graber. 
 
 Fig. 140. — Chordotonal sense 
 organ of aquatic dipterous larva, 
 Corethra plumicornis. cd, cord; eg, 
 chordotonal ganglion; /, fibers of an 
 , integumental nerve; g, ganglion of 
 ventral chain; I, ligament; m, lon- 
 gitudinal mujcles; n, chordotonal 
 nerve; r, rods (nerve terminations); 
 t, tactile setae. — After Graber. 
 
 anterior end to a ligament. Between the cord and the supporting 
 ligament is a small ganglion, which receives a nerve from the principal 
 ganglion of the segment. 
 
 Vision. — The external characters of the two kinds of eyes — ocelli and 
 compound eyes — have already been described. While the lateral ocelli 
 are comparatively simple in structure, consisting of a small number of 
 cells, the dorsal ocelli almost rival the compound eyes in complexity. 
 
 Dorsal Ocelli. — These consist (Fig. 141) of (i) lens, (2) vitreous 
 body, (3) retina, (4) nerve fibers, (5) pigmented hypodermis cells, and (6) 
 
96 
 
 ENTOMOLOGY 
 
 accessory cells, between the retinal cells and the nerve fibers. The lens, 
 usually biconvex in form, is a local thickening of the general cuticula; 
 it is supplemented in its function by the vitreous body, consisting of a 
 layer of transparent hypodermis cells; these in many insects are elon- 
 gate, constituting a vitreous layer of rather more importance than the 
 one represented in Fig. 141. The retina consists 
 of cells more or less spindle-shaped and associated 
 in pairs or in groups of two or three, each group 
 being termed a retinula. The basal end of each 
 retinal cell is continuous with a nerve fiber (Fig. 
 142), according to Redikorzew and others, and in 
 
 Fig. 141. — Median ocellus of honey bee, Apis mellifera, in 
 sagittal section, h, hypodermis; /, lens; n, nerve; p, iris pigment; 
 r, retinal cells; v, vitreous body. — After Redikorzew. 
 
 — n 
 
 Fig. 142. — An ocel- 
 lar retinula of the honey 
 bee, composed of two 
 retinal cells. A, longi- 
 tudinal section; B, 
 transverse section; n, 
 n, nerves; p, pigment; 
 r, rhabdom.- After Red- 
 ikorzew. 
 
 some instances (Calopteryx) a nerve fiber enters 
 the cell. Each retinula contains a longitudinal 
 rod, or rhabdom, in the secretion of which all the 
 cells of the retinula are concerned. Between the 
 retinal cells and nerve fibers are indifferent, or accessory cells. Pig- 
 ment granules, usually black, are contained in these cells, also in 
 the retinal cells and around the lens, in the last instance forming the 
 iris. 
 
 Vision by Ocelli.— Though the ocellus is constructed on somewhat 
 the same plan as the human eye, its capacity for forming images must 
 
ANATOMY AND PHYSIOLOGY 
 
 97 
 
 be extremely limited; for since the form of the lens is fixed and also the 
 distance between the lens and the retina, there is no power of accom- 
 modation, and most external objects are out of focus; to make an 
 image, then, the object must be at one definite distance from the lens, 
 and as the lens is usually strongly convex, this distance must be small; 
 in other words, insects, like spiders, are very near-sighted, so far as the 
 oceUi are concerned; furthermore, the small number of retinal rods 
 implies an image of only the coarsest kind. 
 
 If the compound eyes of a grasshopper are covered with an opaque 
 varnish and the insect is placed in a box with only a single opening, it 
 readily finds its way out by means of its ocelli; if the three ocelli also 
 are covered, however, it no longer does so, 
 except by accident, though it can make its 
 escape when only one of the ocelli is left 
 uncovered. The ocelli, then, can distinguish 
 light from darkness — and they are probably 
 more serviceable to the insect in this way 
 than in forming images. 
 
 Compound Eyes. — As regards delicacy and 
 intricacy of structure, the compound eye of 
 an insect is scarcely if at all inferior to the eye 
 of a vertebrate. In radial section (Fig. 143), 
 a compound eye appears as an aggregation 
 of] similar elongate elements, or ommaiidia, 
 each of which ends externally in a facet. The ^'"y ^43.-Portion of com- 
 
 •' pound eye of fly, Calltphora 
 
 following structures compose, or are concerned vomitoria, radial section, c, cor- 
 
 .,1 1 ,.j. / \ / \ nea; i, iris pigment; n, nerve 
 
 With, each OmmatldlUm: (l) cornea, (2) Crys- fibers; nc, nerve cells; r. retinal 
 
 talline lens, or cone, (t,) rhabdom and retinula, pigment; t, trachea.— After 
 
 / \ • /• • 1 • 7\ / \ r HiCKSON. 
 
 (4) pigment {ins and rehnal), (5) jenestrate 
 membrane, (6) fibers of the optic nerve, (7) trache<B. 
 
 The cornea (Fig. 144) is a biconvex transparent portion of the exter- 
 nal chitinous cuticula. Immediately beneath it are the cone cells, which 
 may contain a clear fluid or else, as in most insects, solid transparent 
 cones. The rhabdom is a transparent chitinous rod or a group of rods 
 (rhabdomeres) situated in the long axis of the ommatidium and sur- 
 rounded by greatly elongated cells, which constitute the retinula. 
 Two zones of pigment are present: an outer zone, of iris pigment, in 
 which the pigment in the form of fine black granules is contained 
 chiefly in short cells that surround the retinula distally; and an inner 
 zone, of retinal pigment, in which the pigment cells are long and slender, 
 7 
 
98 
 
 ENTOMOLOGY 
 
 and enclose the retinula proximally. All these 
 parts are hypodermal in origin, as is also the 
 fenestrate basement membrane, through which 
 pass tracheae and nerve fibers. The nerve 
 fibrillae, which are ultimate branches of the 
 optic nerve, pass into the retinal cells — the 
 end-organs of vision. Under the basement 
 membrane is a fibrous optic tract of com- 
 plex structure. 
 
 Compound eyes are of three types: (i) 
 eucone, in which the cone-cells form solid crys- 
 talhne cones; (2) pseudocone, in which the cone- 
 cells contain a transparent fluid; and (3) acone, 
 in which there are no cones, though the cone- 
 cells are present. 
 
 Physiology. — After much experimentation 
 and discussion upon the physiology of the com- 
 pound eye — the subject of the monumental 
 works of Grenacher and Exner — Miiller's 
 "mosaic" theory is still generally accepted, 
 though it was proposed early in the last cen- 
 tury. It is thought that an image is formed 
 by thousands of separate points of light, each 
 of which corresponds to a distinct field of 
 vision in the external world. Each ommati- 
 dium is adapted to transmit light along its axis 
 only (Fig. 145), as oblique rays are lost by 
 absorption in the black pigment which sur- 
 rounds the crystalline cone and the axial 
 rhabdom. Along the rhabdom, then, light can 
 reach and affect the terminations of the optic 
 nerve. Each ommatidium does not itself form 
 a picture ; it simply preserves the intensity and 
 
 nucleus; nv, nerve fibrillae; r ^ ^^ t r • i 
 
 PC pseudocone; pg\ pg\ cells color of the fight from ouc particular portion 
 containing iris pigment; pg\ f ^^ ^^^ f ^-g-^j^ and whcu this is doue by 
 
 cell containing retinal pigment ; ' •' 
 
 r, one of the six retinal cells hundreds or thousands of contiguous ommati- 
 
 which compose the retinula; Wj, ,. . ,. ah ^i j_ ,i ■ / 
 
 rhabdom. composed of six rhab- dia, an image results. All that the painter 
 
 domeres;!. trachea; <ir. tracheal ^J^gg ^J^q copieS an object, is tO put together 
 vesicle. — After Hickson. ' . ^ . •' ' ^ ° 
 
 patches of light in the same relations of qual- 
 ity and position that he finds in the object itself — and this is essen- 
 
 PiG. 144. — Structure of an 
 ommatidium of Calliphora 
 vomiloria. A, radial section 
 (chiefly); B, transverse sec- 
 tion through middle region; 
 C, transverse section through 
 basal region; hm, basement 
 membrane; c, cornea; n, 
 
ANATOMY AND PHYSIOLOGY 
 
 99 
 
 tially what the compound eye does, so far as can be inferred from its 
 structure. 
 
 Exner, removing the cones with the corneal cuticula (in Lampyris), 
 looked through them from behind with the aid of a microscope and 
 found that the images made by the separate ommatidia were either 
 very close together or else overlapped one another, and that in the 
 latter case the details corresponded; in other words, as many as twenty 
 or thirty ommatidia may co-operate to form an image of the same por- 
 tion of the field of vision; this "superposition" 
 image being correspondingly bright — an advan- 
 tage, probably, in the case of nocturnal insects. 
 
 Large convex eyes indicate a wide field of 
 xdsion, while small numerous facets mean dis- 
 tinctness of vision, as Lubbock pointed out. The 
 closer the object the better the sight, for the 
 greater will be the number of lenses employed 
 to produce the impression, as Mollock says. 
 If Miiller's theory is true, an image may be 
 formed of an object at any reasonable distance, 
 no power of accommodation being necessary ; 
 while if, on the other hand, each cornea with 
 its crystalHne cones had to form an image after 
 the manner of an ordinary hand-lens, only objects f'^; i4S-— Diagram of 
 
 -' _ J ■ J J outer transparent portion of 
 
 at a definite distance could be imaged. an ommatidiiun to illustrate 
 
 The limit of the perception of form by insects ^ay T^fTnTthf repeated 
 
 is placed at about two meters for Law^ym, i.^o reflection and absorption of 
 
 ./ an oblique ray (5), which at 
 
 meters for Lepidoptera, 68 centimeters for length emerges at c. p, iris 
 Diptera and 58 centimeters for Hymenoptera. p^^^^^*- 
 
 It is generally agreed, however, that the compound eyes are specially 
 adapted to perceive movements of objects. The sensitiveness of insects 
 to even sHght movements is a matter of common observation; often, 
 however, these insects can be picked up with the fingers, if the operation 
 is performed slowly until the insect is within the grasp. A moving object 
 affects different facets in succession, without necessitating any turning 
 of the eyes or the head, as in vertebrates. Furthermore, on the same 
 principle, the compound eyes are serviceable for the perception of form 
 when the insect itself is moving rapidly. 
 
 The arrangement of the pigment depends adaptively upon the 
 quality of the light, as Stefanowska and Exner have shown; thus, when 
 the light is too strong, the iris and retinal pigment cells elongate around 
 
lOO ENTOMOLOGY 
 
 the ommatidium and their pigment granules absorb from the cone 
 cells and rhabdom the excess of light. If the light is weak, they shorten, 
 and absorb but a minimum amount of light. In diurnal insects the 
 pigment is adapted to absorb an excess of light; in nocturnal insects, 
 on the contrary, it is adapted to permit a maximum amount of light 
 to reach the retinal cells. 
 
 Origin of Compound Eye.- — The compound eye is often said to 
 represent a group of ocelli, chiefly for the reason that externally there 
 appears to be a transition from simple eyes, through agglomerate eyes, 
 to the facetted type. This plausible view, however, is probably incor- 
 rect, for these reasons among others. In the ocellus, a single lens serves 
 for all the retinulae, while in the compound eye there are as many lenses 
 as there are retinulae. Moreover, ocelli do not pass directly into com- 
 pound eyes, but disappear, and the latter arise independently of the 
 former. 
 
 Probably, as Grenacher holds, both the ocellus and the compound 
 eye are derived from a common and simpler type of eye — are ''sisters," 
 so to speak, derived from the same parentage. 
 
 Perception of Light through the Integument. — In various insects, 
 as also in earthworms, blind chilopods and some other animals, light 
 affects the nervous system through the general integument. Thus 
 eyeless dipterous larvae avoid the light, or, more precisely, they retreat 
 from the rays of shorter wave-length (as the blue), but come to rest in 
 the rays of longer wave-length (red), as if they were in darkness (see 
 page 307). The blind cave-beetles of the genus Anophthalmus react to 
 the light of a candle (Packard). Graber found that a cockroach de- 
 prived of its eyesight could stiU perceive light, but Lubbock found that 
 an ant whose eyes had been covered with an opaque varnish became 
 indifferent to light. 
 
 Color Sense. — Insects undoubtedly distinguish certain colors, 
 though their color sense differs in range from our own. Thus ants avoid 
 violet light as they do sunlight, but probably cannot distinguish red or 
 orange light from darkness; on the other hand, they are extremely 
 sensitive to the ultra-violet rays. Honey bees frequently select blue 
 flowers: white butterflies (Pieris) prefer white flowers, and yellow 
 butterflies (Colias) appear to alight on yellow flowers in preference to 
 white ones (Packard) . In fact, the color sense is largely relied upon by 
 insects to find particular flowers and by butterflies to a large extent to 
 find their mates. To be sure, insects will visit flowers after the brightly 
 colored petals have been removed or concealed, as Plateau found, but 
 
ANATOMY AND PHYSIOLOGY lOI 
 
 this does not prove that the colors are of no assistance to the insect, 
 though it does show that they are not the sole attraction — the odor also 
 being an important guide. The honey bee is able to distinguish color 
 patterns, according to the experiments of C. H. Turner. 
 
 Problematical Sense Organs. — As all our ideas in regard to the 
 sensations of insects are necessarily inferences from our own sensory ex- 
 periences, they are inevitably inadequate. While it is certain that in- 
 sects have at least the senses of touch, taste, smell, hearing and sight, it 
 is also certain that these senses of theirs differ remarkably in range from 
 our own, as we have shown. We can form no accurate conception of 
 these ordinary senses in insects, to say nothing of others that insects 
 have, some of which are probably peculiar to insects. Thus they have 
 many curious integumentary organs which from their structure and 
 nerve connections are inferred to be sensory end-organs, though their 
 functions are either doubtful or unknown. Such an organ is the sensil- 
 lum placodeum (p. 84), the use of which is very doubtful, though the 
 organ is possibly affected by air pressure. Insects are extremely sensi- 
 tive to variations of wind, temperature, moisture and atmospheric 
 pressure, and very likely have special end-organs for the perception of 
 these variations; indeed, the sensilla trichodea are probably afifected 
 by the wind, as we have said. 
 
 The halteres of Diptera, representing the hind wings, contain sensory 
 organs of some sort. They have been variously regarded as olfactory 
 (Lee), auditory (Graber), and as organs of equilibration. When one or 
 both halteres are removed, the fly can no longer maintain its equilibrium 
 in the air, and Weinland holds that the direction of flight is affected by 
 the movements of these "balancers." 
 
 6. Digestive System 
 
 The alimentary tract in its simplest form is to be seen in Thysanura, 
 Collembola and most larvae, in which (Fig. 146) it is a simple tube ex- 
 
 FiG. 146. — Alimentary tract of a collembolan, Orchesella. F, fore gut; H, hind gut; M, 
 mid gut; c, cardiac valve; cm, circular muscle; Im, longitudinal muscle; p, pharynx; py, 
 pyloric valve. 
 
I02 ENTOMOLOGY 
 
 tending along the axis of the body and consisting of three regions, 
 namely, fore, mid and hind gut. These regional distinctions are funda- 
 mental, as the embryology shows, for the middle region is entodermal 
 in origin and the two others are ectodermal, as appears beyond. 
 
 There are many departures from this primitive condition, and the 
 most specialized insects exhibit the following modifications (Figs. 147, 
 148) of the three primary regions : 
 
 Fore intestine {stomodceum) : mouth, pharynx, oesophagus, crop, pro- 
 ventriculus (gizzard), cardiac valve. 
 
 Mid intestine (mesenteron) : ventriculus (stomach) . 
 
 Etind intestine (proctodceum) : pyloric valve, ileum, colon, rectum, 
 anus. 
 
 Stomodaeuni. — The mouth, the anterior opening of the food canal, 
 is to be distinguished from the pharynx, a dilatation for the reception of 
 
 Fig. 147. — Alimentary tract of a grasshopper, Melanoplus differentialis. c, colon; cr, 
 crop; gc, gc, gastric caeca; i, ileum; m, mid intestine, or stomach; mt, Malpighian, or kidney, 
 tubes; o, oesophagus; p, pharynx; r, rectum; s, salivary gland of left side. 
 
 food. In the pharynx of mandibulate insects the food is acted upon by 
 the saliva; in suctorial forms the pharynx acts as a pumping organ, in 
 the mannei" already described. 
 
 The oesophagus is commonly a simple tube of small and uniform 
 caliber, varying greatly in length according to the kind of insect. Pass- 
 ing between the commissures that connect the brain with the suboeso- 
 phageal gangKon (Fig. 115), the oesophagus leads gradually or else 
 abruptly into the crop or gizzard, or when these are absent, directly 
 into the stomach. In addition to its function of conducting food, 
 the oesophagus is sometimes glandular, as in the grasshopper, in which 
 it is said to secrete the "molasses" which these insects emit. 
 
 The crop is conspicuous in most Orthoptera (Fig. 147) and Cole- 
 optera (Fig. 148) as a simple dilatation. In Neuroptera (Fig. 149) its 
 capacity is increased by means of a lateral pocket — the food reservoir; 
 this in Lepidoptera, Hymenoptera and Diptera is a sac (Fig. 150, c) 
 communicating with the oesophagus by means of a short neck or a 
 
ANATOMY AND PHYSIOLOGY 
 
 103 
 
 long tube, and serving as a temporary receptacle for food. In herbiv- 
 orous insects the crop contains glucose formed from starch by the 
 action of saliva or by the secretion of the crop itself; in carnivorous 
 insects this secretion converts albuminoids into assimilable peptone- 
 like substances. 
 
 Next comes the enlargement 
 
 known as the proventriculus, or 
 gizzard, which is present in many 
 insects, especially Orthoptera and 
 Coleoptera (Fig. 148), and is 
 usually found in such mandibulate 
 insects as feed upon hard sub- 
 stances. The proventriculus is 
 
 Fig. 148. — Digestive system of a beetle, 
 Carabus. a, anal gland; c (of fore gut), crop; 
 c (of hind gut), colon, merging into rectum; 
 d, evacuating duct of anal gland; g, gastric 
 caeca; i, ileum; m, mid intestine; mt, Mal- 
 pighian tubes; o, oesophagus; p, proventricu- 
 lus; r, reservoir. — After Kolbe. 
 
 Pig. 149. — Digestive system of Myrme- 
 leon larva, c, caecum; cr, crop; m, mid 
 intestine; mt, Malpighian tubes; s, spin- 
 neret. — After Meinert. 
 
 lined with chitinous teeth or ridges for straining the food, and has power- 
 ful circular muscles to squeeze the food back into the stomach, as well as 
 longitudinal m.uscles for relaxing, or opening, the gizzard. The pro- 
 ventriculus not only serves as a strainer, but also helps to comminute 
 the food, like the gizzard of a bird. 
 
I04 
 
 ENTOMOLOGY 
 
 In most insects a cardiac valve guajrds the entrance to the stomach, 
 preventing the return of food to the gullet. This valve (Figs. 146, 151) 
 
 ' cm 
 
 Fig. 150. — Alimentary tract of a moth. Sphinx, c, food reservoir; cl, colon; cm, 
 cascum; i, ileum; m, mid intestine; mt, Malpighian tubes; o, oesophagus; r, rectum; s, salivary 
 gland. — After Wagner. 
 
 is an intrusion of the stomodaeum into the mesenteron, forming a circu- 
 lar lip which permits food to pass backward, but closes upon pressure 
 from behind. 
 
 Mesenteron. — The ventriculus, otherwise known as the mid intestine, 
 or stomach, is usually a simple tube of large caliber, 
 as compared with the oesophagus or intestine, and into 
 the ventriculus may open glandular blind tubes, or 
 gastric ccBca (Figs. 147, 148) ; these, though numerous 
 in some insects, are commonly few in number and 
 restricted to the anterior region of the stomach. The 
 gastric caeca of Orthoptera secrete a weak acid which 
 emulsifies fats, or one which pa,sses forward into the 
 crop, there to act upon albuminoid substances. In 
 the stomach the food may be acted upon by a fluid 
 secreted by specialized cells of the epithehal wall. 
 In various insects, certain cells project periodically 
 into the lumen of the stomach as papillae, which by a 
 _ process of constriction become separated from the 
 
 valve of young muscid parent cells and mix bodily with the food. Thisphe- 
 /.^^provekScJiu^s^^^i nomenon takes place in the larva oiPtychoptera (van 
 valve. In an older Gchuchten), also in nymphs of Odonata (Necdham), 
 
 larva the valve pro- i i i r • i i 
 
 jects into the mid in- and IS probably of widespread occurrence among m- 
 I.evsky7'^^'''^°'^^" sects- The chief function of the stomach is absorp- 
 tion, which is effected by the general epithelium. 
 Physiologically, the so-called stomach of an insect is quite unlike the 
 stomach of a vertebrate, being more like an intestine. 
 
 Proctodaeum. — At the anterior end of the hind intestine there is 
 usually a pyloric valve, which prevents the contents of the intestine 
 
ANATOMY AND PHYSIOLOGY 
 
 f05 
 
 from returning into the stomach. This valve may operate by means of 
 a sphincter, or constricting, muscle, or may, as in Collembola (Fig. 146), 
 consist of a backward-projecting circular ridge, or lip, which closes 
 upon pressure from behind. 
 
 In its primitive condition the hind intestine is a simple tube (Fig. 
 146). Usually, however, it presents two or even three specialized 
 regions, namely and in order, ileum, colon and rectum (Fig. 147). The 
 hind intestine varies greatly in length and is frequently so long as to be 
 thrown into convolutions (Fig. 152). The ileum is short and stout in 
 grasshoppers (Fig. 147); long, slender and convoluted in many carniv- 
 
 /'r^^ 
 
 Pig. 152. — Digestive system of Belos- 
 toma. c, caecum; I, ileum; w, mid intestine; 
 mt, Malpighian tubes; r, salivary reservoir; 
 5, salivary gland. — After LocY, from the 
 American Naturalist. 
 
 Fig. 153. — Wall of mid intestine of silk- 
 worm, transverse section, b, basement mem- 
 brane; c, circular muscle; /, intima; I, longi- 
 tudinal muscle; n, n, nuclei of epithelial 
 cells; 5, secretory cell. 
 
 orous beetles; and quite short in caterpillars and most other larvae; its 
 function is absorption. The colon, often absent, is evident in Orthop- 
 tera and Lepidoptera and may bear {Benacus, Dytiscus, Silphidse, 
 Lepidoptera) a conspicuous caecal appendage (Figs. 150, 152) of doubt- 
 ful function, though possibly a reservoir for excretions. The colon 
 contains indigestible matter and the waste products of digestion, includ- 
 ing the excretions of the Malpighian tubes. The rectum (Fig. 147) is 
 thick-walled, strongly muscular and often folded internally. Its 
 office is to expel excrementitious matter, consisting largely of the indi- 
 gestible substances chitin, cellulose and chlorophyll. The rectum 
 terminates in the anus, which opens through the last segment of the 
 abdomen, always above the genital aperture. 
 
io6 
 
 ENTOMOLOGY 
 
 g 
 
 Histology. — The epithelial wall of the alimentary tract is a single 
 layer of cells (Fig. 153), which secretes the intima, or lining layer, and 
 the basement membrane — a delicate, structureless enveloping layer. 
 The intima, which is continuous with the external cuticula, is chitinous 
 in the fore and hind gut (which are ectodermal in origin) , but not in the 
 mid gut (entodermal) , and usually exhibits extremely fine transverse 
 striae, which are due probably to minute pore canals. Surrounding 
 the basement membrane is a series of circular muscles and outside these 
 is a layer of longitudinal muscles in the mid gut. In 
 the fore gut the longitudinal muscles are frequently 
 under the circular muscles; and in the hind gut there 
 may be two layers of circular muscles with longitudinal 
 muscles running between them; but there are many 
 variations in the relative positions of the two kinds of 
 muscles in different kinds of insects. The circular 
 muscles serve to constrict the pharynx in sucking insects 
 and, in general, to squeeze backward the contents of the 
 alimentary canal by successively reducing its caliber. 
 The longitudinal muscles, restricted almost entirely to 
 the mid intestine, act in opposition to the constricting 
 muscles to enlarge the lumen of the food canal and in 
 addition to effect peristaltic movements of the stomach. 
 The intima of the crop is sometimes shaped into 
 teeth, and that of the proventricvilus is heavily chitin- 
 ized and variously modified to form spines, teeth or 
 ridges, 
 
 Peritrophic Membrane. — This membrane forms 
 an elastic tube inside the mid intestine and hind in- 
 testine; is derived usually from the epithelial cells 
 of the mesenteron; and is, in some instances at least, 
 renewed periodically. The peritrophic membrane, 
 found in ants, wasps, caterpillars, and larvae and adults 
 of many beetles, etc., is characteristic of insects that consume solid food 
 containing much hard, indigestible matter, and doubtless serves to pro- 
 tect the epithelium of the mid intestine from mechanical injury. 
 
 Salivary Glands. — In their simplest condition, the salivary glands 
 are a pair of blind tubes (Fig. 154), one on each side of the oesophagus 
 and opening separately at the base of the hypopharynx. Commonly, 
 however, the glands open through two salivary ducts into a common, 
 or evacuating, duct; a pair of salivary reservoirs (Fig. 155) may be 
 
 Fig. 154. — A sim- 
 ple salivary gland of 
 CcBcilius. c, canal; d, 
 duct; g, g, glandular 
 cells. — After Kolbe. 
 
ANATOMY AND PHYSIOLOGY 
 
 107 
 
 present and the glands are frequently branched or lobed, and though 
 usually confined to the head, may extend into the thorax or even into 
 the abdomen. • 
 
 Many insects have more than one pair of glands opening into the 
 pharynx or oesophagus ; thus the honey bee has six pairs and Hymenop- 
 
 ., b 
 
 - B. 
 
 Fig. 155. — Right salivary gland of cockroach, ventral 
 aspect, c, common duct; g, gland; h, hypopharynx; r, 
 -After MiALL and Denny. 
 
 reservoir.- 
 
 FiG. 156. — Histology of 
 salivary gland of Ccecilius, 
 radial section, b, basement 
 membrane; c, canal; g, g, 
 glandular cell; i, intima; n, 
 nucleus. — After Kolbe. 
 
 tera as a whole have as many as ten different pairs. Though all these 
 are loosely spoken of as salivary glands, it is better to restrict that 
 term to the pair of glands that open at the hypopharynx. 
 
 All these cephalic glands are evaginations of the stomodaeum (ecto- 
 dermal in origin) and consist of an epithelial layer with the customary 
 intima and basement membrane (Fig. 156). The nuclei are large, as is 
 usually the case in glandular cells, and 
 the cytoplasm consists of a dense 
 framework (appearing in sections as a 
 network) enclosing vacuoles of a clear 
 substanc^the secretion; the chitinous ,P'^- ^s 7. -One of the three-iobed 
 
 ' salivary glands of a mosquito. The 
 
 intima is penetrated by fine pore canals middle lobe secretes the poison.— After 
 
 ,1 1 1 • 1 ,1 .• Macloskie, from the American Nat- 
 
 through which the secretion passes, uraiist. 
 
 In many insects, notably the cockroach, 
 
 the common duct is held distended by spiral threads which give the duct 
 
 much the appearance of a trachea. 
 
 In herbivorous insects the saliva changes starch into glucose, as in 
 vertebrates; in carnivorous forms it acts on proteids and is often used 
 to poison the prey, as in the larva of Dytiscus. In the mosquito each 
 gland is three-lobed (Fig. 157) ; the middle lobe is different in appearance 
 from the two others and secretes a poisonous fluid which is carried out 
 
io8 
 
 ENTOMOLOGY 
 
 along the hypopharynx. Though this poison is said to faciHtate the 
 process of blood-sucking by preventing the coagulation of the blood, its 
 primary use was perhaps to pre\»ent the coagulation of proteids in the 
 juices of plants. 
 
 Malpighian Tubes. — The kidney, or Malpighian, tubes, present in 
 nearly all insects, are long, slender, blind tubes opening into the intestine 
 immediately behind the stomach as a rule (Figs 
 147, 148) , but always into the intestine. The num- 
 ber of kidney tubes is very different in different in- 
 sects; Collembola have none, while Odonata have 
 fifty or more and Locustidae as many as one hun- 
 dred and fifty; commonly, however, there are four 
 or six, in Coleoptera, Lepidoptera and many other 
 
 Fig. 158. — Portion Pig. 159. — Cross-section of Malpighian tube of silkworm 
 
 of Malpighian tube of Bombyx tnori. b, basement membrane; c, crystals; 1, intima 
 
 caterpillar, Samia ce- I, lumen; n, nucleus; p, peritoneal layer. Greatly magnified. 
 cropia, surface view. 
 
 orders. Not more than six and frequently only four occur in the 
 embryo (Wheeler), though these few embryonic tubes may subsequently 
 branch into many. 
 
 The Malpighian tubes (Fig. 158) are evaginations of the proctodaeum 
 and are consequently ectodermal. A cross-section of a tube shows a 
 ring of from one to six or more large polygonal cells (Fig. 159), which 
 often project into the lumen of the tube; the nuclei are usually large and 
 may be branched, as in Lepidoptera. A chitinous intima, traversed by 
 pore canals, lines the tube, and a delicate basement membrane is present, 
 surrounded by a peritoneal layer of connective tissue. Furthermore, 
 the urinary tubes are richly supplied with tracheae. In function, the 
 Malpighian tubes are analogous to the vertebrate kidneys and con- 
 tain a great variety of substances, chief among which are uric acid and its 
 derivatives (such as urate of sodium and of ammonium), calcium oxalate 
 and calcium carbonate. 
 
ANATOMY AND PHYSIOLOGY 
 
 109 
 
 Parts of the fat-body may also be concerned in excretion; thus the 
 fat-body in CoUembola and Orthoptera serves for the permanent storage 
 of urates. 
 
 7. Circulatory System 
 
 Insects, unlike vertebrates, have no system of closed blood-vessels, 
 but the blood wanders freely through the body 
 cavity to enter eventually the dorsal vessel, which 
 resembles a heart merely in being a propulsatory 
 organ. 
 
 Dorsal Vessel. — The dorsal vessel (Figs. 160, 
 164) is a delicate tube extending along the median 
 dorsal line immediately under the integument. 
 A simple tube in some larvae, it consists in most 
 adults chiefly of a series of chambers, each of- which 
 has on each side a valvular opening, or ostium 
 (Fig. 161), which permits the ingress of blood but 
 opposes its egress; within the chambers occur 
 other valvular folds that allow the blood to move 
 forward only. With few exceptions (Ephemeridae) 
 the dorsal vessel is blind behind and the blood can 
 enter it only through the lateral ostia. 
 
 Aorta. — The posterior, or pulsating portion 
 {heart) of the dorsal vessel is confined for the most 
 part to the abdomen; the anterior portion, or aorta, 
 extends as a simple attenuated tube through the 
 thorax and into the head, where it passes under 
 the brain and usually divides into two branches gel of beetk.^LMcanws.^^^ 
 (Fig. 164), each of which may again branch. In ^o"^*^: «^' ^^^^y muscle; o. 
 
 \ , 7 , , 1 1 1 1 1 1 ostium.— After Straus- 
 
 the head the blood leaves the aorta abruptly and Durckheim. 
 enters the general body cavity; 
 
 Alary Muscles. — Extending outward from the "heart," or pro- 
 pulsatory portion, and making with the dorsal wall of the body a pericar- 
 dial chamber, is a loose diaphragm, formed largely by paired fan-like 
 muscles — the alary muscles (Figs. 160, 162). These are thought to assist 
 the heart in its propulsatory action. 
 
 Structure of the Heart.— The wall of the heart is remarkably thin, 
 and consists essentially of a muscular layer containing closely-set circular 
 or spiral fibers and separated longitudinal fibers, with scattered nucle- 
 ated cells among the fibers. This muscular tube is between two layers: 
 
aio 
 
 ENTOMOLOGY 
 
 ail inner membrane, or sarcolemma, and an outer layer of elastic con- 
 nective tissue, the adventitia. 
 
 Pericardial Cells. Nephrocytes. — The pericardial cells occur gener- 
 ally in larvae and imagines in the vicinity of the heart, usually on each 
 side of the heart, and arranged frequently in longitudinal "garland-like" 
 
 Fig. i6i. — Diagram of a portion of the 
 heart of a dragon fly nymph, Epilheca. 
 o, ostium; v, valve; the arrows indicate 
 the course of the blood. — After Kolbe. 
 
 Fig. 162. — Diagrammatic cross-section of 
 pericardial region of a grasshopper, CEdipoda. 
 a, alary muscle; d, dorsal vessel; s, suspensory 
 muscles; sp, septum. — After Graber. 
 
 series. They vary greatly in position, number, form, size and contents, 
 and evidently bear some relation to the circulatory system; though 
 many functions have been assigned to them. In allusion to their 
 supposed excretory function, these cells have been named nephrocytes, 
 the term applying particularly to such cells as select and absorb acid 
 ammonia carmine, when that stain is injected into the living insect. 
 
 Ventral Sinus.— In many if not most insects a pulsatory septum 
 (Fig. 180, v) extends across the floor of the body cavity to form a sinus, 
 
 Fig. 163. — Blood corpuscles of a grasshopper, Slenobothrus. a-f, corpuscles covered 
 with fat-globules; g, corpuscle after treatment with glycerine, showing nucleus. — After 
 Graber. 
 
 in which the blood flows backward, bathing the ventral nerve cord as it 
 goes. This ventral sinus supplements the heart in a minor way, as do 
 also the local pulsatory sacs which have been discovered in the legs 
 of aquatic Hemiptera and the head of Orthoptera. 
 
 Blood. — The blood, or hcemolymph, of an insect consists chiefly of a 
 watery fluid, or plasma, which contains corpuscles or leucocytes. Though 
 
ANATOMY AND PHYSIOLOGY 
 
 usually colorless, the plasma is sometimes yellow (Coccinellidae, 
 Meloidae), often greenish in herbivorous insects from the presence of 
 chlorophyll, and sometimes of other colors; often the blood owes its 
 hue to yellow or red drops of fat on the surface of the blood corpuscles 
 Fig. 163). 
 
 Haemocytes. — The corpuscles or hcBmocytes {leucocytes) are minute 
 nucleated cells, 6 to 30 /x in diameter, variable in form even in the same 
 species, but commonly (Fig. 163) round, oval or ovate in outline, 
 though often disk-shaped, elongate or amoeboid in form. 
 
 Function of the Blood. — The blood 
 of insects contains many substances, 
 including egg albumin, globulin, fibrin, 
 iron, potassium and sodium (Mayer), 
 and especially such a large amount of 
 fatty material that its principal function 
 is probably one of nutrition; the blood 
 of an insect contains no red corpuscles 
 and has little or nothing to do with the 
 aeration of tissues, that function being 
 relegated to the tracheal system. 
 
 Circulation.— The course of the cir- 
 culation is evident in transparent aquatic 
 nymphs or larvae. In odonate or ephe- 
 merid nymphs, currents of blood may be 
 seen (Fig. 164) flowing through the spaces 
 between muscles, tracheae, nerves, etc., 
 and bathing all the tissues; separate Fig- 164.— Diagram to indicate the 
 
 . course of the blood in the nymph of a 
 
 outgomg and mcommg streams may be dragon fly, Epitheca. a, aorta; h. 
 
 distinguished in the antenna and legs; heart; the arrows show directions taken 
 ° ° ' by currents of blood. — After Kolbe. 
 
 the returning blood flows along the sides 
 
 of the body and through the ventral sinus and the pericardial chamber, 
 eventually to enter the lateral ostia of the dorsal vessel. A circulation 
 of blood occurs in the wings of freshly emerged Odonata, Ephemerida, 
 Coleoptera, Lepidoptera, etc., the currents trending along the tracheae; 
 this circulation ceases, however, with the drying of the wings. 
 
 The chambers of the dorsal vessel expand and contract successively 
 from behind forward. At the expansion (diastole) of a chamber its ostia 
 open and admit blood; at contraction (systole) the ostia close, as well as 
 the valve of the chamber next behind, while the chamber next in front 
 expands, affording the only exit for the blood. The valves close partly 
 through blood-pressure and partly by muscular action. 
 
112 ENTOMOLOGY 
 
 The rate of pulsation depends to a great extent upon the activity of 
 the insect and upon the temperature and the amount of oxygen or car- 
 bonic acid gas in the surrounding atmosphere. Oxygen accelerates the 
 action of the heart and carbonic acid gas retards it. A decrease of 8° or 
 io° C. in the case of the silkworm lowers the number of beats from 30 or 
 40 to 6 or 8 per minute. The more active an insect, the faster its heart 
 beats. 
 
 The rate of pulsation is very different in the different stages of the 
 same insect. Thus in Sphinx ligustri, according to Newport, the mean 
 number of pulsations in a moderately active larva before the first molt 
 is about 82 or 83 per minute; before the second molt, 89, sinking to 63 
 before the third molt, to 45 before the fourth, and to 39 in the final 
 larval stage; but the force of the circulation increases as the pulsations 
 decrease in number. During the quiescent period immediately preced- 
 ing each molt, the number of beats is about 30. In the pupal stage 
 the number sinks to 22, and then lowers until, during winter, the pulsa- 
 tions almost cease. The moth in repose shows 41 to 50 per minute, and 
 after flight as many as 139. 
 
 8. Fat-Body 
 
 The fat-body appears (Fig. 165) as many-lobed masses of tissue filling 
 in spaces between other organs and occupying a large part of the body 
 cavity. The distribution of the fat-body is to a certain extent definite, 
 however, for the fat-tissue conforms to the general segmentation and is 
 arranged in each segment with an approach to symmetry. Much of 
 this tissue forms a distinct peripheral layer in each segment, and masses 
 of fat-body occur constantly on each side of the alimentary tract and 
 also at the sides of the dorsal vessel, in the latter case forming the 
 pericardial fat-body. 
 
 Fat-Cells. — The fat-cells (Fig. 166) are large and at first more or 
 less spherical, with a single nucleus (though there are said to be two in 
 Apis and several in Musca), but the cellular structure of the fat- tissue is 
 often difficult to make out because the cells are usually filled with glob- 
 ules of fat (Fig. 167), while old cells break down, leaving only a disorderly 
 network. The fat-cells sometimes contain an albuminoid substance, and 
 usually the fat-body includes considerable quantities of uric acid or its 
 derivatives, frequently in the form of conspicuous concretions. 
 
 Functions. — The physiology of the fat-system is still obscure. 
 Probably the fat-body combines several functions. In caterpillars and 
 other larvae it furnishes a reserve supply of nutriment, at the expense of 
 
ANATOMY AND PHYSIOLOGY 
 
 113 
 
 Fig. 165. — Transverse section of the abdomen of a caterpillar, Pieris rapm. b, blood cor- 
 puscles; c, cuticula; d, dorsal vessel; /, fat-body; g. ganglion; h, hypodermis; I. leg;w, 
 muscle; mi, mid intestine, containing fragments of cabbage leaves; mt, Malpighian tube; s, 
 silk gland; sp, spiracle; tr, trachea. 
 
 which the metamorphosis takes place; the amount of fat increases as 
 the larva grows, and diminishes in the pupal stage, though some of it 
 lasts over to furnish nourishment for the 
 imago and its germ cells. The gradual 
 accumulation of uric acid and urates in 
 the fat-body indicates an excretory func- 
 tion, particularly in Collembola, which 
 have no Malpighian tubes. The intimate ^^^ i66.-Fat-ceiis of a eater- 
 association between the ultimate tracheal pillar, Pieris. a, cells filled with 
 
 , , r . ^ 11 1 J drops of fat; 5, cell freed of fat-drops, 
 
 branches and the fat-body has led some showing nucleus.— After Kolbe. 
 authorities to ascribe a respiratory func- 
 tion to the latter. A close relation of some sort exists also be- 
 tween the fat-system and the blood-system; fat-cells are found free 
 in the blood, and the blood corpuscles originate in the thorax and 
 
114 
 
 ENTOMOLOGY 
 
 abdomen from tissues that can scarcely be distinguished from fat- 
 tissues. The corpuscles {leucocytes, or phagocytes) which in some insects 
 absorb effete larval tissues during metamorphosis have been by some 
 authors regarded as wandering fat-cells. Cells constituting the peri- 
 cardial fat-body are attached to the 
 lateral muscles {alary muscles) of the 
 dorsal vessel, but almost nothing is 
 definitely known as to their function. 
 CEnocytes. — Associated with the 
 fat-body proper and with tracheae as 
 well are the peculiar yellow cells known 
 as cenocytes (Fig. i68), that occur in 
 abdominal segments of larvae. These 
 cells are enormous in size as compared 
 with all other insect-cellsexceptingova, 
 and are essentially isolated from one 
 Fig. 167.— Section through fat-body of a another, though grouped among tra- 
 siikworm. showing nucleated cells, loaded cheal branches into loosc clusters, One on 
 
 with drops of fat. 
 
 each side of a spiracle-bearing segment. 
 
 After arising from the primitive ectoderm the cenocytes never divide, 
 but gradually increase in size (Wheeler), and their size is in a general way 
 proportional to that of the fat-body. 
 
 Their function has been problematical until recently. Many ob- 
 servers have regarded them as ductless glands, having seen "microscop- 
 ical exudations around the periphery of the cytoplasm, 
 especially at times when the nucleus is greatly rami- 
 fied, and therefore manifesting its great activity" 
 (Glaser). 
 
 R. W. Glaser has thrown light upon the nature of 
 the oenocytic fluid. By using three-year-old caterpillars 
 of the leopard moth, Zeuzera pyrina, which have a 
 great amount of fatty tissue and correspondingly large 
 cenocytes, he was able to extract enough of the fluid 
 for chemical experiments. He found by carefully con- ^^^- 168.— CEno- 
 
 -^ -^ cytes and accom- 
 
 ducted tests that the fluid had the power of oxidizing panying tracheae, 
 fats, by means of enzymes known as oxidases (though siik^o^.^"^^'^ °^ ^ 
 no fat-splitting enzyme, or lipase, was present), and 
 concluded that the secretion of the cenocytes is used to oxidize the 
 reserve food stored up by the larva in the form of fat. 
 
 Photogeny. — This phenomenon appears sporadically and by various 
 means in protozoans, worms, insects, fishes and other animals. Lumi- 
 
ANATOMY AND PHYSIOLOGY 115 
 
 nosity in insects, though sometimes merely an incidental and pathologi- 
 cal effect of bacteria, is usually produced by special organs in which 
 hght is generated, probably by the oxidation of a fatty substance. 
 
 There are not many luminous insects. Those best known are the 
 Mexican and West Indian beetles of the genus Pyrophorus (Elateridse) , 
 in which the pronotum bears a pair of luminous spots, and the common 
 fireflies (Lampyrid^). In Lampyridae the light is emitted from the 
 ventral side of the posterior abdominal segments, and the structure of 
 the photogenic organ is essentially the same throughout the family. 
 In Photinus this organ (Fig. 169) consists of two layers; a ventral photo- 
 genic layer and a dorsal reflecting layer. The latter, white and opaque, 
 consists of polygonal cells containing large quantities of crystals of ur- 
 ates; the former layer is composed 
 of tracheal structures and inter- 
 vening parenchyma cells. The 
 tracheae branch profusely in the 
 photogenic layer, where the larger 
 air-tubes are each surrounded by 
 a more or less cylindrical mass of 
 cells; tracheal branches penetrate 
 between the cells of each cylinder, 
 at the edge of which they pass into 
 tracheoles which penetrate the ^ 
 
 photogenic tissue and anastomose ^^^ ,69.-Transverse section of portion of 
 
 with those of adjacent cylinders; photogenic organ of a firefly, Photinus. c, 
 
 1 c A-\^ 4. „„V,^^lo,. cylinder;^, photogeniclayer;*-, reflecting layer; 
 
 in the meshes of the tracheolar ^/trachekf— After Townsend. 
 network is agranular substance of 
 
 fatty nature ("differentiated fat-body"), the oxidation of which is the 
 source of the luminosity, it is inferred. The photogenic tissues of 
 Photinus, after being dried and kept in sealed tubes, have retained their 
 photogenic power for more than eighteen months, glowing after this 
 interval upon the " application of water in the presence of air or oxygen " 
 (McDermott). Three factors are involved in the production of the 
 light: a substance to be oxidized, oxygen and water. 
 
 Professor W. E. Burge has found that the catalase content of a 
 luminous insect where oxidation is presumably more intense is greater 
 than that of a non-luminous insect where oxidation is less intense. 
 
 The rays emitted by the common fireflies are remarkable in being 
 almost entirely light rays. According to Young and Langley, the radia- 
 tions of an ordinary gas-flame contain less than three per cent, of visible 
 
Il6 ENTOMOLOGY 
 
 rays, the remainder being heat or chemical rays, of no value for illumina- 
 ting purposes; while the light-giving efficiency of the electric arc is only 
 ten per cent, and that of sunhght only thirty-five per cent. The luminous 
 efficiency of the firefly is, however, not much under one hundred per 
 cent.; in Photuris pennsylvanica it is about ninety-two per cent., accord- 
 ing to Coblentz — an efficiency as yet unapproached by artificial means. 
 The actinic power of the light is so slight that it affects a photographic 
 plate only after a long exposure. . Coblentz, who has applied most 
 refined methods of measurement to the radiation of fireflies, found 
 that exposures of one to five hours were necessary with the spectro- 
 graph. He was unable to detect any infra-red radiation; the thermal 
 radiation, if present, being immeasurably small as yet. The intensity 
 of the glow averages 3'^o>ooo candle power in our common fireflies, 
 according to Coblentz. 
 
 This luminosity serves to bring the sexes together. "The male flies 
 over the tops of the grasses, weeds, etc., dropping down between them 
 and flashing; any females that come within the range of his flash, answer 
 by their slower flash; if the male sees this answering flash from one, he 
 approaches her, flashes again, to which she answers, and he then finally 
 locates her definitely by means of subsequent flashes," as McDermott 
 says. He found that he coifld get responses from the females by imi- 
 tating the flash of the male with a small electric bulb or even with a com- 
 mon safety match, and that he could deceive the males also by flashing 
 the tiny electric fight after the manner of the female. 
 
 Synchronism. — Several observers in the PhiHppines and East 
 Indies have seen the phenomenon of thousands of fireflies flashing 
 exactly in unison; all the fireflies in the same tree, for example, flashing 
 simultaneously (105-109 flashes per minute, in one instance), with regular 
 intervals of darkness. This rare phenomenon, to which Professor E. S. 
 Morse called attention, has attracted considerable interest in the 
 columns of Science. There seems to be no doubt as to the accuracy of 
 the observations, but an explanation as to how the synchronism is 
 effected and regulated is still lacking. The phenomenon can hardly be 
 due to chance when thousands of individuals are involved. The 
 fireflies referred to, in Siam and the Philippines, belong to the genus 
 Calaphotia (0. A. Reinking). 
 
 9. Respiratory System 
 
 In insects, as contrasted with vertebrates, the air itself is conveyed to 
 the remotest tissues by means of an elaborate system of branching air- 
 
ANATOMY AND PHYSIOLOGY 
 
 117 
 
 tubes, or trachece, which receive air through paired segmentally-arranged 
 spiracles. Each spiracle is commonly the mouth of a short tube which 
 opens into a main tracheal trunk (Fig. 170) extending along the side of 
 the body. From the two main trunks branches are sent which divide 
 and subdivide and terminate in extremely dehcate tubes, which pene- 
 trate even between muscle fibers; between the ommatidia of the com- 
 pound eyes and possibly enter cells. In 
 most cases each main longitudinal trunk 
 gives off in each segment (Fig. 171) three 
 large branches: (i) an upper, or dorsal, 
 branch which goes to the dorsal muscles; 
 (2) a middle, or visceral, branch, which 
 supplies the alimentary tract and the 
 reproductive organs; (3) a lower, or 
 ventral, branch, which pertains to the 
 ventral ganglia and muscles. 
 
 In many swiftly flying insects (dragon 
 flies, beetles, moths, flies and bees) there 
 occur tracheal pockets, or air-sacs, which 
 were formerly and erroneously supposed 
 to diminish the weight of the insect, but 
 are now regarded as simply air-reser- 
 voirs. Sacs filled with air lessen the 
 specific gravity of an insect in a fluid 
 medium; but do not increase the buoy- 
 ancy of an insect in the air, unless the 
 contained air is warmer than the sur- 
 rounding air; and in the case of birds, 
 it has been found that the air contained 
 in the bones, though warmer than the 
 
 „ ,. , ... Fig. 170. — Tracheal system of an 
 
 SUrrOUndmg medmm, has no appreciable insect, a, antenna; b, brain; I, leg; 
 
 effect on flight. "• ^^^^^ ^°'"^; ^' palpus; s, spiracle; 
 
 ^ ' ^ St, spiracular, or stigmatal, branch; t, 
 
 T3rpeS of Tracheation. Two types main tracheal trunk; ?;, ventral branch; 
 
 r , 1 , , T .• • 1 1 J- i>s, visceral branch. — After Kolbe. 
 
 of tracheal system are distmguished tor 
 
 convenience: (i) the primary, open, or holopneustic type described above, 
 in which the spiracles are functional; (2) the secondary, closed, or apneus- 
 tic type, in which the spiracles are either functionless or absent. This 
 type is illustrated in Collembola and such aquatic nymphs and larvae as 
 breathe either directly through the skin or else by means of gills. The 
 two types are connected by all sorts of intermediate stages. 
 
Il8 ENTOMOLOGY 
 
 Tracheal Gills. — In many aquatic nymphs and larvae the spiracles 
 are suppressed (though they become functional in the imago) and res- 
 
 FiG. 171. — Diagrammatic cross-section of the thorax of an insect, a, alimentary canal; 
 d, dorsal vessel; g, ganglion; s, spiracle; w, wing; i, dorsal tracheal branch; 2, visceral 
 branch; 3, ventral branch. 
 
 piration is effected by means of gills; these are cuticular outgrowths 
 which contain tracheas and tracheoles and are commonly lateral or 
 
 caudal in position. Lateral tracheal gills 
 are highly developed in ephemerid 
 nymphs (Fig. 172), in which a pair occurs 
 on some or all of the first seven segments 
 of the abdomen; a few genera have 
 cephalic or thoracic gills. Larvae of Tri- 
 choptera have paired abdominal gills 
 varying greatly in form and position, 
 and Perlidae often have paired thoracic 
 gills. Caudal tracheal gills are conspicu- 
 ous in nymphs of damsel flies (Fig. 173) 
 as three foliaceous appendages. A few 
 coleopterous larvae of aquatic habit, as 
 Gyrinus and Cnemidotus, possess tracheal 
 Jnof a'M^ %Ty„S, 'Xi-S g"'^- ^ ^o also caterpillars of the genus 
 variabilis. Enlarged. Pam/>owya; (Fig. 1 74) , which f eed on the 
 
 leaves of several kinds of water plants. 
 
 Though manifold in form, tracheal gills are usually more or less 
 
 foliaceous or filamentous, presenting always an extensive respiratory 
 
 surface; their integument is thin and the tracheae spread closely beneath 
 
ANATOMY AND PHYSIOLOGY 
 
 119 
 
 Fig. 173. — Caudal 
 gills of a damsel fly 
 nymph, enlarged. 
 
 it. These adaptations are often supplemented by waving movements of 
 the gills, as in May fly nymphs, and by frequent movements of the 
 insect from one place to another. 
 
 Especially noteworthy are the rectal tracheal gills of odonate nymphs. 
 In these insects the lining of the rectum forms numerous papilla) or 
 lamellae, which contain a profusion of delicate tra- 
 cheal branches; these are bathed by water drawn 
 into the rectum and then expelled, at rather irregu- 
 lar intervals. A similar rectal respiration occurs 
 also in ephemerid nymphs and mosquito larvae. 
 
 A few forms, chiefly Perlidae, are exceptional in 
 retaining tracheal gills in the adult stage; in some 
 imagines they are merely vestiges of the nymphal gills, but in others, 
 such SiS Pteronarcys (Fig. 19), which habitually dips into the water 
 and rests in moist situations, the gills probably supplement the spiracles. 
 Further details on the respiration of aquatic insects 
 are given in Chapter IV. 
 
 Blood-gills. — In a few aquatic larvae, Simulium 
 and Chironomus for example, there are thin tubular 
 evaginations of the integument known as blood-gills, 
 into which the blood flows. In trichopterous larvae 
 (caddis-worms) the blood-gills are eversible. Some 
 authors regard the ventral eversible sacs of Scolo- 
 pendrella and Thysanura, as well as the vesicles of 
 the ventral tube of Collembola, as blood-gills. 
 
 Spiracles. — The paired external openings of the 
 tracheae, termed spiracles or stigmata, occur on the 
 sides of the thorax and abdomen; there being not 
 more than one pair to a segment, though not all 
 segments bear them. As a rule, there are two tho- 
 racic and eight abdominal pairs; these belonging to 
 Fig. 174. — Cater- the mesothorax, metathorax, and first eight abdom- 
 £l.a/?. JZTIZ inal segments, respectively. Adult insects do not 
 cheai gills. Length, 15 have morc than ten pairs, with the exception of 
 
 mm. — After Hart. . ^ e \ 
 
 Japyx (see page 60, footnote). 
 
 The spiracles, variable in position, are situated usually between two 
 segments of the body; but often at the anterior borders of the seg- 
 ments to which they belong; though they may occur farther back on 
 the segments. 
 
 In most embryo insects there are eleven pairs of spiracles — three 
 
I20 ENTOMOLOGY 
 
 thoracic and eight abdominal; but in adults the prothoracic pair is 
 
 almost always suppressed. (See page 60.) 
 
 Though tracheae are absent in most Collembola, Sminthurides 
 aquaticus has tracheae in the head, which open through 
 a pair of spiracles on the posterior part of the head, 
 there being a spiracle on each side of the neck. Two 
 other species of Collembola, Sminthurus fuscus and 
 Actaletes neptuni, are likewise known to have such a 
 tracheal system, limited to the head. 
 
 The spiracles are usually provided with bristles, 
 hairs or other processes to exclude dust; or the hairs 
 of the body may serve the same purpose, as in Lepidop- 
 tera and Diptera; in many beetles the spiracles are pro- 
 tected by the elytra; but in other beetles and in many 
 Hemiptera and Diptera the spiracles are unprotected 
 externally. Larvae that live in water or mud may have 
 Fig. 175.— Larva spiracles at the end of a long tube, which can be 
 
 ^ciavipes! ^sh^winl. thrust up into the pure air; this is true of the dipter- 
 
 respiratory tube.— Q^g larvag of Eustalis, BUtacomorpha (Fig. 175) and 
 
 Natural size. — After i \ o i ^/ 
 
 Hart. CuUx (Fig. 232). 
 
 Closure of Spiracles. — As a rule, a spiracle is opened 
 and closed periodically by means of a valve, operated by a special occ/w^or 
 muscle. In dipterous larvae the closure is effected by the contraction of 
 
 Fig. 176. — Apparatus for closing the spiracular trachea in a beetle, Lucanus. A, 
 trachea opened; B, closed; b, bow; bd, band; c, external cuticula; I, lever; m, muscle; s, 
 spiracle; t, trachea. — After Judeich and Nitsche. 
 
 a circular muscle, but Coleoptera and Lepidoptera, among other insects, 
 have a somewhat complex apparatus for closing the trachea immediately 
 behind the spiracle. Thus, in the stag-beetle, a crescentic bow (Fig. 
 176, b) extends half around the trachea, and the rest of the circumfer- 
 ence is spanned by a lever (I) and a band {bd) ; these three chitinous parts. 
 
ANATOMY AND PHYSIOLOGY 
 
 articulated together, form a ring around the trachea. Furthermore, a 
 muscle (m) connects the lever and the band. As the muscle shortens, 
 the lever turning upon the end of the band as a fulcrum, pulls the bow 
 
 Fig. 177. — Structure of a 
 trachea, h, tracheal hypo- 
 dermis; i, intima; I taenidium. 
 
 Fig. 178. — Tracheolar end-network from silk gland 
 of Porthelria dispar. p, peritracheal membrane; t, 
 tracheal capillary. — After Wistinghausen. 
 
 toward the lever and band until the enclosed trachea is pinched together. 
 When the muscle relaxes, the trachea opens by its own elasticity. 
 
 Structure of Tracheae. — The tracheae originate in the embryo as 
 simple in-pocketings of the outer germ layer, or ectoderm, and from 
 
 Pig. 179. — Transverse sections of abdominal segments to illustrate respiratory move- 
 ments. A, cockroach (Blalta); B, bee (Bombus); s, sternum; t, tergum. The dotted lines 
 indicate positions of terga and sterna after expiration; the continuous lines, after inspira- 
 tion. — After Plateau. 
 
 these the countless tracheal branches are derived by the same process of 
 invagination. The lining membrane of a trachea is, then, continuous 
 with the external cuticula, and the cellular wall of a trachea is continu- 
 ous with the rest of the hypodermis. This wall consists of a layer of 
 polygonal cells (Fig, 177) fitting closely together as a pavement epithe- 
 lium. The chitinous lining, or intima, is thickened at regular intervals 
 to form thread-like ridges, which course around the inner circumference 
 
122 ENTOMOLOGY 
 
 in essentially a spiral manner, though the continuity of the so-called 
 spiral thread is frequently interrupted. These elastic threads, or 
 tcBuidia, serve to keep the trachea open without affecting its flexibility. 
 
 On the outer surface of the epithelium is a thin structureless basement 
 membrane. 
 
 Tracheoles. — The ultimate divisions of the air-tubes (Fig. 178) are 
 extremely delicate tubes, or tracheoles, which rarely end bhndly, but 
 anastomose with one another, forming a capillary network of confluent 
 tubes, measuring less than o.ooi mm. in diameter, and filled, not with 
 air, but with a fluid. Respiration takes place doubtless by means of 
 the tracheoles rather than the trachese. 
 
 In a caterpillar, these capillary tubes spread out over the surface of 
 the cells of the silk-glands, according to Wistinghausen; and penetrate 
 into the gland-cells themselves, according to Holmgren; other authors 
 differ also as to the relation of the ultimate branches of the air-tubes to 
 the cells which they serve. 
 
 The tracheoles consist of (i) a well developed peritracheal membrane, 
 which spreads out web-like between the bases of the tubes; and (2) a 
 chitinous intima without taenidia; the tracheoles being connected with 
 the tracheae proper by means of (3) transition cells. 
 
 Unlike tracheae, the tracheolar tubes do not arise directly by in- 
 vagination, but develop each within a single cell of the epithelium of 
 a trachea. 
 
 Respiration. — The external signs of respiration are the regular open- 
 ing and closing movements of some of the spiracles and the rhythmic 
 contraction and expansion of the abdomen. During contraction, the 
 dorsal and ventral walls approach each other (Fig. 179) and during 
 expansion they separate. The tergum moves more than the sternum 
 in Coleoptera and Heteroptera, and vice versa in Locustidae, Odonata, 
 Diptera and aculeate Hymenoptera. The width of the abdomen usu- 
 ally 'changes but little during respiration, for the tergal and sternal 
 movements are taken up by the pleural membranes which, as in the 
 grasshopper, infold at contraction and straighten out at expansion. 
 Other respiratory movements occur, but they are of minor importance. 
 
 The rate of respiration increases or diminishes with the activity of 
 the insect and with temperature and other conditions. In six specimens of 
 Melanoplus diferentialis, held between the fingers, the thoracic spiracles 
 opened and closed respectively 34, 43, 45, 54, 60 and 61 times per 
 minute. Four individuals of M . femur -rubrum under the same circum- 
 stances gave 70, 78, 90 and 92. 
 
ANATOMY AND PHYSIOLOGY 
 
 23 
 
 ,'k 
 
 At expansion inspiration takes place, and at contraction expiration 
 occurs. In the grasshopper, the thoracic spiracles open almost simul- 
 taneously with the expansion of the abdomen. Contraction is effected 
 by special vertical expiratory muscles (Fig. 180), but expansion is due 
 to the elasticity of the abdominal wall, as a rule; this is the reverse of 
 what occurs in mammals, where expiration is passive and inspiration 
 active. Inspiratory muscles are 
 found, however, in Locustidae, Tri- 
 choptera and Hymenoptera. 
 
 Though the respiratory move- 
 Hients of an insect may be studied 
 with a hand-lens, a more precise 
 method is that of Plateau — the chief 
 authority on insect physiology — who 
 made use of the stereopticon to pro- 
 ject an enlarged profile of the insect 
 upon a screen, on which could be 
 marked the different contours of the 
 abdomen at its phases of inspiration 
 and expiration. 
 
 The way in which the air reaches fig. i 80.— Diagrammatic cross-section 
 the finest tracheal branches is not of abdomen of a grasshopper, rroz-idacn^. 
 
 a, dorsal septum, or diaphragm; e*, expira- 
 Clearly ascertained, but it is thought tory muscle; /, fat-body; g, gangHon; K 
 .•i-.-r j-ii-T- 4-u u heart; in, inspiratory muscle; v, ventral 
 
 that air is forced into these tubes by ^.p^^^, ^eiow which is the ventral sinus. 
 
 pressure from the abdominal muscles, The dorsal and ventral septa rise and fall 
 . . periodically. — After Graber. 
 
 while its escape through the spiracles 
 
 is being prevented by the compression of the stigmatal tracheae. 
 The respiratory movements are entirely reflex and are independent 
 of the brain or suboesophageal ganglion, for they continue after decapi- 
 tation and even in the detached abdomen of a grasshopper or dragon 
 fly. Each ventral ganglion of the body is an independent respiratory 
 center for its particular segment. 
 
 10. Reproductive System 
 
 The sexes are always separate in insects, hermaphroditism occurring 
 only as an abnormal condition. The sexual organs, situated in the ab- 
 domen, consist essentially of a pair of ovaries or testes and a pair of ducts 
 (oviducts or seminal ducts, respectively). Primitively, the ducts open 
 separately, as they still do in Ephemeridae, but in almost all other insects 
 
124 
 
 ENTOMOLOGY 
 
 the two ducts enter a common evacuating duct {vagina or ejaculatory 
 duct). The vagina commonly opens just behind the eighth abdominal 
 sternite, and the ejaculatory duct behind the ninth. 
 
 Fig. i8i. — Reproductive system of male 
 beetle, Melolontha. a, accessory gland; c, copu- 
 latory organ; d, ejaculatory duct; s, seminal 
 vesicle; t, testis; 2/,vas deferens. — After Kolbe, 
 
 Fig. 182. — Reproductive system of 
 male Lepidoptera. a, accessory gland; 
 d, ejaculatory duct; /, united testes; v, 
 vas deferens. — After Kolbe. 
 
 Homologies. — As in other animals, the reproductive organs are 
 homologous in the two sexes. Thus: 
 
 Male 
 
 Female 
 
 Testes = Ovaries 
 Seminal ducts = Oviducts 
 Ejaculatory duct = Vagina 
 
 Seminal vesicle = Seminal receptacle 
 Accessory glands = Accessory glands 
 Penis and accessories = Ovipositor 
 
 Male Organs.- — Each testis, though sometimes a single blind tube, is 
 usually a group of tubes or sacs (Fig. 181), testicular follicles , which open 
 into a seminal duct (vas deferens) . In most Lepidoptera the testes are 
 secondarily united into a single mass (Fig. 182) as also in Locustidae. 
 The two seminal ducts enter the common ejaculatory duct, which termi- 
 nates in the intromittent organ, or penis. Often each vas deferens is 
 dilated near its mouth into a seminal vesicle, or reservoir; or there may be 
 only a single seminal vesicle, arising from the common duct. One or 
 more pairs of glands opening into the vasa deferentia or the ductus 
 ejaculatorius secrete a fluid which mixes with the spermatozoa and 
 oftentimes unites them into packets, known as spermatophores. 
 
 All these parts are subservient to the formation, preservation and 
 emission of the spermatozoa. These minute, thread-like bodies (Fig. 
 
ANATOMY AND PHYSIOLOGY 
 
 183) arise in the testicular follicles from a germinal epithelium, and 
 consist, as in vertebrates, of a head, middle-piece and a vibratile tail — 
 without entering into the liner structure. 
 
 Female Organs. — Each ovai^y (Fig. 184) consists of one or more 
 tubes opening into an oviduct. The two oviducts enter a common duct, 
 the vagina, which opens to the exterior, often through an ovipositor. 
 Frequently the vagina is expanded as a pouch, 
 or bursa copulatrix, though in Lepidoptera 
 the bursa and the vagina are distinct from 
 each other and open separately (Fig. 185). 
 In most insects a dorsal evagination of the 
 vagina forms a seminal receptach, or sperma- 
 theca, from which spermatozoa emerge to 
 fertilize the eggs. The accessory glands, 
 either paired or single, provide a secretion for 
 attaching the eggs to foreign objects, cement- 
 ing the eggs together, forming an egg-capsule, 
 etc. 
 
 In each ovarian tube, or ovariole, are found 
 ova in successive stages of growth, the largest 
 and oldest ovum being nearest the oviduct. 
 In the primitive type of egg- tube, as in Thy- 
 sanura and Orthoptera (Fig. 186, A) every 
 chamber contains an ovum; in more special- 
 ized types, every other chamber contains a 
 nutritive cell instead of a germ cell, the nutri- 
 tive cells serving as food for the adjacent ova {B) ; or the nutritive cells, 
 instead of alternating with the ova, may be collected in a special 
 chamber, beyond the ovarian chambers (C). An egg-tube is usually 
 prolonged distally as a terminal filament or suspensor, the free end of 
 which is attached near the dorsal vessel. 
 
 Ovaries and testes arise from indifferent cell or primitive germ cells, 
 which are at first exactly alike in the two sexes. In the female, certain 
 of these cells form ova and others form a, follicle around each ovum (Fig. 
 187). In the male, the primary germ cells form cells termed spermato- 
 gonia; each of these forms a spermatocyte, and this gives rise to four 
 spermatozoa. 
 
 Hermaphroditism. — The phenomenon of hermaphroditism, defined 
 as "the union, real or apparent, of the two sexes in the same individual," 
 occurs among insects only as an extremely rare abnormality (except in 
 
 Fig. 183. — Spermatozoa. 
 A, grasshopper; B, cockroach, 
 Blatla; C, beetle, Copris. — Af- 
 ter BiJTSCHLi and Ballowitz. 
 
126 
 
 ENTOMOLOGY 
 
 Termitoxinia, mentioned beyond). Speyer estimated that in Lepidop- 
 tera only one individual in thirty thousand is hermaphroditic. Bertkau 
 (1889) Hsted 335 hermaphroditic arthropods, of which 8 were crusta- 
 ceans, 2 spiders, 2 Orthoptera, 8 Diptera, 9 Coleoptera, 51 Hymenoptera 
 and 255 Lepidoptera. The large proportion of Lepidoptera is due in 
 great measure to the fact that they are collected oftener thaa 'other 
 insects (excepting possibly Coleoptera) and that sexual dimorphism 
 
 Fig. 184. — Reproductive system of queen 
 honey bee. a, accessory sac of vagina; h, 
 bulb of stinging apparatus; c, colleterial, or 
 cement, gland; o, ovary; od, oviduct; p, 
 poison glands; pr, poison reservoir; r, recep- 
 taculum seminis; re, rectum; v, vagina. — 
 After Leuckart. 
 
 Fig. 185. — Reproductive system of 
 female Lepidoptera. b, bursa copulatrix; /, 
 terminal filament; g, cement glands; o, o, 
 ovaries; od, oviduct; r, receptaculum 
 seminis; v, vagina; vs, vestibule, or entrance 
 to bursa. — After Kolbe. 
 
 is so prevalent in the order that hermaphrodites are easily recognized. 
 
 The most common kind of hermaphroditism is that in which one 
 side is male and the other female, as in Fig. 188. Bertkau found this 
 right-and-left hermaphroditism in 153 individuals. In other instances 
 the antero-posterior kind may occur, as when the fore wings are of one 
 sex and the hind wings of the other; rarely, the characters of the two 
 sexes are intermingled. 
 
 Hermaphroditic insects are such rarities that very few of them have 
 been sacrificed to the dissecting needle in order to determine whether the 
 phenomenon involves the primary organs as well as the secondary 
 sexual characters. Where dissections have been made it has been 
 found usually that hermaphroditism does extend to the reproductive 
 
ANATOMY AND PHYSIOLOGY 
 
 127 
 
 organs themselves. Thus a butterfly with male wings on the right side 
 and female wings on the left would have a testis on the right side of the 
 abdomen and an ovary on the left side. 
 
 True hermaphroditism, existing "only when the essential organs of 
 reproduction are united in one individual," 
 and are functional, is said to occur nor- 
 mally in a peculiar wingless termitophilous 
 fly, Termitoxinia. Other instances of her- 
 maphroditism among insects are, strictly 
 
 Fig. 186. — Types of ovarian 
 tubes. A , without nutritive cells ; 
 B, with alternating nutritive and 
 egg-cells; C, with terminal nutri- 
 tive chamber, c, terminal chamber; 
 e, egg-cell; e/>, follicle epithelium; 
 /, terminal filament; s, strands 
 connecting ova with nutritive 
 chamber; y, yolk, or nutritive 
 cells. — Prom Lang's Lehrbuch. 
 
 Fig. 187. — Ovum of a butterfly, Vanessa, inits fol- 
 licle, e, follicle epithelium; g, germinal vesicle; n, 
 branching nucleus of nutritive cell; o, ovum. — After 
 
 WOODWORTH. 
 
 speaking, examples of gynandromorphism, 
 in which secondary sexual characters of 
 both sexes occur in the same individual. 
 A gynandromorph often has ovaries and 
 testes at the same time, but both are not 
 functional. 
 Parthenogenesis. — Reproduction without fertilization is a normal 
 phenomenon in not a few insects. This parthenogenesis may easily be 
 observed in plant lice. In these insects there are many successive 
 broods consisting of females only, which bring forth living young; at 
 definite intervals, however, and usually in autumn, males appear also, 
 and fertilized eggs are laid which last over winter. This cycKc reproduc- 
 tion, by the way, is known as heterogeny. Among Hymenoptera, 
 parthenogenesis is prevalent, usually alternating with sexual reproduc- 
 tion, as in many Cynipidae. In some Cynipidae, however, males are 
 
128 
 
 ENTOMOLOGY 
 
 Pig. 1 88. — Gynandromorphic gipsy moth, 
 Porthelria dispar; right side, male; left, female. 
 Natural size. — After Taschenberg from Hert- 
 wig's Lehrbuch. 
 
 unknown; such is the case also in some Tenthredinidae. The statement 
 has long been made that the unfertihzed eggs of worker ants, bees and 
 wasps produce invariably males; it has been found, however, that 
 the parthenogenetic worker eggs of the ant Lasius niger may produce 
 normal workers (Reichenbach, 
 Mrs. A. B. Comstock). 
 
 In the honey bee, unfertil- 
 ized eggs produce always males; 
 and it is at present rather gen- 
 erally believed that drones are 
 not produced from fertilized 
 eggs. 
 
 Professor A. F. Shull deter- 
 mined experimentally that un- 
 fertilized eggs of the thysanop- 
 teran, Anthothrips verhasci pro- 
 duce only males; and concluded 
 
 also that fertilized eggs produce only females. Parthenogenesis has 
 been recorded as occurring also in a few moths, some Coccidae and 
 many Thysanoptera. 
 
 Paedogenesis. — In Miastor and a few other genera of Itonididae 
 young are produced by the larva. This extraordinary form of partheno- 
 genesis is termed pedogenesis, and is limited apparently to the family 
 
 Itonididae. The paedogenetic 
 larvae of Miastor (Fig. 189) 
 develop before the oviducts 
 have appeared and escape by 
 the rupture of the mother. 
 After several successive gener- 
 ations of this kind the result- 
 ing larvae pupate and form normal male and female flies . 
 
 An excellent account of Miastor has been given by Dr. Felt, who 
 has discovered this remarkable genus in New York State. 
 
 The pupa of a species of Chironomus occasionally deposits unfer- 
 tihzed eggs, which develop, however, in the same manner as the 
 fertilized eggs of the species. 
 
 Fig. 189. — Young paedogenetic larvae of Miastor 
 in the body of the mother larva. Greatly enlarged. 
 — After PagenstecheR. 
 
CHAPTER III 
 
 DEVELOPMENT 
 
 I. Embryology 
 
 Ovum. — The ovum of an insect, as of any other animal, is a single 
 cell (Fig. 190), witha large nucleus (germinal vesicle), a \a,rge nucleolus, 
 nutritive matter, or yolk {deulo plasm) , contained in cytoplasm, and a 
 cell wall {vitelline membrane) secreted by the ovum. 
 The egg-shell, or chorion, is secreted around the 
 ovum by surrounding ovarian cells. 
 
 Maturation. — As a preparation for fertilization 
 the germinal vesicle divides twice, forming two 
 polar bodies, and as the first of these bodies may 
 itself divide, there result four cells; three of these, 
 however — the polar bodies — are minute and rudi- 
 mentary. 
 
 These phenomena of ovogenesis are paralleled 
 in the development of the spermatozoa, or sperma- 
 togenesis; for the primary spermatocyte gives rise 
 to two secondary spermatocytes, and these to four 
 spermatids, each of which forms a spermatozoon. 
 
 By means of this maturation process the number 
 of chromosomes in the egg-nucleus is reduced to 
 half the number normal for somatic cells (body 
 cells as distinguished from germ cells). A simi- 
 lar reduction occurs also during the develop- 
 ment of the spermatozoon, and when sperm-nucleus 
 and egg-nucleus unite, the resulting nucleus con- 
 tains the normal number of chromosomes. The 
 meaning of these reduction phenomena — highly 
 important from the standpoint of heredity — is a 
 much debated subject. 
 
 Fertilization. — As the eggs pass through the 
 vagina, they are capable of being fertihzed by 
 
 ■ spermatozoa, previously stored in the seminal receptacle. Through 
 the micropyle of the chorion one or more spermatozoa enter and a 
 9 129 
 
 Pig. 190. — Sagittal 
 section of egg of fiy, 
 Musca, in process of fer- 
 tilization, c, chorion; d, 
 dorsal; m, micropyle, 
 with gelatinous exuda- 
 tion; p, male and female 
 pronuclei, before union; 
 pb, polar bodies; pr, 
 peripheral protoplasm; 
 V, ventral; vt, vitelline 
 membrane ; y, yolk. — 
 After H E N K I N G and 
 Blochmann. 
 
I30 
 
 ENTOMOLOGY 
 
 Fig. 191. — Equatorial section of egg of a beetle, 
 Clytra Iceviuscida. b, blastoderm; 5, germ band; 
 y, yolk granule; yc, yolk cell.- — After Lecaillon. 
 
 sperm nucleus unites with the egg-nucleus to form what is known as 
 the segmentation nucleus. Through this union of nuclear substances 
 the qualities of the two parents are combined in the offspring. 
 
 Needless to say, the minute 
 details of the process of fertili- 
 zation are of the highest bio- 
 logical importance. 
 
 Blastoderm. — In an arthro- 
 pod ovum the yolk occupies a 
 central position {centrolecithal 
 type), being enclosed in a thin 
 layer of protoplasm. From the 
 segmentation nucleus just men- 
 tioned are derived many nuclei, 
 some of which migrate out- 
 ward with their attendant pro- 
 toplasm to form with the 
 original peripheral protoplasm 
 a continuous cellular layer, the 
 blastoderm (Fig. 191). 
 Germ Band.— The blastoderm, at first of uniform thickness, be- 
 comes thicker in one region, by cell multiplication, forming the germ 
 hand {primitive streak, etc.); this appears in surface view as an oval 
 or elongate area, denser than the remaining blastoderm, with which 
 it is, of course, continuous. 
 
 Gastmlation. — The germ band next infolds along the median line, 
 
 appearing in cross- 
 section as in Fig. 192 ; 
 the two lips of the 
 median groove dost to- 
 gether over the invagi- 
 nated portion and 
 form an outer layer, or 
 ectoderm (Fig. 193), 
 while the invagi- 
 nated portion spreads 
 out as an inner layer, which is destined to form two layers, known 
 respectively as entoderm and mesoderm. This formation of two primary 
 germ layers by invagination or otherwise is termed gastrulation; it is 
 an important stage in the development of all eggs, and among insects 
 several variations of the process occur. 
 
 Fig. 192. — Transverse section of germ band of Clytra at 
 gastrulation. g, germ band; «, inner layer. — After LecaillON. 
 
DEVELOPMENT 
 
 131 
 
 Amnion and Serosa. — Meanwhile, the blastoderm has been folding 
 over the germ band from either side, as shown in Fig. 192, and at length 
 the two folds meet and unite to form two membranes (Fig. 194), namely, 
 an inner one, or amnion, and an outer one, or serosa. 
 
 ^O^^^' 
 
 Fig. 193. — Transverse section of germ 
 layers and amnion folds of Clytra. a, am- 
 nion; e, ectoderm; i, inner layer (meso- 
 entoderm); s, serosa. — Original, based on 
 L^caillon's figures. 
 
 Fig. 194. — Transverse section of germ 
 layers and embryonal membranes of Clytra. 
 a, amnion; ac, amnion cavity; e, ectoderm; 
 i,- inner layer (meso-entoderm) ; s, serosa. — 
 After Lecaillon. 
 
 Segmentation and Appendages. — On the germ band, which repre- 
 sents the ventral part of the future insect, the body segments are marked 
 off by transverse grooves (Figs. 195, 197) ; this segmentation beginning 
 
 
 
 ii^l^ 
 
 Fig. 195. — Germ band of a beetle, Lina, in three successive stages. A, unsegmented; 
 B, with oral segments demarkated; C, with three oral, three thoracic and two abdominal 
 segments. — After Graber. 
 
 usually at the anterior end of the germ band and progressing backward. 
 Furthermore, an anterior infolding occurs (Fig. 196), forming the stomo- 
 dceum, from which the mouth, pharynx, oesophagus and other parts of 
 the fore gut are to arise; a similar but posterior invagination, or procto- 
 dcBum (Fig. 196), is the beginning, or fundament, of the hind gut. 
 
,'p 
 
 132 ENTOMOLOGY 
 
 At the anterior end of the germ band is a pair of large procephalic 
 lobes (Figs. 195, 197), which eventually bear the lateral eyes, and im- 
 mediately behind these are the 
 fundaments of the antennas. The 
 fundaments of the primary paired 
 appendages are out-pocketings of the 
 ectodermal germ band, and at first 
 antennae, mouth parts and legs are 
 all alike, except in their relative 
 positions. Behind the antennae (in 
 Thysanura and Collembola at least) 
 appears a pair of rudimentary 
 appendages (Fig. 197, i) which are thought to represent the second 
 antennae of Crustacea; instead of developing, they disappear in the 
 embryo or else persist in the adult as mere rudiments. In front of these 
 
 5 Fig. 196. — Diagrammatic sagittal sec- 
 tion of hymenopterous egg to show 
 stomodffial (s) and proctodaeal (p) in- 
 vaginations of the germ band (g). — 
 After Graber. 
 
 
 ,aJ.l.ia:-/i 
 
 
 -t2 
 
 
 -pr 
 
 Fig. 197. — Ventral aspect of germ 
 band of a coUembolan, A nurida tnarit- 
 ima. a, antenna; a^-a", abdominal 
 appendages; i, intercalary append- 
 age; I, labrum; U, left labial append- 
 age; w, mandible; tnx, maxilla; p, 
 procephalic lobe; pr, proctodaeum; 
 "-/', thoracic legs. 
 
 P-4~~ 
 
 si I 
 
 Fig. 198. — Anterior aspect of embryonal mouth 
 parts of a coUembolan, Anurida inaritima. a, 
 antenna ; /, labrum ; Ig, prothoracic leg ; It, left funda- 
 ment of labium; In, lingua; m, mandible; mx, max- 
 illa; p, maxillary palpus; si, superlingua.- — After 
 
 FOLSOM. 
 
 transitory intercalary appendages is the mouth-opening, above which 
 the labrum and clypeus are already indicated by a single, median 
 evagination. Behind the mouth the mandibles, maxillae and labium are 
 
DEVELOPMENT 
 
 ^33 
 
 represented by three pairs of fundaments, and in Thysanura and 
 Collembola a fourth pair is present to form the superlinguae (Fig. 198, si), 
 already referred to. Next in order are the three pairs of thoracic legs 
 (Fig. 197) and then, in many cases, paired abdominal appendages (Figs. 
 197, 199), indicating an ancestral myriopod-like condition; some of these 
 abdominal Hmbs disappear in the embryo but others develop into abdom- 
 inal prolegs (Lepidoptera and Tenthre- ^ ^ 
 dinidae), external genital organs (Orthop- 
 tera, Hymenoptera, etc.) or other structures. 
 The study of these embryonic fundaments 
 sheds much light upon the morphology of 
 the appendages and the subject of segmen- 
 tation. 
 
 Two Types of Germ Bands. — The germ 
 band described above belongs to the simple 
 overgrown type, exemplified in Clytra, in 
 which the germ band retains its original 
 position and the amnion and serosa arise by 
 a process of overgrowth (Figs. 193, 194), as 
 distinguished from the invaginated type, 
 illustrated in Odonata, in which the germ 
 band invaginates into the egg, as in Fig. 
 200, until the ventral surface of the embryo 
 becomes turned around and faces the dorsal 
 side of the egg. In this event, a subse- 
 quent process of revolution occurs, by 
 means of which the ventral surface of the 
 embryo resumes its original position (Fig. 
 201). 
 
 Dorsal Closure. — As was said, the germ 
 band forms the ventral part of the insect. 
 To complete the general form of the body 
 the margins of the germ band extend out- 
 ward and upward (Fig. 202) until they 
 
 finally close over to form the dorsal wall of the insect. Besides this 
 simple method, however, there are several other ways in which the 
 dorsal closure may be effected. 
 
 Nervous System. — Soon after gastrulation, the ventral nervous 
 system arises as a pair of parallel cords from cells (Fig. 203, n) which 
 have been derived by direct proliferation from those of the germ band, 
 
 Fig. 199. — Embryo of CEcan- 
 Ihus, ventral aspect, a, antenna; 
 a^a^, abdominal appendages; e, 
 end of abdomen; /, labrum; li, 
 left fundament of labium; Ip, 
 labial palpus; l^l^, thoracic legs; 
 m, mandible; mp, maxillary- 
 palpus; mx, maxilla; p, pro- 
 cephalic lobe; pr, proctodseum. 
 — After Ayers. 
 
[34 
 
 ENTOMOLOGY 
 
 and are therefore ectodermal in origin. This primitive double nerve 
 cord becomes constricted at intervals into segments, or neuromeres, 
 which correspond to the segments of the germ band. Each neuromere 
 
 Fig. 200.— Diagrammatic sagittal sections to illustrate invagination of germ band in 
 Calopteryx. a, anterior pole; ac, amnion cavity; am, amnion; b, blastoderm; d, dorsal; 
 g, germ band; h, head end of germ band; p, posterior pole; 
 After Brandt. 
 
 serosa; v, ventral; y, yolk.- 
 
 PiG. 201. — Diagrammatic sagittal sections to illustrate revolution of Calopteryx 
 embryo, a, antenna; am, amnion; I, labium; l^P, thoracic legs; w, mandible; mx. maxilla; 
 5, serosa. — After Brandt. 
 
 consists of a pair of primitive ganglia, and these are connected together 
 by paired nerve cords, which later may or may not unite into single 
 cords; moreover, some of the ganglia finally unite to form compound 
 ganglia, such as the brain and the sub oesophageal ganglion. In front of 
 
DEVELOPMENT 
 
 135 
 
 the oesophagus (Fig. 57) are three neuromeres: (i) protocerehrum, which 
 is to bear the compound eyes; (2) deulocerehrum, or antennal neuromere; 
 (3) tritocerehrum, which belongs to the segment which bears the rudi- 
 mentary intercalary appendages spoken of above. Behind the oesopha- 
 gus are, at most, four neuromeres, namely and in order, mandibular, 
 superUtigual (found only in Collembola as yet), maxillary and labial. 
 
 Fig. 202. — Diagrammatic transverse sections to illustrate formation of dorsal wall in 
 the beetle, Leptinotarsa. a, amnion (breaking up in C); g, germ band; 5, serosa.— After 
 Wheeler, from the Journal of Morphology. 
 
 Then follow the three thoracic ganglia and ten or eleven abdominal 
 ganglia. The first three neuromeres always unite to form the brain, 
 and the next four (always three; but four in Collembola and perhaps 
 other insects) , to form the suboesophageal gangHon. Compound 
 ganglia are frequently formed also in the thorax and abdomen by the 
 union of primitive ganglia. 
 
 Tracheae. — The tracheae begin as paired invaginations of the ecto- 
 derm (Fig. 204, /) ; these simple pockets elongate and unite to form the 
 main lateral trunks, from 
 which arise the countless 
 branches of the tracheal 
 system. 
 
 Mesoderm. — From the 
 inner layer which was derived 
 from the germ band by gas- 
 trulation (Figs. 192-194) are 
 formed the important germ 
 
 layers known as mesoderm and entoderm. Most of the layer becomes 
 mesoderm, and this splits on either side into chambers, or ccelom 
 sacs (Fig. 203, c), a pair to each segment. In Orthoptera these 
 coelom sacs are large and extend into the embryonic appendages, but in 
 Coleoptera, Lepidoptera and Hymenoptera they are small. These sacs 
 may share in the formation of the definite body-cavity, though the last 
 arises independently, from spaces that form between the yolk and the 
 
 Pig. 203. — Transverse, section of germ layers 
 of elytra, c, coelom sac; n, neuroblasts (primi- 
 tive nervous cells). — After Lecaillon. 
 
i^b 
 
 ENTOMOLOGY 
 
 mesodermal tissues. From the coelom sacs develop the muscles, fat- 
 body, dorsal vessel, blood corpuscles, ovaries and testes; the external 
 sexual organs, however, as well as the vagina and ejaculatory duct, are 
 ectodermal in origin. 
 
 Entoderm. — At its anterior and posterior ends, the inner layer just 
 referred to gives rise to a mass of cells which are destined to form the 
 mesenteron, from which the mid intestine develops. One mass is ad- 
 jacent to the Wind end of the stomodaeal invagination and the other to 
 that of the proctodaeal in-folding. The two masses become U-shaped 
 (Fig. 205), and the lateral arms of the two elongate and join so that the 
 entodermal masses become connected by two lateral strands of cells; 
 
 Fig. 204. — Transverse section ot abdomen of Clylra embryo at Fig. 205. — Dia- 
 
 an advanced stage of development, a, appendage; e, epithelium of gram of formation 
 
 mid intestine; g, ganglion; m, Malpighian tube; mi, muscular layer of entoderm in Lep- 
 
 of mid intestine; W5, muscle elements; my, mesenchyme (source of linotarsa. <?, e, ento- 
 
 fat-body); s, sexual organ; t, tracheal invagination. — After Lecail- dermal masses; m, 
 
 LON. mesoderm. — A f t e r 
 
 Wheeler. 
 
 by overgrowth and undergrowth from these lateral strands a tube is 
 formed which is destined to become the stomach, and by the disappear- 
 ance of the partitions that separate the mesenteron from the stomodaeum 
 at one end and from the proctodaeum at the other end, the continuity of 
 the alimentary canal is established. ' The fore and the hind gut, then, 
 are ectodermal in origin, and the mid gut entodermal. 
 
 Polyembryony.— In certain Hymenoptera a single egg may give 
 rise to many individuals. Thus in some Chalcididae and Proctotrypidae, 
 according to Marchal, the fertilized ovum segments into many (12-100) 
 embryos, which develop into as many adults, all the individuals from the 
 same ovum being of the same sex. 
 
DEVELOPMENT 
 
 137 
 
 2. External Metamorphosis 
 
 Metamorphosis. — One of the most striking phenomena of insect 
 life is expressed by the term metamorphosis, which means conspicuous 
 change of form after birth. The egg of a butterfly produces a larva; 
 this eats and grows and at length becomes a pupa; which, in turn, de- 
 velops into an imago. These stages are so different (Fig. 28) that with- 
 out experience one could not know that they pertained to the same 
 individual. 
 
 Holometabola. — The more specialized insects, namely, Coleoptera 
 (Fig. 206), Strepsiptera, Neuroptera, Mecoptera, Trichoptera, Lepi- 
 
 FiG. 206. — Cyllene carya. A, larva; B, pupa; C, imago. X 3. 
 
 doptera, Diptera (Figs. 207, 31), Siphonaptera (Fig. 32) and Hymenop- 
 tera (Fig. 287), undergo this indirect, or complete,^ metamorphosis, 
 involving profound changes of form and distinguished by the internal 
 development of the wings and by a pupal stage that is usually inactive, 
 though active in mosquitoes and some midges, and in certain Neuroptera 
 just before the transformation. These insects are grouped together as 
 Holometabola. 
 
 Larvae receive such popular names as "caterpillar" (Lepidoptera) , 
 ''grub" (Coleoptera), and "maggot" (Diptera), while the pupa of a 
 moth or butterfly (especially the latter) is called a "chrysahs." 
 
 'These terms, though somewhat misleading in implication, are currently used. 
 
138 
 
 ENTOMOLOGY 
 
 Heterometabola. — In a grasshopper, as contrasted with a butterfly, 
 the imago, or adult, is essentially like the young at birth, except in hav- 
 ing wings and mature reproductive organs, and the insect is active 
 throughout Hfe, the wings developing externally; hence the meta- 
 morphosis is termed direct, or incomplete. This type of transformation, 
 
 without a true pupal period, is 
 characteristic of the more gener- 
 alized of the metamorphic insects, 
 namely, Orthoptera, Dermaptera, 
 Platyptera, Plecoptera (Fig. 19), 
 Ephemerida (Fig. 20), Odonata 
 (Fig. 2i),Thysanoptera and Hemi- 
 ptera (Fig. 208). These orders 
 constitute the group Heterome- 
 tabola. Within the limits of the 
 group, however, various degrees of 
 metamorphosis occur; thus Plec- 
 optera, Ephemerida and Odonata 
 undergo considerable change of 
 form; a resting, or quiescent, period may precede the imaginal stage, 
 as in Cicada (Fig. 209). In fact, the various kinds of metamorphosis 
 
 Fig 
 
 207. — Phormia regina. 
 puparium; C, imago. 
 
 Fig. 208. — Six successive instars of the squash bug, Anasa trislls. x 2. 
 
 grade into one another in such a way as to make their classification to 
 some extent arbitrary and inadequate. 
 
 As there is no distinction between larva and pupa in most hetero- 
 
DEVELOPMENT 
 
 139 
 
 metabolous insects, it is customary to use the term nymph during the 
 interval between egg and imago. 
 
 As a rare abnormality, a holometabolous larva may possess two 
 pairs of true external wing-pads. This condition has been reported in 
 
 Fig. 209. — Cicada libicen. A, imago emerging from nymphal skin; B, the cast skin; C, 
 imago. Natural size. 
 
 several specimens of the meal worm, Tenebrio molitor (by Heymons), six 
 larvae of the museum beetle, Anthrenus verhasci (A. Busck) and one 
 pyrochroid larva, Dendroides canadensis (P. B. Powell). In these larvae 
 
 Fig. 210. — Eggs of various insects. A, butterfly, Polygonia interrogalionis; B, house 
 fly, Musca domeslica; C, chalcid, Bruchophagus funebris; D, butterfly, Papilio Iroilus; E, 
 midge, Dasyneura trifolii; F, hemipteron, Triphleps insidiosus; G, hemipteron, Podisus 
 maculiventris; H, fly, Drosophila ampelophila. Greatly magnified. 
 
 — all coleopterous — it is comparatively an easy step from the internal 
 wing-rudiment to an external wing-pad, as Dr. W. A. Riley has pointed 
 out. He regards the phenomenon not as an instance of atavism — a 
 harking-back to a period when the larva bore wings — but as an example 
 
I40 
 
 ENTOMOLOGY 
 
 Fig. 211. — Three eggs of the cabbage butter- 
 fly, Pieris rapa. Greatly magnified, but all 
 drawn to same scale. 
 
 of a kind of premature development (known as prothetaly) in which 
 characters normally present in the pupal state are present abnormally in 
 the larva. The latter interpretation is supported by the fact that in 
 Mr. Powell's specimen, in addition to the larval ocelli, the compound 
 
 eyes of the adult are partially 
 developed, and there are more 
 antennal segments than in the 
 normal larva. 
 
 Ametabola. — The most gen- 
 eralized insects, Thysanura and 
 Collembola, develop to sexual 
 maturity without a metamor- 
 phosis; the form at hatching is 
 retained essentially throughout 
 life, there are no traces of wings 
 even in the embryo, and there is no change of habit. These two 
 orders form the group Ametabola. All other insects have a metamor- 
 phosis in the broad sense of the term, and are therefore spoken of as 
 Metahola. In this we follow Packard, rather than Brauer, who uses a 
 somewhat different set of terms to express the 
 same ideas. 
 
 Stadium and Instar. — During the growth 
 of every insect, the skin is shed periodically, 
 and with each molt, or ecdysis, the appearance 
 of the insect changes more or less. The inter- 
 vals between the molts are termed stages, or 
 stadia. ' To designate the insect at any particu- 
 lar stage, the term instar was proposed and is 
 much used; thus the insect at hatching is the 
 first instar, after the first molt the second instar, 
 and so on. 
 
 Eggs. — The eggs of insects are exceedingly 
 diverse in form. Commonly they are more or 
 less spherical, oval, or elongate, but there are 
 innumerable special forms, some of which are 
 quite fantastic. Something of the variety of 
 form is shown in Fig. 210. As regards size, 
 
 most insect eggs can be distinguished by the naked eye; many of 
 them tax the vision, however, for example, the elliptical eggs of 
 Dasyneura leguminicola, which are but .300 mm. in length and .075 
 
 Fig. 212. — Chrysopa, laymg 
 eggs. Slightly enlarged. 
 
DEVELOPMExM I4I 
 
 mm. in width; the oval eggs of the cecropia moth, on the other hand, 
 are as long as 3 mm. 
 
 The egg-shell, or chorion, secreted around the ovum by cells of the 
 ovarian follicle, may be smooth but is usually sculptured, frequently 
 with ridges which, as in lepidopterous eggs, may serve to strengthen the 
 shell. The ornamentation of the egg-shell is often exquisitely beautiful, 
 though the particular patterns displayed are probably of no use, being 
 mcidentally produced as impressions from the cells which secrete the 
 chorion. Variations of form, size and pattern are frequent in eggs 
 of the same species, as appears in Fig. 211. 
 
 Always the chorion is penetrated by one or more openings, constitut- 
 ing the micropyle, for the entrance of spermatozoa. 
 
 As a rule, the eggs when laid are accompanied by a fluid of some sort, 
 which is secreted usually by a cement gland or glands, opening into the 
 vagina. This fluid commonly serves to fasten the eggs to appropriate 
 objects, such as food plants, the skin of other insects, the hairs of 
 mammals, etc.; it may form a pedicel, or stalk, for the egg, as in 
 Chrysopa (Fig. 2.12); may surround the eggs as a gelatinous envelope, 
 as in caddis flies, dragon flies, etc. ; or may form a capsule enclosing the 
 eggs, as in the cockroach. 
 
 The number of eggs laid by one female differs greatly in different 
 species and varies considerably in different individuals of the same 
 species. Some of the fossorial wasps and bees lay only a dozen or so and 
 some grasshoppers two or three dozen, while a queen honey bee may lay 
 a million. Two females of the beetle Prionus laticollis had, respectively, 
 332 and 597 eggs in the abdomen (Mann). A. A. Girault gives the fol- 
 lowing numbers of eggs per female, from an examination of twenty egg- 
 masses of each species: 
 
 M.^xiMUM Minimum Average 
 
 Thyridopteryx ephememformis {hdigwoxm) 1649 465 941 
 
 Malacosoma americana (tent caterpillar) 466 313 375-5 
 
 Chionas pis furf lira (scurfy scale) 84 33 66.5 
 
 Hatching. — Many larvae, caterpillars for example, simply eat their 
 way out of the egg-shell. Some maggots rupture the shell by contor- 
 tions' of the body. Some larvae have special organs for opening the 
 shell; thus the grub of the Colorado potato beetle has three pairs of 
 hatching spines on its body (Wheeler) and the larval flea has on its head 
 a temporary knife-like egg-opener (Packard). The process of hatching 
 varies greatly according to the species, but has received very little 
 attention. 
 
142 
 
 ENTOMOLOGY 
 
 Larva. — Although larvae, generally speaking, differ from one another 
 much less than their imagines do, they are easily referable to their orders 
 and usually present specific differences. Larvae that display individual 
 adaptive characters of a positive kind (Lepidoptera, for example) are 
 easy to place, but larvae with negative adaptive characters (many Dip- 
 tera and Hymenoptera) are often hard to identify. 
 
 Thysanuriform Larvae. — Two types of larvae have been recognized 
 by Brauer, Packard and other authorities: thysanuriform and eruciform; 
 respectively generahzed and specialized in their organization. The 
 former term is applied to many larvae and nymphs (Fig. 213, C) on 
 
 Fig. 213. — Types of larvae. A, B, Thysanura; C, thysanuriform nymph; E-I, cruci- 
 form larvae. A, Campodea; B, Lepisma; C, perlid nymph (Plecoptera) ; D, Libellula (Odo- 
 nata); E, Tenlhredopsis (Hymenoptera); F, Lachnosterna (Coleoptera); G, Melanotus 
 (Coleoptera); H, Bombiis (Hymenoptera); /, Hypoderma (Diptera). 
 
 account of their resemblance to Thysanura, of which Campodea and 
 Lepisma are types. The resemblance lies chiefly in the flattened form, 
 long body, hard plates, long legs and antennae, caudal cerci, well- 
 developed mandibulate mouth parts, and active habits, with the accom- 
 panying sensory specializations. These characteristics are permanent 
 in Thysanura, but only temporary in metamorphic insects, and their 
 occurrence in the latter forms may properly be taken to indicate that 
 these insects have been derived from ancestors which were much like 
 Thysanura. 
 
 Thysanuriform characters are most pronounced in nymphs of Blat- 
 tidae, Forficulidae, Perlidae and Ephemeridae, but occur also in the larvae 
 of some Neuroptera (Mantispa) and Coleoptera (Carabidae and Meloi- 
 dae). These primitive characters are gradually overpowered, in the 
 course of larval evolution, by secondary, or adaptive features. 
 
DEVELOPMENT 
 
 f43 
 
 Eruciform Larvae. — The prevalent type of larva among holometab- 
 olous ipsects is the eruciform (Fig. 213, E-I), illustrated by a caterpillar 
 or a maggot. Here the body is cylindrical and often fleshy; the integ- 
 ument weak; the legs, antennae, cerci, and mouth parts reduced, often 
 to disappearance; the habits sedentary and the sense organs corre- 
 spondingly reduced. These characteristics are interpreted as being 
 results of partial or entire disuse, the amount of reduction being pro- 
 portional to the degree of inactivity. Extreme reduction is seen in the 
 maggots of parasitic and such other Diptera as, securing their food with 
 almost no exertion, are simple in form, thin-skinned, legless, with only 
 a mere vestige of a head and with sensory powers of but the simplest 
 kind. 
 
 Transitional Forms. — The eruciform is clearly derived from the 
 
 Fig. 214. — Mantispa. A, larva at hatching — thysanuriform; B, same larva just before 
 first molt — now becoming eruciform. C, imago, the wings omitted; D, winged imago, 
 slightly enlarged. — A and B after Brauer; C and D after Emerton, from Packard's Text- 
 Book of Entomology, by permission of the Macmillan Co. 
 
 thysanuriform type, as Brauer and Packard have shown, the continuity 
 between the two types being established by means of a complete series 
 of intermediate stages. The beginning of the eruciform type is found 
 in Neuroptera, where the campodeoid sialid larva assumes a quiescent 
 pupal condition. The key to the origin of the complete metamorpho- 
 sis, involving the eruciform condition, Packard finds in the neuropterous 
 genus Mantispa (Fig. 214), the first larva of which is truly campodei- 
 form and active. Beginning a sedentary life, however, in the egg-sac of 
 a spider, it loses the use of its legs and the antennae become partly 
 aborted, before the first molt. In Packard's words, "Owing to this 
 change of habits and surroundings from those of its active ancestors, it 
 
144 ENTOMOLOGY 
 
 changes its form, and the fully grown larva becomes cylindrical, with 
 small slender legs, and, owing to the partial disuse of its jaws, acquires 
 a small, round head." Meloidae (Fig. 220) afford other excellent 
 examples of the transition from the thysanuriform to the cruciform 
 condition during the life of the individual. 
 
 Thysanuriform characters become gradually suppressed in favor of 
 the cruciform, until, in most of the highly developed orders (Mecoptera, 
 Trichoptera, Lepidoptera, Diptera, Siphonaptera and Hymenoptera), 
 they cease to appear, except for a few embryonic traces— an illustration 
 of the principle of ''acceleration in development." 
 
 Growth. — The larval period is pre-eminently one of growth. In 
 Heterometabola, growth is continuous during the nymphal stage, but 
 in Holometabola this important function becomes relegated to the larval 
 stage, and pupal development takes place at the expense of a reserve 
 supply of food accumulated by the larva. 
 
 The rapidity of larval growth is remarkable. Trouvelot found that 
 the caterpillar of Telea polyphemus attains in 56 days 4,140 times its 
 original weight (|^o grain), and has eaten an amount of food 86,000 
 times its primitive weight. Other larvae exceed even these figures; thus 
 the maggot of a common flesh fly attains 200 times its original weight 
 in 24 hours. 
 
 Ecdysis. — The exoskeleton, unfitted for accommodating itself to the 
 growth of the insect, is periodically shed, and along with it go not only 
 such integumentary structures as hairs and scales, but also the chitinous 
 lining, or intima, of the stombdaeum, proctodaeum, tracheae, integumen- 
 tary glands, etc. The process of molting, or ecdysis, in caterpillars is 
 briefly as follows. The old skin becomes detached from the body by an 
 intervening fluid of hypodermal origin; the skin dries, shrinks, is pushed 
 backward by the contractions of the larva, and at length splits near the 
 head, frequently under the neck ; through this split appear the new head 
 and thorax, and the old skin is worked back toward the tail until the 
 larva is freed of its exuvice. The details of the process are, however, by 
 no means simple. Ecdysis is probably something besides a provision 
 for growth, for Collembola continue to molt long after growth has 
 ceased, and the winged May fly sheds its skin once after emergence. 
 The meaning of this is not known, though ecdysis has an excretory 
 importance in the case of Collembola, which are exceptional among 
 insects in having no Malpighian tubes. 
 
 Number of Molts. — The frequency of molting differs greatly in 
 different orders of insects. Locustidae (formerly " Acridiidae ") have 
 
DEVELOPMENT 1 45 
 
 five molts; many Heteroptera, as the chinch bug and squash bug, have 
 five (with six instars) ; the periodical cicada, six (Marlatt) ; the larva of 
 the Colorado potato beetle, three; Lepidoptera usually four or five, but 
 often more, as in Isia Isabella, which molts as many as ten times (Dyar) ; 
 the house fly, Musca domestica, two molts (three larval instars) . Pack- 
 ard suggests that cold and lack of food during hibernation in arctians 
 (as I. Isabella) and partial starvation in the case of some beetles, cause 
 a great number of molts by preventing growth, the hypodermis cells 
 meanwhile retaining their activity. 
 
 The appearance of the insect often changes greatly with each molt, 
 particularly in caterpillars, in which the changes of coloration and 
 armature may have some phylogenetic significance, as Weismann has 
 attempted to show in the case of sphingid larvae. 
 
 Adaptations of Larvae. — Larvae exhibit, innumerable conformities 
 of structure to environment. The greatest variety of adaptive struc- 
 tures occurs in the most active larvae, such as predaceous forms, ter- 
 restrial or aquatic. These have well-developed sense organs, excellent 
 powers of locomotion, special protective and aggressive devices, etc. 
 In insects as a whole, the environment of the larva or nymph and that 
 of the adult may be very different, as in the butterfly or the dragon fly, 
 and the larvae are modified in a thousand ways for their own immediate 
 advantage, without any direct reference to the needs of the imago. 
 
 The chief purpose, so to speak, of the larva is to feed and grow, and 
 the largest modifications of the larva depend upon nutrition. Take as 
 one extreme, the legless, headless, fleshy and sluggish maggot, embedded 
 in an abundance of food, and as the other extreme the active and 
 ''wide-awake" larva of a carabid beetle, dependent for food upon its 
 own powers of sensation, locomotion, prehension, etc., and obHged 
 meanwhile to protect or defend itself. Between these extremes come 
 such forms as caterpillars, active to a moderate degree. The great 
 majority of larval characters, indeed, are correlated with food habits, 
 directly or indirectly; directly in the case of the mouth parts, sensory 
 and locomotor organs, and special structures for obtaining special food; 
 indirectly, as in respiratory adaptations and protective structures, 
 these latter being numerous and varied. 
 
 Larvae that live in concealment, as those that burrow in the ground 
 or in plants, have few if any special protective structures; active larvae, 
 as those of Carabidae, have an armor-like integument, but owe their 
 protection from enemies chiefly to their powers of locomotion and their 
 aversion to Hght (negative phototro pism) ; various aquatic nymphs {Z ait ha, 
 
146 ENTOMOLOGY 
 
 Odonata) are often coated with mud and therefore difficult to distin- 
 guish so long as they do not move; caddis worms are concealed in their 
 cases, and caterpillars are often sheltered in a leafy nest. There is no 
 reason to suppose that insects conceal themselves consciously, however, 
 and one is not warranted in speaking of an instinct for concealment in the 
 case of insects — since everything goes to show that the propensity to 
 hide, though advantageous indeed, is simply a reflex, inevitable, nega- 
 tive reaction to light (negative phototropism) or a positive reaction to 
 contact {positive thigmotropism). 
 
 Exposed, sedentary larvae, as those of many Lepidoptera and Cole- 
 optera, often exhibit highly developed protective adaptations. Cater- 
 pillars may be colored to match their surroundings and may resemble 
 twigs, bird-dung, etc.; or larvae may possess a disagreeable taste or 
 repellent fluids or spines, these odious qualities being frequently 
 associated with warning colors. 
 
 Larvae need protection also against adverse climatal conditions, 
 especially low temperature and excessive moisture. The thick hairy 
 clothing of some hibernating caterpillars, as Isia isabella, doubtless 
 serves to mollify sudden changes of temperature. Naked cutworms 
 hibernate in well-sheltered situations, and the grubs of the common 
 "May beetles," or "June bugs," burrow down into the ground below 
 the reach of frost. Ordinary high temperatures have little effect upon 
 larvae, except to accelerate their growth. Excessive moisture is fatal 
 to immature insects in general — conspicuously fatal to the chinch bug, 
 Rocky Mountain locust, aphids and sawfly larvae. The effect of mois- 
 ture may be an indirect one, however; thus moisture may favor the 
 development of bacteria and fungi, or a heavy rain may be disastrous 
 not only by drowning larvae, but also by washing them off their food 
 plants. 
 
 As a result of secondary adaptive modifications, larvae may differ 
 far more than their imagines. Thus Platygaster in its extraordinary first 
 larval form (Fig. 221) is entirely unlike the larvae of other parasitic 
 Hymenoptera, reminding one, indeed, of the crustacean Cyclops rather 
 than the larva of an insect. As Lubbock has said, the characters of a 
 larva depend (i) upon the group of insects to which the larva belongs 
 and (2) upon the special environment of the larva. 
 
 Pupa. — The term pupa is strictly applicable to holometabolous 
 insects only. Most Lepidoptera and many Diptera have an obtect 
 pupa (Fig. 215), or one in which the appendages and body are compactly 
 united; as distinguished from the free pupa of Neuroptera, Trichoptera, 
 
DEVELOPMENT 
 
 147 
 
 Coleoptera and others, in which the appendages are free (Fig. 206); 
 but this distinction cannot always be drawn sharply. Diptera present 
 also the coarctate type of pupa (Fig. 207), in which the pupa remains 
 enclosed in the old larval skin, or puparium. 
 
 Pupal characters, though doubtless of great adaptive and phylogene- 
 tic significance, have received but little attention. Lepidopterous pupae 
 present many puzzling characters, for example, an eye-like structure 
 (Fig. 216) suggesting an ancestral active condition, such as still occurs 
 among heterometabolous insects. 
 
 Fig. 215. — Obtect 
 pupa of milkweed but- 
 terfly, Anosia plexip- 
 pus, natural size. 
 
 Pig. 216. — Head 
 of chrysalis of Pa- 
 pilio polyxenes, to 
 show eye-like struc- 
 ture. Enlarged. 
 
 Pupation of a Caterpillar.— The process of pupation in a caterpillar 
 has been carefully observed by Riley. The caterpillar of the milkweed 
 butterfly (PI. I, ^) spins a mass of silk in which it entangles its suranal 
 plate and anal prolegs and then hangs downward, bending up the ante- 
 rior part of the body (B) , which gradually becomes swollen. The skin of 
 the caterpillar splits dorsally from the head backward, and is worked 
 back toward the tail (C and D) by the contortions of the larva. 
 
 The way in which the pupa becomes attached to its silken support 
 is rather complex. Briefly, while the larval skin still retains its hold on 
 the support, the posterior end of the pupa is withdrawn from the old 
 integument while the latter is being temporarily gripped between two 
 of the abdominal segments of the pupa, and by the vigorous whirling 
 and twisting of the body the hooks of the terminal cremaster of the pupa 
 are entangled in the silken support. At first the pupa is elongate (£) 
 and soft, but in an hour or so it has contracted, hardened, and assumed 
 its characteristic form and coloration (F). 
 
 Pupal Respiration. — Except under special conditions, pupse breathe 
 by means of ordinary abdominal spiracles. Aquatic pupae have special 
 
148 ^ ENTOMOLOGY 
 
 respiratory organs, such as the tracheal fi.\a.ments of Si mulium (Fig. 233), 
 and the respiratory tubes of Culex (Fig. 232). 
 
 Pupal Protection. — Inactive and helpless, most pupae are concealed 
 in one way or another from the observation of enemies and are pro- 
 tected from moisture, sudden changes of temperature, mechanical shock 
 and other adverse influences. The larvae of many moths burrow into 
 the ground and make an earthen cell in which to 
 pupate; a large number of coleopterous larvae {Lach- 
 A nosterna, Osmoderma, Passalus, Lucanus, etc.) make 
 
 ^^ a chamber in earth or wood, the walls of the cells 
 
 ^^m being strengthened with a cementing fluid or more or 
 
 ^~"'-J less silk, forming a rude cocoon. Silken cocoons are 
 
 fljjB spun by some Neuroptera (Chrysopidae, Fig. 217),. 
 
 ^Hv by Trichoptera (whose cases are essentially cocoons), 
 
 ^Mf Lepidoptera, a few Coleoptera (as Curculionidae, 
 
 ^ Donacia) , some Diptera (as Itonididae) , Siphonaptera, 
 
 and many Hymenoptera (for example, Tenthredi- 
 
 ^^'^- 217— Co- nidae, Ichneumonidae, wasps, bees and some ants). 
 
 coon of Chrysopa, . . 
 
 after emergence of The cocoon-making instinct is most highly devel- 
 
 largf d. ^^ ^ ^ ^^" oped in Lepidoptera and the most elaborate cocoons 
 are those of Saturniidae. The cocoon of Samia 
 cecropia is a tough, water-proof structure and is double (Fig. 218), 
 there being two air spaces around the pupa; thus the pupa is pro- 
 tected against moisture and sudden changes of temperature and from 
 most birds as well, though the downy woodpecker not infrequently punc- 
 tures the cocoon. S. cecropia binds its cocoon firmly to a twig ; Tropcea 
 luna and Telea polyphemus spin among leaves, and their cocoons (with 
 some exceptions) fall to the ground; Callosamia promethea, whose cocoon 
 is covered with a curved leaf, fastens the leaf to the twig with a wrapping 
 of silk, so that the leaf with its burden hangs to the twig throughout the 
 winter. The leaves surrounding cocoons may render them inconspicu- 
 ous or may serve merely as a foundation for the cocoon. While silk and 
 often a waterproof gum or cement form the basis of a cocoon, much 
 foreign material, such as bits of soil or wood, is often mixed in; the 
 cocoons of many common Arctiidae, as Diacrisia virginica and Isia 
 Isabella, consist principally of hairs, stripped from the body of the 
 larva. 
 
 Butterflies have discarded the cocoon, traces of which occur in 
 Hesperiidae, which draw together a few leaves with a scanty supply of 
 silk to make a flimsy substitute for a cocoon. Papilionid and pierid 
 
Successive stages in the pupation of the milkweed caterpillar, Anosia plexippus. Natural 
 
 size. 
 
DEVELOPMENT 15I 
 
 pupae are supported by a silken girdle (Fig. 29), and nymphalid chrysa- 
 lides hang freely suspended by the tail (Fig. 215). 
 
 Cocoon-Spinning. — The caterpillar af Telea polyphemus "feels with 
 its head in all directions, to discover any leaves to which to attach the 
 fibres that are to give form to the cocoon. If it finds the place suitable, 
 it begins to wind a layer of silk around a twig, then a fibre is attached to 
 a leaf near by, and by many times doubling this fibre and making it 
 shorter every time, the leaf is made to approach the twig at the distance 
 necessary to build the cocoon; two or three leaves are disposed like this 
 one and then the fibres are spread between them in all directions, and 
 soon the ovoid form of the cocoon distinctly appears. This seems to 
 
 Fig. 
 
 -Cocoon of Samia cecropia, cut open to show the two silken layers and the 
 enclosed pupa. Natural size. 
 
 be the most difiicult feat for the worm to accompHsh, as after this the 
 work is simply mechanical, the cocoon being made of regular layers 
 of silk united by a gummy substance. The silk is distributed in 
 zigzag lines about one-eighth of an inch long. When the cocoon is 
 made, the worm will have moved his head to and fro, in order to distrib- 
 ute the silk, about two hundred and fifty-four thousand times. After 
 about half a day's work, the cocoon is so far completed that the worm 
 can hardly be distinguished through the fine texture of the wall; then 
 a gummy resinous substance, sometimes of a light brown color, is spread 
 over all the inside of the cocoon. The larva continues to work for four 
 or five days, hardly taking a few minutes of rest, and finally another 
 coating is spun in the interior, when the cocoon is all finished and com- 
 pletely air tight. The fibre diminishes in thickness as the completion 
 of the cocoon advances, so that the last internal coating is not half so 
 thick and so strong as the outside ones." (Trouvelot.) 
 
152 ENTOMOLOGY 
 
 Emergence of Pupa. — Subterranean pupae wriggle their way to 
 
 the surface of the ground, often by the aid of spines (Fig. 219), that 
 
 catch successively into the surrounding soil. These locomotor spines 
 
 may occur on almost any part of the pupa, but occur commonly on the 
 
 abdominal segments, as in lepidopterous pupae; the 
 
 t extremity of the abdomen, also, bears frequently 
 
 one or more spinous projections, as in TipuHdae, 
 Carabidae and Lepidoptera, to assist the escape of 
 the pupa. These structures are found also in pupae, 
 as those of Sesiidae, that force their way out of the 
 stems of plants in which the larvae have lived. The 
 emergence from the cocoon is accomplished in some 
 • cases by the pupa, in others by the imago. Hemero- 
 ^ biidae, Trichoptera and the primitive lepidopteron 
 
 Fig. 219.— Sub- Eriocephala use the pupal mandibles to cut an open- 
 
 terranean pupa of _ _ -^ ^ _ ^ ^ 
 
 Anisoia. Enlarged, ing in the cocoou; whilc many lepidopterous pupae 
 have on the head a beak for piercing the cocoon, or 
 teeth for rending or cutting the silk. 
 
 Eclosion. — During the last few hours before the emergence of a 
 butterfly the colors of the imago develop and may be seen through the 
 transparent skin of the chrysalis (PI. 11 A). No movement occurs, how^- 
 eyer, until several seconds before emergence; then, after a few convul- 
 sive movements of the legs and thorax of the imprisoned insect, the 
 pupa skin breaks in the region of the tongue and legs {B), a secondary 
 split often occurs at the back of the thorax, and the butterfly emerges 
 iC~E) with moist body, elongated abdomen and miniature wings. 
 Hanging to the empty pupa case (F), or to some other available sup- 
 port, the insect dries and its wings gradually expand (G, H) through the 
 pressure of the blood. At regular intervals the abdomen contracts 
 and the wings fan the air, and sooner or later a drop or two of a dull 
 greenish fluid (the meconium) is emitted from the alimentary canal. 
 The expansion of the wings takes place rapidly, and in less than an 
 hour, as a rule, they have attained their full size (/). 
 
 T. polyphemus is "provided with two glands opening into the mouth, 
 which secrete during the last few days of the pupa state, a fluid which is 
 a dissolvent for the gum so firmly uniting the fibres of the cocoon. This 
 liquid is composed in great part of bombycic acid. When the insect has 
 accomplished the work of transformation which is going on under the 
 pupa skin, it manifests a great activity, and soon the chrysahs covering 
 bursts open longitudinally upon the thorax; the head and legs are soon 
 
Successive stages in the emergence of the milkweed butterfly, Anosia plexippus, from the 
 chrysalis. Natural size. 
 
DEVELOPMENT 1 55 
 
 disengaged, and the acid fluid flows from its mouth, wetting the inside of 
 the cocoon. The process of exclusion from the cocoon lasts for as much 
 as half an hour. The insect seems to be instinctively aware [?] that 
 some time is required to dissolve the gum, as it does not make any at- 
 tempt to open the fibres, and seems to wait with patience this event. 
 When the liquid has fully penetrated the cocoon, the pupa contracts its 
 body, and pressing the hinder end, which is furnished with little hooks, 
 against the inside of the cocoon, forcibly extends its body; at the same 
 time the head pushes hard upon the fibres and a little swelling is 
 observed on the outside. These contractions and extensions of the 
 body are repeated many times, and more fluid is added to soften the 
 gum, until under these efforts the cocoon swells, and finally the fibres 
 separate, and out comes the head of the moth. In an instant the legs 
 are thrust out, and then the whole body appears; not a fibre has been 
 broken, they have only been separated. 
 
 "To observe these phenomena, I had cut open with a razor a small 
 portion of a cocoon in which was a living chrysalis nearly ready to trans- 
 form. The opening made was covered with a piece of mica, of the same 
 shape as the aperture, and fixed to the cocoon with mastic so as to make 
 it solid and air-tight; through the transparent mica I could see the move- 
 ments of the chrysalis perfectly well. 
 
 ''When the insect is out of the cocoon, it immediately seeks for a 
 suitable place to attach its claws, so that the wings may hang down, and 
 by their own weight aid the action of the fluids in developing and 
 unfolding the very short and small pad-like wings. Every part of the 
 insect on leaving the cocoon, is perfect and with the form and size of 
 maturity, except the pad-like wings and swollen and elongated abdomen, 
 which still gives the insect a worm-like appearance; the abdomen con- 
 tains the fluids which flow to the wings. 
 
 "When the still immature moth has found a suitable place, it re- 
 mains quiet for a few minutes, and then the wings are seen to grow very 
 rapidly by the afiiux of the fluid from the abdomen. In about twenty 
 minutes the wings attain their full size, but they are still like a piece of 
 wet cloth, without consistency and firmness, and as yet entirely unfit for 
 flight, but after one or two hours they become sufficiently stiff, assuming 
 the beautiful form characteristic of the species" (Trouvelot). The 
 expansion of the wing is due to blood-pressure brought about chiefly by 
 the abdominal muscles. In the freshly-emerged insect, the two mem- 
 branes of the wing are corrugated, and expansion consists in the flatten- 
 ing out of these folds. The wing is a sac, which would tend to enlarge 
 
150 ENTOMOLOGY 
 
 into a balloon-shaped bag, were it not for hypodermal fibres which hold 
 the wing-membranes closely together (Mayer). Tropcea luna and 
 Philosamia cynthia cut and force an opening through the cocoon by 
 means of a pair of saw-like organs, one at the base of each front wing. 
 
 The cocoons of Samia cecropia and Callosamia promethea do not 
 have a gummy coating over the entire interior. In each case the end 
 through which the moth emerges is composed of silken fibres loosely 
 pulled together and not covered with a gummy substance. It is as if 
 each layer of the cocoon was spun into a fringe at this end, the fringes 
 of all layers being bunched together forming a Httle cone. Jn the co- 
 coon of Samia cecropia, it is possible to push a pencil through this 
 fringe with apparently no effort. The fibres part readily, it being neces- 
 sary to break only a few in the extreme outside layer. The same can 
 be said of the cocoon of C. promethea (H. B. Weiss). 
 
 The temperature inside a cocoon is practically the same as that of the 
 surrounding air, there being a constant tendency for the inside tem- 
 perature to approach that of its surroundings. Sudden changes of 
 temperature do not occur within a cocoon. When the outside tem- 
 perature is suddenly lowered, as from io° C to o° C, the temperature in 
 a cocoon falls gradually, and even during a gradual rise the cocoon- 
 temperature lags behind that of its surroundings, on account of the poor 
 conducting qualities of air and silk (H. B. Weiss). 
 
 Hypermetamorphosis. — In a few remarkable instances, metamor- 
 phosis involves more than three stages, owing to the existence of super- 
 numerary larval forms. This phenomenon of hypermetamorphosis 
 occurs notably in the coleopterous genera Melo'e, Epicauta, Sitaris 
 and Rhipiphorus, in Strepsiptera and in several parasitic Hymenoptera. 
 
 In the oil-beetle, Melo'e, as described by Riley, the newly-hatched 
 larva {triungulin) is active and campodea-form. It climbs upon a 
 flower and thence upon the body of a bee {Anthophora) , which carries 
 it to the nest, where it eats the egg of the bee. After a molt, the larva 
 though still six-legged, has become cylindrical, fleshy and less active, 
 resembling a lamellicorn larva; it now appropriates the honey of the bee. 
 With plenty of rich food at hand the larva becomes sluggish, and after 
 another molt appears as a pseudo-pupa, with functionless mouth 
 parts and atrophied legs. From this pseudo-pupa emerges a third 
 larval form, of the pure cruciform type, fat and apodous like the bee- 
 larvae themselves. After these four distinct stages the larva becomes 
 a pupa and then a beetle. 
 
 Epicauta, another meloid, has a similar history. The triungulin 
 
DEVELOPMENT 
 
 :57 
 
 (Fig. 220, A) of E. vittata burrows into an egg-pod of Melanoplus differ- 
 entialis and eats the eggs of that grasshopper. After a molt the second 
 larva {carabidoid form) appears; this (B) is soft, with reduced legs and 
 mouth parts and less active than the triungulin. A second molt and 
 the scarabceidoid form of the second larva is assumed; the legs and mouth 
 parts are now rudimentary and the body more compact than before. 
 A third and a fourth molt occur with little change in the form of the 
 second larva, which is now in its ultimate stage (C) . After the fifth 
 molt, however, the coarctate larva, or pseudo-pupa, appears; this {D) 
 hibernates and in spring sheds its skin and becomes the third larva, 
 
 Fig. 220. — Stages in the hypermetamorphosis of Epicauta. A, triungulin; B, carabi- 
 doid stage of second larva; C, ultimate stage of second larva; D, coarctate larva; E, pupa; F, 
 imago. E is species cinerea; the others are viltata. All enlarged except F. — After Riley, 
 from Trans. St. Louis Acad. Science. 
 
 which soon transforms to a true pupa (£), from which the beetle (F) 
 shortly emerges. Thus the pupal stage is preceded by at least three 
 distinct larval stages. 
 
 Strepsiptera, the subject of two important volumes by Dr. W. D. 
 Pierce, are all hypermetamorphic. These parasites affect almost 
 exclusively Hymenoptera and Homoptera, causing the "stylopized" 
 condition known to collectors of bees, wasps or bugs, in which the pres- 
 ence of the parasite is indicated by a flat disk-like plate (in the female 
 parasite) or a tuberculate rounded projection (male) protruding from 
 between segments of the abdomen. The male is winged but the female 
 is maggot-like and sedentary, a mere sac of eggs, often two thousand 
 or more in number, which hatch inside the body of the mother into active 
 little hexapodous thysanuriform larvae known as triiingulinids . These 
 
158 
 
 ENTOMOLOGY 
 
 are probably carried by the host to flowers or other places where they 
 are able to attach themselves to the bodies of their future hosts. After 
 penetrating into the body of the host the larva grows rapidly ; with the 
 first molt the eyes and legs are lost, the second instar being scarabae- 
 idoid in form; after the second molt the male and female larvae differ 
 in development. 
 
 The most extraordinary metamorphoses have been found among 
 parasitic Hymenoptera, as in Platygaster, a proctotrypid which infests 
 the larva of Cecidomyia. The egg of Platygaster, according to Ganin, 
 
 Pig. 221. — Stages in the hypermetamorphosis of Platygaster. A, first larva; B, second 
 larva; C, third larva; a, antenna; h, brain;/, fat-tissue; h, hind intestine; m, mandible; mo, 
 mouth; ms, muscle; w, nerve cord; r, reproductive organ of one side; s, salivary gland; t, 
 trachea. — After Ganin. 
 
 hatches into a larva of bizarre form (Fig. 221, A), suggesting the crusta- 
 cean Cyclops, rather than an insect. This first larva has a blind food 
 canal and no nervous, circulatory or respiratory systems. After a 
 molt the outHneis oval {B), and there are no appendages as yet, though 
 the nervous system is partially developed. Another molt, and the 
 third larva appears (C), elHptical in contour, externally segmented, with 
 tracheae and a pair of mandibles. From now on, the development is 
 essentially like that of other parasitic Hymenoptera. 
 
 Equally anomalous are the changes undergone by Polynema, a proc- 
 totrypid parasite in the eggs of dragon flies, and by the proctotrypid 
 Teleas, which affects the eggs of the tree cricket {(Ecanthus). In all 
 these cases the larvae go through changes which in most other insects are 
 confined to the egg stage. In other words, the larva hatches before its 
 embryonic development is completed, so to speak. 
 
DEVELOPMENT 159 
 
 Significance of Metamorphosis. — "The essential features of meta- 
 morphosis," says Sharp, "appear to be the separation in time of growth 
 and development and the limitation of the reproductive processes to a 
 short period at the end of the individual life." 
 
 The simplest insects, Thysanura, have no metamorphosis, and show 
 no traces of ever having had one. Hence it is inferred that the first 
 insects had none; in other words, the phenomenon of metamorphosis 
 originated later than insects themselves. Successive stages in the 
 evolution of metamorphosis are illustrated in the various orders of 
 insects. 
 
 The distinctive mark of the simplest metamorphosis, as in Orthop- 
 tera and Hemiptera, is the acquisition of wings; growth and sexual 
 development proceeding essentially as in the non-metamorphic insects 
 (Thysanura and Collembola) . Here the development of wings does not 
 interfere with the activity of the insect; its food habits remain unaltered; 
 throughout life the environment of the individual is practically the same. 
 Even when considerable difference exists between the nymphal and 
 imaginal environments, as in Ephemerida and Odonata, the activity of 
 the individual may still be continuous, even if somewhat lessened as the 
 period of transformation approaches. 
 
 With Neuroptera, the pupal stage appears. In these and all other 
 holometabolous insects the larva accumulates a surplus of nutriment 
 sufficient for the further development, which becomes condensed into 
 a single pupal stage, during which external activity ceases temporarily. 
 
 With the increasing contrast between the organization of the larva 
 and that of the imago, the pupal stage gradually becomes a necessity. 
 Metamorphosis now means more than the mere acquisition of wings, for 
 the larva and the imago have become adapted to widely different en- 
 vironments, chiefly as regards food. The caterpillar has biting mouth 
 parts for eating leaves, while the adult has sucking organs for obtaining 
 liquid nourishment; the maggot, surrounded by food that may be ob- 
 tained almost without exertion, has but minimum sensory and locomotor 
 powers and for mouth parts only a pair of simple jaws; as contrasted 
 with the fly, which has wings, highly developed mouth parts and sense 
 organs, and many other adaptations for an environment which is 
 strikingly unKke that of the larva; so also in the case of the higher 
 Hymenoptera, where maternal or family care is responsible for the help- 
 less condition of the larva. 
 
 Thus it is evident that the change from larval to imaginal adapta- 
 tions is no longer congruous with continuous external activity; a quies- 
 
l6o ENTOMOLOGY 
 
 cent period of reconstruction becomes inevitable (though this statement 
 does not, of course, explain anything). 
 
 As was. said, the cruciform type of larva has been derived from the 
 thysanuriform type, the strongest evidence of this being the fact that 
 among hypermetamorphic insects, the change from the one to the other 
 takes place during the lifetime of the individual. Furthermore, the 
 cruciform condition is plainly an adaptive one, brought about by an 
 abundant and easily obtainable supply of food. The lack of a thysanuri- 
 form stage in the development of the most specialized cruciform larvae, 
 as those of flies and bees, is regarded by Hyatt and Arms as an illustra- 
 tion of the general principle known as "acceleration of development," 
 according to which newer and useful adaptive characters tend to appear 
 earlier and earlier in the development, gradually crowding upon and 
 forcing out older and useless characters. In connection with this sub- 
 ject, the appearance of temporary abdominal legs in embryo bees is 
 significant, as indicating an ancestral active condition. In accounting 
 for the evolution of metamorphosis, the theory of natural selection finds 
 one of its most important applications. 
 
 3. Internal Metamorphoses 
 
 In Heterometabola, the internal post-embryonic changes are as di- 
 rect as the external changes of form; in Holometabola, on the contrary, 
 not all the larval organs pass directly into imaginal organs, for certain 
 larval tissues are demolished and their substance reconstructed into 
 imaginal tissues. When indirect, the internal metamorphosis is 
 nevertheless continuous and gradual, without the abruptness that 
 characterizes the external transformation. In the larval stage imaginal 
 organs arise and grow; in the pupal stage the purely larval organs 
 gradually disappear while the imaginal organs are continuing their 
 development. 
 
 Phagocytes.^The destruction of larval tissues, or histolysis, is due 
 often to the amoeboid blood corpuscles, known as leucocytes or phago- 
 cytes, which attack some tissues and absorb their material, but later 
 are themselves food for the developing imaginal tissues. The construc- 
 tion of tissues is termed histogenesis. 
 
 In Coleoptera the degeneration of the larval muscles is entirely 
 chemical, there being no evidence of phagocytosis, according to Dr. 
 R. S. Breed. Berlese, indeed, goes so far as to deny in general the 
 destructive action of leucocytes on larval tissues. 
 
DEVELOPMENT 
 
 l6l 
 
 Imaginal Buds. — The wings and legs of a fly originate in the larva 
 in the form of cellular masses, termed imaginal buds, or histoblasts, as 
 Weismann discovered. Thus in the larva of Corethra, there are in 
 each thoracic segment a pair of dorsal buds and a pair of ventral buds 
 (Fig. 222), each bud being clearly an evagination of the hypodermis 
 at the bottom of a previous invagination. The six ventral buds form 
 the legs eventually; of the dorsal buds, the middle and posterior pairs 
 form, respectively, the wings and the halteres, and the anterior pair 
 
 Fig. 222. — Diagram- 
 matic transverse section of 
 Corethra larva, to show 
 imaginal buds of wings (w) 
 and legs (I); h, hypoder- 
 mis; i, integument. — Modi- 
 fied from Lang's Lehrbuch. 
 
 C D 
 
 Pig. 223. — Diagrammatic t-ransverse sections of muscid 
 larvae, to show imaginal buds, h, larval hypodermis; i, larval 
 integument; ih, imaginal hypodermis; I, imaginal bud of leg; 
 w, imaginal bud of wing. — Modified from Lang's Lehrbuch. 
 
 form the pupal respiratory processes. Each imaginal bud is situated in 
 a peripodal cavity, the wall of which (peripodal membrane) is continu- 
 ous with the general hypodermis; as the legs and wings develop, they 
 emerge from their peripodal sacs and become free. 
 
 In Corethra but little histolysis occurs, most of the larval structures 
 passing directly into the corresponding structures of the adult. Core- 
 thra is, indeed, in many respects intermediate between heterometabo- 
 lous and holometabolous insects as regards its internal changes. 
 
 Muscidae. — In Muscidae, as compared with Corethra, the imaginal 
 buds are more deeply situated, the peripodal membrane forming a 
 
l62 
 
 ENTOMOLOGY 
 
 stalk (Fig. 223), and the processes of histolysis and histogenesis become 
 extremely complicated. The hypodermis, muscles, alimentary canal 
 and fat-body are gradually broken down and remodeled, and part of 
 the respiratory system is reorganized, though the dorsal vessel and the 
 
 central nervous system, uninterrupted in 
 their functions, undergo comparatively 
 little alteration. 
 
 The imaginal hypodermis of the tho- 
 rax arises from thickenings of the peri- 
 podal membrane which spread over the 
 larval hypodermis, while the latter is 
 gradually being broken down by the 
 leucocytes; in the head and abdomen 
 the process is essentially the same as in 
 the thorax, the new hypodermis arising 
 from imaginal buds. 
 
 Most of the larval muscles, excepting 
 the three pairs of respiratory muscles, 
 undergo dissolution. The imaginal 
 muscles have been traced back to meso- 
 dermal cells such as are always associated 
 with imaginal buds. 
 
 Hymenoptera and Lepidoptera. — 
 The internal transformation in Hymen- 
 optera, according to Bugnion, is less pro- 
 found than in Muscidae and more exten- 
 sive than in Coleoptera and Lepidoptera. 
 The internal metamorphosis in Lepidop- 
 tera resembles in many respects that of 
 Corethra. In both these orders the dorsal 
 pair of prothoracic buds is absent. In 
 a full-grown caterpillar the fundaments of the imaginal legs and 
 wings (Fig. 224) may be seen, the wings in a frontal section of the 
 larva appearing as in Fig. 225. Many of the details of the internal 
 metamorphosis in Lepidoptera have been described by Newport and 
 Gonin. Figure 226, after Newport, shows some of the more evi- 
 dent internal differences in the larva, pupa and imago of a lepidop- 
 terous insect. 
 
 Significance of Pupal Stage. — To repeat — among holometabolous 
 insects the function of nutrition becomes relegated to the larval stage 
 
 Pig. 224. — Imaginal buds of full 
 grown larva of Pieris, dorsal aspect. 
 b, brain; m, mid intestine; s^, pro- 
 thoracic spiracle; s*, first abdominal 
 spiracle; sg, silk gland; /, pro- 
 thoracic bud; II, bud of fore wing; 
 III, bud of hind wing. — After 
 Gonin. 
 
DEVELOPMENT 
 
 163 
 
 "^iSsiuiuiin^j^ 
 
 Fig. 225. — Section through left hind wing in larva of Pieris rapce, the section being a 
 frontal one of the caterpillar; the base of the wing is anterior in position, and the apex 
 posterior, c, cuticula; //, hypodermis; t, trachea; w, developing wing. — After Mayer. 
 
 Pig. 226. — Internal transformations of Sphinx ligustri. A, larva; B, pupa; C, moth; 
 a, aorta; an, antenna; b, brain; /, fore intestine; fr, food reservoir; h, hind intestine; ht, 
 heart; tn, mid intestine; mt, Malpighian tubes; p. proboscis; s, suboesophageal ganglion; 
 t, testis; tg, thoracic ganglia; v, ventral nerve cord. — After Newport. 
 
I 64 ENTOMOLOGY 
 
 and that of reproduction to the imaginal stage. Larva and imago 
 become adapted to widely different environments. So dissimilar 
 are the two environments that a gradual change from the one to the 
 other is no longer possible; the revolutionary changes in structure 
 necessitate a temporary cessation of external activity. 
 
CHAPTER IV 
 
 ADAPTATIONS OF AQUATIC INSECTS 
 
 Ease, versatility and perfection of adaptation are beautifully exem- 
 plified in aquatic insects. 
 
 Systematic Position. — Aquatic insects do not form a separate group 
 in the system of classification, but are distributed among several orders, 
 of which Plecoptera, Ephemerida, Odonata and Trichoptera are pre- 
 eminently aquatic. One third of the families of Heteroptera and less 
 than one fourth those of Diptera are more or less aquatic. One tenth 
 of the famihes of Coleoptera frequent the water at one stage or another, 
 two famihes of Neuroptera, and only half a dozen genera of Lepidoptera. 
 A few Collembola live upon the surface of water; and several Hymenop- 
 tera, though not strictly aquatic, are known to parasitize the eggs and 
 larvae of aquatic insects. 
 
 The change from the terrestrial to the aquatic habit has been a 
 gradual change of adaptation, not an abrupt one. Thus at present there 
 are some tipulid larv^ that inhabit comparatively dry soil; others live 
 in earth that is moist; many require a saturated soil near a body of 
 water and many, at length, are strictly aquatic Among beetles, also, 
 similar transitional stages are to be found. 
 
 Food. — Insects have become adapted to utilize with remarkable 
 success the immense and varied supply of food that the water affords. 
 Hosts of them attack such parts of plants as project above the surface of 
 the water, and the caterpillar of Paraponyx (Fig. 174) feeds on sub- 
 merged leaves, especially of Vallisneria, being in this respect almost 
 unique among Lepidoptera. Hydrophilid beetles and many other 
 aquatic insects devour submerged vegetation. The larvae of the chry- 
 someHd genus Donacia find both nourishment and air in the roots of 
 aquatic plants. Various Collembola subsist on floating alg^e, and larvae 
 of mosquitoes and black-flies on microscopic organisms near the surface, 
 while larvae of midges, Chironomus, find food in the sediment that accu- 
 mulates at the bottom of a body of water. 
 
 Predaceous species abound in the water. The backswimmer, 
 Notonecta (Fig. 227) approaches its prey from beneath, clasps it with 
 the front pair of legs and pierces it. The water scorpions, Nepa and 
 
 16s 
 
i66 
 
 ENTOMOLOGY 
 
 Ranatra, likewise have prehensile front legs along with powerful piercing 
 organs. The electric light bugs, Belostoma and Benacus (Fig. 23) even 
 kill small fishes by their poisonous punctures. Some other kinds, as the 
 water-skaters (Gerridae, Fig. 228), depend on dead or disabled insects. 
 The species of Eydrophilus (Fig. 229) are to some extent carnivorous as 
 
 Fig. 227.- — Backswimmer, Notonecta 
 lata, natural size. 
 
 Pig. 228. 
 
 -Water-skater, Gerris remigis, 
 natural size. 
 
 larvae but phytophagous as imagines, while Dytiscidae (diving beetles) 
 are carnivorous throughout life. Aquatic insects eat not only other 
 insects, but also worms, crustaceans, mollusks or any other available 
 animal matter. 
 
 Even aquatic insects are not exempt from the attacks of parasitic 
 species. A few Hymenoptera actually enter the water to find their 
 victims, for example, the ichneumon Agriotypus, 
 which lays its eggs on the larvae of caddis flies. 
 
 Locomotion. — Excellent adaptations for 
 aquatic locomotion are found in the common 
 Hydrophilus triangularis (Fig. 229). Its general 
 form reminds one of a boat, and its long legs 
 resemble oars. The smoothly elHptical contour 
 and the polished surface serve to lessen resistance. 
 Owing to the form of the body (Fig. 230, A) and 
 the presence of a dorsal air-chamber under the 
 elytra, the back of the insect tends to remain 
 uppermost, while in the backswimmer, Notonecta 
 (Fig. 230, B), on the other hand, the conditions 
 are reversed, and the insect swims with its back 
 downward. The legs of Hydrophilus, excepting the 
 first pair, are broad and thin (Fig. 231, A) and the tarsi are fringed with 
 long hairs. When swimming, the "stroke" is made by the flat surface, 
 aided by the spreading hairs; but on the "recover," the leg is turned so 
 
 Fig. 229. — Hydroph- 
 ilus triangularis, nat- 
 ural size. 
 
ADAPTATIONS OF AQUATIC INSECTS 
 
 167 
 
 as to cut the water, while the hairs fall back against the tarsus from the 
 resistance of the water, as the leg is being drawn forward. The hind 
 
 A B 
 
 Fig. 230. — Transverse sections of {A) Hydrophilus and (B) Nolonecla. e, elytron; h, 
 hemelytron; I, metathoracic leg. 
 
 legs, being nearest the center of gravity, are of most use in swimming, 
 though the second pair also are used for this purpose; indeed, a terrestrial 
 insect, finding itself in the 
 water, instinctively relies 
 upon the third pair of legs 
 for 1 ocomotion. Hydro- 
 philus uses its oar-like legs 
 alternately, in much the 
 same sequence as land 
 insects, but Cyhister and 
 other Dytiscidas, which 
 are even better adapted 
 than Hydrophilus for 
 aquatic locomotion, move 
 the hind legs simultane- 
 ously, and therefore can 
 swim in a straight line, 
 without the wobbling and 
 less economical m o v e- 
 ments that characterize 
 Hydrophilus. 
 
 Larvae of mosquitoes 
 propel themselves b y 
 means of lashing, or undu- 
 latory, movements of the 
 
 abdomen. A peculiar mode of locomotion is found in dragon fly 
 nymphs, which project themselves by forcibly ejecting a stream of 
 water from the anus. 
 
 Fig. 231. — Left hind legs of aquatic beetles. A, 
 Hydrophilus triangularis; B, Cybister fimbriolatus; c, 
 coxa; /, femur; s, spur; /, tarsus; ti, tibia; tr, tro- 
 chanter. 
 
i08 
 
 ENTOMOLOGY 
 
 On account of the large amount of air that they carry about, most 
 aquatic imagines are lighter than the water in which they live, and 
 therefore can rise without effort, but can descend only by exertion, and 
 can remain below only by clinging to 
 chance stationary objects. The mosquito 
 larva (Fig. 232, ^) is often heavier than 
 water, but the pupa (Fig. 232, B) is lighter, 
 and remains clinging to the surface film. 
 
 The tension of this surface film is suffi- 
 cient to support the weight of an insect 
 up to a certain limit, provided the insect 
 has some means of keeping its body dry. 
 This is accompKshed usually by hairs, 
 set together so thickly that water cannot 
 penetrate between them. As the legs and 
 body of Gerris are rendered water-proof 
 by a velvety clothing of hairs, the insect, 
 though heavier than water, is able to skate 
 about on the surface. Gyrinus, by means 
 of a similar adaptation, can circle about 
 on the surface film, and minute collembo- 
 lans leap about on the surface as readily 
 as on land. 
 
 The modifications of the legs for swim- 
 ming have often impaired their usefulness 
 for walking, so that many aquatic Coleop- 
 tera and Hemiptera can move but awk- 
 wardly on land. When walking, it is inter- 
 esting to note, Cyhister and some other 
 aquatic forms no longer move their hind 
 legs simultaneously as they do in swim- 
 ming, but use them alternately, like ter- 
 restrial species. 
 
 The adaptations for swimming do not 
 necessarily affect the power of flight. 
 Dytiscus, Hydrophilus, Gyrinus, Notonecta, Benacus and many other 
 Coleoptera and Hemiptera leave the water at night and fly around, 
 often being found about electric lights. 
 
 Respiration. — Aquatic insects have not only retained the primitive, 
 or open {holopneustic) type of respiration, characterized by the presence 
 
 Fig. 232. — Larva {A) and pupa 
 {B) of mosquito, Culex pipiens. 
 r, respiratory tube; /, tracheal 
 gills. 
 
ADAPTATIONS OF AQUATIC INSECTS 1 69 
 
 of spiracles, but have also developed an adaptive, or closed (apneustic) 
 type, for utilizing air that is mixed with water. 
 
 Through minor modifications of structure and habit, many holo- 
 pneustic insects have become fitted for an aquatic life. In these in- 
 stances the insects have some means of carrying down a supply of air 
 from the surface of the water. Thus the backswimmer, Notonecta, 
 bears on its body a silvery film of air entangled in closely set hairs, 
 which exclude the water. The whirhgig beetle, Gyrinus, descends 
 with a bubble of air at the end of the abdomen. Dytiscus and Hydro- 
 philus have each a capacious air-space between the elytra and the 
 abdomen, into which space the spiracles open. The water scorpions, 
 Nepa and Ranatra, have each a long respiratory organ composed of two 
 valves, which lock together to form a tube that communicates with the 
 single pair of spiracles situated near the end of the abdomen. The 
 mosquito larva, hanging from the surface film, breathes through a 
 cyhndrical tube (Fig. 232, A, r) projecting from the penultimate 
 abdominal segment; the pupa, however, bears a pair of respiratory 
 tubes on the back of the thorax (Fig. 232, B, r, r), which is now upward, 
 probably in order to facilitate the escape of the fly. The rat-tailed 
 maggot (Eristalis), three quarters of an inch long, has an extensile 
 caudal tube seven times that length, containing two tracheae terminating 
 in spiracles, through which air is brought down from above the mud in 
 which the larva lives. Similarly, in the dipterous larva, Bitlacomor pha 
 clavipes (Fig. 175), the posterior segments of the abdomen are attenu- 
 ated to form a long respiratory tube. The larva of Donacia appears 
 to have no special adaptations for aquatic respiration except a pair of 
 spines near the end of the body, for piercing air chambers in the roots 
 of the aquatic plants in which it dwells. 
 
 The simplest kind of apneustic respiration occurs in aquatic nymphs 
 such as those of Ephemerida and Agrionidae, whose skin at first is thin 
 enough to allow a direct aeration of the blood. This cutaneous res- 
 piration is possible during the early life of many aquatic species. 
 
 Branchial respiration is, however, the prevalent type among aquatic 
 nymphs and is perhaps the most important of their adaptive character- 
 istics. Thin-walled and extensive outgrowths of the integument, con- 
 taining tracheal branches or, rarely, only blood {Blood gills) enable 
 these forms to obtain air from the water. May fly nymphs (Figs. 20, 
 A ; 170), with their ample waving gills, offer familiar examples of branch- 
 ial respiration. Tracheal gills are very diverse in form and situation, 
 occurring in a few species of May fly nymphs on the thorax or head, 
 
170 
 
 ENTOMOLOGY 
 
 though commonly restricted to the sides of the abdomen, where they 
 occur in pairs or in paired clusters (Fig. 20, A). Caudal gills are found 
 in agrionid nymphs (Fig. 173). The aquatic caterpillars of Pam^ow;>a 
 (Fig. 174) are unique among Lepidoptera in having gills, which are 
 filamentous in this instance. 
 
 Caddis worms, enclosed in their cases, maintain a current of water by 
 means of undulatory movements of the body, and the larvae and pupae 
 of most black-flies (Simuliidae, Fig. 233) secure a continuous supply of 
 fresh air simply by fastening themselves to rocks in swiftly flowing 
 streams. 
 
 Rectal respiration is highly developed in dragon fly nymphs. In 
 these, the rectum is lined with thousands of 
 tracheal branches, which are bathed by water 
 drawn in from behind, and then expelled. 
 
 All these kinds of respiration— cutaneous, 
 branchial and rectal — occur in young ephemerid 
 nymphs; while mosquito larvae have in addition 
 spiracular respiration. 
 
 With the arrival of imaginal life, tracheal 
 gills disappear, except in Perlidae, and even in 
 these insects the gills are of little, if any, use. 
 
 Marine Insects. — Except along the shore, 
 the sea is almost devoid of insect life, the excep- 
 tions being a few chironomid larvae which have 
 been dredged in deep water, and fifteen species 
 of Halohates (belonging to the same family as 
 our famihar pond-skaters), which are found on warm smooth seas, 
 where they subsist on floating animal remains. 
 
 Between tide-marks may be found various beetles and collembolans, 
 which feed upon organic debris; as the tide rises, the former retreat, 
 but the latter commonly burrow in the sand or under stones and become 
 submerged, for example the common Anurida maritima. 
 
 Insect Drift.— Seaweed or other refuse cast upon the shore harbors 
 a great variety of insects, especially dipterous larvae, staphylinid scaven- 
 gers and predaceous Carabidae. On the shores of inland ponds and 
 lakes a similar assemblage of insects may be found feeding for the most 
 part on the remains of plants or animals, or else on one another. During 
 a strong wind, the leeward shore of a lake is an excellent collecting 
 ground, as many insects are driven against it. On the shores of the 
 Great Lakes insects are occasionally cast up in immense numbers, form- 
 
 FlG. 233. — Simulium;. 
 A, larva; B, pupa, show- 
 ing respiratory filaments. 
 
ADAPTATIONS OF AQUATIC INSECTS 17I 
 
 ing a broad windrow, fifty or perhaps a hundred miles long. Needham 
 has described such an occurrence on the west shore of Lake Michigan, 
 following a gale from the northeast. In this instance, a liter of the 
 drift contained nearly four thousand insects, of which 66 per cent, were 
 crickets (Nemobius), 20 per cent. Locustidae, and the remainder mostly 
 beetles (Carabidae, Scarabaeidae, Chrysomelidae, Coccinellidae, etc.), 
 dragon flies, moths, butterflies {Anosia, Pieris, etc.) and various 
 Hemiptera, Hymenoptera and Diptera. A large proportion of the insects 
 were aquatic forms, such as Hydrophilus, Cybister, Zaitha, and a species 
 of caddis fly; these had doubtless been carried out by freshets, while the 
 butterflies and dragon flies had been borne out by a strong wind from 
 the northwest, after which all were driven back to the coast by a north- 
 east wind. While some of these insects survived, notably Coccinellidae, 
 Trichoptera, Asilidae, Locustidae and Gryllidae, nearly all the rest were 
 dead or dying, including the dragon flies, flies, bumblebees and wasps. 
 Foraging Carabidae were observed in large numbers, also scavengers of 
 the families Staphylinidae, Silphidae and Dermestidae. 
 
 On the seashore and on the shores of the Great Lakes, the salient 
 features of insect life are essentially the same. Similar species occur in 
 the two places with similar biological relations, on account of the general 
 similarity of environment. 
 
 Origin of the Aquatic Habit. — The theory that terrestrial insects 
 have arisen from aquatic species is no longer tenable, for the evidence 
 shows that the terrestrial type is the more primitive. Aquatic insects 
 still retain the terrestrial type of organization, which remains unob- 
 scured by the temporary and comparatively slight adaptations for an 
 aquatic life. Thus, the development of tracheal gills has involved no 
 important modification of the fundamental plan of tracheal respiration. 
 It is significant, moreover, that the most generalized, or most primitive, 
 insects — Thysanura — are without exception terrestrial. Aquatic in- 
 sects do not constitute a phylogenetic unit, but represent various orders, 
 which are for the most part undoubtedly terrestrial, notwithstanding the 
 fact that a few of these orders (Plecoptera, Ephemerida, Odonata, Tri- 
 choptera) are now wholly aquatic in habit. Adaptations for an aquatic 
 existence have arisen independently and often, in the most diverse 
 orders of insects. 
 
CHAPTER V 
 
 COLOR AND COLORATION 
 
 The naturalist distinguishes between the terms color and coloration. 
 A color is a single hue, while coloration refers to the arrangement of colors. 
 
 Sources of Color. — The colors of insects are classed as (i) pigmental 
 {chemical)., those due to internal pigments; (2) structural {physical), 
 those due to structures that cause interference or reflection of light; 
 and (3) combination colors {chemico-physical) , which are produced in 
 both ways at once. 
 
 Structural Colors. — The iridescence of a fly's wing and that of a 
 soap bubble are produced in essentially the same way. The wing, how- 
 ever, consists of two thin, transparent, slightly separated lamellae, which 
 diffract white light into prismatic rays, the color differences depending 
 upon differences in the distance between the two membranes. 
 
 The brilliant iridescent hues of many butterfly scales are due to the 
 diffraction of light by fine, closely parallel striae (Fig. 95) just as in the 
 case of the "dift'raction gratings" used by the physicist, which consist of 
 a glass or metalHc plate with parallel equidistant diamond rulings of 
 microscopic fineness. The particular color produced depends in both 
 cases upon the distance between the striae. Though almost all lepidop- 
 terous scales are striated, it is only now and then that the striae are 
 sufficiently close together to give diffraction colors. In a Brazilian 
 species of Apatura the iridescent scales have 1,050 striae to themilhmeter, 
 and in a species of Morpho, according to Kellogg, the iridescent pig- 
 mented scales have 1,400 striae per millimeter, the striae being only 
 .0007 mm. apart; while in some of the finest Rowland gratings they 
 number about 1,200 per millimeter. 
 
 In the well known diamond beetle the green dots of the elytra are 
 depressions from which spring brilliant and exquisitely colored scales, 
 the colors varying throughout the range of the spectrum; green, however, 
 predominating. These colors are due to diffraction from regular stria- 
 tions, with a "grating" space of a thousandth to a two-thousandth of a 
 millimeter. On immersing the specimen in oil or other liquid little or 
 no change is observed, except in those specimens in which a small 
 communicating aperture exists in the neck of the scale. The oil can be 
 
 172 
 
COLOR AND COLORATION 1 73 
 
 seen gradually to till the interior, and simultaneously all trace of color 
 vanishes (except sometimes a faint greenish surface color). It appears, 
 then, that the color in this case is due to fine striations on the interior 
 surface of the scale. (Michelson.) 
 
 The interference coIofs of butterfly scales may be due, not only to 
 surface markings, but also to the lamination of the scale and to the 
 overlapping of two or more scales. In beetles the brilliant blues and 
 greens, and iridescence in general, are sometimes produced by minute 
 lines or pits that diffract the light. According to Tower, "The pits 
 alone, however, are powerless to produce any color; it is only when they 
 are combined with a highly reflecting and refractive surface lamella and 
 a pigmented layer below that the iridescent color appears. The action 
 of light is in this case the same as in the plain metaUic coloring, excepting 
 that each pit acts as a revolving prism to disperse different wave-lengths 
 of light in different directions, and the combined result is iridescence. 
 The existence of minute pits over the body surface is of common occur- 
 rence, but it is only when they are combined as above that iridescent 
 colors occur." 
 
 The production of color by "metallic" reflection deserves more 
 attention than it has received from naturalists. The metallic colors 
 of birds and insects have been studied precisely by Professor Michelson, 
 who has proved that they are due to the same causes in both animals 
 and metals. The metals, on account of their extraordinary opacity, 
 throw back practically all the light that strikes them, thus giving the 
 characteristic brilliant reflections; the distance to which light can pen- 
 etrate in most metals being only a small fraction of a light wave, so 
 that a wave-motion such as constitutes light, strictly speaking, can 
 not be propagated at all. As this opacity may be different for different 
 colors, some would be transmitted more freely than others, so that the 
 resulting transmitted light would be colored; and the reflected Ught 
 would be approximately complementary to the transmitted color. 
 (Michelson.) Thus the reflected light from the metal gold is yeUow, 
 the transmitted light being blue. In certain pigeons, peacocks, hum- 
 ming birds, as well as a number of butterflies, beetles and other insects, 
 the brilliant metaUic colors are due to an extremely thin surface film 
 which has optical qualities like those of metals. This film in the case 
 of the coppery wing cover of a beetle was calculated by Micheson to be 
 less than a ten-thousandth of a milHmeter in thickness. 
 
 In animals, as in metals, these colors are brilliant because a large 
 percentage of the incident light is reflected. The color of the reflected 
 
174 ENTOMOLOGY 
 
 light is complementary to that of the transmitted. Furthermore, the 
 color of the reflected light changes when the surface is inclined, the color 
 always approaching the violet end of the spectrum as the incidence 
 increases. "If the color of the normal reflection is violet the Hght 
 vanishes (changing to ultra-violet), and if -the normal radiation be 
 infra-red it passes through red, orange, and yellow as the incidence 
 increases." (Michelson.) 
 
 Professor Michelson states that the metallic and spectrum colors 
 of the tiger beetles, CicindelidcB, are chiefly if not entirely true surface 
 or metalHc colors, produced by a film of ultra-microscopic thickness, 
 probably less than a ten-thousandth of a millimeter. This film must 
 be lacking in the dead black variety of Cicindela scutellaris, which is 
 without trace of color, hke a piece of black paper, Michelson is 
 inclined to attribute differences in the colors to differences in the chemi- 
 cal constitution of the film, and color changes during ontogeny to 
 changes in chemical constitution, but states that this would be very 
 difficult to demonstrate on account of the minuteness of the film. 
 (Shelford.) 
 
 Silvery white effects are usually caused by the total reflection of 
 light from scales or other sacs that are filled with air; the same silvery 
 appearance is given also by air-filled tracheae and by the air bubbles 
 that many aquatic insects carry about under water. 
 
 Violet, blue-green, coppery, silver and gold colors are, with few 
 exceptions, structural colors. (Mayer.) 
 
 Pigmental Colors. — These are either cuticular or hypodermal. The 
 predominant brown and black colors of insects are made by pigment 
 diffused in the outer layer of the cuticula (Fig. 90). Cockroaches are 
 almost white just after a molt, but soon become brown, and many 
 beetles change gradually from brown to black. In these cases it is 
 apparently significant that the cuticular pigments lie close to the surface 
 of the skin, i. e., where they are most exposed to atmospheric influences. 
 Gortner found that the black cuticular pigment in the Colorado potato 
 beetle {Leptinotarsa) and the brown or black . pigments of the tiger 
 beetles (Cicindela) belong to the group of melanins and are produced by 
 oxidation, induced by an oxidase; that when all oxygen is absent no 
 pigmentation takes place. 
 
 The cuticular pigments are derived, of course, from the underlying 
 hypodermis cells, and these cells themselves, moreover, usually contain 
 (i) colored granules or fatty drops which give red, yellow, orange and 
 sometimes white or gold colors as seen through the skin; (2) diffused 
 
COLOR AND COLORATION 1 75 
 
 chlorophyll (green) or xanthophyll (yellow), taken from the food plant. 
 Unlike the structural colors, which are persistent, these hypodermal 
 colors often change after death, though less rapidly when the pigments 
 are tightly enclosed, as in scales or hairs. Though white and green are 
 structural colors as a rule, they are due to pigments in Pieridag, Lycaeni- 
 dae and some Geometridae. 
 
 Frequently a color pattern consists partly of cuticular and partly of 
 hypodermal colors, the hypodermal or sub-hypodermal color forming "a 
 groundwork upon which the pattern is cut out by the cuticular color." 
 (Tower.) Thus in the Colorado potato beetle, Leptinotarsa decemlineata, 
 the pattern ''is composed of a dark cuticular pigment upon a yellow 
 hypodermal background." 
 
 The pigment present in the cuticula of tiger beetles is essentially all 
 in the primary cuticula, and is always either brown or black. In 
 certain areas the primary cuticula is pigmented and in certain areas 
 clear and transparent. This gives the color pattern. The secondary 
 cuticula beneath the unpigmented areas is full of pore canals and large 
 air-filled interlamellar spaces, and these give the efifect of a white or 
 straw color depending upon the color of the secondary cuticula itself. 
 (Shelford.) 
 
 Combination Colors. — The splendid changeable hues of Apatura, 
 Euplcea and other tropical butterflies depend upon the fact that their 
 scales are both pigmented and striated. Under the microscope, certain 
 Apatura scales are brown by transmitted light and violet by reflected 
 light, and to the unaided eye the color of the wing is either brown or 
 violet, according as the light is received respectively from the pigment 
 or from the striated surfaces of the scales. 
 
 Nature of Pigments. — Some pigments are taken bodily from the 
 food; others are manufactured indirectly from the food, and some of 
 these are excretory products. 
 
 The green color of many caterpillars and grasshoppers is due to 
 chlorophyll, which tinges the blood and shows through the transparent 
 integument. Mayer has found that scales of Lepidoptera contain only 
 blood while the pigment is forming; that the first color to appear upon 
 the pupal wings is a dull ochre or drab — the same color that the blood 
 assumes when it is removed from the pupa and exposed to the air ; also 
 that pigments like those of the wings may be manufactured artificially 
 from pupal blood. Pieridae are peculiar in thenature of their pigments, 
 as Hopkins has shown. The white pigment of this family is uric acid 
 and the reds and yellows of Pieris, Colias and Papilio are due to deriva- . 
 
176 ENTOMOLOGY 
 
 tives of uric acid; the yellow pigment, termed lepidotic acid, precedes 
 the red in time of appearance, the latter being probably a derivative 
 of the former. The green pigments of some Papilionidae, Noctuidse, 
 Geometridae and Sphingidae are also said by some investigators to be 
 products of uric acid, which in insects as in other animals is primarily 
 an excretory, or waste, product. 
 
 Effects of Food on Color. — Besides chlorophyll, to which various 
 caterpillars, aphids and other forms owe their green color, the yellow 
 constituent of chlorophyll, namely xanthophyll, frequently imparts its 
 color to plant-eating insects, while some phytophagous species are dull 
 yellow or brown from the presence of tannin, taken from the food plant. 
 Most pigments, however, are elaborated from the food by chemical 
 processes that are not well understood. 
 
 Many who have reared Lepidoptera extensively know that the color 
 of the imago is influenced by the character of the larval food, other con- 
 ditions being equal, and are able at will to effect certain color changes 
 simply by feeding the larvae from birth upon particular kinds of plants. 
 In this country we have few observations upon the subject, but in Europe 
 the effects of food upon coloration have been ascertained in the case of 
 many species of Lepidoptera. According to Gregson, Hybernia defolia- 
 ria is richly colored when fed upon birch, but is dull colored and almost 
 unmarked when fed on elm. Pictet, by feeding larvae of Vanessa 
 urticxB on the flowers instead of the leaves of the nettle obtained the 
 variety known as urticoides. Food affects the color of the larva also, 
 as Poulton found in the case of caterpillars of Tryphcena pronuba, all 
 from the same batch of eggs. When fed with only the white midribs 
 of cabbage leaves, the larvae remained almost white for a time, but 
 afterward showed a moderate amount of black pigment; when fed with 
 the yellow etiolated heart-leaves or the dark green external leaves, 
 however, the larvae all became bright green or brown — the same pigment 
 being derived indifferently from etiolin (probably the same substance 
 as xanthophyll) or chlorophyll. 
 
 Though the pigments may differ in color or amount according to 
 the kind of food, the color patterns vary without regard to food. Thus 
 Callosamia promethea, Leptinotarsa decemlineata (Colorado potato 
 beetle), CoccineUidae (lady-bird beetles) and a host of other insects 
 exhibit extensive individual variations in coloration under precisely 
 the same food conditions. Caterpillars of the same kind and age are 
 often very differently marked when feeding upon the same plant; for 
 example, Chloridea obsoleta (corn worm) and the sphingid Deilephila 
 
COLOR AND COLORATION 1 77 
 
 Uneata. Furthermore, striking changes of coloration accompany each 
 molt in most caterpillars, but particularly those of butterflies, and 
 these changes may prove to have an important phylogenetic signifi- 
 cance. Individual differences of coloration apart from those due to the 
 direct action of food, light, temperature and other environmental 
 conditions are to be explained by heredity. 
 
 Effects of Light and Darkness.— Sunlight is an important factor in 
 the development of most animal pigments, as they will not develop in 
 its absence. The collembolan Anurida maritima is white at hatching, 
 but soon becomes indigo blue, unless shielded from sunhght, in which 
 event it remains white until exposed to the sunhght, when it assumes the 
 blue color. Subterranean or wood-boring larvae are commonly white 
 or yellow, but never highly colored. The most notable instances, 
 however, are furnished by cave insects. These, like other cavernico- 
 lous animals, are characteristically white or pale from the absence of 
 pigment, if they live in regions of continual darkness, but have more or 
 less pigmentation in proportion respectively to the greater or less 
 amount of sunlight to which they have access. 
 
 Curiously enough, light often hastens the destruction of pigment in 
 insects that are no longer alive, for which reason it is necessary to keep 
 cabinet specimens in the dark as much as possible. Life is evidently es- 
 sential for the sustention or renewal of the pigments. 
 
 A chrysalis not infrequently matches its surroundings in color. This 
 phenomenon has been investigated by Poulton, who has proved that the 
 color of the chrysalis is determined largely by the prevalent color of 
 the surroundings during the last few days of larval life. Larvae of the 
 cabbage butterfly, Pieris rapcB, raised upon the same food plant (all 
 other conditions being made as nearly equal as possible) produced dark 
 pupae if kept in darkness for a few days just before pupation; yellow 
 light arrested the formation of the dark pigment and gave green pupae; 
 while light colors in general gave light-colored pupae. This color 
 resemblance is commonly assumed to be of protective value, and per- 
 haps it is. Nevertheless, it is a direct effect of light, and does not need 
 to be explained by natural selection, even though it cannot be denied 
 that natural selection may have helped in its production. 
 
 Poulton extended his studies to the adaptive coloration of caterpillars 
 and has published the results of an extensive series of experiments which 
 prove that the colors of certain caterpillars also are directly produced by 
 the same colors in the surrounding light. Gastropacha quercifolia, which 
 always rests by day on the older wood of its food plant, was given black 
 
1 78 ENTOMOLOGY 
 
 twigs, reddish brown sticks, lichens, etc., to rest upon, and though all the 
 larvae were from the same cluster of eggs, and had been fed in the same 
 way, each larva gradually assumed the color or colors of its resting place, 
 resulting in exquisite examples of protective resemblance, the most re- 
 markable of which were those in which the larvae assumed the variegated 
 coloration of lichens. Only the younger larvae, however, proved to be 
 susceptible to the colors of the environment; unlike those of Amphidasis 
 hetidaria, in which the older larvae also were sensitive to the surrounding 
 light. Here again, natural selection is unnecessary, even if not super- 
 fluous, as an explanation of this kind of protective coloration. 
 
 Professor W. M. Wheeler has suggested that "such phenomena as 
 the permanent protective coloration of insects may be regarded as the 
 stereotyped, highly specialized end-stage of a more ancient ability 
 actively to change color in response to color changes in the environment, 
 an abiHty still possessed by some primitive insects like the grasshoppers 
 and mantids, though much more pronounced in cephalopod mollusks, 
 fishes, amphibia and Hzards." 
 
 Effects of Temperature. — The amount of a pigment in the wing of a 
 butterfly depends in great measure upon the surrounding temperature 
 during the pupal stage, when the pigments are forming. Black or brown 
 spots have been enlarged artificially by subjecting chrysalides to cold; 
 hence it is probable that the characteristically large black spots on the 
 under side of the wings of the spring brood of our Cyaniris pseudargiolus 
 are simply a direct effect of cold upon the wintering chrysalides. 
 Similarly the spring brood (variety marcia) of Phyciodes tharos owes its 
 distinctive coloration to cold, as Edwards has proved experimentally. 
 Lepidoptera have been the subject of very many temperature experi- 
 ments, some of which will be mentioned presently in the consideration 
 of seasonal coloration. 
 
 Speaking generally, warmth (except in melanism) tends to induce a 
 brightening and cold a darkening of coloration, the darkening 
 being due to an increased amount of black or brown pigment. Temper- 
 ature, whether high or low, seldom if ever produces new pigments, 
 but simply alters the amount and distribution of pigments that are 
 present already. 
 
 Effects of Moisture. — Very Httle is known as to the effects of mois- 
 ture upon coloration. The dark colors of insular or coastal insects as 
 contrasted with inland forms, and the predominance of dull or suffused 
 species in mountainous regions of high humidity, have led observers 
 occasionally to ascribe melanism and sufusion to humidity. In these 
 
COLOR AND COLORATION 1 79 
 
 cases, however, the possible influence of low temperature and other 
 factors must be taken into consideration. The experiments of Merrifield 
 and of Standfuss showed no effect of moisture upon lepidopterous pupae. 
 
 Pictet has found, however, that humidity acting on the caterpillars 
 of Vatiessa urtica and V. polychloros has a conspicuous effect on the 
 coloration of the butterflies. Thus when the caterpillars were fed for 
 ten days with moist leaves, the resulting butterflies had abnormal 
 black markings on the wings, and the same results followed when the 
 larvas were kept in an atmosphere saturated with moisture. 
 
 Climatal Coloration. — The brilliant and varied colors of tropical 
 insects are popularly ascribed to intense heat, light and moisture; and 
 the dull monotonous colors of arctic insects, similarly to the surrounding 
 climatal conditions Climate undoubtedly exerts a strong influence 
 upon coloration, but the precise nature of this influence is obscure and will 
 remain so until more is known about the effects separately produced by 
 each of the several factors that go to make up what is called cHmate. 
 
 The prevalence of intense and varied colors among tropical insects 
 is doubtless somewhat exaggerated, for the reason that the highly 
 colored species naturally attract the eye to the exclusion of the less 
 conspicuous forms. Indeed, Wallace assures us that, although tropi- 
 cal insects present some of the most gorgeous colors in the whole realm 
 of nature, there are thousands of tropical species that are as dull colored 
 as any of the temperate regions. Carabidae, in fact, attain their greatest 
 brilliancy in the temperate zone, according to Wallace, though butter- 
 flies certainly show a larger proportion of vivid and varied colors in the 
 tropics. Mayer finds, in the widely distributed genus Papilio, that 200 
 South American species display but 36 colors, while 22 North American 
 species show 17. While the number of species in South America is 
 nine times as great as in North America, the number of colors displayed 
 is only a little more than twice as great; hence Mayer concludes that 
 the richer display of colors in the tropics may be due to the far greater 
 number of species, which gives a better opportunity for color sports to 
 arise; and not to any direct influence of the climate. Furthermore, the 
 number of broods which occur in a year is much greater in the tropics 
 than in the temperate zones, so that the tropical species must possess a 
 correspondingly greater opportunity to vary. 
 
 Albinism and Melanism. — These interesting phenomena, wide- 
 spread among the higher animals, have often been attributed to tempera- 
 ture, but albinism and melanism are, in some instances at least, 
 strongly inherited without regard to temperature. 
 
l8o ENTOMOLOGY 
 
 Albinism is exceptional whiteness or paleness of coloration, and is 
 due usually to deficiency of pigment, but in some instances (Pieridae) 
 to the presence of a white pigment. 
 
 The common yellow butterfly, Colias philodice, and its relatives, 
 are frequently albinic. Scudder observed that albinism among butter- 
 flies in America appears to be confined to a few Pieridae, and to be re- 
 stricted to the female sex; is more common in subarctic and subalpine 
 regions than in lower latitudes and altitudes, and only in the former 
 places includes all the females. At low altitudes, however, instead of ap- 
 pearing early in the year as might be expected, the albinic forms appear 
 during the warmer months. 
 
 The experiments made by Gerould on C. philodice show that the 
 number of albinic female offspring from white females crossed with 
 yellow males is in accordance with Mendelian law. Albinism is not 
 entirely confined to the female as Scudder thought, for white males 
 occur, though they are extremely rare. ''They may be expected in 
 regions where the white female is especially abundant" (Gerould). 
 
 In Europe there are many albinic species of butterflies, and they 
 are by no means confined to family Pieridae. 
 
 Melanism is unusual blackness or darkness of coloration. As to 
 how it is produced little is known, though warmth is probably the most 
 potent influence, and some attribute it to moisture, as was mentioned. 
 Pictet obtained partial melanism in Vanessa urticce and V. polychloros 
 by subjecting the larvae to moisture. 
 
 In warm latitudes, some females of our Papilio glaucus are blackish 
 brown with black markings, instead of being, as usual, yellow with 
 black markings. In the South, some males of the spring brood of 
 Cyaniris pseudargiolus are partly or wholly brown instead of blue. 
 A melanic male of Colias philodice occurs as an extremely rare muta- 
 tion. A melanic variety of pomace fly, Drosophila, with a black body, 
 follows the Mendelian law in its appearance in breeding experiments. 
 
 Seasonal Coloration. — When butterflies have more than one brood 
 in a year, the broods usually differ in aspect, sometimes so much that 
 their specific identity is revealed only by rearing one brood from 
 another. The same species may exist under two or more distinct 
 forms during the same season — in other words, may be seasonally dimor- 
 phic, trimorphic or polymorphic. 
 
 Thus Polygonia interrogationis has two forms, fabricii and umhrosa. 
 which differ not only in coloration, but even in the form of the wings 
 
COLOR AND COLORATION 
 
 ;8] 
 
 and the genitalia. In New England fahricii hibernates and produces 
 umbrosa. as a rule, while umhrosa usually yields fahricii. 
 
 The little, blue butterfly, Cyaniris pseudargiolus (Fig. 234), is poly- 
 morphic to a remarkable degree. In the high latitudes of Canada a 
 
 Fig. 234. — Cyaniris pseudargiolus; 
 
 A, form lucia; B, violacea; C, pseudargiolus proper. 
 Natural size. 
 
 single brood {lucia) occurs. About Boston the same spring brood ap- 
 pears, but under two forms: an earlier variety {lucia), which is small, 
 with large black markings beneath; and a later variety (violacea), 
 which is typically larger, with smaller black spots, though it varies 
 into the form lucia. Finally, 
 in summer, a third form 
 {pseudargiolus proper) 
 appears, as the product of 
 lucia or else the joint prod- 
 uct of lucia and violacea, and 
 this is still larger, but the 
 black spots are now faint. 
 In the warm South the spring 
 form is violacea, but while 
 some of the males are blue, 
 others are melanic, as just 
 mentioned — a dimorphic con- 
 dition which does not occur 
 in the North. Violacea then 
 produces pseudargiolus, in 
 which, however, all the males are blue. 
 
 ' Iphiclides ajax (Fig. 235) is another polymorphic butterfly whose 
 life history is complex. The three principal varieties of this species, 
 known respectively as marcellus, telamonides and ajax, differ not only in 
 coloration, but also in size and form; marcellus appears first, in spring; 
 telamonides appears a little later (though before marcellus has disap- 
 peared); and ajax is the summer form; as the season advances the 
 
 Pig. 235. — Iphiclides ajax, form telamonides, on 
 flower of button bush. Reduced. 
 
l82 
 
 ENTOMOLOGY 
 
 varieties become successively larger, with longer tails to the hind 
 wings. 
 
 Now Edwards submitted chrysalides of the summer form ajax to 
 cold and thereby obtained, in the same summer, butterflies with the 
 form of ajax but the markings of the spring form telamonides . Some of 
 the chrysalides, however, lasted over until the next spring and then gave 
 telamonides. 
 
 In Phyciodes tharos (Fig. 236) the spring and summer broods, termed 
 respectively marcia and morpheus, were at first regarded as distinct 
 species. In marcia the hind wings are heavily and diffusely marked 
 beneath with strongly contrasting colors, while in morpheus they are 
 plain and but faintly marked. Edwards placed upon ice eighteen 
 chrysalides that normally would have produced morpheus; but instead 
 
 Fig. 236. — Phyciodes tharos; A, spring form, marcia; B, summer form, morpheus; under 
 surfaces. Natural size. 
 
 of this, the fifteen imagines that emerged were all of the spring form 
 marcia and were smaller than usual. Pupae derived from eggs of marcia 
 gave, after artificial cooling, not morpheus , but marcia again. The 
 evident conclusion is that the distinctive coloration of the spring variety 
 is brought about by low temperature. In Labrador, only one brood 
 occurs — marcia; in New York, the species if digoneutic (two-brooded) 
 and in West Virginia polygoneuiic (several-brooded) . 
 
 Extensive temperature experiments upon seasonal dimorphism in 
 Lepidoptera have been conducted in Europe by some of the most com- 
 petent biologists. Weismann found that pupse of the summer form of 
 Pieris napi, if placd on ice, disclosed the darker winter form, usually 
 in the same season, though sometimes not until the next spring. It was 
 found impossible, however, to change the winter variety into the sum- 
 mer one by the application of heat. Similar results have attended the 
 important and much-discussed experiments of Dorfmeister, Weismann 
 and others upon Vanessa levana-prorsa and other species, from which it 
 has been inferred by Weismann that the winter form is the primary. 
 
COLOR AND COLORATION 1 83 
 
 older, and more stable of the two forms, and the summer form a second- 
 ary, newer, and less stable variety; since the latter form only, as a rule, 
 responds much to thermal influences. Weismann argued that, in addi- 
 tion to the direct effect of temperature, alternative inheritance also 
 plays an important part in the production of seasonal varieties. He 
 tried to show, moreover, that each seasonal variety is colored in adapta- 
 tion to its particular environment and that this adaptation may have 
 been brought about by natural selection — though he did not succeed 
 in this respect. 
 
 In several instances, local varieties have been artificially produced 
 as results of temperature control. Thus Standfuss produced in Ger- 
 many, by the application of cold, individuals of Vanessa urticcB which 
 were indistinguishable from the northern variety polaris; and from 
 pupae of Vanessa cardui, by warmth, a very pale form like that found in 
 the tropics; and, by cold, a dark variety similar to one found in Lapland. 
 
 Shelford, by subjecting a pupa of a tiger beetle, C. tranqueharica 
 {vulgaris) to cold moist conditions (mean temperature, 12° C; moist) 
 obtained, in Chicago, a color variety hke one that occurs naturally in 
 the eastern mountains. 
 
 In a second instance, both pattern and color were modified by hot 
 dry conditions (mean temperature, 37° C; dry), and a variety obtained 
 such as occurs in the western states. 
 
 In a third experiment, both pattern and color were modified by hot 
 wet conditions (37° C; moist), and a variety produced like one in the 
 moist southern states. 
 
 These investigators and others, notably Merrifield and Fischer, have 
 accumulated a considerable mass of experimental evidence, the inter- 
 pretation of which is in many respects difficult, involving as it does, not 
 merely the direct effect of temperature upon the organism, but also deep 
 questions of heredity, including reversion, individual variation, and the 
 inheritance of acquired characters. 
 
 The seasonal increase in size that is noticeable, as in C. pseudargiolus 
 and /. ajax, is doubtless an expression of increasing metabolism due to 
 increasing temperature. Warmth, as is well known, stimulates growth, 
 and cold has a dwarfing effect. While this is true as a rule, there are 
 some apparent exceptions, however. Thus Standfuss found that some 
 caterpillars were so much stimulated by unusual warmth that they 
 pupated before they were sufficiently fed, and gave, therefore, under- 
 sized imagines. A moderate degree of warmth, however, undoubtedly 
 hastens growth. 
 
1 84 
 
 ENTOMOLOGY 
 
 Sexual Coloration. — The sexes are often distinguished by colora- 
 tional as well as structural differences. Colorational antigeny (this 
 word signifying secondary sexual differences of whatever sort) is most 
 prevalent among butterflies, in which it is the extreme phase of that 
 
 
 
 
 IHHI 
 
 It-e^ 
 
 ■^ A 
 
 
 ^^^ 
 
 ^^^ r't ^aj 
 
 ^™- i? ^^ 
 
 ^^»- j^^ ^vj:^ 
 
 fS^^^^-^L^Mk 
 
 l^^ff^f^'^-r-^Jm 
 
 W"^- ~>l^l 
 
 ^k^ '^ /p 
 
 hIr*sLj»^L^^H 
 
 lK^w/''^'A 
 
 i^\vv'^-^ ^H 
 
 ^Mfjti./'/ /A 
 
 1^'^^ ^^^1 
 
 ^^Hh^// ^^Kk 
 
 
 
 ^'v-X^^j^l 
 
 Fig. 237. — Pieris prolodice; male (on the left) and female (on the right). Natural size. 
 
 differentiation of ornamentation for which Lepidoptera are unrivaled. 
 
 The male of Pieris protodice (Fig. 237) has a few brown spots on the 
 front wings; the female is checkered with brown on both wings. In 
 Colias philodice (Fig. 238) and C. eurytheme the marginal black band of 
 the front wings is sharp and uninterrupted 
 in the male, but diffuse and interrupted by 
 yellow spots in the female. In the genus 
 Papilio the sexes are often distinguished by 
 colorational differences and in Hesperiidas 
 the males often have an oblique black dash 
 across the middle of each front wing. Callo- 
 samia promethea (Fig. 239), the gipsy moth 
 and many other Lepidoptera exhibit colora- 
 tional antigeny. In not a few Sesiidae the 
 sexes differ greatly in coloration. Thus in 
 the male of the peach tree borer {Aegeria 
 exitiosa) all the wings are colorless and 
 transparent; while in the female the front 
 wings are violet and opaque and the fourth 
 abdominal segment is orange above. The 
 same sex may present two types of coloration, as in males of Cyaniris 
 pseudargiolus and females oi Papilio glaucus, already mentioned. Papilio 
 merope, of South Africa, is remarkable in having three females, which are 
 entirely different in coloration from one another and from the male. 
 
 Fig. 238. — Colias philodice; 
 right fore wing of male (above) 
 and of female (below). Nat- 
 ural size. 
 
COLOR AND COLORATION 
 
 i8S 
 
 There is no longer any doubt, it may be added, as to the specific 
 identity of these forms. 
 
 Next to Lepidoptera, Odonata most frequently show colorational 
 antigeny. The male of Calopteryx maculata is velvety black; the female 
 smoky, with a white pterostigmatal spot. Among Coleoptera, the male 
 of Hoplia trifasciata is grayish and the female reddish brown; a few 
 more examples might be 
 given, though sexual dif- 
 ferences in coloration are 
 comparatively rare among 
 beetles. Of Hymenoptera, 
 some of the Tenthredinidae 
 exhibit colorational 
 antigeny. 
 
 Among tropical butter- 
 flies there are not a few 
 instances in which the 
 special coloration of the 
 female is adaptive — har- 
 monizing with the sur- 
 roundings or else imitating 
 with remarkable precision 
 the coloration of another 
 species which is known 
 to be immune from the 
 attacks of birds — as de- 
 scribed beyond. In this 
 way, as Wallace suggests, 
 the egg-laden females may 
 escape destruction, as they 
 sluggishly seek the proper 
 plants upon which to lay 
 their eggs. Here would 
 be a fair field for the operation of natural selection. 
 
 In most insects, however, sexual differences in coloration are ap- 
 parently of no protective value and are usually so trivial and variable 
 as probably to be of no use for recognition purposes. The usual state- 
 ment that these differences facilitate sexual recognition is a pure as- 
 sumption, in the case of insects, and one that is inadequate in spite of 
 its plausibility, for (i) it is extremely improbable from our present 
 
 Fig. 239. 
 
 Callosamia promethea. A, male, clinging to 
 cocoon; B, female. Reduced. 
 
I 86 ENTOMOLOGY 
 
 knowledge of insect vision that insects are able to perceive colors except 
 in the broadest way, namely, as masses; (2) the great majority of insect 
 species show no sexual differences in coloration; (3) when colorational 
 antigeny is present it is probably unnecessary,- to say the least, for 
 sexual recognition. Thus, notwithstanding the marked dissimilarity 
 of coloration in the two sexes of C. promethea, the males, guided by an 
 odor, seek out their mates even when the wings of the female have been 
 amputated and male wings glued in their place, as Mayer found. 
 
 Hence, when useless, colorational antigeny cannot have been de- 
 veloped by natural selection and may be due simply to the extended 
 action of the same forces that have produced variety of coloration in 
 general. 
 
 Origin of Color Patterns. — Tower, who has written an important 
 work on the colors and color patterns of Coleoptera, finds that each of 
 the black spots on the pronotum of the Colorado potato beetle (Fig. 240) 
 "is developed in connection with a muscle, and marks the point of at- 
 tachment of its fibres to the cuticula." Thus the color pattern, in its 
 origin, is not necessarily useful. This point is so important that we 
 quote Tower's conclusions in full. ''The most important and widely 
 disseminated of insect colors are those of the cuticula . . . these 
 colors develop as the cuticula hardens, and appear first, as a rule, upon 
 sclerites to which muscles are attached. In one of the earlier sections of 
 this paper I showed that the pigment develops from before backward 
 and, approximately, by segments, excepting that it may appear upon 
 the head and most posterior segments simultaneously. 
 
 "In ontogeny color appears first, as a rule, over the muscles which 
 become active first, or upon certain sclerites of the body. These are 
 usually the head muscles, although exceptions are not infrequent. It 
 should be remembered that as the color appears the cuticula hardens, 
 and, considering that muscles must have fixed ends for their action, it 
 seems that there is a definite relation between the development of color, 
 the hardening of the cuticula, and the beginning of muscular activity; 
 the last being dependent upon the second, and, incidentally, accom- 
 panied by the first. As muscular activity spreads over the animal the 
 cuticula hardens and color appears, so that color is nearly, if not 
 wholly, segmentally developed. 
 
 "The relation which exists between cuticular color and the stift'ening 
 of the cuticula is thus a physiological one, the cuticula not being able to 
 harden without becoming yellow or brown. What bearing has this 
 upon the origin of color patterns? In the lower forms of tracheates, 
 
COLOR AND COLORATION 1 87 
 
 such as the Myriapods, colors appear as segmental repetitions of spots 
 or pigmented areas which mark either important sclerites or muscle 
 attachments. On the abdomens of insects, where segmentation is best 
 observed, color appears as well-defined, segmentally arranged spots, 
 but on the thorax segmentation is obscured and lost upon the head. Of 
 what importance, then is pigmentation? And how did it arise? If the 
 ontogenetic stages offer any basis for phylogenetic generalization, we 
 may conclude that cuticula color originated in connection with the 
 hardening of the integument of the ancestral tracheates as necessary to 
 the muscular activity of terrestrial life. The primitive colors were 
 yellows, browns and blacks, corresponding well with the surroundings 
 in which the first terrestrial insects are supposed to have lived. The 
 color pattern was a segmental one, showing repetition of the same spots 
 upon successive segments, as upon the abdomen of Coleoptera. 
 
 "So firmly have these characters become ingrained in the tracheate 
 series, and so important is this relation of the hardening of the cuticula 
 to the musculature and to the formation of body sclerites, that even the 
 most specialized forms show this primitive system of coloration; and, 
 although there may be spots and markings which have no connection 
 with it, still the chief color areas are thus closely associated." 
 
 Development of Color Patterns. — Although the causes of colora- 
 tion are, for the most part, obscure, it is possible, nevertheless, to point 
 out certain paths along which coloration appears to have developed. 
 These paths have been determined by the comparison of color patterns 
 in kindred groups of insects and the study of colorational variations in 
 adults of the same species. Butterflies, moths and beetles have 
 naturally been preferred as subjects by most students. 
 
 The most primitive colors among moths are uniform dull yellows, 
 browns and drabs — the same colors that the pupal blood assumes when 
 it is dried in the air. These simple colors prevail on the hind wings of 
 most moths and on the less exposed parts of the wings of highly colored 
 butterflies. The hind wings of moths are, as a rule, more primitively 
 colored than the front ones because, as Scudder says, "all differentiation 
 in coloring has been greatly retarded by their almost universal conceal- 
 ment by day beneath the overlapping front wings." Exceptions to 
 this statement are found in Geo'metridas and such other moths as rest 
 with all the wings spread. "In such hind wings we find that the sim- 
 plest departure from uniformity consists in a deepening of the tint next 
 the outer margin of the wing; next we have an intensification of the 
 deeper tint along a line parallel to the margin; it is but a step from this 
 
1 88 ENTOMOLOGY 
 
 condition to a distinct line or band of dark color parallel to the margin. 
 Or the marginal shade may, in a similar way, break up into two or more 
 transverse and parallel submarginal lines, a very common style of 
 ornamentation, especially in moths. Or, again, starting with the 
 submarginal shade, this may send shoots or tongues of dark color a 
 short distance toward the base, giving a serrate inner border to the 
 marginal shade; when now this breaks up into one, two, or more lines 
 or narrow stripes, these stripes become zigzag, or the inner ones may be 
 zigzag, while the outer ones are plain — a very common phenomenon. 
 
 "A basis such as this is .sufficient to account for all the modifications 
 of simple transverse markings which adorn the wings of Lepidoptera." 
 
 Briefly, one or more bands may break up into spots or bars, the 
 breaks occurring either between the veins or, more commonly, at the 
 veins; and in the latter event, short bars or more or less quadrate or 
 rounded spots arise in the interspaces. From simple round spots there 
 may develop, as Darwin and others have shown, many-colored eye-like 
 spots, or ocelli. 
 
 Mayer gives the following laws of color pattern: "(a) Any spot 
 found upon the wing of a butterfly or moth tends to be bilaterally sym- 
 metrical, both as regards form and color; and the axis of symmetry is a 
 line passing through the center of the interspace in which the spot is 
 found, parallel to the longitudinal nervures. (b) Spots tend to appear 
 not in one interspace only, but in homologous places in a row of adjacent 
 interspaces, (c) Bands of color are often made by the fusion of a row 
 of adjacent spots, and, conversely, chains of spots are often formed by 
 the breaking up of bands, (d) When in process of disappearance, bands 
 of color usually shrink away at one end. (e) The ends of a series of spots 
 are more variable than the middle. (/) The position of spots situated 
 near the outer edges of the wing is largely controlled by the wing folds 
 or creases." 
 
 These results have been arrived at chiefly by the study of the varia- 
 tions presented by color patterns. 
 
 Variation in Coloration. — It is safe to say that no two insects are 
 colored exactly alike Some species, however, are far more variable 
 than others. Catocala ilia, for example, occurs under more than fifty 
 varieties, each of which might be given a distinctive name, were it not 
 for the fact that these varieties run into one another. One may examine 
 hundreds of potato beetles {L. decemlineata) without finding any two 
 that have precisely the same pattern on the pronotum. The range of 
 
COLOR AND COLORATION 1 89 
 
 this variation in this species is partially indicated in Fig. 240, and that 
 of Cicindela in Fig. 241. 
 
 Individuals of Cicindela vary in pattern in a few definite directions, 
 and the patterns that characterize the various species appear to be 
 tixations of individual variations. According to Dr. G. H. Horn: (i) 
 The type of marking is the same in all our species. (2) Assuming a well- 
 marked species, tranqueharica {vulgaris, Fig. 241, /) as a central type, 
 the markings of other species vary from that type, (a) by a progressive 
 spreading of the white, {b) by a gradual thinning or absorption of the 
 white, (c) by a fragmentation of the markings, {d) by linear supplemen- 
 tary extension. (3) Many species are practially invariable (i.e., the 
 individual variations are small in amount as compared with those in 
 other species) . These fall into two series : (a) those of the normal type, 
 as tranqueharica, hirticoUis and tenuisignata; (b) those in which some 
 modification of the type has become permanent, probably through 
 isolation, as marginipennis, togala and lemniscata. (4) Those species 
 which vary do so in one direction only. New types of pattern, of 
 specific value, appear to have arisen by the isolation and perpetuation 
 of individual variations. 
 
 . Professor Shelford, in his important monograph on the colors of 
 these beetles, draws the following conclusions, among others: 
 
 Longitudinal stripes in which pigment usually occurs lie in the area 
 of the chief tracheal trunks of the elytron; there are seven cross bands in 
 which pigment does not develop; the second and third and fifth and 
 sixth of these are often joined to make one of each pair. 
 
 Pigment usually occurs about the bases of hairs, which usually lie 
 in the lines of the tracheae. 
 
 In ontogeny the elytra show a spotted condition corresponding to the 
 system of cross bands and longitudinal stripes. The longitudinal 
 stripes are usually more pronounced. 
 
 The characteristic markings of the group are composed of spots or 
 elements joined in the longitudinal light stripe areas and areas of cross 
 bands, with the loss of various spots or elements which occur in onto- 
 geny; joinings are sometimes obHque, and when so markings are some- 
 times parallel with the curved end of the elytron. 
 
 Certain particular types of markings made up of a few elements joined 
 in a particular way characterize the majority of species of the group. 
 
 These markings as derived from the cross and longitudinal bands are 
 angular; reduction of angles, straightening and turning into oblique 
 
I go ENTOMOLOGY 
 
 positions parallel with the end of the elytron characterize modifications 
 of markings. The response to stimuli (high temperature) is in the 
 same direction. 
 
 Response to other stimuli appears to be in the direction of 
 concentric extension of the markings. 
 
 The color patterns and structure to which they are related constitute 
 a mechanism, the directions of movement of which are hmited, i.e., 
 easier in some directions than others; the color pattern plans break 
 when the related structures do; hereditary changes and fluctuations 
 due to stimulation during ontogeny are in the same direction; laws 
 governing the mechanism are the same throughout. 
 
 Variations in general fall into two classes: continuous {individual 
 variations) and discontinuous (mutations) . The former are always pres- 
 ent, are slight in extent and intergrade with one another; they are 
 distributed symmetrically about a mean condition. The latter are 
 occasional, of considerable extent and sharply separated from the 
 normal condition. 
 
 R. H. Johnson published an important statistical study on evo- 
 lution in the color pattern of the lady-beetles. He found both con- 
 tinuous and discontinuous variations present; that the color pattern is 
 capable of modification by the environment; that some modifications 
 are hereditary characters and others not. 
 
 Replacements. — Examples of the replacement of one color by 
 another are familiar to all collectors. The red of Vanessa atalanta and 
 CoccinelHdae may be replaced by yellow. These two colors in many 
 butterflies and beetles are due to pigments that are closely related to 
 each other chemically. Thus in the chrysomeHd Lina lapponica 
 the beetle at emergence is pale but soon becomes yellow with black 
 markings, and after several houts, under the influence of sunlight, the 
 yellow changes to red ; the change may be prevented, however, by keep- 
 ing the beetle in the dark. After death, the red fades back through 
 orange to yellow, especially as the result of exposure to sunlight. 
 Yellow in place of red, then, may be attributed to an arrested develop- 
 ment of pigment in the living insect and to a process of reduction in the 
 dead insect, metabolism having ceased. 
 
 Yellow and green are similarly related. The stripes of Pcecilocapsus 
 lineatus are yellow before they become green, and after death fade back 
 to yellow. As the green pigment in most, if not all, phytophagous in- 
 sects is chlorophyll, these color changes are probably similar to those 
 that occur in leaves. Leaves grown in darkness are yellow, from the 
 
COLOR AND COLORATION 
 
 ^ ■•»/•*- 
 
 U' 
 
 
 
 12 
 
 m 
 
 16 
 
 •\ s 
 
 Fig. 240. — Colorational variations of the pronotum of the Colorado potato beetle, Lepti 
 notarsa decemlineata. 
 
ENTOMOLOGY 
 
 m 
 
 \ fi 
 
 Fig. 241. — Elytral color patterns of Cicindela. 1—8 illustrate reduction^of dark 
 area; 9-14, extension of dark area; 15, 16, formation of longitudinal vitta; 17, 18, linear ex- 
 tension of markings, i, C. tranquebarica; 2, fortnosa; 3, formosa; 4, pamphila; 5, limhala; 6, 
 togata; 7, gratiosa; 8, hamala; 9, tenuisignata; 10, marginipennis; 11, carthagena; 12, sex- 
 giUtata; 13, carthagena; 14, splendida; 15, pusilla; 16, lemniscata; 17, gabhi; 18, dorsalis. — 
 After Horn, from Entomological News. 
 
COLOR AND COLORATION 1 93 
 
 presence of etiolin, and do not turn green until they are exposed to sun- 
 light (or electric light), without which chlorophyll does not develop; 
 and as metabolism ceases, chlorophyll disintegrates, as in autumn, 
 leaving its yellow constituent, xanthophyll, which is very likely the 
 same substance as etiolin. 
 
 Cicindela sexguttata and Calosoma scrutator are often blue in place of 
 green. These colors in these beetles are structural, and their variations 
 are to be attributed to slight differences in the structure of the surface. 
 
 Green grasshoppers occasionally become pink toward the close of 
 summer. No explanation has been offered for this phenomenon, though 
 it may be remarked that when grasshoppers are killed in hot water the 
 normal green pigment turns to pink. 
 
 These changes of color are apparently of no use to the insect, being 
 merely incidental effects of Hght, temperature or other inorganic 
 influences. 
 
CHAPTER VI 
 
 ADAPTIVE COLORATION 
 
 Protective Resemblance. — Every naturalist knows of many ani- 
 mals that tend to escape detection by resembling their surroundings. 
 This phenomenon of protective resemblance is richly exemplified by in- 
 sects, among which one of the most remarkable cases is furnished by the 
 Kallima butterflies, especially K. inachis of India and K. paralekta of the 
 Malay Archipelago. The former species (Fig 242) is conspicuous when 
 on the wing; its bright colors, however, are confined to the upper surfaces 
 of the wings, and when these are folded together, as in repose, the insect 
 
 Fig. 242.- 
 
 -Kallima inachis; A, upper surface; B, with wings closed, showing resemblance 
 to a leaf. X 3-^. 
 
 resembles to perfection one of the dead leaves among which it is accus- 
 tomed to hide. The form, size and color of the leaf are accurately re- 
 produced, the petiole being simulated by the tails of the wings. Two 
 parallel shades, one light and one dark, represent, respectively, the 
 illuminated and the shaded side of a mid-rib, and the side-veins as well 
 are imitated; there are even small scattered black spots resembling 
 those made on the leaf by a species of fungus. Furthermore, the butter- 
 fly habitually rests, not among green leaves, where it would be conspicu- 
 ous, but among leaves with which it harmonizes in coloration. 
 Notwithstanding some discussion as to whether it usually rests in pre 
 
 ^9\ 
 
ADAPTIVE COLORATION 
 
 195 
 
 cisely the same position as a leaf, this insect certainly deceives experi- 
 enced entomologists and presumably eludes birds and other enemies by 
 means of its deceptive coloration. 
 
 Some of the tropical Phasmida^ counterfeit sticks, green leaves, or 
 dead leaves with minute accuracy. Our common phasmids, Diaphero- 
 
 
 
 
 Fig. 243. — Manomera hlatchleyi, on a twig. 
 Natural size. 
 
 Fig. 244. — Calocala lacrymosa; A, upper sur- 
 face; B, with wings closed, and resting on bark. 
 Reduced. 
 
 mera femorata and Manomera hlatchleyi (Fig. 243), are well known as 
 "stick insects;" indeed, it is not necessary to go beyond the temperate 
 zone to find plenty of examples of protective resemblance. Geometrid 
 caterpillars imitate twigs, holding the body stiffly from a branch and 
 frequently reproducing the form and coloration of a twig with striking 
 exactitude; and the moths of the same family are often colored like the 
 bark against which they spread their wings. Even more perfectly do the 
 Catocala moths resemble the bark upon which they rest (Fig. 244), with 
 their conspicuous and usually showy hind wings concealed under the pro- 
 
196 
 
 ENTOMOLOGY 
 
 tectively colored front wings. The caterpillars of Basilarchia archippus 
 and Papilio thoas, as well as other larvae and not a few moths, resemble 
 closely the excrements of birds. Numerous grass-eating caterpillars are 
 striped with green, as is also a sphingid species {Ellema harrisii) that 
 lives among pine needles." The large green sphinx caterpillars (Fig. 66) 
 perhaps owe their inconspicuousness partly to their oblique lateral 
 stripes, which cut a mass of green into smaller areas. The caterpillar 
 of Schizura ipomosce (Fig. 245), which is green with brown patches, rests 
 for hours along the eaten or torn edge of a basswood leaf, in which posi- 
 
 FiG. 245. — Caterpillar of Schizura ipomcea clinging to a torn leaf. Natural size. 
 
 tion it bears an extremely deceptive resemblance to the partially dead 
 border of a leaf. The weevils that drop to the ground and remain 
 immovable are often indistinguishable to the collector on account of 
 their Hkeness to bits of soil or little pebbles. Everyone has noticed 
 the extent to which some of the grasshoppers resemble the soil in color. 
 The CaroHna locust, Dissosteira Carolina, which varies greatly in 
 color, ranging from ashy gray to yellowish or to reddish brown, is 
 commonly found on soil of its own color. Along the Atlantic coast, the 
 seaside locust, Trimerotropis maritima, is practically invisible against 
 the gray sand of the seashore, to which it restricts itself. The same 
 species of grasshopper occurs inland also, as in Illinois and Michigan, 
 along the shores of lakes, and is then pale brown, Hke the sands that it 
 
ADAPTIVE COLORATION 
 
 197 
 
 frequents. Another grasshopper of the same genus, Trimerotropis 
 saxatilis (Fig. 246) occurs only on rock-surfaces, either bare or Hchen- 
 crusted. This grasshopper, mottled with several colors but especially 
 yellow, black and greenish, is conspicuous when flying but indistinguish- 
 able when resting on a patch of lichens (Fig. 246 B) . Where the grass- 
 hopper occurs among Hchen-covered rocks, as in southern IlHnois, it 
 does not ahght by haphazard as a rule, but habitually flies from one 
 patch of lichens to another. 
 
 Instances such as this give support to the opinion that "protective 
 resemblances" are not always merely accidental occurrences; since the 
 protective colors are rendered effective by special habits of the insect. 
 
 Pig. 246. — Triynerolropis saxatilis. A, with wings of right side spread. B, with wings 
 closed, and resting on lichens. Natural size. 
 
 This particular grasshopper, it may be added, is sluggish, and incKned 
 to remain where it alights — an advantageous habit under the circum- 
 stances. The case is not so simple as that of a caterpillar that is green 
 simply because it feeds on chlorophylls. 
 
 Adventitious Resemblance. — If, instead of hastily ascribing all 
 cases apparently of protective resemblance to the action of natural 
 selection, one inquires into the structural basis of the resemblance in 
 each instance, it is found that some cases can be explained, without the 
 aid of natural selection, as being direct effects of food, light or other 
 primary factors. Such cases, then, are in a sense accidental. For ex- 
 ample, many inconspicuous green insects are green merely because 
 chlorophyll from the food-plant tinges the blood and shows through the 
 skin. If it be argued that natural selection has brought about a thin 
 and transparent skin, it may be replied that the skin of a green cater- 
 
198 ENTOMOLOGY " 
 
 pillar is by no means exceptional in thinness or transparency. More- 
 over, many leaf-mining caterpillars are green, simply because their food 
 is green; for, living as they do within the tissues of leaves and surrounded 
 by chlorophyll, their own green color is of no advantage, but is merely 
 incidental. 
 
 Again, in the "protectively" colored chrysaHdes experimented upon 
 by Poulton, the color was directly influenced by the prevailing color 
 of the light that surrounded the larva during the last few days before 
 pupation. Of course, it is conceivable that natural selection may have 
 preserved such individuals as were most responsive to the stimulus of 
 the surrounding light; nevertheless the fact remains that these resem- 
 blances do not demand such an explanation, which is, in other words, 
 superfluous. 
 
 Indeed, a great many of the assumed examples of "protective re- 
 semblance" are very far-fetched. On the other hand, when the re- 
 semblance is as specific and minutely detailed as it is in the Kallima 
 butterflies — where, moreover, special instincts are involved — the phe- 
 nomenon can scarcely be due to chance; the direct and uncombined 
 action of such factors as food or light is no longer sufiicient to explain 
 the facts — although these and other factors are undoubtedly important 
 in a primary, or fundamental, way. Here natural selection becomes 
 useful, as enabling us to understand how original variations of structure 
 and instinct in favorable directions may have been preserved and ac- 
 cumulated until an extraordinary degree of adaptation has been attained. 
 
 Value of Protective Resemblance.— The popular opinion as to 
 the efficiency of protective resemblances is undoubtedly an exaggerated 
 one, owing mainly to the false assumption that the senses of the lower 
 animals are co-extensive in range with our own. As a matter of fact, 
 birds detect insects with a facility far superior to that of man, and 
 destroy them by the wholesale, in spite of protective coloration. Thus, 
 as Judd has ascertained, no fewer than three hundred species of birds 
 feed upon protectively colored grasshoppers, which they destroy in 
 immense numbers, and more than twenty species prey upon the twig- 
 like geometrid larvae; while the weevils that look like particles of soil, 
 and the green-striped caterpillars that assimilate with the surrounding 
 foliage are constantly to be found in the stomachs of birds. 
 
 After all, however, protective resemblance may be regarded as ad- 
 vantageous upon the whole, even if it is ineffectual in thousands of in- 
 stances. An adaptation may be successful even if it does fall short of 
 perfection; and it should be borne in mind that the evolution of protect- 
 
ADAPrrV'E COLORATION 1 99 
 
 ive resemblances among insects has probably been accompanied on the 
 part of birds by an increasing ability to discriminate these insects from 
 their surroundings. 
 
 Warning Coloration. — In strong contrast to the protectively 
 colored species, there are many insects which are so vividly colored as 
 to be extremely conspicuous amid their natural surroundings. Such 
 are many Hemiptera (LygcBus, Murgantia), Coleoptera {Necrophorus, 
 Lampyridae, Coccinellidae, Chrysomelida;), Hymenoptera (MutilHdae, 
 Vespidie), and numerous caterpillars and butterflies. Conspicuous col- 
 ors, being frequently — though not always — associated with qualities 
 that render their possessors unpalatable or offensive to birds or other 
 enemies, are advantageous if, by insuring ready recognition, they ex- 
 empt their owners from attack. 
 
 Efficiency of Warning Colors. — Owing to much disagreement as 
 to the actual value of "warning" colors, several investigators have made 
 many observations and experiments upon the subject. Tests made by 
 offering various conspicuous insects to birds, lizards, frogs, monkeys and 
 other insectivorous animals have given diverse results, according to 
 circumstances. Thus, one gaudy caterpillar is refused by a certain bird 
 at once, or else after being tasted, but another and equally showy cater- 
 pillar is eaten without hesitation. Or, an insect at first rejected may at 
 length be accepted under stress of hunger; or a warningly colored form 
 disregarded by some animals is accepted by others. Moreover, some 
 of the experiments with captive insectivorous animals are open to ob- 
 jection on the score of artificiality. 
 
 Nevertheless, from the data now accumulated, there emerge some 
 conclusions of definite value. Frank Finn, whose conclusions are quoted 
 beyond, has found in India that the conspicuous colors of some butter- 
 flies, (Danainae, Acrcsa, violce, Delias eucharis, Papilio aristolochice) are 
 probably effective as "warning" colors. Marshall found in South 
 Africa that mantids, which would devour most kinds of butterflies, in- 
 cluding warningly colored species, refused Acrcea, which appeared to be 
 not only distasteful but even unwholesome; Acrcea is eaten, however, 
 by the predaceous Asilidse, which feed indiscriminately upon insects — 
 for example, beetles, dragon flies and even stinging Hymenoptera. The 
 masterly studies of Marshall and Poulton strongly support the general 
 theory of warning coloration. 
 
 In this country, much important evidence upon the subject has been 
 obtained by Dr. Judd from an extensive examination of the stomach- 
 contents of birds, supplemented by experiments and field observations. 
 
200 ENTOMOLOGY 
 
 Judd says that the harlequin cabbage bug (Murgantia histrionica) and 
 other large showy bugs are usually avoided by birds; that the showy, 
 ill-flavored lady-beetles (Coccinellidas) and Chrysomelidae such as the 
 elm leaf beetle, Diabrotica, and Leptinotarsa (Doryphora), possess 
 comparative immunity from birds; and that Macrodactylus, Chauliog- 
 nathus and Cyllene are highly exempt from attack. Such cases, he 
 adds, are comparatively few among insects, however, and in general, 
 warning colors are effective against some enemies but ineffective against 
 others. 
 
 Generally speaking, hairs, stings and other protective devices are 
 accompanied by conspicuous colors — though there are many exceptions 
 to this rule. These warning colors nevertheless fail to accomplish their 
 supposed purpose in the following instances, given by Judd. Taking in- 
 sects that are thought to be protected by an offensive odor or a dis- 
 agreeable taste: Heteroptera in general are eaten by all insectivorous 
 birds, the squash bug by hawks and the pentatomids by many birds; 
 among Carabidse with their irritating fluids, Harpalus caliginosus and 
 pennsyhanicus are food for the crow, catbird, robin and six others; 
 Carabus and Calosoma are relished by crows and blackbirds; Silphidae 
 are taken by the crow, loggerhead shrike and kingbird ; and Leptinotarsa 
 decemlineata is eaten by at least six kinds of birds: wood thrush, rose- 
 breasted grosbeak, quail, crow, cuckoo and catbird. Of hairy and spiny 
 caterpillars, Arctiidae are eaten by the robin, bluebird, catbird, cuckoo 
 and others; the larvae of the gipsy moth are food for the blue-jay, robin, 
 chickadee, Baltimore oriole and many others [thirty-one birds, in Massa- 
 chusetts]; and the spiny caterpillars of Vanessa antiopa are taken by 
 cuckoos and orioles. Of stinging Hymenoptera, bumblebees are eaten 
 by the bluebird, blue- jay and two flycatchers; the honey bee, by the 
 wood pewee, phoebe, olive-sided flycatcher and kingbird; Andrena by 
 many birds, and Vespa and Polistes by the red-bellied woodpecker, king- 
 bird, and yellow-belhed flycatcher. 
 
 These facts by no means invalidate the general theory, but they do 
 show that "disagreeable" qualities and their associated color signals 
 are of httle or no avail against some enemies. The weight of evidence 
 favors the theory of warning coloration in a qualified form. While con- 
 spicuous colors do not always exempt their owners from destruction, 
 they frequently do so, by advertising disagreeable attributes of one sort 
 or another. 
 
 The evolution of warning coloration is explained by natural selec- 
 tion; in fact, we have no other theory to account for it. The colors 
 
ADAPTIVE COLORATION . 20I 
 
 themselves must have been present, however, before natural selection 
 could begin to operate; their origin is a question quite distinct from that 
 of their subsequent preservation. 
 
 Protective Mimicry. — This interesting and highly involved phe- 
 nomenon is a special form of protective resemblance in which one species 
 
 Pig. 
 
 -A, Anosia plexippus, the "model;" B, Basilarchia archippus, the 
 Natural size. 
 
 imitates the appearance of another and better protected species, there- 
 by sharing its immunity from destruction. Though it attains its high- 
 est development in the tropics, mimicry is well illustrated in temperate 
 regions. A familiar example is furnished by Basilarchia archippus 
 (Fig. 247, B), which departs widely from the prevailing dark coloration 
 of its genus to imitate the milkweed butterfly, Anosia plexippus. The 
 latter species, or "model," appears to be unmolested by birds, and the 
 former species, or "mimic," is thought to secure the same exemption 
 
202 ENTOMOLOGY 
 
 from attack by being mistaken for its unpalatable model. The common 
 drone-fly, Eristalis tenax (Fig. 248, B) mimics a honey bee in form, size, 
 coloration and the manner in which it buzzes about flowers, in company 
 with its model; it does not deceive the kingbird and the flicker, however. 
 Some Asilidae (robber flies) are remarkably hke bumblebees in superfi- 
 cial appearance and certain Syrphus flies (flower flies) mimic wasps 
 with more or less success. The beetle Casnonia bears a remarkable 
 resemblance to the ants with which it lives. 
 
 The classic cases are those of the Amazonian Heliconiidae and 
 Pieridae, in which mimicry was first detected by Bates. The Heli- 
 coniidae are abundant, vividly colored and eminently free from the 
 attacks of birds and other enemies of butterflies, on account of their 
 
 Fig. 248. — Protective mimicry. A, drone bee, Apis melUfera; B, drone fly, Eristalis tenax. 
 
 Natural size. 
 
 disagreeable odor and taste. Some of the Pieridae — a family funda- 
 mentally different from Hehconiidae — imitate the protected Heliconiidae 
 so successfully, in coloration, form and fhght, that while other Pieridae 
 are preyed upon by many foes, the mimicking species tend to escape 
 attack. 
 
 The family Heliconiidae, referred to by Bates, comprised what are 
 now known as the subfamilies Heliconiinae, Ithomiinae and Danainae; 
 simflarly, Pieridae and Papilionidas are now often termed respectively 
 Pierinae and Papilioninae. Ithomiinae are mimicked also by PapiHo- 
 ninae and by moths of the famihes Castniidae and Pericopidae. 
 
 The discoveries of Bates in tropical South America were paralleled 
 and supported by those of Wallace in India and the Malay Archipelago 
 (where Danainae are the chief "models"), and of Trimen in South Africa 
 (where Acraeinae and Danainae serve as models). Trimen discovered a 
 most remarkable case, in which three species of Danais are mimicked, 
 each by a distinct variety of the feijiale of Papilio cenea {merope). 
 
ADAPTR'E COLORATION 203 
 
 So much for that kind of mimicry — but how is the following kind to 
 be explained? The Ithomiinoe of the Amazon valley have the same 
 form and coloration as the Heliconiinae, but the Ithomiime themselves 
 are already highly protected. The answer is that this resemblance is of 
 advantage to both groups, as it minimizes their destruction by birds — 
 these having to learn but one set of warning signals instead of two. 
 This is the essence of Miiller's famous explanation, which will presently 
 be stated with more precision. There are two kinds of mimicry, then: 
 (i) the kind described by Bates, in which an edible species obtains 
 security by counterfeiting the appearance of an inedible species; (2) that 
 observed by Bates and interpreted by Miiller, in which both species are 
 inedible. These two kinds are known respectively as Batesian and 
 Miillerian mimicry, though some writers prefer to limit the term mimi- 
 cry to the Batesian type. 
 
 Wallace's Rules. — The chief conditions under which mimicry occurs 
 have been stated by Wallace as follows: 
 
 "i. That the imitative species occur in the same area and occupy 
 the very same station as the imitated. 
 
 "2. That the imitators are always the more defenceless. 
 
 "3. That' the imitators are always less numerous in individuals. 
 
 "4. That the imitators differ from the bulk of their aUies. 
 
 "5. That the imitation, however minute, is external and visible 
 only, never extending to internal characters or to such as do not affect 
 the external appearance." 
 
 These rules relate chiefly to the Batesian form of mimicry and need 
 to be altered to apply to the Miillerian kind. 
 
 The first criterion given by Wallace is evidently an essential one and 
 it is sustained by the facts. It is also true that mimic and model occur 
 usually at the same time of year; Marshall found many new instances 
 of this in South Africa. In some cases of mimicry, strange to say, the 
 precise model is unknown. Thus some Nymphalidae diverge from their 
 relatives to mimic the Euploeinae, though no particular model has been 
 found. In such instances, as Scudder suggests, the prototype may exist 
 without having been found; may have become extinct; or the species 
 may have arrived at a general resemblance to another group without 
 having as yet acquired a likeness to any particular species of the group, 
 the general likeness meanwhile being profitable. 
 
 The second condition named by Wallace is correct for Batesian 
 but not for Miillerian mimicry. 
 
 The fulfilment of the third condition is requisite for the success 
 
204 ENTOMOLOGY 
 
 of Batesian mimicry. Bates noted that none of the pierid mimics were 
 so abundant as their heliconiid models. If they were, their protection 
 would be less; and should the mimic exceed its model in numbers, 
 the former would be more subject to attack than the latter. Some- 
 times, indeed, as Miiller found, the mimic actually is more common than 
 the model; in which event, the consequent extra destruction of the 
 mimic would — at least theoretically — reduce its" numbers back to the 
 point of protection. 
 
 In Miillerian mimicry, however, the inevitable variation in abun- 
 dance of two or more converging and protected species is far less dis- 
 astrous; though when two species, equally distasteful, are involved, 
 the rarer of the two has the advantage, as Fritz Miiller has shown. His 
 lucid explanation is essentially as follows : 
 
 Suppose that the birds of a region have to destroy 1,200 butter- 
 flies of a distasteful species before it becomes recognized as such, and 
 that there exist in this region 2,000 individuals of species A and 10,000 
 of species B; then, if they are different in appearance, each will lose 
 1,200 individuals, but if they are deceptively alike, this loss will be di- 
 vided among them in proportion to their numbers, and A will lose 200 
 and B 1,000. A accordingly saves 1,000, or 50 per cent, of the total 
 number of individuals of the species, and B saves only 200, or 2 per cent. 
 Thus, while the relative numbers of the two species are as i to 5, the 
 relative advantage from their resemblance is as 25 to i. 
 
 If two or more distasteful species are equally numerous, their re- 
 semblance to one another brings nearly equal advantages. In cases of 
 this kind — and many are known — it is sometimes impossible to dis- 
 tinguish between model and mimic, as all the participants seem to 
 have converged toward a common protective appearance, through an 
 interchange of features — the "reciprocal mimicry" of Dr. Dixey. 
 
 Marshall argues, however, against this diaposematism, maintaining 
 that in the case of two participants in Miillerian mimicry the evolution 
 of the mimetic pattern has been in one direction only — toward the more 
 abundant species — any variations in the opposite direction being dis- 
 advantageous. 
 
 From this explanation, the superior value of Miillerian as compared 
 with Batesian mimicry is evident. 
 
 The fourth condition — that the imitators differ from the bulk of 
 their allies — holds true to such a degree that even the two sexes of the 
 same species may differ extremely in coloration, owing to the fact that 
 the female has assumed the likeness of some other and protected species. 
 
ADAPTIVE COLORATION 205 
 
 The female of Papilio cenea, indeed, occurs (as was just mentioned) 
 under three varieties, which mimic respectively three entirely dis- 
 similar species oiDanais, and none of the females are anything like their 
 male in coloration. 
 
 The generally accepted explanation for these remarkable but numer- 
 ous cases in which the female alone is mimetic, is that the female, bur- 
 dened with eggs and consequently sluggish in flight and much exposed 
 to attack, is benefited by imitating a species which is immune; while 
 the male has had no such incentive — so to speak — to become mimetic. 
 Of course, there has been no conscious evolution of mimicry. 
 
 Wallace's fifth stipulation is important, but should read this way: 
 "The imitation, however minute, is but external and visible usually, 
 and never extends to internal characters which do not affect the exter- 
 nal appearance." For, as Poulton points out, the alertness of a beetle 
 which mimics a wasp, implies appropriate changes in the nervous and 
 muscular systems. In its intent, however, Wallace's rule holds good, 
 and by disregarding it some writers strain the theory of mimicry be- 
 yond reasonable limits. Some have said, for example, 
 that the resemblance between caddis flies and moths (^^f% gn^ 
 is mimicry; when the fact is that this resemblance iT/^^Sl^ 
 is not merely superficial but is deep-seated ; the entire | | \^ 
 
 organization of Trichoptera shows that they are / N 
 closely related to Lepidoptera. This likeness P'^- 249.— a 
 
 ^1 ^ • • -I . re •. J tettigomid, Myrme- 
 
 expresses, then, not mimicry, but ainmty and cophana fail ax, 
 parallel development. The same objection applies ^nt ""^ TwrcTnatui"! 
 to the assumed cases of mimicry within the limits length. Prom 
 of a single family, as between two genera of Heli- wattenwyl. 
 coniidas or between the chrysomelid genera Lema 
 and Diabrotica. The more nearly two species are related to each other, 
 the more probable it becomes that their similarity is due — not to mimi- 
 cry — but to their common ancestry. 
 
 On the other hand, the resemblance frequently occurs between 
 species of such different orders that it cannot be attributed to affinity. 
 Illustrations of this are the mimicry of the honey bee by the drone fly, 
 and the many other instances in which stinging Hymenoptera are 
 counterfeited by harmless flies or beetles. A tettigoniid of the Sudan 
 resembles an ant (Fig. 249), and the resemblance, by the way, is ob- 
 tained in a most remarkable manner. Upon the stout body of this 
 orthopteron the abdomen of an ant is delineated in black, the rest of 
 the body being light in color and inconspicuous by contrast with the 
 
2o6 ENTOMOLOGY 
 
 black. Indeed the various means by which a superficial resemblance is 
 brought about between remotely related insects are often extraordinary. 
 
 Irrespective of affinity, insects of diverse orders may converge in 
 wholesale numbers toward a central protected form. The most com- 
 plete examples of this have been brought to light by Marshall and 
 Poulton, in their splendid work on the bionomics of South African 
 insects, in which is given, for instance, a colored plate showing how 
 closely six distasteful and dominant beetles of the genus Lycus are 
 imitated by almost forty species of other genera — a remarkable ex- 
 ample of convergence involving no less than eighteen families and 
 five orders, namely, Coleoptera, Hymenoptera, Hemiptera, Lepidoptera 
 and Diptera. Excepting a few unprotected, or Batesian, mimics (a fly 
 and two or three beetles), this association is one between species that 
 are already protected, by stings, bad tastes or other peculiarities. 
 In other words, here is Miillerian mimicry on an immense scale; and 
 if Miillerian mimicry is profitable when only two species are concerned, 
 what an enormous benefit it must be to each of forty participants ! 
 
 Strength of the Theory. — Evidently the theory of mimicry rests 
 upon the assumption that the mimics, by virtue of their mimicry, are 
 specially protected from insectivorous foes. Formerly, however, there 
 was altogether too little evidence bearing upon the assumption itself, 
 though this was supported by such scattered observations as were 
 available. The oft-repeated assertion that this lack of evidence was 
 due simply to inattention to the subject, has been proved to be true 
 by the decisive results gained in the tropics by several competent 
 investigators who have been able to give the subject the requisite 
 amount of attention. 
 
 From his observations and experiments in India, Frank Finn con- 
 cludes: 
 
 "i. That there is a general appetite for butterflies among insec- 
 tivorous birds, even though they are rarely seen when wild to attack 
 them. 
 
 "2. That many, probably most, species dislike, if not intensely, at 
 any rate in comparison with other butterflies, the warningly-colored 
 Danainae, Acraa viola, Delias eucharis, and Papilio aristolochicB; ot 
 these the last being the most distasteful, and the Danainae the least so. 
 
 "3. That the mimics of these are at any rate relatively palatable, 
 and that the mimicry is commonly effectual under natural conditions. 
 
 ''4. That each bird has separately to acquire its experience, and well 
 remembers what it has learned. 
 
ADAPTR'E COLORATION 207 
 
 "That therefore on the whole, the theory of Wallace and Bates is 
 supported by the facts detailed in this and my former papers, so far as 
 they deal with birds (and with the one mammal used). Professor 
 Poulton's suggestion that animals may be forced by hunger to eat un- 
 palatable forms is also more than confirmed, as the unpalatable forms 
 were commonly eaten without the stimulus of actual hunger — generally, 
 also, I may add, without signs of dislike." 
 
 Though insects have many vertebrate and arthropod enemies, it is 
 probable that the evolution of mimetic resemblance, implying warning 
 coloration, has been brought about chiefly by insectivorous birds. 
 
 Neglecting papers of minor importance, we may pass at once to the 
 most important contribution upon this subject — the voluminous work 
 of Marshall and Poulton upon mimicry and warning colors in South 
 African insects. These investigators have found that birds are to be 
 counted as the principal enemies of butterflies; that the Danainae and 
 Acraeinse, which are noted as models, are particularly immune from de- 
 struction, while unprotected forms suffer; and that mimicking, though 
 palatable, species share the freedom of their models. The same is true 
 of beetles, of which Coccinellidse, Malacodermidse (notably Lycus) 
 Cantharidae and many Chrysomelidae serve as models for many other 
 Coleoptera, being "conspicuous and constantly refused by insect- 
 eaters." In short, the splendid work of Marshall and Poulton tends to 
 place the theory of Batesian and Miillerian mimicry upon a substantial 
 foundation of observational and experirnental evidence. 
 
 In regard to the important question — do birds avoid unpalatable 
 insects instinctively or only as the result of experience — the evidence is 
 all one way. Several investigators, including Lloyd Morgan, have 
 found that newly-hatched birds have no instinctive aversions as regards 
 food, but test everything, and (except for some little parental guidance) 
 are obliged to learn for themselves what is good to eat and what is not. 
 This experimental evidence that the discrimination of food by birds is 
 due solely to experience, was evidently highly necessary to place the 
 theory of mimicry — especially the Miillerian theory — upon a sound 
 basis. 
 
 Though butterflies as a group are much subject to the attacks of 
 birds in the tropics, it has been asserted that butterflies in temperate 
 regions are as a whole almost exempt from the attacks of birds, and that 
 consequently the mimicry of the monarch (Fig. 247) by the viceroy is 
 of no advantage. In answer to this assertion Marshall has pubhshed a 
 long list of references showing that butterflies are attacked by birds 
 
2o8 ENTOMOLOGY 
 
 more commonly than has been generally supposed. At the same time 
 there is no proof that the viceroy profits at present by its mimetic 
 pattern, though it may have done so in the past. In any event, the 
 departure of archippus from its congeners toward one of the Danainae — a 
 famous group of "models" in the tropics — is unintelligible except as an 
 instance of mimicry. 
 
 Granting that mimicry is upon the whole advantageous, it becomes 
 important to learn just how far the advantage extends; and we find that 
 mimicry is not of universal effectiveness. Even the highly protected 
 Heliconiinas and Danainse are food for some predaceous insects. In 
 this country, as Judd has observed, the drone-fly {Eristalis tenax), which 
 mimics the honey bee, is eaten by the kingbird and the phcebe; the 
 kingbird, indeed, eats the honey bee itself, but is said to pick out the 
 drones; chickens also discriminate between drones and workers, eating 
 the former and avoiding the latter. Bumblebees and wasps, imitated 
 by many other insects, are themselves eaten by the kingbird, catbird 
 and several other birds, though it is not known whether the stingless 
 males of these are singled out or not. Such facts as these do not discredit 
 the general theory of mimicry but point out its limits. 
 
 Evolution of Mimicry. — Natural selection gives an adequate ex- 
 planation of the evolution of a mimetic pattern. Before accepting this 
 explanation, however, we must inquire: (i) What were the first stages 
 in the development of a mimetic pattern? (2) What evidence is there 
 that every step in this development was vitally useful, as the theory de- 
 mands that it should be? These pertinent questions have been 
 answered by Darwin, Wallace, Miiller, Dixey and several other 
 authorities. 
 
 The incipient mimic must have possessed, to begin with, colors or 
 patterns that were capable of mimetic development; evidently the raw 
 material must have been present. Now Miiller and Dixey in particular 
 have called attention to the fact that many pierids have at least touches 
 of the reds, yellows and other colors that are so conspicuous in the heli- 
 coniids. More than this, however, Dixey has demonstrated — as appears 
 clearly from his colored figures — a complete and gradual transition from 
 a typical non-mimetic pierid, Pieris locusta, to the mimetic pierid 
 Mylothris pyrrha, the female of which imitates Heliconius numata. He 
 traces the transition chiefly through the males of several pierid species — 
 for the males, though for the most part white (the typical pierid color), 
 "show on the under surface, though in varying degrees, an approach 
 towards the Heliconiine pattern that is so completely imitated by their 
 
ADAPTIVE COLORATION 209 
 
 mates. These partially developed features on the under surface of the 
 males enable us to trace the history of the growth of the mimetic 
 pattern." Starting from Pieris locusta, it is an easy step to Mylothris 
 lypera, thence to M. lorena, and from thtfe to the mimetic M. pyrrha. 
 "Granted a beginning, however small, such as the basal red touches in 
 the normal Pierines, an elaborate and practically perfect mimetic 
 pattern may be evolved therefrom by simple and easy stages." 
 
 Furthermore (in answer to the second question), it does not tax the 
 imagination to admit that any one of these color patterns has — at least 
 occasionally — been sufficiently suggestive of the heliconiid type to pre- 
 serve the hfe of its possessor; especially when both bird and insect were 
 on the wing and perhaps some distance apart, when even a momentary 
 flash of red or yellow from a pierid might be enough to save it from 
 attack. 
 
 It is highly desirable, of course, that this plausible explanation 
 should be tested as far as possible by observations in the field and by 
 experiments as well. 
 
 Mimicry and Mendelism. — The weight of evidence is at present 
 vastly in favor of the theory of mimicry as against any other explanation 
 of the facts, even though the theory is sometimes stretched to impossible 
 limits by some of its enthusiastic adherents. The only opposing opinion 
 that has sufficient plausibility to demand much consideration as yet 
 is that of Punnett. 
 
 In India and Ceylon the butterfly Papilio polytes has in addition to 
 the normal female a second form of female which mimics P. aristolochia 
 and a third which imitates P. hector; polytes being palatable to birds 
 and its two models unpalatable. 
 
 This case, described by Wallace more than fifty years ago, is one of 
 the classic examples of mimicry. Punnett holds, however, that these 
 resemblances are of no practical value and that natural selection htis 
 played no part in the formation of these polymorphic forms and suggests 
 that Mendehsm offers a better explanation of the phenomenon— a 
 suggestion that should be tested experimentally. 
 
 Adaptive Colors in General.— Several classes of adaptive colors 
 have been discriminated and defined by Poulton, whose classification, 
 necessarily somewhat arbitrary but nevertheless very useful, is given 
 below, in its abridged form. 
 
ENTOMOLOGY 
 
 III. 
 
 APATETIC COLORS.— Colors resembling some part of the environment or the 
 appearance of another species. 
 
 A. Cryptic Colors. — Protective and Aggressive Resemblances. 
 
 1. Procryptic colors. — Protective Resemblances. — Concealment as a pro- 
 
 tection against enemies. Example: Kallima butterfly. 
 
 2. Anticryptic colors. — Aggressive Resemblances. — Concealment in order to 
 
 facilitate attack. Example: Mantids with leaf-like appendages. 
 
 B. PsEUDOSEMATic COLORS. — False warning and signalling colors. 
 
 1. Pseudaposematic colors.- — Protective Mimicry. Example: Bee-like fly. 
 
 2. Psendepisematic colors. — Aggressive INIimicry and Alluring Coloration. 
 
 Examples: Volucella, resembling bees (Fig. 250); Flower-like mantid. 
 SEMATIC COLORS.— Warning and SignalUng Colors. 
 
 1. Aposematic colors. — Warning Colors. — Examples: Gaudy colors of stinging 
 
 insects. 
 
 2. Episematic colors. — Recognition Markings. 
 EPIGAMIC COLORS.— Colors Displayed in Courtship. 
 
 Such of these classes as have not already been discussed need brief 
 reference. 
 
 Aggressive Resemblances. — The resemblance of a carnivorous 
 animal to its surroundings may not only be protective but may also 
 
 Fig. 250. — Aggressive mimicry. On the left, a bee, Bombus maslrucatus; on the right, 
 fly, Volucella bombylans. Natural size. 
 
 enable it to approach its prey undetected, as in the case of the polar bear 
 or the tiger. Among insects, however, the occurrence of aggressive 
 resemblance is rather doubtful, even in the case of the leaf-Hke mantids. 
 
 Aggressive Mimicry. — Under this head are placed those cases in 
 which one species mimics another to which it is hostile. The best 
 known instance is furnished by European flies of the genus Volucella ^ 
 whose larvae feed upon those of bumblebees and wasps. The flies bear 
 a close resemblance to the bees, owing to which it is supposed that the 
 former are able to enter the nests of the latter and lay their eggs. 
 
 Alluring Coloration. — The best example of this phenomenon is 
 afforded by an Indian mantid, Gongylus gongyloides, which resembles so 
 perfectly the brightly colored flowers among which it hides that insects 
 actually fly straight into its clutches. 
 
ADAPTIVE COLORATION 211 
 
 Recognition Markings.— Though these are apparently important 
 among mammals and birds, as enabling individuals of the same species 
 quickly to recognize and follow one another, no special markings for 
 this purpose are known to occur among insects, not excepting the gre- 
 garious migrant species, such as Anosia plexippus and the Rocky 
 Mountain locust. 
 
 Epigamic Colors. — Among birds, frequently, the bright colors of 
 the male are displayed during courtship, and their evolution has been 
 attributed by Darwin and many of his followers to sexual selection — a 
 highly debatable subject. Among insects, however, no such phenome- 
 non has been found; whenever the two sexes differ in coloration the 
 difference does not appear to faciHtate the recognition of even one sex 
 by the other. 
 
 Evolution of Adaptive Coloration. — Natural selection is the only 
 theory of any consequence that explains the highly involved phenomena 
 oi adaptive coloration. Against such vague and unsupported theories 
 as the action of food, climate, laws of growth or sexual selection, natural 
 selection alone accounts for the multitudinous and intricate correlations 
 of color, pattern, form, attitude, movement, place, time, etc., that are 
 necessary to the development of a perfect case of protective resemblance 
 or mimicry. Natural selection cannot, of course, originate colors or any 
 other characters, its action being restricted to the preservation and 
 accumulation of such advantageous variations as may arise, from what- 
 ever causes. As Poulton says, the vast body of facts, utterly meaning- 
 less under any other theory, become at once intelligible as they fall 
 harmoniously into place under the principle of natural selection, to 
 which, indeed, they yield the finest kind of support. 
 
CHAPTER VII 
 
 INSECTS IN RELATION TO PLANTS 
 
 Insects, in common with other animals, depend for food primarily 
 upon the plant world. No other animals, however, sustain such intimate 
 and complex relations to plants as insects do. The more luxuriant and 
 varied the flora, the more abundant and diversified is its accompanying 
 insect fauna. 
 
 Not only have insects become profoundly modified for using all kinds 
 and all parts of plants for food and shelter, but plants themselves have 
 been modified to no small extent in relation to insects, as appears in their 
 protective devices against unwelcome insects, in the curious formations 
 known as "galls," the various insectivorous plants, and especially the 
 omnipresent and often intricate floral adaptations for cross-polhnation 
 through the agency of insect visitors. .Though insects have laid plants 
 under contribution, the latter have not only vigorously sustained the 
 attack but have even pressed the enemy into their own service, as it were. 
 
 Numerical Relations. — The number of insect species supported by 
 one kind of plant is seldom small and often surprisingly large. The 
 poison ivy {Rhus toxicodendron) is almost exempt from attack, though 
 even this plant is eaten by a leaf-mining caterpillar, two pyralid larvae 
 and the larva of a scolytid beetle (Schwarz, Dyar) . Horse-chestnut 
 and buckeye have perhaps a dozen species at most; elm has eighty; 
 birches have over one hundred, and so have maples; pines are known to 
 harbor 170 species and may jdeld as many more; while our oaks sustain 
 certainly 500 species of insects and probably twice as many. Turn- 
 ing to cultivated plants, the clover is affected, directly or indirectly, by 
 about 200 species, including predaceous insects, parasites, and flower- 
 visitors. Clover grows so vigorously that it is able to withstand a great 
 deal of injury from insects. Corn is attacked by about 200 species, of 
 which 50 do notable injury and some 20 are pests. Apple insects num- 
 ber some 400 species. 
 
 Not uncommonly, an insect is restricted to a single species of plant. 
 Thus the caterpillar of Heodes hypophlceas feeds only on sorrel {Rumex 
 acetosella), so far as is known. The chrysomelid Chrysochus auratus 
 appears to be limited to Indian hemp {Apocynum androscemifolium) and 
 
INSECTS IN RELATION TO PLANTS 
 
 213 
 
 to milkweed (Asclepias). In many instances an insect feeds indiffer- 
 ently upon several species of plants provided these have certain attri- 
 butes in common. Thus Argynnis cybele, aphrodite and atlantis eat the 
 leaves of various species of violets, and the Colorado potato beetle eats 
 different species of Solanum. Papilio thoas feeds upon orange, prickly 
 ash and other Rutaceae. Anosia plexippus eats the various species of 
 Asclepias and also Apocynum androscemifolium; while Chrysochus also 
 is Hmited to these two genera of plants, as was said. These plants agree 
 in having a milky juice; in fact the two genera are rather nearly related 
 botanically. The common cabbage butterfly {Pieris rapes) though con- 
 fined for the most part to Cruciferae, such as cabbage, mustard, turnip, 
 
 radish, horse-radish, etc., often devel- a 
 
 ops upon Tropceolum, which belongs to 
 Geraniaceae; all its food plants, how- 
 ever, have a pungent odor, which is 
 probably the stimulus to oviposition. 
 
 Most phytophagous insects range 
 over many food plants. The cecropia 
 caterpillar has more than sixty of 
 these, representing thirty-one genera 
 and eighteen orders of plants; and the 
 tarnished plant bug [Lygus pratensis) 
 feeds indifferently on all sorts of herb- 
 age, as does also the caterpillar of Dia- 
 crisia virginica. Many of the insects 
 of apple, pear, quince, plum, peach, 
 and other plants of the family Rosaceae 
 occur also on wild plants of the same 
 
 family; and the worst of our corn and wheat insects have come from 
 wild grasses. As regards number of food plants, the gipsy moth "holds 
 the record," for its caterpillar will eat almost any plant. In Massachu- 
 setts, according to Forbush and Fernald, it fed in the field upon 78 
 species of plants, in captivity upon 458 species (30 under stress of 
 hunger, the rest freely), and refused only 19 species, most of which 
 (such as larkspur and red pepper) had poisonous or pungent juices, 
 or were otherwise unsuitable as food. The migratory locust is noto- 
 riously omnivorous, and perhaps eats even more kinds of plants than 
 the gipsy moth. 
 
 Galls.— Most of the conspicuous plant outgrowths known as "galls" 
 are made by insects, though many of the smaller plant galls are made 
 
 Pig. 251. — Holcaspis globulus. A, 
 galls on oak, natural size; B, the gall- 
 maker, twice natural length. 
 
214 
 
 ENTOMOLOGY 
 
 by mites (Acarina) and a few plant excrescences are due to nematode 
 worms and to fungi. 
 
 Among insects, Cynipidae (Hymenoptera) are pre-eminent as gall- 
 
 FiG. 252 
 
 of Holcaspis duricoria, on oak. Natural size. 
 
 makers and next to these, Itonididae (Diptera), Aphididae and 
 Psyllidae (Hemiptera) ; a few gall-insects occur among Tenthredinidae 
 (Hymenoptera) and Trypetidae (Diptera), 
 and one or two among Coleoptera and 
 Lepidoptera. 
 
 Cynipidae affect the oaks (Figs. 251, 
 252) far more often than any other plants, 
 though not a few species select the wild 
 rose. Itonidid galls occur on a great 
 variety of plants, and those of aphids on 
 elm (Fig. 253), poplar, and many other 
 plants; while psyllid galls are most fre- 
 quent on hackberry. The galls may occur 
 anywhere on a plant, from the roots to 
 the flowers or seeds, though each gall- 
 maker always works on the same part 
 of its plant, — root, stem, bud, leaf, leaf- 
 vein, flower, seed, etc. 
 
 Galls present innumerable forms, but 
 the form and situation of a gall are 
 usually characteristic, so that it is often 
 possible to classify galls as species even before the gall-maker is known. 
 Gall-Making. — The female simply lays the egg on the epidermis, or 
 else punctures the plant and deposits an egg in or near the cambium, or 
 any other tissue capable of growth; the egg hatches and the surrounding 
 plant tissue is stimulated to grow rapidly and abnormally into a gall, 
 
 Pig. 253. — Cockscomb gall of 
 Colopha ulmicola, on elm. Slightly 
 reduced. 
 
INSECTS IN RELATION TO PLANTS 215 
 
 which serves as food for the larva; this transforms within the gall and 
 escapes as a winged insect. The physiology of gall-formation is far 
 from being understood. It has been found that the mechanical irrita- 
 tion from the ovipositor is not the initial stimulus to the development 
 of a gall; neither is the fluid which is injected by the female during 
 oviposition, this fluid being probably a lubricant; if the egg is removed, 
 the gall does not appear. Ordinarily the gall does not begin to grow 
 until the egg has hatched, and then the gall grows along with the larva; 
 exceptions to this are found in some Tenthredinidae in which the egg it- 
 self increases in volume, when the gall may grow with the egg. It 
 appears that the larva exudes some fluid which acts upon the proto- 
 plasm of certain plant cells (the cambium and other cells capable of 
 further growth and multiplication) in such a way as to stimulate their 
 increase in size and number. The following observations on this subject 
 by A. Cosens are important. The cells of the plant that immediately 
 surround the larva are known as nutritive cells. In Cynipidae the 
 larva gradually withdraws the contents of these cells, by means of the 
 mouth and not by absorption, and the cells gradually collapse. The 
 proportion of sugar to starch decreases from the inside of the nutritive 
 zone (nearest the larva) to the outside. This is owing to an enzyme 
 that changes starch into sugar, the source of this enzyme being probably 
 a pair of salivary glands that open externally on each side just below the 
 mouth of the larva. The larva by accelerating the rate of change from 
 starch to sugar renders available to the plant more food than usual and 
 therefore stimulates the activity of the protoplasm toward greater cell- 
 growth and more rapid cell-reproduction. Thus the gall as well as the 
 larva draws food from the nutritive zone. 
 
 Why the gall should have a distinctive, or specific, form, it is not yet 
 known. There is no evidence that the form is of any adaptive impor- 
 tance, and the subject probably admits of a purely mechanical explana- 
 tion. One factor in determining the form of the gall is the direction in 
 which the stimulus is apphed; a spherical cynipid gall arising when the 
 influence is about equally distributed in all directions (Cosens) . 
 
 Gall Insects. — The study of gall insects is in many respects difficult. 
 It is not at all certain that an insect which emerges from a gall is the 
 species that made it; for many species, even of Cynipidae, make no galls 
 themselves but lay their eggs in galls made by other species. Such 
 guest-insects are termed inquilines. Furthermore, both gall-makers 
 and inquihnes are attacked by parasitic Hymenoptera, making the in- 
 terrelations of these insects hard to determine. Many species of insects 
 
2l6 ENTOMOLOGY 
 
 feed upon the substance of galls; thus Sharp speaks of as many as thirty 
 different kinds of insects, belonging to almost all the orders, as having 
 been reared from a single species of gall. 
 
 Parthenogenesis and Alternation of Generations. — Parthenogenesis 
 has long been known to occur among Cynipidae. It has repeatedly 
 been found that of thousands of insects emerging from galls of the 
 same kind, all were females. In one such instance the females were 
 induced by Adler to lay eggs on potted oaks, when it was found that the 
 resulting galls were quite unlike the original ones, and produced both 
 sexes of an insect which had up to that time been regarded as another 
 species. Besides parthenogenesis and this alternation of generations, 
 many other complications occur, making the study of gall-insects an 
 intricate and highly interesting subject. 
 
 Plant-Enemies of Insects. — Most of the flowering plants are com- 
 paratively helpless against the attacks of insects, though there are many 
 devices which preveint "unwelcome" insects from entering flowers, for 
 instance the sticky calyx of the catchfly {Silene virginica), which 
 entangles ants and small flies. A few plants, however, actually feed 
 upon insects themselves. Thus the species of Drosera, as described in 
 Darwin's classic volume on insectivorous plants, have specialized leaves 
 for the purpose of catching insects. The stout hairs of these leaves end 
 each in a globular knob, which secretes a sticky fluid. When a fly 
 ahghts on one of these leaves the hairs bend over and hold the insect; 
 then a fluid analogous to the gastric juice of the human stomach exudes, 
 digests the albuminoid substances of the insect and these are absorbed 
 into the tissues of the leaf; after which the tentacles unfold and are 
 ready for the next insect visitor. The Venus's flytrap is another well 
 known example; the trap, formed from the terminal portion of a leaf, 
 consists of two valves, each of which bears three trigger-like bristles, 
 and when these are touched by an insect the valves snap together and 
 frequently imprison the insect, which is eventually digested, as before. 
 In the common pitcher-plants, the pitcher, fashioned from a leaf, is lined 
 with downward pointing bristles, which allow an insect to enter but 
 prevent its escape. The bottom of the pitcher contains water, in 
 which ma^ be found the remains of a great variety of insects which 
 have drowned. There are even nectar glands and conspicuous colors, 
 presumably to attract insects into these traps, where their decomposi- 
 tion products are more or less useful to the plant. In Pinguicula the 
 margin of a leaf rolls over and envelops insects that have been caught 
 by the glandular hairs of the upper surface of the leaf, a copious secretion 
 
INSECTS IN RELATION TO PLANTS 
 
 217 
 
 digests the softer portions of the insects, and the dissolved nitrogenous 
 matter is absorbed into the plant. Utricularia has little bladders which 
 entrap small aquatic insects. These plants are only partially dependent 
 on insect-food, however, for they all possess chlorophyll. 
 
 Bacteria cause epidemic diseases among insects, as in the flacherie 
 of the silkworm; and fungi of a few groups are spe- 
 cially adapted to develop in the bodies of living fl 
 insects. 
 
 Those who rear insects know how frequently 
 caterpillars and other larvae are destroyed by fungi 
 that give the insects a powdered appearance. These 
 fungi, referred to the genus Isaria, are in some cases 
 known to be asexual stages of forms of Cordyceps, 
 which forms appear from the bodies of various larvae, 
 pupae and imagines as long, conspicuous, fructifying 
 sprouts (Fig. 254). 
 
 The chief fungous parasites of insects belong to 
 the large family Entomophthoracese, represented by 
 the common Empusa nmsccB (Fig. 255) which affects 
 various flies. In autumn, especially in warm moist 
 weather, the common house fly may often be seen 
 in a dead or dying condition, sticking to a window- 
 pane, its abdomen distended and presenting alter- 
 nate black and white bands, while around the fly 
 at a little distance is a white powdery ring, or halo. 
 The white intersegmental bands are made by threads 
 
 of the fungus just named, and the white halo by 
 
 countless asexual spores known as conidia, which 
 
 have been forcibly discharged from the swollen 
 
 threads that bore them (Fig. 255) by pressure, result- 
 ing probably from the absorption of moisture. These 
 
 spores, ejected in all directions, may infect another 
 
 fly upon contact and produce a growth of fungus 
 
 threads, or hyphcE, in its body. The fungus may be propagated also 
 
 by means of resting spores, as found by Thaxter, our authority on the 
 
 fungi of insects. 
 
 Empusa aphidis is very common on plant lice and is an important 
 
 check upon their multipHcation. Aphids killed by this fungus are 
 
 found cUnging to their food plant, with the body swollen and discolored. 
 
 Empusa grylli attacks crickets, grasshoppers, caterpillars and other 
 
 Pig. 254. — Fruc- 
 tifying sprouts . of 
 a fungus, Cordyceps 
 ravenelit, a r i s'i n g 
 from the body of a 
 white grub, Lachno- 
 sterna. Slightly 
 reduce d. — A f t e r 
 Riley. 
 
2l8 
 
 ENTOMOLOGY 
 
 forms. Curiously enough, grasshoppers affected by this fungus almost 
 always crawl to the top of some plant and die in this conspicuous position. 
 Sporotrichum, a genus of hyphomycetous fungi, affects a great 
 variety of insects, spreading within the body of the host and at length 
 emerging to form on the body of the insect a dense white felt-like 
 covering, this consisting chiefly of myriads of spores, by means of which 
 healthy insects may become infected. Under favorable conditions, 
 especially in moist seasons, contagious fungous diseases constitute one 
 of the most important checks upon the increase of insects and are 
 therefore of vast economic importance. Thus the termination (in i^ 
 
 
 Fig. 255. — Empusa mtisccB, the common fly-fungus. A, house fly (Musca domeslica), 
 surrounded by fungus spores (conidia) ; B, group of conidiophores showing conidia in 
 several stages of development; C, basidium [h) bearing conidium (c) before discharge. 
 B and C after Th.\xter. 
 
 of a disastrous outbreak of the chinch bug in Illinois and neighboring 
 states "was apparently due chiefly, if not altogether, to parasitism by 
 fungi." Artificial cultures of the common Sporotrichum glohulijerum 
 have been used extensively as a means of spreading infection among 
 chinch bugs and grasshoppers, with, however, but moderate success. 
 Transmission of Diseases of Plants.— Not a few bacterial and fun- 
 gous diseases of plants are known to be transmitted by insects. M. B. 
 Waite proved experimentally that the bacillus causing fire blight of 
 pear, apple and other pomaceous trees is carried by honey bees and 
 other insects from flower to flower, multiplies in the nectar, and enters the 
 host plant. Bees, wasps and flies obtain the bacilli from the exudation 
 from old cankers and carry the organisms either to blossoms or to young 
 
INSECTS IN RELATION TO PLANTS 219 
 
 growing shoots. Other investigators have found that apple aphids, 
 leafhoppers, the tarnished plant bug {Lygus pratensis) and the shot-hole 
 borer {Scolytus rugulosus) are also responsible for the inoculation of 
 fruit trees with the bacilli of blight. 
 
 Dr. E. F. Smith demonstrated that cucurbit wilt is spread, probably 
 exclusively, by insects, particularly the striped and the twelve-spotted 
 cucumber beetles {Diahrotica vittata and D. duodecim punctata, respect- 
 ively), which introduce the bacilli of the disease into the plants as they 
 feed. Some of the beetles carry the bacillus over winter, in the alimen- 
 tary tract, and infect young plants with the wilt in spring. 
 
 The spores of the fungous disease known as brown rot of peach and 
 plum are probably carried by bees, wasps and certain other insects, 
 and introduced into wounds in the fruits made by themselves or other 
 insects. The plum curculio almost certainly leaves these spores in 
 punctures that it makes. 
 
 Cankers of Leptosphceria on apple bark occur around the oviposition 
 wounds made by tree-crickets {(Ecanthus), and it has been shown experi- 
 mentally that these insects convey the spores of the disease both 
 externally and internally and inoculate them into the host plant. 
 Typical cankers on apple branches have been obtained artficially by 
 inoculation with feces of tree-crickets fed on spores of the disease. 
 
 The mosaic diseases of cucumber, potato and tobacco are trans- 
 mitted by plant lice. The spores of bitter rot of apples are conveyed 
 from decaying apples to sound fruits by pomace flies (Drosophila). 
 
 Insects in Relation to Flowers. — Among the most marvelous phe- 
 nomena known to the biologist are the innumerable and complex 
 adaptations by means of which flowers secure cross pollination through 
 the agency of insect visitors. Cross fertilization is actually a necessity 
 for the continued vigor and fertility of flowering plants, and while some 
 of them are adapted for cross pollination by wind or water, the majority 
 of flowering plants exhibit profound modifications of floral structure for 
 compelling insects (and a few other animals, as birds or snails) to carry 
 pollen from one flower to another. ' In general, the conspicuous colors 
 of flowers are for the purpose of attracting insects, as are also the odors 
 of flowers. Night-blooming flowers are often white or yellow and as a 
 rule strongly scented. Colors and odors, however, are simply indica- 
 tions to insects that edible nectar or pollen is at hand. Such is the 
 usual statement, and it is indeed probable that insects actually do asso- 
 ciate color and nectar, even though they will fly to bits of colored paper 
 almost as readily as they will to flowers of the same colors. It is not 
 
2 20 ENTOMOLOGY 
 
 to be supposed, however, that insects feahze that they confer any benefit 
 upon the plant in the flowers of which they find food. At any rate, 
 most flowers are so constructed that certain insects cannot get the 
 nectar or pollen without carrying some pollen away, and cannot enter 
 the next flower of the same kind without leaving some of this pollen 
 upon the stigma of that flower. Take the iris, for example, which is 
 admirably adapted for pollination by a few bees and flies. 
 
 Iris. — In the common blue-flag {Iris versicolor, Fig. 256) each of the 
 
 Fig. 256. — Bumblebee (Bo7nbiis) entering flower of blue-flag (Iris versicolor). Slightly 
 
 reduced. 
 
 three drooping sepals forms the floor of an arched passageway leading 
 to the nectar. Over the entrance and pointing outward is a movable 
 lip (Fig. 257, /), the outer surface of which is stigmatic. An entering 
 bee hits and bends down the free edge of this lip, which scrapes pollen 
 from the back of the insect and then springs back into place. Within 
 the passage, the hairy back of the bee rubs against an overhanging 
 anther (an) and becomes powdered with grains of pollen as the insect 
 pushes down towards the nectar. As the bee backs out of the passage 
 
INSECTS IN RELATION TO PLANTS 
 
 it encounters the guardian lip again, but as this side of the lip cannot 
 receive pollen, immediate close pollination is prevented. Of course, 
 it is possible for bees to enter another part of the same flower or another 
 flower of the same plant, but as a matter of fact, they habitually fly 
 away to another plant; moreover, as Darwin found, foreign pollen is 
 prepotent over pollen from the same flower. It may be added that 
 bees and other poUenizing insects ordi- 
 narily visit in succession several flowers 
 of the same kind. 
 
 Orchids. — The orchids, with their 
 fantastic forms, are really elaborate 
 traps to insure cross pollination. In 
 some orchids {Hahenaria and others) 
 the nectar, lying at the bottom of a 
 long tube, is accessible only to the long- 
 tongued Sphingidae. While probing for 
 the nectar, a sphinx moth brings each 
 eye against a sticky disk to which a 
 pollen mass is attached, and flies away 
 carrying the mass on its eye. Then 
 these pollinia bend down on their stalks 
 in such a way that when the moth 
 thrusts its head into the next flower 
 they are in the proper position to 
 encounter and adhere to the stigma. 
 The orchid Angr cecum sesquipedale, of 
 Madagascar, has a nectary tube more 
 
 than eleven inches long, from which Darwin inferred the existence of a 
 sphinx moth with a tongue equally long. 
 
 Milkweed. — The various milkweeds are fascinating subjects to the 
 student of the interrelations of flowers and insects. The flowers, like 
 those of orchids, are remarkably formed with reference to cross pollina- 
 tion by insects. As a honey bee or other insect crawls over the flowers 
 (Fig. 258, yl) to get the nectar, its legs slip in between the pecuUar nec- 
 tariferous Jwods situated in front of each anther. As a leg is drawn up- 
 ward one of its claws, hairs, or spines frequently catches in a V-shaped 
 fissure (/, Fig. 258, B) and is guided along a sHfto a notched disk, or cor- 
 puscle (Fig. 258, C, d). This disk cHngs to the leg of the insect, which 
 carries off by means of the disk a pair of pollen masses, or pollinia (Fig. 
 258, C). When first removed from their enclosing pockets, or anthers, 
 
 Fig. 257. — Section to illustrate 
 cross pollination of Iris, an, anther; 
 I, stigmatic lip; n, nectary; s, sepal. 
 
222 ENTOMOLOGY 
 
 these thin spatulate pollinia lie each pair in the same plane, but in a few 
 seconds the two pollinia twist on their stalks and come face to face in 
 such a way that one of them can be easily introduced into the stigmatic 
 chamber of a new flower visited by the insect. Then the struggles of the 
 insect ordinarily break the stem, or retinaculum, of the poUinium and 
 free the insect. Often, however, the insect loses a leg or else is per- 
 manently entrapped, particularly in the case of such large-flowered 
 milkweeds as Asclepias cornuti, which often captures bees, flies and 
 moths of considerable size. Pollination is accomplished by a great 
 
 Fig. 258. — Structure of milkweed flower (Asclepias incarnata) with reference to cross 
 pollination. A, a single flower; c, corolla; h, hood; B, external aspect of fissure (/) leading 
 up to disk and also into stigmatic chamber; h, hood; C, pollinia; d, disk. Enlarged. 
 
 variety of insects, chiefly Hymenoptera, Diptera, Lepidoptera and 
 Coleoptera. These insects when collected about milkweed flowers 
 usually display the pollinia dangUng from their legs, as in Fig. 259. 
 
 The details of pollination may be gathered by a close observer from 
 observations in the field and may be demonstrated to perfection by using 
 a detached leg of an insect and dragging it upward between two of the 
 hoods of a flower; first to remove the pair of pollinia and then again 
 to introduce one of them into an empty stigmatic chamber. 
 
 Yucca. — An extraordinary example of the interdependence of plants 
 and insects was made known by Riley, whose detailed account is here 
 summarized. The yuccas of the southern United States and Mexico 
 are among the few plants that depend for pollination each upon a single 
 species of insect. The pollen of Yucca filamentosa cannot be introduced 
 into the stigmatic tube of the flower without the help of a Httle white 
 
INSECTS IN RELATION TO PLANTS 
 
 Fig. 259. — A wasp, Spliex ichneu- 
 mon e a, with pollinia of milkweed 
 attached to its legs. Slightly enlarged. 
 
 tineid moth, Proniiha yuccasella, the female of which pollenizes the flower 
 and lays eggs among the ovules, that her larvae may feed upon the young 
 seeds. While the male has no unusual structural peculiarities, the 
 female is adapted for her special work 
 by modifications which are unique 
 among Lepidoptera, namely, a pair 
 of prehensile and spinous maxillary 
 "tentacles" (Fig. 260, A) and a long 
 protrusible ovipositor {B) which com- 
 bines in itself the functions of a lance 
 and a saw. 
 
 The female begins to work soon 
 after dark, and will continue her opera- 
 tions even in the light of a lantern. 
 Clinging to a stamen (Fig. 261) she 
 scrapes off pollen with her palpi and 
 shapes it into a pellet by using the front legs. After gathering pollen 
 from several flowers she flies to another flower, as a rule, thrusts her 
 long flexible ovipositor into the ovary (Fig. 262) and lays a slender egg 
 
 alongside seven or eight of 
 the ovules. After laying one 
 or more eggs she ascends the 
 pistil and actually thrusts 
 pollen into the stigmatic tube 
 and pushes it in firmly. The 
 ovules develop into seeds, 
 some of which are consumed 
 by the larvae, though plenty 
 are left to perpetuate the 
 plant itself. Three species 
 of Pronuha are known, each 
 restricted to particular 
 species of Yucca. Riley says 
 that Yucca never produces 
 seed where Pronuba does not 
 occur or where she is excluded 
 artificially, and that artificial 
 pollination is rarely so suc- 
 
 FiG. 260. — Pronuha yuccasella. A, maxillary 
 tentacle and palpus; B, ovipositor. — After Riley. 
 Figures 260-262 are republished from the Third 
 Report of the Missouri Botanical Garden, by 
 permission. 
 
 cessful as the normal method. 
 Why does the insect do this? 
 
 The little nectar secreted at the base 
 
224 
 
 ENTOMOLOGY 
 
 of the pistil appears to be of no consequence, at present, and the stig- 
 matic fluid is not nectarian; indeed, the tongue of Pronuha, used in 
 clinging to the stamen, seems to have lost partially or entirely its 
 sucking power, and the alimentary canal is regarded as functionless. 
 Ordinarily it is the flower which has become adapted to the insect, 
 which is enticed by means of pollen or nectar, but here is a flower which — 
 though entomophilous in general structure — has apparently adapted 
 itself in no way to the single insect upon which it is dependent for the 
 continuance of its existence. More than this, the insect not only labors 
 
 Fig. 261. — Pronuha yuccasella, 
 female, gathering pollen from anthers 
 of Yucca. Enlarged. 
 
 Fig. 262. 
 
 -Pronuha moth ovipositing in flower of 
 Yucca. Slightly reduced. 
 
 without compensation in the way of food, but has even become highly 
 modified with reference to the needs of the plant, — its special modifica- 
 tions being unparalleled among insects with the exception of bees, and 
 being more puzzHng than the more extensive adaptations of the bees 
 when we take into consideration the impersonal nature of the operations 
 of Pronuha. Further investigation may render these extraordinary 
 interrelations more intelligible than they are at present. 
 
 The bogus Yucca moth {Prodoxus quinquepunctella) closely resembles 
 and associates with Pronuha but oviposits in the flower stalks of Yucca 
 and has none of the special adaptive structures found in Pronuha. 
 
 As regards floral adaptations, these examples are sufi&cient for pres- 
 ent purposes; many others have been described by the botanist; in fact, 
 the adaptations for cross pollination by insects are as varied as the 
 flowers themselves. 
 
INSECTS IN RELATION TO PLANTS 
 
 225 
 
 Insect Pollenizers.— The great majority of entomophilous flowers 
 are pollenized by bees of various kinds; the apple, pear, blackberry, 
 raspberry and many other rosaceous plants depend chiefly upon the 
 honey bee, while clover cannot set seed without the aid of bumblebees 
 or honey bees, assisted by wild bees such as Tetralonia and Melissodes. 
 LiUes and orchids frequently employ butterflies and moths, as well as 
 bees, and the milkweed is adapted in a remarkable manner for pollination 
 by butterflies, moths and some wasps, as was described. Honeysuckle, 
 lilac, azalea, tobacco. Petunia, Datura and many other strongly scented 
 and conspicuous nocturnal flowers attract for their own uses the long- 
 tonged sphinx moths (Fig. 263) ; the evening primrose, like milkweed, 
 is a favorite of noctuid moths. 
 UmbeUiferous plants are pollen- 
 ized chiefly by various flies, but 
 also by bees and wasps. Pond 
 lilies, golden rod and some other 
 flowers are pollenized largely by 
 beetles, though the flowers exhibit 
 no special modifications in relation 
 to these particular insects. It is 
 noteworthy that polhnation is per- 
 formed only by the more highly 
 organized insects, the bees head- 
 ing the list. 
 
 Of all the insects that haunt the 
 same flower, it frequently happens 
 that only a few are of any use to the 
 flower itself; many come for pollen 
 
 only; many secure the nectar illegitimately; thus bumblebees puncture 
 the nectaries of columbine, snapdragon and trumpet creeper from the 
 outside, and wasps of the genus Odynerus cut through the corolla of 
 Pentestemon Icevigatus, making a hole opposite each nectary; then there 
 are the many insects that devour the floral organs, and the insects which 
 are predaceous or parasitic upon the others. In the Iris, according to 
 Needham, two small bees {Clisodon terminalis and Osmia distincta) are 
 the most important pollenizers, and next to them a few syrphid flies, 
 while bumblebees also are of some importance. The beetle Trichius 
 piger and several small flies obtain pollen without assisting the plant, 
 and Pamphila, Eudatnus, Chrysophanus and some other butterflies 
 succeed after many trials in stealing the nectar from the outside (Fig. 
 
 Pig. 263. — Protoparce sexla visiting flower 
 of Petunia. Reduced. 
 
2 26 ENTOMOLOGY 
 
 264). A weevil {Mononychus vulpeculus) punctures the nectary, and 
 the flowing nectar then attracts a great variety of insects. Grass- 
 hoppers and caterpillars eat the flowers, an ortalid fly destroys the buds, 
 and several parasitic or predaceous insects haunt the plant ; in all, more 
 than sixty species of insects are concerned in one way or another with 
 the Iris. 
 
 Fig. 264. — A butterfly, Polites peckius, stealing nectar from a flower of Iris versicolor. 
 Slightly reduced. 
 
 Modifications of Insects with Reference to Flowers. — While the 
 manifold and exquisite adaptations of the flower for cross polhnation 
 have engaged universal attention, very little has been recorded con- 
 cerning the adaptations of insects in relation to flowers. In fact, 
 the adaptation is largely one-sided; flowers have become adjusted to 
 the structure of insects as a matter of vital necessity — to put it that 
 way — while insects have had no such urgent need — so to speak — in rela- 
 tion to floral structure. They have been influenced by floral structure to 
 some extent however, and in some cases to a very great extent, as ap- 
 pears from their structural and physiological adaptations for gathering 
 and using pollen and nectar. 
 
INSECTS IN RELATION TO PLANTS 
 
 227 
 
 Among mandibulate insects, beetles and caterpillars that eat the 
 floral envelopes show no special modifications for this purpose; pollen- 
 feeding beetles, however, usually have the mouth parts densely clothed 
 with hairs, as in Euphoria (Fig. 265). In suctorial insects, the mouth 
 parts are frequently formed with reference to floral structure; this is 
 the case in many butterflies and particularly in Sphingidae, in which the 
 length of the tongue bears a direct relation to the depth of the nectary 
 in the flowers that they visit. According to MiiUer, the mouth parts of 
 Syrphida?, Stratyomyiidae and Muscidae are specially adapted for feed- 
 
 FiG. 265. — A, right mandible; B, right maxilla; C, hypo- 
 pharynx, of a pollen-eating beetle. Euphoria inda. Enlarged. 
 (The mandibles are remarkable in being two-lobed.) 
 
 Fig. 266. — Pollen-gath- 
 ering hair from a worker 
 honey bee, with a pollen 
 grain attached. Greatly 
 magnified. 
 
 ing on pollen. In Apidae, the tongue as compared with that of other 
 Hymenoptera, is exceptionally long, enabling the insect to reach deep 
 into a flower, and is exquisitely specialized (Fig. 129) for lapping up 
 and sucking in nectar. 
 
 Pollen-gathering flies and bees collect pollen in the hairs of the body 
 or the legs ; these hairs, especially dense and often twisted or branched 
 (Figs. 266, 91) to hold the pollen, do not occur on other than pollen- 
 gathering species of insects. Caudell found that out of 200 species of 
 Hymenoptera only 23 species had branched hairs and that these species 
 belonged without exception to the pollen-gathering group Anthophila, 
 no representative of which was found without such hairs. Similar 
 
228 
 
 ENTOMOLOGY 
 
 branched hairs occur also on the flower-frequenting Bombyliidae and 
 Syrphidae. 
 
 The most extensive modifications in relation to flowers are found in 
 Fronuba, as already described, and above all in Apidae, especially the 
 honey bee. 
 
 Honey Bee.- — The thorax and abdomen and the bases of the legs 
 are clothed with flexible branching hairs (Fig. 266), which entangle 
 
 Fig. 267. — Adaptive modifications of the legs of the worker honey bee. A, outer 
 aspect of left hind leg; B, portion of left middle leg; C, inner aspect of tibio-tarsal region of 
 left hind leg; D, tibio-tarsal region of left fore leg; a, antenna comb; au, auricle; b, brush; 
 c, coxa; co, corbiculum;/, femur; p, pecten; pc, pollen combs; s, spur; sp, spines; ss, spines; t, 
 trochanter; ii, tibia; v, velum; w, so-called wax pincers; 1-5, tarsal segments; i, metatarsus, 
 or planta. 
 
 pollen grains. These are combed out of the gathering hairs by means 
 of special pollen combs (Fig. 267, C, pc) on the inner surface of the 
 planta of the hind tarsus, the middle legs also assisting in this operation. 
 From these combs, the pollen is transferred to the pollen baskets, or 
 corbicula (Fig. 267, A, co), of the outer surface of each hind tibia, the 
 pollen from one side being transferred to the corbiculum of the opposite 
 side. This is accomplished in the following, manner: the left pecten 
 combs out the pollen from the right planta and a mass of pollen forms 
 just above the left pecten at the lower end of the corbiculum; this mass 
 . gradually grows larger and is pushed up along the corbiculum by the 
 
INSECTS IN RELATION TO PLANTS 229 
 
 upward movement of the auricle: Further details are given by Casteel, 
 whose admirably precise and thorough studies on the manipulation of 
 pollen and wax by the honey bee have corrected certain prevalent 
 errors and added much to our knowledge of the subject. Arriving at 
 the nest, the hind legs are thrust into a cell and the mass of pollen on 
 each corbiculum is pried out by means of a spur situated at the apex 
 of the middle tibia (Fig. 267, B, s), this lever being slipped in at the 
 upper end of the corbiculum and then pushed along the tibia under the 
 mass of pollen; the spur is used also in cleaning the wings, which ex- 
 plains its presence on queen and drone, as well as worker, but the pollen- 
 gathering structures of the hind legs are confined to the worker. 
 The so-called wax-pincers of the hind legs (Fig. 267, A, C, w) at the 
 tibio-tarsal articulation, have nothing to do with the transfer of wax 
 scales from the abdomen to the mouth, according to Casteel; a wax scale 
 being removed from its pocket by becoming impaled on stiff spines 
 at the distal end of the inner face of the planta. 
 
 For cleaning the antennae, a front leg is passed over an antenna, 
 which slips into a semicircular scraper (Fig. 267, D, a) fashioned from 
 the basal segment of the tarsus; when the leg is bent at the tibio-tarsal 
 articulation, an appendage, or velum {v) of the tibia falls into place to 
 complete a circular comb, through which the antenna is drawn. This 
 comb is itself cleaned by means of a brush of hairs (6) on the front margin 
 of the tibia. A series of erect spines (sp) along the anterior edge of the 
 first tarsal segment is used as an eye brush, to remove pollen grains or 
 other foreign bodies from the hairs of the compound eyes. The labium 
 and maxillae (Fig. 56) are exquisitely constructed with reference to 
 gathering and sucking nectar; the maxillae are used also to smooth the 
 cell walls of the comb; the mandibles (Fig. 56, md), notched in queen 
 and drone but with a sharp entire edge in the worker, are used for cut- 
 ting, scraping and moulding wax, as well as for other purposes. The 
 entire digestive system of the honey bee is adapted in relation to nectar 
 and pollen as food; the proventriculus forms a reservoir for honey and 
 is even provided at its mouth with a rather complex apparatus for strain- 
 ing the honey from the accompanying pollen grains, as described by 
 Cheshire. The wax glands (Fig. 104) are remarkable speciahzations in 
 correlation with the food habits, as are also the various cephaHc glands, 
 the chief functions of which are given as: (i) digestion, as the conversion 
 of cane sugar into grape sugar, and possibly starch into sugar; (2) the 
 chemical alteration of wax; (3) the production of special food substances, 
 which are highly important in larval development. 
 
230 
 
 ENTOMOLOGY 
 
 Numerous special sensory adaptations also occur. In fact, the 
 whole organization of the honey bee has become profoundly modified 
 in relation to nectar and pollen. Many other insects have the same 
 food but none of them sustain such intimate relations to the flowers as 
 do the bees. 
 
 Ant-plants. — There are several kinds of tropical plants which are 
 admirably suited to the ants that inhabit them. Indeed, it is often as- 
 serted that these plants have become modified with special reference to 
 their use by ants, though this is a gratuitous and improbable assumption. 
 
 Belt found several species of Acacia in Nicaragua and the Amazon 
 valley which have large hollow stipular thorns, inhabited by ants of the 
 genus Pseudomyrma. The ants enter by boring a hole near the apex of 
 
 Fig. 268. — Acacia sphcerocephala, an ant-plant, b, one of the " Belt's bodies"; g, gland; 
 s, s, hollow stipular thorns, perforated by ants. Reduced. — From Strasburger's Lehrbiich 
 der Botanik. 
 
 a thorn (Fig. 268, s). The plant affords the ants food as well as shelter, 
 for glands ig) at the bases of the petioles secrete a sugary fluid, while 
 many of the leaflets are tipped with small egg-shaped or pear-shaped 
 appendages {h) known as "Belt's bodies," which are rich in albumin, 
 fall off easily at a touch, and are eaten by the ants. These ants drive 
 away the leaf-cutting species, incidentally protecting the tree in which 
 they live. 
 
 The ant- trees {Cecropia adenopus) of Brazil and Central America 
 have often been referred to by travelers. When one of these trees is 
 handled roughly, hosts of ants rush out from small openings in the stems 
 and pugnaciously attack the disturber. Just above the insertion of 
 each leaf is a small pit (Fig. 269, a, b) where the wall is so thin as to form 
 a mere diaphragm, through which an ant (probably a fertilized female) 
 bores and reaches a hollow internode. To establish communication be- 
 tween the internodal chambers, the ants bore through the intervening 
 
INSECTS IN RELATION TO PLANTS 
 
 23] 
 
 septa (Fig. 270). They seldom leave the Cecropia plant, unless dis- 
 turbed, and even keep herds of aphids in their abode. The base of each 
 petiole bears (Fig. 271) tender little egg-like bodies ("Miiller's bodies") 
 which the ants detach, store away and eat ; the presence of these bodies 
 is a sure sign that the tree is uninhabited by these ants, which, by the 
 way, belong to the genus Azteca. 
 
 It is too much to assert that the ants protect the Cecropia plant in 
 return for the food and shelter which they obtain. All ants are hostile 
 
 Fig. 269. — Portion of young stem of Cecropia aden- 
 opus showing internodal pits, o and b. Natural size. 
 Figures 269-271 are from Schimper's Pflanzengeo- 
 graphie. 
 
 Fig. 270. — Cecropia adenopus. 
 Portion of a stem, split so as to 
 show internodal chambers and the 
 intervening septa perforated by 
 ants. 
 
 to all other species of ants, with few exceptions, and even to other col- 
 onies of their own species; so that their assaults upon leaf-cutting ants 
 are by no means special and adaptive in their nature, and any protec- 
 tion that a plant derives therefrom is merely incidental. Furthermore, 
 hollow stems, glandular petioles and pitted stems are of common 
 occurrence when they bear no relation to the needs of ants. These 
 interrelations of ants and plants are too often misinterpreted in 
 popular and uncritical accounts of the subject. 
 
 The interesting habits of the leaf-cutting ants in relation to the 
 
ENTOMOLOGY 
 
 plants that they attack are described in a subsequent chapter, where 
 will be found also an account of the Harvesting ants. 
 
 The epiphytic plants Myrmecodia and Hydnophytum, of Java, form 
 
 / 
 
 
 
 Fig. 271. — Cecropiaadenopus. Base of Fig. 272. — Hydnophytum monlannm. Sec- 
 
 petiole showing "Muller's bodies." tionof pseudo-bulb, to show chambers inhabited 
 Slightly reduced. by ants. One-fourth natural size. — A f t e r 
 
 FOREL. 
 
 spongy bulb-like masses, the chambers of which are usually tenanted by 
 ants, which rush forth when disturbed. These lumps (Fig. 272) are 
 primarily water-reservoirs, but the ants utilize them by boring into them 
 and from one chamber into another. In plants of the genus Humholdtia 
 the ants can enter the hollow internodes through openings that already 
 exist. 
 
CHAPTER VIII 
 
 INSECTS IN RELATION TO OTHER AXIM.VLS 
 
 On the one hand, insects may derive their food from other animals, 
 either living or dead; on the other hand, insects themselves are food for 
 other animals, especially fishes and birds, against which they protect 
 themselves by various means, more or less effective. These topics form 
 the principal subject of the present chapter. 
 
 Predaceous Insects. — Innumerable aquatic insects feed largely or 
 entirely upon microscopic Protozoa, Rotifera, Entomostraca, etc.; this 
 is especially the case with culicid (mosquito) and chironomid( midge) 
 larvae. Many aquatic Hemiptera and Coleoptera prey upon planarians, 
 nematodes, annelids, molluscs and crustaceans; Belostoma (the electric 
 light bug) sometimes pierces the bodies of tadpoles and small fishes; 
 Dytiscus also kills young fishes occasionally and is distinctly carnivorous 
 both as larva and imago. Among terrestrial insects, the ground beetles, 
 Carabidae, are notably predaceous, preying not only upon other insects 
 but also upon molluscs, myriopods, mites and spiders. Ants do not 
 hesitate to attack all kinds of animals; in the tropics the wandering 
 ants (Eciton) attack lizards, rats and other vertebrates, and it is said 
 that even huge serpents, when in a torpid condition, are sometimes 
 killed by armies of these pugnacious insects. 
 
 Mosquitoes affect not only mammals but also, though rarely, fishes 
 and turtles. The gadflies (Tabanidae) torment horses and cattle by 
 their punctures; and the black-flies, or buffalo gnats {Simulium), per- 
 secute horses, mules, cattle, fowls, and frequently become unendurable 
 even to man. The notorious tsetse fly {Glossina morsitans) of South 
 Africa spreads a deadly disease among horses, cattle and dogs, by inocu- 
 lating them with a protozoan blood-parasite, to the effects of which, 
 .fortunately, man is not susceptible. 
 
 Parasitic Insects. — Insects belonging to several diverse orders have 
 become peculiarly modified to exist as parasites either upon or within 
 the bodies of birds or mammals. 
 
 Almost all birds are infested by Mallophaga, or bird lice, of which 
 Kellogg has catalogued 264 species from 257 species of North American 
 birds. Sometimes a species of Mallophaga is restricted to a single 
 
234 ENTOMOLOGY 
 
 species of bird, though in the majority of cases this is not so. Several 
 mallophagan species often infest a single bird; thus nine species occur 
 on the hen, and no less than twelve" species, representing five genera, on 
 the American coot. These parasites spread by contact from male to 
 female, from old to young, and from one bird to another when the birds 
 are gregarious. When a single species of bird louse occurs on two or 
 more hosts, these are almost always closely allied, and Kellogg has sug- 
 gested the interesting possibility that such a species has persisted un- 
 changed from a host which was the common ancestor of the two or more 
 present hosts. Mallophaga are not altogether limited to birds, how- 
 ever, for they may be found on cattle, horses, cats, dogs, and some other 
 mammals; Kellogg records eighteen species from fifteen species of mam- 
 mals. These biting lice feed, not upon blood, but upon epidermal 
 cells and portions of feathers or hairs. They have fiat tough bodies 
 (Fig. i8), with no traces of wings, and a large head with only simple eyes; 
 the eggs are glued to feathers or hairs. 
 
 Mammals only are infested by the sucking lice, or Pediculidae. 
 These (Fig. 24) have a large oval or rounded abdomen, no wings, a 
 small head, minute simple eyes or none, and claws that are adapted to 
 clutch hairs; the eggs are glued to hairs. Sucking Hce affect horses, 
 cattle, sheep, dogs, monkeys, seals, elephants, etc., and man is para- 
 sitized by three species, namely, the head louse (Pediculus humanus 
 capitis), the body louse {Pediculus humanus corporis), and the crab 
 louse {Phthirius pubis) . 
 
 An anomalous beetle, Platypsyllus castoris, occurs throughout North 
 America and also in Europe as a parasite of the beaver. 
 
 The iieas, allied to Diptera but constituting a distinct order (Siphon- 
 aptera), are familiar parasites of chickens, cats, dogs and human beings. 
 These insects (Fig. 32) are well adapted by their laterally compressed 
 bodies for slipping about among hairs, and their saltatory powers and 
 general elusiveness are well known. Their wings are reduced to mere 
 rudiments, their eyes when present are minute and simple and their 
 mouth parts are suctorial. 
 
 Among Diptera, there are a few external parasites, the best known 
 of which is the sheep tick {Melophagus ovinus), though several highly 
 interesting but little-studied forms are parasitic upon birds and bats. 
 
 The larvae of the bot-flies (CEstridae) are common internal parasites 
 of mammals. The sheep bot-fly {CEstrus avis) deposits her eggs or 
 larvae on the nostrils of sheep; the maggots develop in the frontal sinuses 
 of the host, causing vertigo or even death, and when full grown escape 
 
INSECTS IN RELATION TO OTHER ANIMALS 235 
 
 through the nostrils and pupate in the soil. The horse bot-fly {Gastro- 
 philus equi) glues its eggs to the hairs of horses, especially on the fore 
 legs and shoulders, whence the larvae are licked off and swallowed; once 
 in the stomach, the bots fasten themselves to its lining, by means of 
 special hooks, and withstand almost all efforts to dislodge them ; though 
 when the bots have attained their growth they release their hold and 
 pass with the excrement to the soil. Bots of the genus Hypoderma form 
 tumors on cattle and other mammals, domesticated or wild. The ox- 
 warble (//. lineata, Fig. 213, /) reaches the oesophagus of its host in the 
 same manner as the horse bot, according to Curtice, but then makes 
 its way into the subcutaneous tissue and causes the well-known tumors 
 on the back of the animal; when full grown the bots squirm out of these 
 tumors and drop to the ground, leaving permanent holes in the hide. 
 
 Parasitism in General. — Parasitic insects evidently do not consti- 
 tute a phylogenetic unit, but the parasitic habit has arisen independently 
 in many different orders. These insects do, however, agree superficially, 
 in certain respects, as the result of what may be termed convergence of 
 adaptation. Thus a dipterous larva, living as an internal parasite, in 
 the presence of an abundant supply of food, has no legs, no eyes or anten- 
 nae, and the head is reduced to a mere rudiment, sufficient simply to 
 support a pair of feeble jaws; the skin, moreover, is no longer armor-like 
 but is thin and delicate, the body is compact and fleshy, and the diges- 
 tive system is of a simplified type. The same modifications are found in 
 hymenopterous larvae, under similar food-conditions, except that the 
 head undergoes less reduction. The various external parasites lack 
 wings, almost invariably, and the eyes, instead of being compound, 
 are either simple or else absent. In some special cases, as in a few 
 dipterous parasites of birds and bats, the wings are present, either 
 permanently or only temporarily, enabhng the insects to reach their 
 hosts. 
 
 This so-called parasitic degeneration, widespread among animals in 
 general and consisting chiefly in the reduction or loss of locomotor and 
 sensory functions in correlation with an immediate and plentiful supply 
 of food, results in a simplicity of organization which is to be regarded — 
 not as a primitive condition — but as an expression of what is, in one 
 sense, a high degree of specialization to peculiar conditions of life. 
 This exquisite degree of adaptation to a special environment, however, 
 sacrifices the general adaptability of the animal, — makes it impossible 
 for a parasite to adapt itself to new conditions; and while parasitism 
 may be an immediate advantage to a species, there are few parasites 
 
236 ENTOMOLOGY 
 
 that have attained any degree of dominance among animals. Ichneu- 
 monidas, to be sure, are remarkably dominant among insects, but their 
 parasitic adaptations are limited for the most part to the larval stage, 
 and the adults may be said to be as free for new adaptations as are any 
 other Hymenoptera. 
 
 Scavenger and Carrion Insects. — Not a few families of Diptera 
 and Coleoptera derive their food from dead animal matter. The 
 aquatic families Dytiscidae and Gyrinidae are largely scavengers. 
 Among terrestrial forms, Silphidae feed on dead animals of all kinds; 
 the burying beetles (Necrophorus), working in pairs, undermine and 
 bury the bodies of birds, frogs and other small animals, and lay their 
 eggs in the carcasses; Histeridae and Staphylinidae are carrion beetles, 
 and Dermestidae attack dried animal matter of almost every description, 
 their depredations upon furs, feathers, museum specimens, etc., being 
 famihar to all. Ants are famous as scavengers, destroying decaying 
 organic matter in immense quantities, particularly in the tropics. 
 Many Scarabaeidae feed upon excrementitious matter, for example the 
 "tumble-bugs," which are frequently seen in pairs, laboriously rolUng 
 along or burying a large ball of dung, which is to serve as food for the 
 larva. 
 
 Insects as Food for Vertebrates.— Lizards, frogs, and toads are 
 insectivorous, especially toads. The American toad feeds chiefly upon 
 insects, which form 77 per cent, of its food for the season, the remainder 
 consisting of myriopods, spiders, Crustacea, molluscs and worms, accord- 
 ing to the observations of A. H. Kirkland, who states that Lepidoptera 
 form 28 per cent, of the total insect food, Coleoptera 27, Hymenoptera 
 19 and Orthoptera 3 per cent. The toad does not capture dead or 
 motionless insects but uses its extensile sticky tongue to Kck in moving 
 insects or other prey, which it captures with surprising speed and preci- 
 sion. In the cities one often sees many toads under an arc-light engaged 
 in catching insects that fall anywhere near them. Though its diet is 
 varied and somewhat indiscriminate, the toad consumes such a large 
 proportion of noxious insects, such as May beetles and cutworms, that 
 it is unquestionably of service to man. 
 
 Moles are entirely insectivorous and destroy large numbers of white 
 grubs and caterpillars; field mice and prairie squirrels eat many insects, 
 especially grasshoppers, and the skunk revels in these insects, though it 
 eats beetles frequently, as does also the raccoon, which is to some extent 
 insectivorous. Monkeys are omnivorous but devour many kinds of 
 insects. 
 
INSECTS IN RELATION TO OTHER ANIMALS 237 
 
 With these hasty references, we may pass at once to the subject of 
 the insect food of fishes and birds. 
 
 Insects in Relation to Fishes. — Insects constitute the most impor- 
 tant portion of the food of adult fresh water fishes, furnishing forty 
 per cent, of their food, according to Dr. Forbes, from whose valuable 
 writings the following extracts are taken. 
 
 "The principal insectivorous fishes are the smaller species, whose 
 size and food structures, when adult, unfit them for the capture of Ento- 
 mostraca, and yet do not bring them within reach of fishes or Mollusca. 
 Some of these fishes have peculiar habits which render them especially 
 dependent upon insect Hfe, the Httle minnow Phenacohius, for example, 
 which, according to my studies, makes nearly all its food from insects 
 (ninety-eight per cent.) found under stones in running water. Next are 
 the pirate perch, Aphredoderus (ninety-one per cent.), then the darters 
 (eighty-seven per cent.), the croppies (seventy-three per cent.), half- 
 grown sheepshead (seventy-one p&c cent.), the shovel fish (fifty-nine per 
 cent.), the chub minnow (fifty-six per cent.), the black warrior sunfish 
 {ChcBnohryttus) and the brook silversides (each fifty-four per cent.) , and 
 the rock bass and the cyprinoid genus Notropis (each fifty-two per 
 cent.). 
 
 "Those which take few insects or none are mostly the mud-feeders 
 and the ichthyophagous species, Amia (the dog-fish) being the only 
 exception noted to this general statement. Thus we find insects wholly 
 or nearly absent from the adult dietary of the burbot, the pike, the gar, 
 the black bass, the wall-eyed pike, and the great river catfish, and from 
 that of the hickory shad and the mud-eating minnows (the shiner, the 
 fathead, etc.). It is to be noted, however, that the larger fishes all go 
 through an insectivorous stage, whether their food when adult be almost 
 wholly other fishes, as with the gar and the pike, or molluscs, as with the 
 sheepshead. The mud-feeders, however, seem not to pass through this 
 stage, but to adopt the limophagous habit as soon as they cease to 
 depend upon Entomostraca. 
 
 "Terrestrial insects, dropping into the water accidentally or swept 
 in by rains, are evidently diHgently sought and largely depended upon 
 by several species, such as the pirate perch, the brook minnow, the top 
 minnows or kilHfishes (cyprinodonts) the toothed herring and several 
 cyprinoids {Semotilus, Pimephales and Notropis). 
 
 "Among aquatic insects, minute slender dipterous larvse, belonging 
 mostly to Chironomus, Corethra and allied genera are of remarkable 
 importance, making, in fact, nearly one tenth of the food of all the fishes 
 
238 ENTOMOLOGY 
 
 studied. They are most abundant in Phenacohius and Etheostoma, 
 which genera have become especially adapted to the search for these 
 insect forms in shallow rocky streams. Next I found them most gener- 
 ally in the pirate perch, the brook silversides, and the stickleback, in 
 which they averaged forty-five per cent. They amounted to about one 
 third the food of fishes as large and important as the red horse and the 
 river carp, and made nearly one fourth that of fifty-one buffalo fishes. 
 They appear further in considerable quantity in the food of a number of 
 the minnow family {Notropis, Fimephales, etc.), which habitually fre- 
 quent the swift waters of stony streams, but were curiously deficient in 
 the small collection of miller's thumbs (Cottidae) which hunt for food in 
 similar situations. The sunfishes eat but few of this important group, 
 the average of the family being only six per cent. 
 
 ''Larvae of aquatic beetles, notwithstanding the abundance of some 
 of the forms, occurred in only insignificant ratios, but were taken by 
 fifty-six specimens, belonging to nineteen of the species,— more fre- 
 quently by the sunfishes than by any other group. The kinds most 
 commonly captured were larvae of Gyrinidae and Hydrophilidae ; where- 
 as the adult surface beetles themselves {Gyrinus, Dineutes, etc.) — whose 
 zigzag-darting swarms no one can have failed to notice — were not once 
 encountered in my studies. 
 
 "The almost equally well-known slender water-skippers [Gerris] seem 
 also completely protected by their habits and activity from capture 
 by fishes, only a single specimen occurring in the food of all my specimens. 
 Indeed, the true water bugs (Hemiptera) were generally rare, with the 
 exception of the small soft-bodied genus Corixa which was taken by 
 one hundred and ten specimens, belonging to twenty-seven species, 
 — most abundantly by the sunfishes and top minnows. 
 
 "From the order Neuroptera [in the broad sense] fishes draw a 
 larger part of their food than from any other single group. In fact, 
 nearly a fifth of the entire amount of food consumed by all. the adult 
 fishes examined by me consisted of aquatic larvae of this order, the great- 
 er part of them larvae of day flies (Ephemeridae), principally of the genus 
 Hexagenia. These neuropterous larvae were eaten especially by the 
 miller's thumb, the sheepshead, the white and striped bass, the common 
 perch, thirteen species of the darters, both the black bass, seven of the 
 sunfishes, the rock bass and the croppies, the pirate perch, the brook 
 silversides, the sticklebacks, the mud minnow, the top minnows, the 
 gizzard shad, the toothed herring, twelve species each of the true 
 minnow family and of the suckers and buffalo, five catfishes, the dog- 
 
INSECTS IN RELATION TO OTHER ANIMALS 239 
 
 fish, and the shovel fish, — seventy species out of the eighty-seven which 
 I have studied. 
 
 "Among the above, I found them the most important food of the 
 white bass, the toothed herring, the shovel fish (fifty-one per cent.), and 
 the croppies; while they made a fourth or more of the alimentary con- 
 tents of the sheepshead (forty-six per cent.), the darters, the pirate 
 perch, the common sunfishes (Lepomis and Chanohryltus) , the rock 
 bass, the little pickerel, and the common sucker (thirty-six per 
 cent.). 
 
 "Ephemerid larvae were eaten by two hundred and thirteen speci- 
 mens of forty-eight species— not counting young. The larva of Hexa- 
 genia, one of the commonest of the 'river flies,' was by far the most 
 important insect of this group, this alone amounting to about half of 
 all the Neuroptera eaten. It made nearly one half of the food of the 
 shovel fish, more than one tenth that of the sunfishes, and the princi- 
 pal food resource of half-grown sheepshead; but was rarely taken by 
 the sucker family, and made only five per cent, of the food of the catfish 
 group. 
 
 "The various larvae of the dragon flies, on the other hand, were much 
 less frequently encountered. They seemed to be most abundant in 
 the food of the grass pickerel (twenty-five per cent.) and next to that, 
 in the croppie, the pirate perch, and the common perch (ten to thirteen 
 percent.). 
 
 "Case-worms (Phryganeidae) were somewhat rarely found, rising to 
 fifteen per cent, in the rock bass and twelve per cent, in the minnows of 
 the Hybopsis group, but otherwise averaging from one to six per cent, 
 in less than half of the species." 
 
 Insects in Relation to Birds. — From an economic point of view the 
 relations between birds and insects are extremely important, and from 
 a purely scientific standpoint they are no less important, involving as 
 they do biological interactions of remarkable complexity. 
 
 The prevalent popular opinion that birds in general are of inesti- 
 mable value as destroyers of noxious insects is a correct one, as Dr. 
 Forbes proved, from his precise and extensive studies upon the food of 
 Ilhnois birds, involving a laborious and difficult examination of the 
 stomach contents of many hundred specimens. All that follows is 
 taken from Forbes, when no other author's name is mentioned, and 
 though the percentages given by him apply to particular years and would 
 undoubtedly vary more or less from year to year, they are here for con- 
 venience regarded as representative of any year and are spoken of in 
 
240 ENTOMOLOGY 
 
 the present tense. About two thirds of the food of birds consists of 
 insects. 
 
 Robin. — The food of the robin in Ilhnois, from February to May in- 
 clusive, consists almost entirely of insects; at first, larvae of Bibio albi- 
 pennis for the most part, and then caterpillars and various beetles. When 
 the small fruits appear, these are largely eaten instead of insects; thus 
 in June, cherries and raspberries form fifty-five per cent, and insects 
 (ants, caterpillars, wireworms and Carabidae) forty-two per cent, of the 
 food; and in July, raspberries, blackberries and currants form seventy- 
 nine per cent, and insects (mostly caterpillars, beetles and crickets) but 
 twenty per cent, of the food. In August, insects rise to forty-three per 
 cent, and fruits drop to fifty-six per cent., and these are mostly cherries, 
 of which two thirds are wild kinds. In September, ants form fifteen 
 per cent, of the food, caterpillars five per cent, and fruits (mostly grapes, 
 mountain-ash berries and moonseed berries) seventy per cent. In 
 October, the food consists chiefly of wild grapes (fifty- three per cent.), 
 ants (thirty-five per cent.), and caterpillars (six per cent.). 
 
 For the year, judging from the stomach contents of one hundred and 
 fourteen birds, garden fruits form only twenty-nine per cent, of the food 
 of the robin, while insects constitute two thirds of the food. The results 
 are confirmed by those of Professor Beal in Michigan, who found that 
 more than forty-two per cent, of the food of the robin consists of insects 
 with some other animal matter, the remainder being made up of various 
 small fruits, but notably the wild kinds. 
 
 Upon the whole, the robin deserves to be protected as an energetic 
 destroyer of cutworms, white grubs and other injurious insects, and the 
 comparatively few cultivated berries that the bird appropriates are 
 ordinarily but a meagre compensation for the valuable services rendered 
 to man by this familiar bird. 
 
 Catbird. — Not so much can be said for the catbird, however, for, 
 though its food habits are similar to those of the robin, it arrives later 
 and departs earher, with the result that it is less dependent than the 
 robin upon insects and that berries form a larger percentage of its 
 total food. 
 
 In May, eighty-three per cent, of the food of the catbird consists of 
 insects, mostly beetles (Carabidae, Rhynchophora, etc.), crane-flies, 
 ants and caterpillars (Noctuidae) ; while dry sumach berries are eaten to 
 the extent of seven per cent. For the first half of June, the record is 
 much the same, with an increase, however, in the number of May 
 
INSECTS IN RELATION TO OTHER ANIMALS 24I 
 
 beetles eaten; in the second half of the month the food consists chiefly 
 of small fruits, especially raspberries, cherries and currants; so that for 
 the month as a whole, only forty-nine per cent, of the food is made up 
 of insects. This falls to eighteen per cent, in July, when three quarters 
 6f the food consists of small fruits, mostly blackberries, however. In 
 August, with the diminution of the smaller cultivated fruits, the per- 
 centage of insects rises to forty-six per cent., nearly one half of which is 
 made up of ants and the rest of caterpillars, grasshoppers, Hemiptera, 
 Coleoptera, etc. In September, with the appearance of wild cherries, 
 elderberries, Virginia creeper berries and grapes, these are eaten to the 
 extent of seventy-six per cent., the insect element of the food falling to 
 twenty-one per cent., of which almost half consists of ants, and the 
 remainder of beetles and a few caterpillars. 
 
 For the entire year, as appears from the study of seventy specimens 
 by Forbes, insects form forty-three per cent, of the food of the catbird 
 and fruits fifty-two per cent. As the injurious insects killed are offset 
 by the beneficial ones destroyed, "the injury done in the fruit-garden by 
 these birds remains without compensation unless we shall find it in the 
 food of the young," says Professor Forbes. And this has been found, to 
 the credit of the catbird; for Weed learned that the food of three nest- 
 lings consisted of insects, sixty-two per cent, of which were cutworms 
 and four per cent, grasshoppers; while Judd found that fourteen nest- 
 lings had eaten but four per cent, of fruit, the diet being chiefly ants, 
 beetles, caterpillars, spiders and grasshoppers. In fact, Weed believes 
 that, on the whole, the benefit received from the catbird is much greater 
 than the harm done, and that its destruction should never be permitted 
 except when necessary in order to save precious crops. 
 
 Bluebird. — The excellent reputation which the bluebird bears every- 
 where as an enemy of noxious insects is well deserved. From a study of 
 one hundred and eight Illinois specimens, Forbes finds that seventy- 
 eight per cent, of the food for the year consists of insects, eight per cent, 
 of Arachnida, one per cent, of Julidse and only thirteen per cent, of 
 vegetable matter, edible fruits forming merely one per cent, of the entire 
 food. The insects eaten are mostly caterpillars (chiefly cutworms), 
 Orthoptera (grasshoppers and crickets) and Coleoptera (Carabidae and 
 Scarabaeidae) . Though some of the insects are more or less beneficial to 
 man, such as Carabidae and Ichneumonidae (respectively predaceous and 
 parasitic), the beneficial elements form only twenty-two per cent, of the 
 food for the year, as against forty-nine percent, of injurious elements, the 
 remaining twenty- nine per cent, consisting of neutral elements. The food 
 
242 » ENTOMOLOGY 
 
 of the nestlings, according to Judd, is essentially like that of the adults, 
 being "beetles, caterpillars, grasshoppers, spiders and a few snails." 
 
 Other Insectivorous Birds. — Weed and Dearborn, from whose 
 excellent work the following notes are taken, find that the common 
 chickadee devours immense numbers of canker worms, and that more 
 than half its food during winter consists of insects, largely in the form of 
 eggs, including those of the common tent caterpillar (C. americana), 
 the fall webworm {H. cunea) and particularly plant lice, whose eggs, 
 small as they are, form more than one fifth of the entire food ; more than 
 four hundred and fifty of them are sometimes eaten by a single bird in 
 one day, and the total number destroyed annually is inconceivably 
 large. The house wren is almost exclusively insectivorous, feeding 
 upon caterpillars and other larvae, ants, grasshoppers, gnats, beetles, 
 bugs, spiders, and myriopods. The swallows, also, are highly insecti- 
 vorous; ''most of their food is captured on the wing, and consists of 
 small moths, two-winged flies, especially crane flies, beetles in great 
 variety, flying bugs, and occasionally small dragon flies. The young 
 are fed with insects." Ninety per cent, of the food of the kingbird 
 "consists of insects, including such noxious species as May beetles, 
 click-beetles, wheat and fruit weevils, grasshoppers, and leafhoppers." 
 The honey bees eaten by this bird are insignificant in number. Wood- 
 peckers destroy immense numbers of wood-boring larvae, bark-insects, 
 ants, caterpillars, etc. The cuckoos "are unique in having a taste for 
 insects that other birds reject. Most birds are ready to devour a smooth 
 caterpillar that comes their way, but they leave the hairy varieties 
 severely alone. The cuckoos, however, make a specialty of devouring 
 such unpalatable creatures; even stink bugs and the poisonous spiny 
 larvae of the lo moth are freely taken." Caterpillars form fifty per 
 cent, of the food for the year; Orthoptera (grasshoppers, katydids, and 
 tree crickets), thirty per cent.; Coleoptera and Hemiptera, six per cent, 
 each; and flies and ants are taken in small quantities. "The nestling 
 birds are fed chiefly with smooth caterpillars and grasshoppers, their 
 stomachs probably being unable to endure the hairy caterpillars. All 
 in all, the cuckoos are of the highest economic value. They do no 
 harm and accomplish great good. If the orchardist could colonize 
 his orchards with them, he would escape much loss." The quail feeds 
 largely upon insects during the summer, frequently eating the Colorado 
 potato beetle and the army worm; the prairie hen has similar food 
 habits but lives almost exclusively on grasshoppers, when these are 
 abundant. 
 
INSECTS IN RELATION TO OTHER ANIMALS 243 
 
 The Insect Food of Birds. — ''There are few groups of injurious 
 insects that enter so largely into the composition of the food of birds as 
 do the locusts, or short-horned grasshoppers, of the family Acridiidce 
 [now Locustidajj. The enormous destructive power of these insects 
 is well known, but our indebtedness to birds in checking their oscilla- 
 tions is less generally recognized." Professor Aughey, who has made 
 extensive studies upon the relation of birds to the Rocky Mountain 
 locust, found that upon one occasion 6 robins had eaten 265 of these 
 insects, 5 catbirds 152, 3 blue-birds 67, 7 barn swallows 139, 7 night 
 hawks 348, 16 yellow-billed cuckoos 416, 8 flickers 252, 8 screech owls 
 219, and I humming bird 4; while crows and blue-jays had eaten large 
 numbers of the locusts; and grouse, quail and prairie hen, enormous num- 
 bers. Even shore birds, such as geese, ducks, gulls and pelicans came to 
 share in the feast. Aughey estimated that the locusts eaten in one day 
 by the passerine birds of the eastern half of Nebraska were sufficient to 
 destroy in a single day 174,397 tons of crops, valued at $1,743.97. 
 
 Weed and Dearborn state that, of Hemiptera, Jassidae are very often 
 found in the stomachs of birds, and that aphids and their eggs form a 
 large part of the food of many of the smaller birds, such as the warblers, 
 nuthatches, kinglets and chickadees. A large proportion of the cater- 
 pillars of the Lepidoptera are eagerly devoured by birds, forming an 
 important element of the food of many species. The hairy caterpillars 
 are eaten by cuckoos and blue-jays and the large saturniid caterpillars, 
 such as cecropia and polyphemus, by some of the hawks. Almost all 
 kinds of Goleoptera are food for birds, but especially the grubs of Scara- 
 baeidae, which are eagerly devoured by robins, blackbirds, crows and 
 other birds. Of the Diptera, Itonididae and other gnats are eaten 
 by swallows, swifts and night hawks; while crane flies, TipuHdae, are 
 often found in the stomachs of birds. Among Hymenoptera, ants are 
 eaten extensively by woodpeckers, catbirds and many other species, as 
 are also Ichneumonidae and other parasitic forms — these last by the 
 flycatchers in particular. 
 
 The Regulative Action of Birds upon Insect Oscillations.^ The worst 
 injuries by insects are done by species that fluctuate excessively in 
 number as the result of variations in those manifold forces that act as 
 checks upon the multiplication of the species. 
 
 In order to determine whether birds do anything to reduce existing 
 oscillations of injurious insects, Professor Forbes made studies upon the 
 food of birds which were shot in an IlHnois apple orchard which was 
 being ravaged by canker-worms. In this orchard, birds were present in 
 
244 ENTOMOLOGY 
 
 extraordinary number and variety, there being at least thirty-five 
 species-, most of which were studied by Forbes, from whose exhaustive 
 tables the following food-percentages are taken: 
 
 Birds Insects, Canker-worms, 
 
 Examined Per Cent. Per Cent. 
 
 Robin 9 93 21 
 
 Catbird 14 98 ^5 
 
 Brown Thrush 4 94 12 
 
 Bluebird 5 9S 12 
 
 Black-capped Chickadee 2 100 61 
 
 House Wren 5 91 46 
 
 Tennessee Warbler i 100 80 
 
 Summer Yellow Bird 5 94 67 
 
 Black- throated Green Warbler i 100 7° . 
 
 Maryland Yellow-throat 2 100 37 
 
 Baltimore Oriole 3 1°° 40 
 
 To quote Forbes: "Three facts stand out very clearly as results of 
 these investigations: i. Birds of the most varied character and habits, 
 migrant and resident, of all sizes, from, the tiny wren to the blue-jay, 
 birds of the forest, garden and meadow, those of arboreal and those of 
 terrestrial habits, were certainly either attracted or detained here by the 
 bountiful supply of insect food, and were feeding freely upon the species 
 most abundant. That thirty-five per cent, of the food of all the birds 
 congregated in this orchard should have consisted of a single species of 
 insect, is a fact so extraordinary that its meaning can not be mistaken. 
 Whatever power the birds of this vicinity possessed as checks upon 
 destructive irruptions of insect life was being largely exerted here to 
 restore the broken balance of organic nature. And while looking for 
 their influence over one insect outbreak we stumbled upon at least two 
 others, less marked, perhaps incipient, but evident enough to express 
 themselves clearly in the changed food ratios of the birds. 
 
 "2. The comparisons made show plainly that the reflex efi'ect of this 
 concentration on two or three unusually numerous insects was so widely 
 distributed over the ordinary elements of their food that no especial 
 chance was given fcir the rise of new fluctuations among the species 
 commonly eaten. That is to say, the abnormal pressure put upon the 
 cankerworm and vine-chafer was compensated by a general diminution 
 of the ratios of all the other elements, and not by a neglect of one or two 
 alone. If the latter had been the case, the criticism might easily have 
 been made that the birds, in helping to reduce one oscillation, were 
 setting others on foot. 
 
 "3. The fact that, with the exception of the indigo bird, the species 
 
INSECTS IN RELATION TO OTHER ANIMALS 245 
 
 whose records in the orchard were compared with those made elsewhere 
 had eaten in the former situation as many caterpillars other than canker- 
 worms as usual, simply adding their canker-worm ratios to those of other 
 caterpillars, goes to show that these insects are favorites with a majority 
 of birds." 
 
 The Relations of Birds to Predaceous and Parasitic Insects. — The 
 false assumption is often made that a bird is necessarily inimical to 
 man's interest whenever it destroys a parasitic or a predaceous insect. 
 Weed and Dearborn attack this assumption as follows: 
 
 "Suppose an ichneumon parasite is found in the stomach of a robin 
 or other bird: it may belong to any one of the following categories: 
 
 "i. The primary parasite of an injurious insect. 
 
 "2. The secondary parasite of an injurious insect. 
 
 "3. The primary parasite of an insect feeding on a noxious plant. 
 
 "4. The secondary parasite of an insect feeding on a noxious plant. 
 
 "5. The primary parasite of an insect feeding on a wild plant of no 
 economic value. 
 
 "6. The secondary parasite of an insect feeding on a wild plant of no 
 economic value. 
 
 "j. The primary parasite of a predaceous insect. 
 
 "8. The primary parasite of a spider or a spider's egg. 
 
 "This hst might easily be extended still farther, and the assumption 
 that the parasite belongs to the first of these categories is unwarranted 
 by the facts and does violence to the probabilities of the case. 
 
 "A correct idea of the economic role of the feathered tribes may be 
 obtained only by a broader view of nature's methods, — a view in which 
 we must ever keep before the mind's eye the fact that all the parts of 
 the organic world, from monad to man, are linked together in a thousand 
 ways, the net result being that unstable equilibrium commonly called 
 'the balance of nature.'" 
 
 The general subject of food relations and interactions of insects is 
 taken up in the chapter on ecology (page 373). 
 
 Efficiency of Protective Adaptations of Insects. — Interesting from 
 a scientific point of view are the various adaptations by means of which 
 insects are protected more or less from their bird enemies. Colora- 
 tional adaptations having been discussed in another chapter, there 
 remain for consideration— (i) hairs, (2) stings, (3) odors, flavors and 
 irritants. Most of what follows is from an admirable paper by Dr. Judd, 
 whose data are based upon his examination of the stomach contents of 
 fifteen thousand birds. 
 
246 ENTOMOLOGY 
 
 Hairs. — " Excepting two species of cuckoos, no species of bird in the 
 eastern United States, so far as I am aware, makes a business of feeding 
 upon hairy caterpillars." Judd observed that the fall web worm, 
 Hyphantria cunea, infesting a pear tree was not at all molested, in spite 
 of the fact that the tree was tenanted by three broods of birds at the 
 time, namely, kingbirds, orchard orioles and English sparrows. The 
 hairy arctiid caterpillars, however, are eaten by a few birds : the robin, 
 bluebird, catbird, sparrowhawk, cuckoos and shrikes; and the spiny 
 larvae of Vanessa antiopa by cuckoos and the Baltimore oriole; while 
 the hairy caterpillars of the gipsy moth are known to be eaten in Massa- 
 chusetts by no fewer than thirty-one species of birds, notably cuckoos, 
 Baltimore oriole, catbird, chickadee, blue- jay, chipping sparrow, robin, 
 vireos and the crow, these birds being of no little assistance in the sup- 
 pression of this pest. These are exceptional cases, however, and in 
 general the hairiness of caterpillars appears to be a highly effective 
 protection against most birds. 
 
 Stings. — Some birds (chewink, young ducks) are fatally affected by 
 eating honey bees. The blue-jays, however, will eat Bombus (bumble- 
 bees) and Xylocopa, and flycatchers and swallows feed habitually upon 
 stinging Hymenoptera, particularly Scoliidae, while a great many birds 
 eat Myrmicidae, or stinging ants. The formic acid of ants does not 
 protect them from wholesale destruction by birds; Judd found three 
 thousand ants in the stomach of a flicker. "Stingless ants pretend to 
 sting but many birds they do not deceive." The stinging caterpillar 
 of Automeris io is occasionally eaten by the yellow-billed cuckoo. 
 Aside from these exceptions, the stings of insects are an extremely 
 efficient means of defence. 
 
 Odors, Flavors and Irritants. — The malodorous Heteroptera in 
 general are food for most birds; Lygus, Reduviidae (assassin bugs) and 
 Pentatomidae (stink bugs) are eaten by song sparrows, and £w5c/?w/w5 by 
 blackbirds and crows. The odors of Heteroptera are by no means 
 universally protective. 
 
 Among Coleoptera, the showy, ill-scented or ill-flavored Coccinellidae 
 (lady beetles) are eaten by very few birds — the flycatchers and swallows 
 — and are refused by caged blue-jays and song sparrows even when 
 these birds are hungry. Of Chrysomehdae, the Colorado potato beetle 
 is refused by the catbird, blue-jay and song sparrow, and Diabrotica 
 is not often eaten, except by catbirds and thrushes. "The smaller 
 Carabidae (ground beetles) whether stinking or not, are eaten by 
 practically all land birds." Crows, blackbirds and jays eagerly swallow 
 
INSECTS IN RELATION TO OTHER ANIMALS 247 
 
 the showy Calosoma scrutator, and the first two birds are especially fond 
 of Harpalus caliginosus and H. pennsylvanicus , and feedGalerita to their 
 young. "A score of smaller Carabidae (ground beetles) and Chryso- 
 melidae (leaf beetles) metallic and conspicuously colored, are habitually 
 eaten by birds that have an abundance of other insect food to pick from." 
 
 The stenches of Lampyrida? (firefly family) appear to be more effec- 
 tive than those of Carabidae. Telephorus is occasionally eaten, but Pho- 
 tinus rarely if at all. Chauliognathus is not eaten by many birds 
 (though flycatchers and swallows select this insect) and the genus is 
 regarded unfavorably by caged catbirds and blue-jays. 
 
 In regard to other insects, Judd finds that Epicauta (blister beetle) 
 with its irritant fluid, is immune from all but the kingbird; Cyllene 
 seldom occurs in the stomachs of birds; May flies and caddis flies, 
 however, are terribly persecuted, but swiftly flying Diptera and Odonata 
 are highly immune. 
 
 From such facts as these, Judd properly infers, "not cases of protec- 
 tion and nori^protection, but cases of greater and lesser efficiency of 
 protective devices." 
 
CHAPTER IX 
 
 TRANSMISSION OF DISEASES BY INSECTS 
 
 It is commonly known that some kinds of insects are of vital impor- 
 tance to man as agents in the transmission of certain diseases. In 
 recent years immense progress has been made in our knowledge of insect- 
 borne diseases. 
 
 Malaria 
 
 So far as is known, malaria is transmissible only through the agency 
 of mosquitoes. 
 
 The malaria "germ," discovered in 1880 by the French army surgeon 
 Laveran, may be found as a pale, amoeboid organism {Laverania, 
 Fig. 273) in the red blood corpuscles of persons afflicted with the disease. 
 This organism {schizont, 2) grows at the expense of the haemoglobin of 
 the corpuscle (3-5) and its growth is accompanied by. an increasing 
 deposit of black granules (melanin), which are doubtless excretory in 
 their nature. At length, the amoebula divides into many spores (mero- 
 zoites, 6) which by the disintegration of the corpuscle are set free in the 
 plasma of the blood. Here many if not most of the spores, and the 
 pigment granules as well, are attacked and absorbed by leucocytes, or 
 white blood corpuscles, while some of the spores may invade healthy red 
 corpuscles and develop as before. The period of sporulation, as Golgi 
 found, is coincident with that of the "chill" experienced by the patient; 
 and quinine is most effective when administered just before the sporula- 
 tion period. The destruction of red blood corpuscles explains the pallid, 
 or ancemic, condition which is characteristic of malarial patients. In 
 three or four days the number of red corpuscles may be reduced from 
 5,000,000 per cubic millimeter — the normal number — to 3,000,000; and 
 in three or four weeks of intermittent fever, even to 1,000,000. 
 
 Authorities recognize at least three species of malaria parasites 
 affecting man: (i) the tertian (Plasmodium vivax), with an asexual cycle 
 of forty-eight hours, causing the fever to recur every two days; (2) 
 the quartan (P. malarice), with a cycle of sbventy-two hours, causing 
 fever every third day; and (3) the suhtertian or malignant form (Laver- 
 ania falciparum) of which there are three varieties (perhaps species) , 
 with cycles of twenty-four or forty-eight hours, according to the variety. 
 
 248 
 

 Pig. 273. — Life history of malaria parasite, Lai'drawja/a/ci^arMTW. i, sporozoite, intro- 
 duced by mosquito into human blood; the sporozoite becomes a schizont. 2, young schi- 
 zont, which enters a red blood corpuscle. 3, young schizont in a red blood corpuscle. 4, 
 full-grown schizont, containing numerous granules of melanin. 5, nuclear division prei)ara- 
 tory to sporulation. 6, spores, or merozoites, derived from a single mother-cell. 7, young 
 macrogametocyte (female), derived from a merozoite and situated in a red blood corpuscle. 
 7a, young microgametocyte (male) derived from a merozoite. 8, full-grown macrogameto- 
 cyte. 8a, full-grown microgametocyte. In stages 8 and 8a the parasite is taken into the 
 stomach of a mosquito; or else remains in the human blood. 9, mature macrogamete, 
 capable of fertilization; the round black extruded object may probably be termed a "polar 
 body." 9a, mature microgametocyte, preparatory to forming microgametes. 96, resting 
 cell, bearing six flagellate microgametes (male). 10, fertilization of a macrogamete by a 
 motile microgamete. The macrogamete next becomes an ookinete. 11, ookinete, or 
 wandering cell, which penetrates into the wall of the stomach of the mosquito. 12, 
 ookinete in the outer region of the wall of the stomach, i.e., next to the body cavity. 13, 
 young oocyst, derived from the ookinete. 14, oocyst, containing sporoblasts, which are to 
 develop into sporozoites. 15, older oocyst. 16, mature oocyst, containing sporozoites, 
 which are liberated into the body cavity of the mosquito and carried along in the blood 
 of the insect. 17, transverse section of salivary gland of an Anopheles mosquito, showing 
 sporozoites of the malaria parasite in the gland cells surrounding the central canal. 
 
 1-6 illustrate schizogony (asexual production of spores); 7-16, sporogony (sexual pro- 
 duction of spores). 
 
 After Grassi and Leuckart, by permission of Dr. Carl Chun. 
 
 249 
 
250 ENTOMOLOGY 
 
 Two or more sets of parasites in the human blood, sporulating at 
 different times, may cause the fever to recur at intervals that are 
 apparently irregular. 
 
 After several successive asexual generations, there are produced 
 merozoites which develop — no longer into schizonts — but into sexual 
 forms, or gavietes. These occur in red blood corpuscles either as 
 macrogametocytes (female, 7, 8) or as microgametocytes (male, 7a, 8a), 
 in which forms the parasite is introduced into the stomach of a mosquito 
 which has been feeding upon the blood of a malarial patient. The 
 macrogametocyte now leaves its blood corpuscle and becomes a spherical 
 macrogamete (9) ; and the microgametocyte also becomes spherical 
 {ga) ; but the latter puts forth a definite number {six, in L. falciparum, 
 gb) of flagella, or microgametes, which separate off as motile male bodies, 
 capable of fertihzing the macrogametes. A microgamete penetrates a 
 macrogamete (10) and the nucleus of the one unites with that of the 
 other. The fertilized macrogamete, or zygote, now becomes a migrating 
 cell, or ookinete (11), which penetrates almost through the wall of the 
 stomach of the mosquito (12) and then becomes a resting cell, or cyst. 
 This oocyst (13) grows rapidly and its contents develop, by direct nuclear 
 division, into sporohlasts (14, 15), which differentiate into spindle- 
 shaped sporozoites (16, 17). The sporozoites are liberated into the 
 body cavity of the mosquito, carried in the blood to the salivary glands 
 (as well as elsewhere) and thence along the hypopharynx into the 
 body of a human being, bird or other animal attacked by the 
 insect. 
 
 The role of the mosquito as the intermediary host of malarial organ- 
 isms was discovered by Manson and Ross and confirmed by Koch, Stern- 
 berg and others. It has been found repeatedly that certain mosquitoes 
 (Anopheles) after feeding on the blood of a malarial patient can transmit 
 the disease by means of their "bites" to healthy persons. Thus, 
 Anopheles mosquitoes were fed on the blood of malarial subjects in 
 Rome and then sent to London, where a son of Dr. Manson allowed him- 
 self to be bitten by the insects. Though previously free from the 
 malarial organism, he contracted a well-marked infection as the result 
 of the inoculation. 
 
 Furthermore, it is highly probable that malaria cannot be trans- 
 mitted to man except through the agency of the mosquito. This ap- 
 pears from the oft-cited experiment of Doctors Sambon and Low on the 
 Roman Campagna, a place notorious for malaria. There the experi- 
 menters lived during the malarial season of 1900, freely exposed to the 
 
TRANSMISSION OF DISEASES BY INSECTS 25 1 
 
 emanations from the marsh and taking no precautions except to screen 
 their house carefully against mosquitoes and to retire indoors before 
 the insects appeared in the evening. Simply by excluding Anopheles 
 mosquitoes, with which the Campagna swarmed, these investigators 
 remained perfectly immune from the malaria which was ravaging the 
 vicinity. 
 
 In a later experiment on the island of Formosa, one company of 
 Japanese soldiers was protected from mosquitoes and suffered no 
 malaria, while a second and unprotected company contracted the 
 disease. 
 
 The evident preventive measures to be taken against malaria are 
 (i) the avoida;nce of mosquito bites, by means of screens, and washes of 
 eucalyptus oil, camphor, oil of pennyroyal, oil of tar, etc., appHed to 
 exposed parts of the body; (2) the isolation of malarial patients from 
 mosquitoes, in order to prevent infection; (3) the destruction of mosqui- 
 toes in their breeding places, especially by the use of kerosene and by 
 drainage. During unavoidable exposure in malarious regions, quinine 
 should be taken in doses of six to ten grains during the day at intervals 
 of four or five days (Sternberg) . 
 
 In Macedonia in 191 6 there were some 800,000 cases of malaria, 
 with 2,000 deaths in the French and AlHed army. Where the disease 
 was most severe Anopheles mosquitoes were present in enormous num- 
 bers. A striking peculiarity of this epidemic was the marked failure 
 of quinine as a preventive or remedy. This failure was explained as 
 being due to the development of quinine-resistant strains of the malaria 
 parasites. 
 
 Culex and Anopheles.^ — More than five hundred species of mosqui- 
 toes have been described. Of these only the genus Anopheles transrhits 
 malaria to man; though in India, Ross found that Culex transmits a 
 form of malaria to sparrows. These two common genera are easily 
 distinguishable. In Culex the wings are clear; in Anopheles they are 
 spotted with brown. In Culex when resting, the axis of the body 
 forms a curved line, the insect presenting a hump-backed appearance; 
 in Anopheles the axis forms a straight line. Culex has short maxillary 
 palpi, while in Anopheles they are almost as long as the proboscis. The 
 note of the iemale Anopheles is several tones lower than that of Culex, 
 and only the female is bloodthirsty, by the way. As regards eggs, 
 larvae and pupae, the two genera differ greatly. The eggs of Culex are 
 laid in a mass and those of Anopheles singly; the larvae of Culex hang 
 from the surface film of a pool at an angle of about forty-five degrees, 
 
252 ENTOMOLOGY 
 
 while those of Anopheles are almost parallel with the surface of the 
 water in which they Uve. 
 
 The bite of an Anopheles is not necessarily injurious, of course, unless 
 the insect has had recent access to a malarious person. Anopheles may 
 be present where there is no malaria. On the other hand, it has been 
 found impossible to prove that malaria exists where there are no Anoph- 
 eles mosquitoes. Finally, fevers are sometimes diagnosed as malarial 
 which are not so. 
 
 Possibly the malarial parasite can complete its cycle of development 
 in other animals than man. It is also possible that originally the mala- 
 rial organism was derived by mosquitoes from the stems or other parts 
 of aquatic plants, and that its effects on man are incidental phenomena. 
 
 Yellow Fever 
 
 From 1793 to 1900 there occurred in the United States not less than 
 half a million cases of yellow fever and one hundred thousand deaths 
 from the disease. New Orleans suffered the worst with more than forty- 
 one thousand deaths, followed by Philadelphia with ten thousand and 
 Memphis with almost eight thousand; while Charleston, New York 
 City and Norfolk, Virginia, lost together more than ten thousand lives. 
 
 The enormous financial loss from all the epidemics of yellow fever is 
 beyond exact computation; the epidemic of 1878 cost New Orleans more 
 than ten million dollars. 
 
 Yellow fever is now within human control ; with no thanks to those 
 who at first violently opposed the theory, and later denied the fact, of 
 its transmission by mosquitoes. 
 
 Until 1 901 yellow fever was fought energetically, but fought in the 
 dark. An immense amount of energy was misdirected and millions of 
 dollars wasted in the fight. On the supposition that bacteria were the 
 cause of the disease, methods of quarantine, burning and fumigation 
 were employed that destroyed an enormous amount of property includ- 
 ing valuable cargoes, and paralyzed the business and social activities of 
 great cities. 
 
 Official accounts of yellow fever published before 1900 often describe 
 the disease as being due to some insidious poison borne by the air and 
 introduced into the human body, probably through the respiratory 
 system. It was observed that the disease was often conveyed down 
 the wind, that it was not carried far from the nearest focus of infection, 
 that infection was less liable to occur in daylight than by night, and 
 
TRANSMISSION OF DISEASES BY INSECTS 253 
 
 that cases arose on shore when the only source of infection was a ship 
 that had not yet touched the land. These facts and many others 
 which formerly involved the disease in mystery, are now quite intelli- 
 gible in the hght of the mosquito- theory of transmission. 
 
 Finlay's Work. — The pioneer work leading toward the control of 
 yellow fever was done by Dr. Charles J. Finlay, of Havana, Cuba, who 
 not only advocated the mosquito-theory strongly for many years, but 
 also inoculated by means of mosquitoes ninety human subjects, some 
 of whom came down with what he believed to be a mild form of yellow 
 fever. His valuable work prepared the way for the briUiant investi- 
 gations of Major Reed and his associates. 
 
 United States Yellow Fever Commission. — Major Walter Reed 
 was president of the board of medical ofhcers sent to Cuba in June, 1900, 
 to study the acute infectious diseases of the island; his associates were 
 James Carroll, Jesse W. Lazear and A. Agramonte. 
 
 At that time Sanarelli's theory as to the bacillary causation of yellow 
 fever was in favor, though Reed and Carroll has already shown that the 
 bacillus of Sanarelli bore no special relation to the disease. After further 
 investigations on this subject in Cuba, with negative results, the com- 
 mission "concluded to test the theory of Finlay," in Dr. Reed's words. 
 For this purpose General Leonard Wood, the mihtary governor of Cuba, 
 gave permission for experiments on human beings and granted a liberal 
 sum of money for the reward of volunteer subjects. 
 
 The commission succeeded in demonstrating how yellow fever is 
 transmitted; after that the methods of prevention to be employed were 
 evident. 
 
 The experiments, planned and directed by Major Reed, are models 
 of their kind. All possible sources of error were excluded; hence there 
 was no uncertainty in the interpretation of the results, the accuracy of 
 which has been confirmed by subsequent commissions and by many 
 independent investigators. 
 
 In the value of his services Major Walter Reed ranks among the 
 greatest benefactors of mankind. Before his death, which occurred in 
 1902, he received great honors for his brilliant achievements. 
 
 Experiments in Cuba. — For experimental purposes Major Reed es- 
 tablished a camp about four miles from Havana. To prevent the 
 introduction of the fever from the outside the inmates of the camp were 
 rigidly quarantined; non-immunes were confined to the camp or, if re- 
 leased, not allowed to return. In order that the study of yellow fever 
 might not be complicated by the presence of any other disease, a com- 
 
2 54 ENTOMOLOGY 
 
 plete record was kept of the health of every subject; furthermore, ample 
 time was allowed for any possible development of the disease within the 
 camp before the experiments were begun. In short, the precautions 
 taken were so thorough that yellow fever never appeared in the camp 
 except at the will of the experimenters. 
 
 Harmlessness of Fomites. — In a specially constructed building, 
 which was screened against mosquitoes and purposely ill-ventilated, 
 volunteers slept for twenty nights with bedding and clothing that had 
 been contaminated by yellow fever patients, and tried in every other 
 way to contract the disease, if possible, from the fomites, or belongings, 
 of fever subjects; yet the health of these volunteers remained unimpaired; 
 though they were not immunes, for some of them were subsequently 
 infected artificially by means of mosquitoes. 
 
 Transmission by Transfusion. — It was found that the disease could 
 be conveyed to non-immunes by the subcutaneous injection of blood 
 taken from the veins of patients during the first three days of the disease. 
 
 Experiments with Mosquitoes. — These experiments were made at 
 a time of the year when there was the least chance of acquiring the dis- 
 ease naturally. The mosquitoes used were bred from the eggs and kept 
 active by being maintained at a summer temperature. From time to 
 time some of them were taken away to a yellow fever hospital, fed on the 
 blood of patients and applied to non-immunes in the camp at varying 
 intervals from the time of feeding. The occupants of the camp were, of 
 course, protected carefully from accidental mosquito bites. When a 
 subject came down with yellow fever as the result of an experimental 
 inoculation he was at once removed from the camp to a yellow fever 
 hospital. 
 
 In a mosquito-proof building a single room was divided into two 
 compartments simply by means of a partition of wire netting. On one 
 side of the screen infected mosquitoes were liberated; and a brave non- 
 immune, who had been in quarantine for thirty-two days, entered the 
 compartment, allowed himself to be bitten several times, and contracted 
 the disease. In the opposite compartment, free from mosquitoes, non- 
 immunes slept with perfect safety ; and the other room became harmless 
 as soon as the mosquitoes were removed. 
 
 In another experiment the subject acquired the disease by thrusting 
 his arm into a jar of infected mosquitoes. Eighteen non-immunes were 
 inoculated, ten of them successfully. It was demonstrated that yellow 
 fever is transmitted by the bite of a mosquito, and in no other way 
 except by the artificial injection of diseased blood. The mosquito can 
 
TRANSMISSION OF DISEASES BY INSECTS 
 
 255 
 
 obtain infected blood from a patient during only the first three days of 
 his disease; in other words, the patient is no longer a menace to other 
 persons after three days from the time when he comes down with yellow 
 fever, which is from three to six days after the bite. 
 
 After biting a patient the mosquito cannot convey the infection until 
 at least twelve days have elapsed; thereafter it can transmit the disease 
 for certainly six weeks and possibly eight weeks. 
 
 Dr. James Carroll allowed himself to be bitten by an infected mos- 
 quito and consequently suffered a severe attack of yellow fever. He 
 recovered from this, but was left with an affection of the heart from 
 which he died in 1907. 
 
 Dr. Lazear failed to acquire the disease artificially, early in the 
 course of the experiments; but a little later, while visiting yellow fever 
 patients in a hospital, was bitten by a mosquito which he deliberately 
 allowed to remain on his hand. Five days later he came down with 
 yellow fever, which caused his death. His life was a sacrifice for the 
 benefit of the human race. 
 
 Yellow Fever Mosquito.— The mosquito that transmits this fever 
 is Aedes argenteus {Aedes calopus, Stegomyia fasciata) and no other 
 species is as yet known to be concerned in the disease. A. argenteus is 
 limited to warm regions; at a temperature less than 68° F. the eggs do not 
 hatch, and below 62° F. the female does not bite (Reed). The depend- 
 ence of the insect upon warmth for its development explains the 
 cessation of the disease in New Orleans in December, with a mean 
 temperature of 55.3° F. and in cities farther north when frost comes. 
 In Cuba and Brazil the fever has occurred every month in the year. 
 Cause of Yellow Fever. — The specific cause of yellow fever eluded 
 detection for many years and was regarded by many investigators as 
 being ultra-microscopic. The U. S. Commission produced the disease 
 by the injection of blood serum that had been passed through a bacteria- 
 proof filter. Blood from a subject in whom the disease had been pro- 
 duced by transfusion was capable of infecting a third person. 
 
 The weight of evidence indicated that the unknown cause of yellow 
 fever was an organism rather than a toxin, and in 19 19 the organism was 
 discovered by Noguchi to be a spirochaete, which he named Leptospira 
 icteroides. During his investigations in Guayaquil Noguchi succeeded 
 in isolating this spirochaete from the blood of patients and from mos- 
 quitoes as well. He obtained pure cultures of the parasite by inoculat- 
 ing guinea pigs with blood from patients, and was able to produce the 
 disease by inoculation in guinea pigs, dogs and marmosets. 
 
256 ENTOMOLOGY 
 
 Following his discovery, Dr. Noguchi, of the Rockefeller Institute 
 for Medical Research, prepared from the organisms a vaccine, which 
 has been administered to many thousand persons with results that are 
 reported to be distinctly encouraging. 
 
 Control of Yellow Fever. — The preventive measures based upon the 
 facts learned by the U. S. Army Commission were wonderfully suc- 
 cessful. In February, 1901, Major W. C. Gorgas began a campaign to 
 eradicate the disease in Havana. His efforts were directed against 
 mosquitoes. Every case of fever had to be reported promptly to the 
 authorities. Then the patient was isolated and all the rooms in the 
 building and in neighboring houses fumigated and the doors and 
 windows screened. Standing water in which mosquitoes might develop 
 was drained or treated with petroleum, and water tanks and barrels 
 were screened. 
 
 In September, 1901, the last case of yellow fever arose in Havana, 
 where the disease had prevailed for 1 50 years, with an annual mortality 
 of 500 to 1600 or more. Cases are now and then brought into Havana 
 from Mexico or Central America but are treated under screens in the 
 regular hospitals with impunity. 
 
 Yellow Fever in New Orleans. — In 1905 the last epidemic of yellow 
 fever occurred in New Orleans. It might have been checked at its 
 inception had not the authorities adopted a policy of secrecy in regard 
 to the presence of the disease. The city was freed from the fever before 
 frost came, by the same methods that had proved successful in Cuba; 
 but not without organized work of the most strenuous kind on the part 
 of the citizens, under the direction of the U. S. Public Health and 
 Marine-Hospital Service. At present the yellow fever mosquito is 
 said to be a rarity in Louisiana owing to the vigorous measures enforced 
 in its suppression throughout the state. 
 
 Fever in the Canal Zone. — The Panama Canal zone was formerly 
 one of the most unhealthful places on earth, chiefly on account of the 
 prevalence of malaria and yellow fever. When the United States ac- 
 quired the zone in 1904 it was realized that the first step toward building 
 the great canal was to protect the health of all those immediately con- 
 cerned in the undertaking, and the sanitation of the isthmus was placed 
 in charge of one eminently quaHfied for the work. Colonel W. C. Gorgas. 
 
 He adapted the methods he had used in Cuba to the conditions 
 existing on the isthmus, with the result that every year the death rate 
 decreased until in 1908 it became, among eight thousand white 
 Americans living there, 9.72 per thousand, "a rate no higher than for a 
 

 TRAXs;\rissi(>x of diseases by insects 257 
 
 similar population in the healthiest localities in the United States, and 
 much lower than that for most parts of the country." The Sanitary 
 Department has succeeded in driving yellow fever from the isthmus and 
 in checking malaria and other diseases to such a degree that the canal 
 zone is no longer an unhealthful place. 
 
 After serving as Surgeon General of the United States Army from 
 1 9 14 to 19 1 8, W. C. Gorgas entered the service of the International 
 Health Board, and was organizing an international campaign against 
 yellow fever at the time of his death in London, July 4, 1920. 
 
 General Gorgas attained international preeminence for his ability 
 in organizing and conducting operations of magnitude against insect- 
 borne diseases. On account of his services in the protection of human 
 life his assistance was sought by foreign nations, and he received higHl ^ 
 honors. . • /\ 
 
 Typhoid Fever rv r** 
 
 Ski 
 
 The specific cause of typhoid fever is Bacillus typhosus. In bBte^"" 
 human body this bacillus occurs chiefly in the intestines; but also in ofieQ * 
 urinary bladder and usually in the blood of infected persons. 
 
 The excreta of typhoid subjects contain the virulent bacilli; an(^s,| 
 some persons, even after recovery, continue to be "chronic carriers" of 
 the disease for many years. 
 
 Transmission. — The typhoid bacillus is introduced into the human 
 system by eating or drinking. Most epidemics are due to infected 
 water and many to milk; occasionally the disease is acquired from raw 
 vegetables or from oysters contaminated with sewage. Often the 
 bacillus is conveyed to food by human hands and possibly it is some- 
 times carried by dust, cockroaches or ants; but there is no doubt that 
 the disease is transmitted by certain flies, particularly the true house 
 fly, Muse a domes tica, which is by far the commonest fly found generally 
 in houses, and becomes a serious menace to health during epidemics of 
 typhoid fever. 
 
 The house fly is well adapted by its structure and habits to carry 
 bacteria. The adults often feed on substances contaminated with 
 typhoid or other bacteria and these infected substances cling readily 
 to the hairs of the insect, especially those of the feet, and to the pro- 
 boscis. The larvse develop chiefly in horse manure, but also in other 
 kinds of excreta, some of which may contain virulent typhoid 
 bacilli. 
 
250 ENTOMOLOGY 
 
 Transmission by Flies. — During the Spanish- American war typhoid 
 fever occurred in every American regiment and raged in many of 
 the concentration camps, in consequence of which a special commission 
 was appointed to investigate the origin and spread of the disease in the 
 army. A report by one of the members of the commission, Doctor 
 Vaughan, presents the following conclusions: 
 
 "a. Flies swarmed over infected fecal matter in the pits and then 
 visited and fed upon the food prepared for the soldiers at the mess tents. 
 In some instances where lime had recently been sprinkled over the con- 
 tents of the pits, flies with their feet whitened with lime were seen 
 walking over the food. 
 
 "6. Officers whose mess tents were protected by means of screens 
 suffered proportionally less from typhoid than did those whose tents 
 were not so protected. 
 
 "c. Typhoid fever gradually disappeared in the fall of 1898, with 
 the approach of cold weather, and the consequent disabling of the fly. 
 
 "It is possible for the fly to carry the typhoid bacillus in two ways. 
 In the first place, fecal matter containing the typhoid germ may adhere 
 to the fly and be mechanically transported. In the second place, it is 
 possible that the typhoid bacillus may be carried in the digestive organs 
 of the fly and may be deposited with its excrement." 
 
 Similar conclusions in regard to the agency of flies in the spread of 
 enteric fever among troops have been reached also by investigators in 
 Bermuda, South Africa and India. 
 
 Firth and Horrocks fed house flies on material contaminated with 
 Bacillus typhosus and then obtained cultures of the bacillus from objects 
 to which the flies had access. In another experiment they obtained 
 cultures from the heads, bodies, wings and legs of such flies. Other 
 investigators have obtained Bacillus typhosus from flies captured in 
 rooms occupied by typhoid cases. 
 
 Faichnie caught flies in a place where there was an outbreak of ty- 
 phoid fever, held them on a sterilized needle and passed them through a 
 flame until legs and wings were scorched; after which he obtained the 
 typhoid bacillus from the mashed bodies of the flies, the bacilli having 
 been present in the ahmentary tract, without doubt. 
 
 Faichnie also obtained cultures of Bacillus typhosus from the intes- 
 tines of flies which had developed from larvae fed on feces containing the 
 bacillus. 
 
 Jordan states that the bacilli survive the passage of the ahmentary 
 canal of the fly. 
 
TRANSMISSION OF DISEASES BY INSECTS 259 
 
 Ficker recovered typhoid bacilli from flies twenty-three days after 
 they had been infected. 
 
 In fact, a great amount of evidence has accumulated proving that 
 flies transmit not only the bacilli of typhoid fever, but many other 
 bacteria, and often in enormous numbers. For example, Esten and 
 Mason in their study of the sources of bacteria in milk, collected and 
 examined flics from stables, pig-pens, houses and other places, and found 
 an average of 1,222,570 bacteria per fly; the majority of these being 
 objectionable kinds of bacteria. 
 
 Musca Domestica. — A single female of the common house fly lays 
 in all some six hundred eggs. In midsummer, in Washington, D. C, 
 the eggs hatch in about eight hours; the larval period is from four to 
 five days and the pupal period five days, making the cycle about ten 
 days in length. In cooler parts of the season the cycle requires more 
 time and in warm climates it may be as short as eight days. The 
 number of generations in Washington is probably not more than 
 nine (Howard). 
 
 Control. — One of the best baits for flies in houses is formalin, which 
 is poisonous to flies but harmless to man. This is prepared by diluting 
 formaldehyde with five or six times as much water and exposing it in 
 shallow dishes, the addition of a little sugar or milk making the solution 
 more attractive to flies, which drink it and quickly die. Pyrethrum is 
 efl'ective against flies, but only when it is pure and has been kept from 
 exposure to the air. Pyrethrum, the chief basis of all the common 
 insect powders, is applied by being puffed through a bellows or by being 
 burned. The powder may be moistened and shaped into cones which 
 when lighted at the top burn slowly and give off fumes that are suffocat- 
 ing to insects. 
 
 Dr. Howard estimates that more than ten million dollars are spent 
 every year in screening houses in the United States. Another enormous 
 sum is spent for fly papers and fly traps. The efficient way to deal with 
 the fly problem, however, is to prevent the insects from breeding, Ex- 
 crementitious substances should be enclosed in such a way as to prevent 
 the access of flies, or should be treated in a way to kill the larvae therein; 
 one of the simplest methods of treating stable manure being to spread 
 it out to dry, since the maggots cannot develop without moisture. 
 
 For detailed information on everything of importance relating to 
 the house fly, and particularly on the mitigation of the fly-nuisance by 
 concerted action in communities, Dr. Howard's admirable book on the 
 house fly should be consulted. 
 
26o ENTOMOLOGY 
 
 Plague 
 
 In the ancient history of Europe epidemics of plague occupy a large 
 place. For many years this pestilence has thrived in China and India, 
 and following an outbreak in 1894 in Hong Kong, the plague reached 
 the western hemisphere for the first time, appearing in Brazil, Argentina 
 and other South American countries, in Mexico and San Francisco. 
 
 The cause of plague is Bacillus pestis, an organism abundant in the 
 secretions and excretions of plague-stricken animals. 
 
 Three varieties of the disease are distinguished as follows: 
 
 (i) the bubonic, in which the bacilli cause enlargements of lymphatic 
 glands ; 
 
 (2) the septiccBmic, characterized by the presence of large numbers 
 of bacilli in the blood and highly virulent; 
 
 (3) the pneumonic, in which the respiratory organs are affected, the 
 sputum showing the bacilli in enormous numbers; this form, relatively 
 rare, is the most fatal. 
 
 Transmission. — Plague is primarily a disease of rats, an epidemic 
 of plague in these animals having often been observed to precede as 
 well as accompany an epidemic among human beings. The disease 
 affects also mice, cats, dogs, calves, sheep, pigs, ducks, geese and many 
 other animals. 
 
 Though rats and other of the lower animals may contract the septi- 
 caemic type of the disease from feeding on parts of animals killed by 
 plague or on cultures of Bacillus pestis, the disease is commonly trans- 
 mitted among rats neither by contact nor through the atmosphere, but 
 by means of fleas. Healthy rats in association, with diseased rats do 
 not become infected as long as fleas are excluded; but a transfer of fleas 
 from the latter to the former starts the disease. By various experi- 
 ments the Indian Plague Commission demonstrated the important part 
 played by rat-fleas in the transmission of plague. Zirolia found that 
 the bacilli even multiply in the mid-intestine of the flea, retaining their 
 virulence for a week or more. Bacot found that the European rat-flea 
 {Ceraiophyllus fasciatus) remained infective, when isolated from a 
 host, for forty-seven days. 
 
 The weight of evidence, both observational and experimental, 
 shows that plague is transmitted from rats to man by several species 
 of fleas and also by bedbugs. Verjbitski, whose experiments on this 
 subject were particularly precise and thorough, found that plague can 
 be conveyed by the bites of these insects and that the opening made 
 
TRANSMISSION OF DISEASES BY INSECTS 261 
 
 by the bite affords entrance to plague bacilli when the bodies of the 
 insects are crushed or when the infected feces are introduced by the 
 rubbing or scratching of the wound. 
 
 The species of rat-flea most common in the orient is the cosmo- 
 politan "plague flea," Xenopsylla cheopis. 
 
 In the United States the most common rat flea is Ceratophyllus 
 j'asciatus. The common cat and dog flea, Clenocephalus canis, affects 
 rats as does the human flea, Pulex irritans; and all these species are 
 known to bite man. 
 
 Plague in San Francisco. — Plague, long dreaded in American sea- 
 ports, Anally entered San Francisco in 1900, killed 114 persons in the 
 next four years, became dormant and broke forth again, with violence, 
 in 1907. The city, just beginning to recover from the great fire of the 
 year before, was in a frightful sanitary condition and most of the popu- 
 lation, engaged in the work of reconstruction, paid little attention to 
 the deaths from plague and at first gave little aid toward the suppression 
 of the disease. As may be imagined, the campaign against the dis- 
 ease undertaken by the U. S. Public Health and Marine-Hospital 
 Service was carried on in the face of great odds. It was, however, con- 
 ducted most efficiently and successfully under the command of Dr. 
 Rupert Blue (later Surgeon-General), who wisely attacked the disease 
 by attacking the rat population. 
 
 The labor involved in starving out the rats, trapping or poisoning 
 them, and making buildings rat-proof by the use of concrete or sheet 
 iron, was immense; but the undertaking was nevertheless carried to a 
 successful conclusion. More than one million rats were killed and the 
 disease was checked. 
 
 In California plague affects ground squirrels, which doubtless con- 
 tract the disease from the rats that use the runways of the squirrels in 
 the fields. 
 
 Trypanosomiases 
 
 Some of the diseases known as trypanosomiases are among the dead- 
 liest that affect man and other vertebrates, and pathogenic trypano- 
 somes — the organisms causing these diseases — have received an 
 immense amount of study during recent years. 
 
 Trypanosomes. — The organisms under consideration are flagellate 
 protozoans. A typical trypanosome, for example, T. lewisi (Fig. 274) 
 of the rat, is essentially an elongated cell, tapering at each end, serpen- 
 
262 
 
 ENTOMOLOGY 
 
 tine in form and with no definite cell-wall. A round or oval nucleus is 
 present, also a peculiar chromatin body situated often near the poste- 
 rior end of the cell and termed the hlepharoplast. Along one side of the 
 cell is a delicate protoplasmic contractile membrane, the undulating 
 membrane, along the edge of which is a marginal cord, which arises by- 
 growth from the hlepharoplast and is continued beyond the anterior 
 end of the cell as a vibratile flagellum. 
 
 Asexual reproduction is by means of a longitudinal division of the 
 cell body, preceded by division of the flagellum, hlepharoplast and 
 nucleus, the nucleus dividing amitotically. In 
 regard to the existence of sexual stages, or 
 gametes, the results of investigators seem to 
 be inconclusive as yet. 
 
 In a film of fresh blood under the microscope, 
 any active trypanosomes in the field of view 
 attract attention as centers of commotion among 
 the red blood corpuscles, which are pushed aside 
 by the lashing, twisting and other movements of 
 the trypanosomes. 
 
 The nutrition is by means of osmosis. Try- 
 panosomes have not been seen to attack erythro- 
 cytes, but according to MacNeal and Novy 
 haemoglobin is useful if not indispensable to 
 them. 
 
 All five classes of vertebrates serve as hosts 
 for trypanosomes, of which more than seventy 
 species have received names. Most of these 
 species are carried from one vertebrate host to 
 another by means as yet unknown, but about 
 20 per cent, are known or suspected to be 
 transmitted by an intermediate invertebrate host. Thus trypano- 
 somes of frogs are conveyed by leeches ; pigeons are infected by mos- 
 quitoes, rats by sucking lice and fleas, and many mammals through the 
 agency of blood-sucking flies of the genus Glossina, and probably also 
 by Stomoxys and certain Tabanidee. 
 
 Tsetse Flies. — The name tsetse fly, originally limited to Glossina 
 morsitans (Muscidse) is now used for any of the fifteen known species 
 of the genus. These flies are a little larger than the common house fly 
 {Musca domestica) . Their wings, in the resting position, overlap exactly 
 (Fig. 275) instead of being separated at the tips. The proboscis pro- 
 
 2 74. — Trypano- 
 soma lewisi. b, hlepharo- 
 plast; /, flagellum; m, 
 marginal cord; w. nucleus; 
 tt, undulating membrane. 
 Greatly magnified. 
 
TRANSMISSION OF DISEASES BY INSECTS 
 
 263 
 
 Fig. 
 
 275. — Tsetse fly, Glossina 
 morsilans. X 2}^^. 
 
 jects forward, and is stout, owing to the ensheathing palpi; the base of 
 the labium forms a prominent bulb. These are the more conspicuous 
 characters that serve to distinguish tsetse flies from other blood-sucking 
 flies with which they might be confused. 
 
 The mode of reproduction as described by Brauer is similar to that 
 of the group of parasitic flies known as Pupipara. The fly produces a 
 full-grown larva, which at once creeps to 
 some resting place and forms a black 
 puparium. 
 
 Tsetse flies frequent hot, humid regions, 
 near bodies of water, and are restricted to 
 shaded situations, never occurring on the 
 open plains. Both sexes are bloodthirsty 
 but bite only during the daytime as a rule; 
 though they may bite at night when the 
 moonlight is bright. Travelers take advan- 
 tage of the habits of the fly to journey by 
 night; spending the day in an open unin- 
 fested place. 
 
 Nagana. — The colon'zation of South 
 Africa was greatly retarded by nagana, a disease invariably fatal to 
 the horse, donkey and dog, and usually fatal to cattle, but not affect- 
 ing man. Livingstone and other explorers in regions where nagana is 
 prevalent record their having been bitten by tsetse flies thousands of 
 times with no result other than a slight irritation. 
 
 Bruce was the first to prove the identity of nagana and tsetse-fly 
 disease and to demonstrate the role of the fly in the transmission of the 
 disease. His investigations, begun in Zululand in 1894, are of funda- 
 mental importance and have given an immense stimulus to the study 
 of trypanosomes. 
 
 After finding that no bacteria were concerned in nagana, Bruce dis- 
 covered trypanosomes in the blood of cattle affected with the disease. 
 He inoculated their blood into healthy horses and dogs and in a few days 
 the blood of these animals was teeming with trypanosomes. Then he 
 took healthy animals from the mountain on which he had located his 
 headquarters down into the "fly country;" there they contracted the 
 tsetse-fly disease and showed in their blood trypanosomes indistinguish- 
 able from those of nagana. 
 
 Horses taken into the fly country but not allowed to eat or drink 
 there, took the disease; furthermore, supplies of grass and water brought 
 
264 
 
 ENTOMOLOGY 
 
 from the fly country and fed to healthy horses failed to convey the 
 disease. 
 
 Then the influence of the fly was tested. Tsetse flies caught in the 
 lowland, carried to the mountain and placed at once on healthy animals 
 gave rise to the disease; but the flies never retained the power of infect- 
 ing a healthy animal for more than forty-eight hours after feeding upon 
 a sick animal. Thus wild flies, kept without food for three days and 
 then fed on a healthy dog, never gave rise to the disease. The fly alone 
 transmitted the disease; and this by means of trypanosomes adhering 
 to the proboscis either inside or out. Bruce found 
 these organisms in the digestive tract also, but 
 with no change in their form. 
 
 He discovered further that buffaloes, antelopes 
 and many other wild animals carried the parasite 
 in their blood, and was able by injecting this 
 blood to transmit the disease to healthy domesti- 
 cated animals. The parasites were never numer- 
 ous in the blood of their wild hosts, however, and 
 the latter seemed to be unaffected by their pres- 
 ence. The ''big game" of Africa serves, gener- 
 ally speaking, as a reservoir for supplies of 
 trypanosomes. 
 
 The species of parasite that Bruce studied is 
 named Trypanosoma hrucei (Fig. 276). The flies 
 concerned are Glossina morsitans, G. pallidipes and 
 G.fusca, particularly the first two, the distribution 
 of which coincides with that of nagana. 
 
 No certain remedies for the disease are yet known. Human serum 
 injected into infected animals causes the trypanosomes to disappear, 
 at least, temporarily; but this fact is of more scientific interest than 
 practical importance. The precaution of traveling by night is often 
 adopted. Creolin and some other substances rubbed on animals 
 serve to repel the flies, and the smoke of encampments drives them away. 
 The protection of horses by means of screens is of course effective. 
 
 Human Trypanosomiasis. — Sleeping sickness is most prevalent in 
 the Congo basin, whence it has spread rapidly in equatorial Africa, where 
 it kills about fifty thousand natives every year. The reported cases of 
 recovery are so extremely rare that the mortality is placed at one 
 hundred per cent. 
 
 In the first stage of the disease, marked by the appearance of 
 
 -Trypano- 
 
 FiG. 276 
 S07na brucei. Greatly 
 magnified. 
 
TRANSMISSION OF DISEASES BY INSECTS 265 
 
 trypanosomes in the blood, negroes show no symptoms as a rule, though 
 whites are subject to fever. The symptoms may appear as early as 
 four weeks after infection or as late as seven years. 
 
 In the second stage trypanosomes appear in the cerebro-spinal fluid 
 and in large numbers in the lymphatic glands, those of the neck, axillae 
 and groins becoming enlarged. There is tremor of the tongue and 
 hands, drowsiness, emaciation and mental degeneration. The drowsi- 
 ness passes into periods of lethargy which become gradually stronger 
 until the patient becomes comatose and dies. Some victims do not 
 sleep excessively, but are lethargic, and "profoundly indifferent to all 
 going on around them." 
 
 There is some disagreement among authors as to the precise effects 
 of trypanosomes on human tissues and organs, but the evidence indi- 
 cates at least that trypanosomes produce a toxin which sets up irrita- 
 tions of the lymphatic glands in general and those of the brain in 
 particular. Many of the symptoms of trypanosomiasis are traceable 
 primarily to inflammation of the lymphatics of the nervous system. 
 
 The specific cause of sleeping sickness is T. gambiense, discovered in 
 1 901 by Forde and named by Button. Two eminent English investi- 
 gators of sleeping sickness, Button and TuUock, sacrificed their lives to 
 the. disease they were studying. 
 
 As the result of the labors of many investigators, human trypano- 
 somiasis is now well understood. Bruce and Nabarro demonstrated by 
 means of inoculation experiments with monkeys that T. gambiense is 
 transmitted chiefly, if not solely, by a tsetse fly, Glossina palpalis. 
 They and Greig showed that the distribution of the disease in Uganda 
 coincided with that of the fly. In some regions where the fly is present 
 the disease is unknown; which means simply that cases of the disease 
 have not yet been introduced. 
 
 Notwithstanding the great activity in the study of this disease no 
 good remedy for it has been found. Wise travelers in tropical Africa 
 take every precaution against being bitten by tsetse flies. Much effort 
 is being exerted to check the spread of the disease among the natives in 
 some of the infected regions; chiefly by removing patients from the fly 
 region, by screening dwellings or by building them away from the dainp 
 and marshy areas where the flies breed. 
 
 FiLARIASIS 
 
 The first disease found to be transmitted by an insect was filariasis, 
 the subject of important investigations by Manson, Bancroft and others. 
 
266 ENTOMOLOGY 
 
 This disease of tropical and subtropical regions is caused by a thread- 
 worm, or nematode, known as Filaria bancrofti, which occurs in the 
 blood of man and of several of the lower animals as a slender larva 
 (microfilaria) about one-quarter of a millimeter in length. At night 
 these larvse swarm in the peripheral circulation, from which they are 
 taken into the ahmentary canal of a blood-sucking mosquito (chiefly 
 Culex quinquefasciatus) . In the mid-intestine of the mosquito the larva 
 escapes from its sheath and penetrates into muscular tissue, where it 
 grows and develops for two or three weeks, after which it goes to some 
 other part of the mosquito's body, often to the base of the proboscis, 
 whence the larvae are carried into the blood of some vertebrate host, 
 there to develop to sexual maturity. 
 
 The larvae are often common in human blood without seeming to 
 injure the host in any way, but the adults (three or four inches long and 
 often found in groups) and ova that have escaped from the parent 
 female sometimes obstruct the lymphatic canals and cause enormous" 
 swellings of feet, legs, arms or other parts of the human body; this 
 condition being known as elephantiasis. 
 
 Typhus 
 
 War and typhus have always gone hand in hand. Crowded and 
 uncleanly conditions in camps and prisons are most favorable to the 
 propagation of the disease. 
 
 Recent History. — The last scourge of typhus in Serbia began in 
 October, 19 14 among Austrian prisoners, who spread the disease over 
 the country. No adequate means of checking the disease existed, and 
 in January, 191 5 the epidemic was raging. In April there were 9,000 
 deaths per day; the total mortahty for the first five months of 191 5 
 being more than 100,000. This epidemic was checked largely by the 
 energetic efforts of Dr. R. P. Strong and his fellow- workers. 
 
 Syria suffered from typhus in 191 6, with more than 1,000 deaths 
 daily. In Roumania, 1916-1919, the mortahty was 26,000. Mexico 
 City had 11,000 cases of typhus in December, 1915. In the United 
 States the disease occurs now and then in a small way, but especially 
 among immigrants. 
 
 Cause. — The specific cause of typhus can not as yet be named with 
 certainty. It may be a certain spirochaete discovered in 191 7' by 
 Futaki, who found it in the liver and urine of typhus victims, as well as 
 in a monkey after inoculation with infected human blood. Others 
 have ascribed the disease to bacilli. 
 
TRANSMISSION OF DISEASES BY INSECTS 267 
 
 Transmission. — Whatever the organism may be, the fact is now 
 established that typhus is transmitted by human lice. Nicolle, Comte 
 and Conseil, working in northern Africa (1909), conveyed the disease 
 by the injection of human blood to a chimpanzee; then from the 
 chimpanzee to a macaque monkey; and, by means of human body lice, 
 from this animal to other monkeys. Drs. Ricketts and Wilder 
 performed similar experiments in Mexico City (19 10) with similar 
 results. They found that monkeys kept free from lice remained 
 healthy, but contracted the disease after inoculation by means of body 
 lice which had fed on the blood of typhus patients. They showed also 
 the strong probability that infection is transmitted through the eggs 
 to the next generation of lice, which through this indirect infection can 
 cause typhus in monkeys and presumably in man also. It has been 
 found that both the body louse {Pediculus corporis) and the head louse 
 {P. capitis) transmit typhus, but bedbugs and fleas are not impHcated. 
 
 The brilliant work of Dr. H. T. Ricketts was cut short by his death, 
 in 191 o, from typhus contracted during his experiments. 
 
 Control. — A typhus patient is harmless as a source of contagion in 
 the absence of human Hce, the agents of transmission. Lice, as is well 
 known, crawl readily from man to man in crowded quarters, and inhabit 
 the clothing as well as the body, particularly the underclothing, the 
 seams of which may contain the eggs in immense numbers. Eradica- 
 tion of lousiness means freedom from typhus. During the World War, 
 Great Britain, France and Germany were successful in protecting their 
 armies from the ravages of typhus by the use of methods, often elabo- 
 rate, directed against the Hce, or "cooties." These methods, which 
 are generally known, consisted of (i) the thorough cleansing of the 
 surface of the human body; (2) the disinfection of clothing and other 
 belongings, and of the living quarters, by various physical or chemical 
 processes. 
 
 Relapsing Fever 
 
 Relapsing or recurrent fever is less fatal than typhus, but Hke the 
 latter is conveyed by lice (though not exclusively) and accompanies 
 war. The disease has often raged in Europe; the last epidemic, early 
 in the recent war, being exceptionally severe in Serbia. 
 
 The cause of relapsing fever is the genus Spirochceta, of which 
 different species produce various types of the disease in different parts 
 of the world. 
 
268 - ENTOMOLOGY 
 
 Nicolle and his colleagues demonstrated in 1913 that the European 
 and North African form of the disease is transmitted by the body 
 louse, and the head louse as well, though not by their bites. When 
 the lice are crushed and the infected contents of their bodies rubbed into 
 wounds made by the lice, or into abrasions of the skin, or are transferred 
 as by the fingers to a mucous membrane, such as the conjunctiva of 
 the eye, the disease is produced. 
 
 It was proved that, in some instances at least, infection could be 
 transmitted through the eggs to the lice of the next generation. The 
 European form of the disease may be conveyed by the bedbug also, 
 according to some investigators. In central Africa a common tick 
 is the agent of transmission, and in Mexico and Central America ticks 
 and bedbugs are suspected. 
 
 Trench Fever 
 
 One of the most disabling diseases in the Great War was trench 
 fever. The experiments made by British and American investigators 
 in 19 1 8 proved that this disease also is transmitted by the body louse, 
 Pediculus corporis. The physical cause of the fever is conveyed in the 
 feces of the lice and inoculation occurs through scratching by the victim, 
 and possibly also by means of punctures made by the hce. The specific 
 cause of trench fever is, however, not actually known as yet. 
 
 Other Diseases 
 
 Cholera is undoubtedly transmitted by flies. As long ago as 1899 
 Dr. Nuttall wrote: "The body of evidence as to the role of flies in the 
 diffusion of cholera is, I believe, absolutely convincing." 
 
 Dysentery is probably carried by fhes, as Dr. Orton and others have 
 inferred from their experiments. 
 
 Spillman and Haushalter, as well as several others, examined flies 
 that had fed on tubercular sputum and found in the intestinal contents 
 and in the dejections of these flies the bacilli of tuberculosis. 
 
 Dr. F. T. Lord summarizes his important investigations on this 
 subject as foflows: 
 
 " I. Flies may ingest tubercular sputum and excrete tubercle bacilli, 
 the virulence of which may last for at least fifteen days. 
 
 "2. The danger of human infection from the tubercular fly-specks 
 is by the ingestion of the specks on food. Spontaneous liberation of 
 
TRANSMISSION OF DISEASES BY INSECTS 269 
 
 tubercle bacilli from fly-specks is unlikely. If mechanically disturbed, 
 infection of the surrounding air may occur." 
 
 If it is true that tuberculosis can be transmitted by means of food, 
 as experiments with some of the lower animals seem to indicate, the 
 house fly is evidently a factor that must be reckoned with in the fight 
 against this disease. 
 
 There is conclusive evidence that Egyptian ophthalmia is trans- 
 mitted by flies and it is highly probable that certain other infections 
 of the eye are conveyed by the same means. 
 
 The bacillus of the deadly disease anthrax can be transmitted by 
 tabanid flies and stable flies, Stomoxys. 
 
 Dr. H. Graham and others have proved that dengue is conveyed by 
 two species of mosquitoes, the common house mosquito of the tropics 
 {Culex quinquejasciatus) and the yellow fever mosquito {Aedes argenteus). 
 
 Phlebotomus fever of Mediterranean regions and India is known to 
 be carried by a sand iiy, Phlebotomus; and the peculiar Oroya fever of 
 Peru is possibly transmitted by a fly of the same genus. 
 
 There is partial proof that the destructive kala-azar in India is 
 disseminated by the common Indian bedbug. 
 
 Tropical sore is probably spread by flies of some kind. 
 
 In Ceylon, the skin disease known as yaws is conveyed by the com- 
 mon house fly, Musca domestica; and in the West Indies, probably by 
 common flies of the genera Oscinis and Sarcophaga. 
 
 In 191 2 Professor M. J. Rosenau and Dr. C. T. Brues announced 
 that they had succeeded in transmitting infantile paralysis (polio- 
 myelitis) to monkeys by means of the stable fly, Stomoxys calcitrans, 
 and their results were confirmed by Dr. J. F, Anderson. Whether 
 this is the usual means of transmission among human beings it remains 
 to be determined. There is also some experimental evidence that the 
 disease may be carried by the bedbug. 
 
 Rocky Mountain spotted fever was proved by Ricketts in 1906 
 to be conveyed by two or more common species of wood ticks of the 
 genus Dermacentor. 
 
 Smith and Kilborne demonstrated that the destructive Texas fever 
 of cattle, due to a protozoan parasite, is transmitted by a common tick 
 Margaropus annulatus. The adoption of methods of pasturing that 
 enable cattle to avoid the ticks has been highly successful. 
 
CHAPTER X 
 
 INTERRELATIONS OF INSECTS 
 
 Insects in general are adapted to utilize all kinds of organic matter 
 as food, and they show all gradations of habit from herbivorous to carniv- 
 orous. The many forms that derive their food from the bodies of other 
 insects may conveniently be classed as predaceous or parasitic. 
 
 Predaceous Insects. — Among Orthoptera, Mantidae are notably 
 predatory, their front legs (Fig. 64, C) being well fitted for grasping and 
 killing other insects. The predaceous odonate nymphs have a peculiar 
 hinged extensible labium with which to gather in the prey. The adults 
 catch with surpassing speed and precision 
 a great variety of flying insects, mostly 
 small forms, but occasionally butterflies of 
 considerable size. The eyes of a dragon 
 fly are remarkably large; the legs form a 
 spiny basket, probably to catch the prey, 
 which is instantly stripped and devoured, 
 these operations being facilitated by the 
 » excessive mobility of the head. The 
 
 f' hemipterous families Corixidae, Notonec- 
 
 % tidae (Fig. 227), Nepidae, Belostomidae 
 
 (Fig. 23), Naucoridae (Fig. 64, D) Redu- 
 viidae and Phymatidae are predaceous, with 
 raptorial front legs and sharp beaks. 
 Some of the Pentatomidae (Fig. 277) are 
 of considerable economic value on account 
 of their predaceous habits. Most of the Neuroptera feed upon other 
 insects. The Myrmeleon larva (ant-lion) digs a funnel-shaped pitfall, 
 at the bottom of which it buries itself to await the fall of some 
 unlucky ant. The Chrysopa larva (aphis-lion) impales an aphid on 
 the points of its mandibles and sucks the blood through a groove 
 along each mandible (Fig. 46, E), the maxilla fitting against this 
 groove to form a closed channel. Several families of Coleoptera 
 are almost entirely predaceous. Among aquatic beetles, Dytiscidae 
 are carnivorous both as larvae and imagines, Gyrinidag subsist chiefly 
 
 270 
 
 Fig. 277. — Nymph of Podisus 
 maculivenlris sucking the blood 
 from a clover caterpillar, Colias 
 philodice. Natural size. 
 
INTERRELATIONS OF INSECTS 27 1 
 
 upon disabled insects, but occasionally eat plant substances, and 
 Hydrophilidas as larvae catch and devour other insects, though some 
 of the beetles of this family {H. triangularis, for example, Fig. 229) feed 
 largely if not entirely upon vegetation. Of terrestrial Coleoptera, the 
 tiger beetles (Cicindelidae) are strictly predaceous upon other insects. 
 The Cicindela larva lives in a burrow in the soil and lies in wait for 
 passing insects; a pair of hooks on the fifth segment of the abdomen 
 serves to prevent the larva from being jerked out of its burrow by the 
 struggles of its captive. The large family Carabidae is chiefly predace- 
 ous; these "running beetles," both as larvae and adults easily overtake 
 and capture other terrestrial insects. The Carabidae, are by no means 
 exclusively carnivorous, however, for many of them feed to some extent 
 upon fungus spores, pollen, ovules, root-tips and other vegetable matter, 
 as Forbes has found ; Harpalus caliginosus eats the pollen of the ragweed 
 in autumn ; Galerita janus eats caterpillars and occasionally the seeds 
 of grasses; but Calosoma appears to be strictly carnivorous, feeding 
 chiefly upon caterpillars and being in this respect of considerable 
 economic importance. As a whole, Carabidae prefer animal food, as 
 appears from the fact that when canker worms, for instance, are unusu- 
 ally abundant these form a correspondingly large percentage of carabid 
 food, the increase being compensated by a diminution in the amount 
 of vegetable food taken. (Forbes.) Coccinellid larvae (excepting Epi- 
 lachna, which eats leaves) feed almost entirely upon plant lice and con- 
 stitute one of the most effective checks upon their multiplication; the 
 beetles eat aphides, but also fungus spores and pollen in large quantities. 
 Though Lepidoptera are pre-eminently phytophagous, the larva of 
 Feniseca tarquinius is unique in feeding solely upon plant lice, particular- 
 ly the woolly Schizoneura tessellata of the alder. Among Diptera, 
 Asilidae, Midaidae, There vidae and Empididae are the chief predaceous 
 families. Asilidae (robber-flies) ferociously attack not only other flies, 
 but also beetles, bumblebees, butterflies, and dragon flies; as larvae 
 they feed largely upon the larvae of beetles. Many of the larvas of 
 Syrphidae prey upon plant lice, and the larvae of Volucella feed in Europe 
 on the larvae of bumblebees and wasps. Of Hymenoptera, the ants are 
 to a great extent predaceous, attacking all sorts of insects, but particu- 
 larly soft-bodied kinds; while Vespidae feed largely upon other insects, 
 though like the ants they are fond of the nectar of flowers and the juices 
 of fruits. 
 
 Parasitic Insects. — Though very many insects occur as external 
 parasites on the bodies of birds and mammals, very few occur as such on 
 
272 
 
 ENTOMOLOGY 
 
 the bodies of other insects; one of the few is Braula ccBca, a wingless 
 dipteron found on the body of the honey bee. 
 
 A vast number of insects, however, undergo their larval develop- 
 ment as internal parasites of other insects, and most of these parasites 
 belong to the two most specialized orders, Diptera and Hymenoptera. 
 
 The larvae of Bombyliidae feed upon the eggs of Orthoptera and upon 
 larv£e of Lepidoptera and Hymenoptera. Tachinidae are the most 
 important dipterous parasites of other insects and lay their eggs most 
 frequently upon caterpillars; the larvae bore into their victim, develop 
 
 Fig. 278. — Megarhyssa atrata, drilling in tree trunk. 
 
 Macnamara. 
 
 Natural size. — From Charles 
 
 within its body, and at length emerge as winged insects. These parasites 
 often render an important service to man in checking the increase of 
 noxious Lepidoptera. 
 
 The great majority of insect parasites — many thousand species — 
 belong to the order Hymenoptera, constituting one of the primary 
 divisions of the order. They are immensely important from an eco- 
 nomic standpoint, particularly the Ichneumonidae, of which more than 
 ten thousand species are already known. Our most conspicuous 
 ichneumonids are the two species of Megarhyssa, M. atrata (Fig. 278), 
 and M. lunator with their long ovipositors (three inches long in 
 lunator, and four to four and three-quarters inches in atrata) . Mega- 
 rhyssa bores into the trunks of trees in order to reach the burrows of 
 
INTERRELATIONS OF INSECTS 
 
 273 
 
 another large hymenopteron, Tremex columba (Fig. 30), upon whose 
 larvae the larva of Megarhyssa feeds. 
 
 The enormous family Braconidoe, closely related to Ichneumonidae, 
 is illustrated by the common Apanteles coiigregaius, which lays its eggs 
 in the caterpillars of various Sphingidae. The parasitic larvae feed upon 
 the blood and possibly also the fat-body of their host, and at length 
 emerge and spin their cocoons upon the exterior of the caterpillar (Fig. 
 279), sometimes to the number of several hundred. Species of Aphidins 
 transform within the bodies of plant lice, one to each host, and the imago 
 cuts its way out through a circular opening with a correspondingly 
 
 Pig. 279. — A tomato worm, Proloparce sexla, bearing cocoons of the parasitic Apanteles 
 congregatus. Natural size. 
 
 circular lid. Chalcididae, of which some four thousand species are 
 known, are usually minute and parasitic; though some are phytopha- 
 gous, for example, species of Harmolita (Isosoma) which live in wild or 
 cultivated grasses, and the clover seed-midge Bruchophagus funebris. 
 Chalcids affect a great variety of insects of one stage or another, such 
 as caterpillars, pupas, cockroach eggs, plant lice and scale insects; 
 while some of them develop in cynipid galls, either upon the larvae of 
 the gall-makers or upon the larvae of inquilines. Giard in France reared 
 more than three thousand chalcids {Copidosoma truncatellum) from a 
 single caterpillar of Plusia. Proctotrypidae are remarkable as parasites. 
 Most of them are minute; indeed, this family and the coleopterous family 
 Trichopterygidae contain the smallest winged insects known — species 
 but one-third or one-fourth of a millimeter long. A large proportion 
 
274 ENTOMOLOGY 
 
 of the Proctotrypidae are parasitic in the eggs of other insects or of 
 spiders, several sometimes developing in the same egg; others affect 
 odonate nymphs and coleopterous or dipterous larvae, while several 
 species have been reared from itonidid and cynipid galls, and 
 many proctotrypids are parasites of other parasitic insects — in other 
 words, are hyper parasites. 
 
 Hyperparasitism. — Not only are primary parasites frequently 
 attacked by other, or secondary, parasites, but tertiary parasitism is 
 known to occur in a few instances, and there is some reason to believe 
 that even the quaternary type exists among insects, as in the following 
 case. 
 
 The caterpillar of Hemerocampa leucostigma defoliates shade trees 
 in the northeastern United States. An enormous increase of this 
 species in the city of Washington in 1895 was attended by a 
 corresponding increase of parasitic and predaceous species, and this unu- 
 sual opportunity for the study of parasitism was made the most of by 
 Dr. Howard, from whose admirable paper these facts are taken. 
 
 The primary parasites of H. leucostigma numbered 23 species — 17 
 Hymenoptera and 6 Diptera; of the hyperparasites (all hymenopterous) 
 13 were secondary, 2 and probably 5 were tertiary, and one of these 
 (Asecodes alhitarsis) may under certain conditions prove to be a quater- 
 nary parasite. To illustrate — The ichneumon Pimpla inquisitor, an 
 important primary parasite of lepidopterous larvas, lays its eggs in cater- 
 pillars of H. leucostigma; its larvae suck the blood of their host and at 
 length spin their cocoons within the loose cocoon of the Hemerocampa. 
 These cocoons have yielded a well-known secondary parasite, the chalcid 
 Dibrachys houcheanus. Now another chalcid, Asecodes alhitarsis, has 
 been seen to issue from a pupa of this Dibrachys, thus establishing terti- 
 ary parasitism. Furthermore, it is quite possible that Dibrachys 
 itself is a tertiary parasite, in which event the Asecodes might become 
 a parasite of the quaternary order. 
 
 Economic Importance of Parasitism. — If a primary parasite js 
 beneficial, its own parasites are indirectly injurious, generally speaking; 
 while those of the third and the fourth order are respectively beneficial 
 and injurious. The last two kinds are so rare, however, as to be of no 
 practical importance from an economic standpoint. The first two kinds 
 are of immense economic importance, particularly the primary parasites. 
 " Outbreaks of injurious insects," says Howard, " are frequently stopped 
 as though by magic by the work of insect enemies of the species. Hub- 
 bard found, in 1880, that a minute parasite, Tricho gramma pretiosa, alone 
 
INTERRELATIONS OF INSECTS 275 
 
 and unaided, almost annihilated the fifth brood of the cotton worm in 
 Florida, fully ninety per cent, of the eggs of this prolific crop enemy 
 being infested by the parasite. In 1895, in the city of Washington, 
 more than ninety-seven per cent, of the caterpillars of one of our 
 most important shade-tree pests [Hemerocampa, as just mentioned] 
 were destroyed by parasitic insects, to the complete relief of the city the 
 following year. The Hessian fly, that destructive enemy to wheat 
 crops in the United States, is practically unconsidered by the wheat 
 growers of certain states, for the reason that whenever its numbers 
 begin to be injuriously great its parasites increase to such a degree as to 
 prevent appreciable damage. 
 
 "The control of a plant-feeding insect by its insect enemies is an ex- 
 tremely complicated matter, since, as we have already hinted, the 
 parasites of the parasites play an important part. The undue multipli- 
 cation of a vegetable feeder is followed by the undue multiplication of 
 parasites, and their increase is followed by the increase of 
 hyperparasites. Following the very instance of the multiplication of 
 the shade tree caterpillar just mentioned, the writer [Howard] was able 
 to determine this parasitic chain during the next season down to quater- 
 nary parasitism. Beyond this point, true internal parasitism probably 
 did not exist, but even these quaternary parasites were subject to 
 bacterial or fungus disease and to the attacks of predatory insects. 
 
 *'The prime cause of the abundance or scarcity of a leaf-feeding 
 species is, therefore, obscure, since it is hindered by an abundance of 
 primary parasites, favored by an abundance of secondary parasites 
 (since these will destroy the primary parasites), hindered again by an 
 abundance of tertiary parasites, and favored again by an abundance of 
 quaternary parasites." 
 
 Entomologists have made many attempts to import and propagate 
 insect enemies of various introduced insect pests, and some of their 
 efforts have been crowned with success, as was notably the case when 
 Novius cardinalis, a lady-bird beetle, was taken from Australia to Cali- 
 fornia to destroy the fluted scale. 
 
 Form of Parasitic Larvae. — The peculiar environment of parasitic 
 larvae is responsible for profound changes in their organization. These 
 larvae, in general, are apodous, the body is compact and the head is more 
 or less reduced, sometimes to the merest rudiment. These characters, 
 occurring also in such dipterous larvae as Hve in a mass of decaying or- 
 ganic matter, and again in those hymenopterous larvae whose food is pro- 
 vided by the mother or by nurses, are to be attributed to the presence 
 
276 ENTOMOLOGY 
 
 of a plentiful supply of food, obtainable with little or no exertion, and 
 indicate, not primitive simplicity of organization, but a high degree of 
 speciahzation, as we have said before. The embryonic development of 
 parasitic larvae is frequently highly anomalous, as appears in the chapter 
 on development. 
 
 Maternal Provision. — Excepting several families of Hymenoptera 
 and the Termitidae, few insects make any special provision for the wel- 
 fare of the young beyond laying the eggs in some appropriate situation. 
 Many insects, as walking-sticks (Phasmidae) and some butterflies 
 {Argynnis) simply drop their eggs to the ground, leaving the young to 
 shift for themselves. Most insects, however, instinctively lay their 
 eggs in situations where the larva is sure to find its proper food near at 
 hand. Thus various flies and beetles deposit their eggs on decaying 
 animal matter, butterflies and moths are more or less restricted to par- 
 ticular species of plants, and parasitic Hymenoptera to certain species of 
 insects. The beetles of the genus Necrophorus go so far as to bury the 
 body of a bird, mouse or other animal in which the eggs are to be laid; 
 and in this instance the male assists the female in undermining and 
 afterward covering the body. A similar co-operation of the two sexes 
 occurs in the scarabaeid beetles known as "tumblebugs," a pair of which 
 may often be seen rolling along laboriously a ball of dung which is to 
 serve as larval food. The female mole-cricket {Gryllotalpa) is said to 
 care for her eggs and even to feed the young at first. 
 
 Hymenoptera display all degrees of complexity in regard to maternal 
 provision. Tenthredinidae simply lay their eggs on the proper food 
 plants or else insert them into the tissues of the plants. Sphecina make 
 a nest, provision it with food and leave the young to care for themselves. 
 Queen wasps and bumblebees go a step further in feeding the first larvae 
 and carrying them to maturity. Finally, in the honey bee the care of 
 the young is at once relegated by the queen to other individuals of the 
 colony, as is also the case among ants. 
 
 Some of the most elaborate examples of purely maternal provision 
 are found among the digger wasps and the solitary wasps; these in- 
 stances are highly interesting, involving as they do an intricate co-ordi- 
 nation of many reflex actions — as appears in the discussion of insect 
 behavior. 
 
 Among the Sphecina, or digger wasps, the female makes a nest by 
 burrowing into the ground, by mining into such pithy plants as elder or 
 sumach, or else by plastering bits of mud together. The nest is provi- 
 sioned with insects or spiders which have been stung in such a way as 
 
INTERRELATIONS OF INSECTS 277 
 
 usually to be paralyzed, without being actually killed. The various 
 species of Sphecina frequently select particular species of insects or 
 spiders as food for the young. Pepsis Jormosa (Pompilidaj) uses taran- 
 tulas for this purpose; Sphecius speciosus (Bembecidie) stores her nest 
 with a cicada; Nyssonidae pick out certain species of Membracidae ; 
 mud-daubers (Sphecidae) use spiders; and other families of Sphecina 
 capture bees, beetles, plant lice or other insects, as the case may be. 
 The solitary wasps (Eumenidae) are similar to the digger wasps in habits. 
 
 Of the solitary bees, Megachile is well known for its habit of cutting 
 pieces out of rose leaves; it uses oblong pieces to form a thimble-shaped 
 tube which, after being stored with pollen and nectar, is plugged with a 
 circular piece of leaf. The larval cells are made either in tunnels ex- 
 cavated in wood by the mother or else in cracks or other chance cavities. 
 
 One of the carpenter bees, Ceratina dupla, which builds in the hollow 
 stem of a plant a series of larval cells separated by partitions, is said by 
 Comstock to watch over her nest until the young mature. 
 
 The transition from the solitary to the social habit is indicated in the 
 lifq-histories of wasps and bumblebees, where a solitary queen founds 
 the colony but soon relegates to other individuals all duties except that 
 of egg-laying. The social insects will now be considered. 
 
 Termites 
 
 Though popularly known as "white ants," the termites are quite 
 different from true ants, being indeed not very far removed from the 
 most primitive insects. In view of the extreme contrast in structure 
 and development between termites and ants, it is remarkable that the 
 two groups should have much the same kind of complex social 
 organization. 
 
 Classes of Termites.^ — In general, four principal kinds of adults are 
 produced in a community of termites, namely — workers, soldiers, fertile 
 males and fertile females. 
 
 The workers (Fig. 280, A) which are ordinarily the most numerous,- 
 are of either sex, but their reproductive organs are undeveloped. A 
 worker ant or .bee, is, however, always a female. The termite workers, 
 as the name impHes, do most of the work; they make the nest, provide 
 food, feed and care for the young and the royal pair, and attend to 
 many other domestic duties. 
 
 The soldiers, like the workers, are of either sex, with undeveloped 
 sexual organs. With monstrous mandibles and head (Fig. 280, B), 
 
278 
 
 ENTOMOLOGY 
 
 their chief duty apparently is to defend the colony, though they fre- 
 quently fail to do so. 
 
 The winged males. and females (Fig. 280, C) which are sexually ma- 
 
 FiG. 280. — Various forms of Reticulitermes lucifugus. A, adult worker; B, soldier; C, 
 perfect winged insect; D, perfect insect after shedding the wings; E, young complementary 
 queen; F, older complementary queen. Enlarged. — After Grassi and Sandi.^s. 
 
 ture, swarm from the nest and mate. After the nuptial flight the pair 
 burrow into some crevice and shed the wings, which break off each along 
 a peculiar transverse suture, leaving four triangular 
 stumps (Fig. 280, D). The king and queen found 
 a new colony and may live for several years, shelt- 
 ered in a special chamber; the queen, meanwhile, 
 becoming enormously distended (Fig. 281) with eggs 
 and almost incapable of locomotion. The prolificacy 
 of the queen is astonishing; she can lay thousands 
 of eggs, sometimes at the rate of sixty per minute. 
 She is the nucleus of the colony, and should she 
 become incapacitated, is replaced by one or more 
 substitute queens, which have been developed to 
 meet the emergency; similarly, a substitute king is 
 matured upon occasion. These substitutes (Fig. 
 280, E) differ from the primary pair in having 
 nymphal wing pads in place of the remains of func- 
 tional wings. 
 
 In regard to Termopsis angusticollis, in California, 
 Dr. Heath says that if only one of the royal pair be 
 destroyed usually only one substitution form is 
 developed, but when both perish, from ten to forty 
 substitutes appear, according to the size of the colony. 
 
 In all, three types of reproductive forms are recognized : ^r^/ form, 
 
 Fig. 281. — Queen 
 of Termes obesus. 
 Natural size. — After 
 Hagen. 
 
INTERRELATIONS OF INSECTS 279 
 
 true kings and queens, with functional wings or their remnants; second 
 form, substitute males or females, with short wing pads; third form, 
 ergatoid, or worker-like, males or females, without wings, this type 
 being rather rare. 
 
 In certain tropical species there are two types of soldiers, and two of 
 workers; so that adults of either sex may occur under seven different 
 forms in the same colony. 
 
 Origin of Castes. — Grassi maintains that all the forms are ahke at 
 birth except as regards sex, and that the differences between worker 
 and soldier, which are independent of sex, depend probably upon nutri- 
 tion. Grassi attributes all the diversities of caste, except the sexual 
 ones, to the character and amount of the food. 
 
 C. B. Thompson states that at hatching there are two kinds of 
 nymphs (i) the "reproductive," which develop into the fertile castes, 
 and (2) the ''worker-soldier" nymphs, which become the sterile castes; 
 these two types being distinguishable by internal differences in the brain, 
 compound eyes, and sex organs. 
 
 Food.— The food of termites is of six kinds: (i) wood; (2) matter 
 emitted from the oesophagus or rectum, termed respectively stomodasal 
 and proctodaeal food; (3) cast skins and other exuvialstuflf ; (4) the bodies 
 of their companions; (5) saliva; (6) water. Of these the proctodaeal 
 food is the favorite. Nymphs receive at first only saliva; later they get 
 stomod^eal and proctodaeal food until, finally, they are able to eat wood 
 — the staple food of a termite. 
 
 American Species. — Our common termite is Reticulitermes jiavipes, 
 which occurs throughout the United States, excavating its galleries in 
 decaying logs, stumps or other dead wood. The nuptial flight of this 
 species takes place in spring, when the two sexes swarm in numbers that 
 are sometimes enormous. One swarm, as recorded by Hagen, appeared 
 as a dense cloud, and was being followed and attacked by no less than 
 fifteen species of birds, among which were robins, bluebirds and sparrows; 
 some of the robins were so gorged to the mouth with termites that their 
 beaks stood open. Though plenty of winged females are said to occur 
 in the swarming season, the true queen of R. fiavipes is extremely rare, 
 the queen usually found being evidently, from her undeveloped wings, 
 a substitute queen. 
 
 The European species Reticulitermes lucifugus has been found 
 recently in Massachusetts. Most species of termites occur in warm 
 climates, however. North of Mexico thirty-six species are known, 
 
28o 
 
 ENTOMOLOGY 
 
 most of which have come from the south, and more species are liable to 
 be introduced at any time (Banks). 
 
 Architecture. — While many termites simply burrow in dead wood, 
 other species construct more elaborate nests. A Jamaican species 
 builds huge nests in the forks of trees, with covered passageways leading 
 to^the ground. 
 
 In parts of Africa and Australia, where they are free from disturbance, 
 
 Fig. 282. — Termite mound, Kimber- 
 ley type, Australia. — After Saville- 
 Kent. 
 
 Fig. 2S3. — Mound of the "com- 
 pass" termite of North Australia. — 
 After Saville-Kent. 
 
 termites erect huge mounds, frequently six to ten and sometimes 
 eighteen or twenty feet high, with galleries extending as far below the 
 surface of the ground as they do above it. These immense structures 
 (Fig. 282) consist chiefly of earth, cemented by means of some secretion 
 into a stony clay, with which also much excrementitious matter is mixed ; 
 they are pyramidal, columnar, pinnacled or of various other forms, ac- 
 cording to the species, and are perforated by thousands of passages and 
 chambers, while there are underground galleries extending away from 
 the mound to a distance of often several hundred feet. 
 
INTERRELATIONS OF INSECTS 201 
 
 An extraordinary type of mound is constructed by the "compass" 
 or "meridian," termites of North Australia, for their wedge-shaped 
 mounds (Fig. 283), commonly eight or ten feet high, though sometimes 
 as high as twenty feet, are directed north and south with surprising accu- 
 racy. By means of this orientation the exposure to the heat of the sun is 
 reduced to the minimum, as occurs also in the case of many Austrahan 
 plants, the leaves of which present their edges instead of their faces to 
 the sun. 
 
 More than one species of termite may inhabit a single nest; in one 
 South African nest Haviland found live species of termites and three of 
 ants. The widely distributed genus Eutermes is essentially a group of 
 inquiline, or guest, species. Termite mounds afford shelter to scor- 
 pions, snakes, lizards, rats, and -even birds, some of which nest in them. 
 The Australian bushmen hollow out the mounds to make temporary 
 ovens, and even eat the clay of which they are composed, while hill- 
 tribes of India are accustomed to eat the termites themselves, the 
 flavor of which is said to be delicious. 
 
 Ravages. — In tropical regions the amount of destruction done by 
 termites is enormous, and these formidable pests are a constant source 
 of consternation and dread. They emit a secretion that corrodes 
 metals and even glass, while anything made of wood is simply at their 
 mercy. Always avoiding the light, they hollow out floors, rafters or 
 furniture, leaving only a thin outer shell, and as a result of their in- 
 sidious work a chair or a table may unexpectedly crumble at a touch. 
 Jamestown, the capital of St. Helena, was largely destroyed by termites* 
 (1870) and had to be rebuilt on that account. 
 
 In the United States and Europe few species of termites occur, and 
 they do little injury as compared with the tropical species; though our 
 common Reticulitermes flavipes occasionally damages woodwork, books, 
 plants, etc., in an extensive way, particularly in the Southern states. 
 
 Termitophilism. — Associating with termites are found various 
 other arthropods, mostly insects. The relations of these termitophilous 
 forms to the termites are, so far as is known, similar to those described 
 beyond between myrmecophilous species and ants. 
 
 Honey Bee 
 
 For more than three thousand years the honey bee has been almost 
 unique among insects as an object of human care and study. It was 
 highly prized by the old Greeks and Romans (as appears from the writ- 
 
282 
 
 ENTOMOLOGY 
 
 ings of Aristotle, 330 B. C, and Cato, about 200 B. C.) and actually 
 worshiped as a symbol of royalty by the ancient Egyptians, through 
 whose papyri and scarabs the honey bee may be traced back to the time 
 of Rameses I., or 1400 B. C. 
 
 The honey bee, unhke domesticated animals, is so little dependent 
 upon man that it readily returns to a wild hfe. Under many dis- 
 tinct races, which are due largely to human intervention. Apis niel- 
 lifera is widely distributed over the earth. 
 
 Castes.— The species comprises three kinds of individuals: queen, 
 drone and worker (Fig. 284) . The workers are females with an atrophied 
 reproductive system. They constitute the vast majority in any colony 
 and are the only kind that is commonly seen out of doors. Upon the 
 industrious workers falls the burden of the labor; they build the comb, 
 
 Fig. 2f 
 
 A B C 
 
 -The honey bee, Apis mellifera. A, queen; B, drone; C, worker. Natural size. 
 
 nurse the young, gather foCd, clean and repair the nest, guard it from 
 intruders, control larval development, expel the drones — briefly, the 
 workers alone are responsible for the general management of the com- 
 munity. Though hibernating workers Hve eight or nine months, the 
 other workers live but from five to twelve weeks. 
 
 The term queen is, of course, a misnomer, for the government of 
 the hive is anything but monarchical. The chief duties of the queen, 
 or mother, are simply to lay eggs and to lead away a swarm. She is able 
 to deposit as many as 4,000 eggs in twenty-four hours. After a single 
 mating, the spermatozoa retain their vitality in the spermatheca of the 
 queen for three or four years — the lifetime of a queen. The males, or 
 drones, apart from their occasional sexual usefulness, are of little or no 
 service, and their very name has become an expression for laziness. 
 
 The Comb. — Wax, of which the comb is built, is made from honey or 
 sugar, many pounds (twenty, according to Huber) of honey being re- 
 quired to make one pound of wax. The workers, gorged with nectar, 
 cling to one another in a dense heated mass until the white films of wax 
 
INTERRELATIONS OF INSECTS 
 
 >83 
 
 appear underneath the abdomen (Fig.. 104) ; these are transferred to the 
 mouth, as described on page 229, and are masticated with a fluid, 
 secreted by cephalic glands, which alters the chemical composition of 
 the wax and makes it plastic. 
 
 The workers now contribute their wax to form a vertical, hanging 
 septum, on the opposite sides of which they proceed to bite out pits — 
 
 the bottoms of the future cells — using the 
 
 excavated wax in making the cell walls. The 
 bottom of each cell consists of three rhombic 
 plates (Fig. 285, A), and the cells of one side 
 interdigitate with those of the other side (Fig. 
 285, B) in such a way that each rhomb serves 
 for two cells at once. Wax is such a precious 
 substance that it is used (instinctively, how- 
 ever) always with the greatest economy; the 
 cell walls, are scraped to a thinness of 3-^80 or 
 }ioo of an inch, and nowhere is more wax used 
 than is suflBcient for strength; one pound of wax 
 makes from 35,000 to 50,000 worker cells. The 
 cells, at first circular in cross section, become 
 hexagonal from the mutual interference of 
 workers on opposite sides of the same wall; 
 the form is, however, by no means a regular 
 hexagon in the mathematical sense, for it is difficult to find a cell with 
 errors of less than 3 or 4 degrees in its angles. (Cheshire.) Worker 
 cells are one fifth of an inch in diameter, while the larger cells, destined 
 for drones or to hold honey, are one quarter of an inch across. 
 
 To strengthen the edges of cells or to fill crevices, the workers use 
 propolis, the sticky exudation from the buds or leaf axils of poplar, fir, 
 horse-chestnut or other trees; though they will utilize instead such arti- 
 ficial substances as grease, pitch or varnish. As winter approaches, the 
 bees apply the propolis liberally, making their abode tight and 
 comfortable. 
 
 Larval Development. — When the brood cells are ready, the queen, 
 attended by workers, lays an egg in each cell and has no further con- 
 cern as to its fate. After three days the egg discloses a footless grub 
 (Figs. 286, 287) which depends at first upon the milky food that bathes 
 it and has been supplied from the mouths of the worker nurses. Later 
 the larva is weaned by its nurses to pollen, honey and water. As the 
 stomach and the intestine of the larva do not communicate with each 
 
 Fig. 285. — A, bases of 
 comb cells; B, section of 
 comb. Somewhat e n- 
 larged. — After Cheshire. 
 
284 
 
 ENTOMOLOGY 
 
 Other, the excretions of the larva cannot contaminate the surrounding 
 nutriment, and are retained until the final molt. Five days after 
 
 hatching, the larva spins its cocoon, 
 the workers having meanwhile cov- 
 ered the larval cells with a porous 
 cap of wax and pollen (Fig. 287) 
 and on the twenty-first day after 
 the egg was laid the winged worker 
 bee cuts its way out, assisted in 
 this operation by the ever-attentive 
 nurses. Now, after acquiring the 
 use of its faculties, the newly 
 emerged bee itself assumes the 
 duties of a nurse, but as soon as 
 its cephalic nursing glands are 
 exhausted it becomes a forager. 
 This account applies to the worker; 
 the three kinds of individuals differ 
 Fig. 286.— Comb of honey bee, showing in respect to the number of days 
 the insect in various stages. At the right required for development, as 
 
 are large queen cells. — After Benton. ^ _ '^ ' 
 
 appears in the following table, 
 from Phillips: 
 
 Queen. . 
 Worker. 
 Drone. . 
 
 Egg. 
 
 Larva. 
 
 Pupa. 
 
 Total 
 
 3 
 
 s'A 
 
 jH 
 
 16 
 
 3 
 
 6 
 
 12 
 
 21 
 
 3 
 
 6}^ 
 
 I4>2 
 
 24 
 
 The cells in which queens develop (Fig. 286) are quite different from 
 worker or drone cells, being much larger, more or less irregular in form, 
 and vertical instead of 
 
 horizontal; they are ^^l P 
 
 attached usually to the 
 lower edge of a comb or 
 else to one of the side 
 edges. 
 
 Other Facts.— The 
 entire organization of the 
 honey bee has been pro- 
 foundly modified with ref- 
 erence to floral structure; the life of the bee is wrapped up in that of 
 the flower. The more important structural adaptations of bees in 
 
 Fig. 287. — Honey bee. /, feeding larva; p, pupa; 
 s, spinning larva. — After Cheshire. 
 
INTERRELATIONS OF INSECTS 285 
 
 relation to flowers have been described, as well as many of their sensory 
 peculiarities; there remain to be added, however, some other items of 
 interest, chosen from the many. 
 
 A colony of bees in good condition at the opening of the season con- 
 tains a laying queen and some 30,000 to 40,000 worker bees, or six to 
 eight quarts by measurement. Besides this there should be four, five, 
 or even more combs fairly stocked with developing brood, with a good 
 supply of honey about it. Drones may also be present, even to the 
 number of several hundred. 
 
 Ordinarily the queen mates but once, flying from the hive to meet 
 the drone high in the air, when five to nine days old usually. Seminal 
 fluid sufficient to impregnate the greater number of eggs she will deposit 
 during the next two or three years (sometimes even four or five years) 
 is stored at the time of mating in a sac— the spermatheca, opening into 
 the egg-passage. 
 
 The liquid secreted in the nectaries of flowers is usually quite thin, 
 containing, when just gathered, a large percentage of water. Bees suck 
 or lap it up from such flowers as they can reach with their flexible, suck- 
 ing tongue, 0.25 to 0.28 inch long. This nectar is taken into the honey 
 sac, located in the abdomen, for transportation to the hive. Besides 
 being thin, the nectar has at first a raw, rank taste, usually the flavor 
 and odor peculiar to the plant from which gathered, and these are fre- 
 quently far from agreeable. To make from this raw product the health- 
 ful and delicious table luxury which honey constitutes — "fit food for the 
 gods" — is another of the functions peculiar to the worker bee. The 
 first step is the stationing of workers in lines near the hive entrances. 
 These, by incessant buzzing of their wings, drive currents of air into and 
 out of the hive and over the comb surfaces. If the hand be held before 
 the entrance at such a time a strong current of warm air may be felt 
 coming out. The loud buzzing heard at night during the summer time 
 is due to the wings of workers engaged chiefly in ripening nectar. In- 
 stead of being at rest, as many suppose, the busy workers are caring for 
 the last-gathered lot of nectar and making room for further accessions. 
 This may go on far into the night, or even all night, to a greater or less 
 extent, the loudness and activity being proportionate to the amount and 
 thinness of the liquid. Frequently the ripening honey is removed from 
 one set of cells and placed in others. This may be to gain the use of 
 certain combs for the queen, or possibly it is merely incidental to the 
 manipulation the bees wish to give it. When, finally, the process has 
 been completed, it is found that the water content has usually been re- 
 
286 ENTOMOLOGY 
 
 duced to lo or 12 per cent., and that the disagreeable odors and flavors, 
 probably due to volatile oils, have also been driven off in a great measure, 
 if not wholly, by the heat of the hive, largely generated by the bees. 
 During the manipulation an antiseptic (formic acid) , secreted by glands 
 in the head of the bee, and possibly other glandular secretions as well 
 have been added. The finished product is stored in waxen cells above 
 and around the brood nest and the main cluster of bees, as far from the 
 entrance as it can be and still be near to the brood and bees. The work 
 of sealing with waxen caps then goes forward rapidly, the covering being 
 more or less porous. Each kind of honey has its distinctive flavor and 
 aroma, derived, as already indicated, mainly from the particular blos- 
 soms by which it was secreted, but modified and softened by the 
 manipulation given it in the hives. The last three paragraphs are taken 
 from Benton's useful manual. 
 
 The phenomenon of "swarming" results from the tremendous re- 
 productive capacity of the queen, though it is immediately an instance 
 of positive phatotropism, as Kellogg has shown. Accompanied by most of 
 the workers, the old queen abandons the hive to establish a new colony. 
 The workers that remain behind have provided against this contingency, 
 however, and the departed queen is soon replaced by a new one. 
 
 Determination of Caste.- — The difference between queen and worker 
 depends solely upon nutrition, both forms being derived from precisely 
 the same kind of egg. To produce a queen, a large cell of special form 
 is constructed, and its occupant, instead of being weaned, is fed almost 
 entirely upon the highly nutritious secretion which worker grubs receive 
 only at first and in limited quantity. This nitrogenous food, the prod- 
 uct of cephalic glands, develops the reproductive system in proportion 
 to the amount received. Drone larvae get much of it, though not so 
 much as queens, while an occasional excess of this "royal jelly" is 
 beheved to account for the abnormal appearance of fertile workers. 
 
 Parthenogenesis, or reproduction without fertilization, is known to 
 occur in the bee, as well as in various other insects. The always un- 
 fertilized eggs of workers produce invariably drones, as do also unfertil- 
 ized eggs of the queen. 
 
 Dzierzon's Theory. — The much discussed theory of Dzierzon, pro- 
 posed more than seventy-five years ago, is essentially as follows: (i) 
 the queen is able "at will" to lay either male or female eggs; (2) all 
 the eggs in the ovaries would develop into males if unfertihzed, but 
 fertihzed eggs produce females. 
 
 It is a matter of common observation that the queen is able to lay 
 
INTERRELATIONS OF INSECTS 287 
 
 female eggs in worker or queen cells, and male eggs in drone cells; but 
 the means by which she exercises control over the fertilization of the 
 eggs is not understood. 
 
 It is known that unfertilized eggs produce always drones, and at 
 present it is generally beheved by geneticists that drones never 
 come from fertilized eggs. The principal reasons for this opinion 
 are these: (i) if a pure-bred queen of one race is crossed with a drone 
 of another race, the female progeny (workers or queens) have hybrid 
 characters, but the male offspring have only characters of the maternal 
 race; (2) eggs from worker or queen cells contain spermatozoa; those 
 from drone cells do not. 
 
 Bumblebees 
 
 Familiar as the bumblebees are, their habits have been little studied 
 in this country, though in England ''bumblebees" have formed the 
 subject of an interesting volume by Sladen. The queen hibernates and 
 in spring starts a colony, utilizing frequently for this purpose the 
 deserted nest of a field mouse or sometimes the burrow of a mole or 
 gopher. The queen lays her eggs in a small mass of pollen mixed with 
 nectar (Putnam) . The larvae eat out cavities in the mass of food and 
 when full grown spin silken cocoons, from which the imago cuts its 
 way out; the empty cocoon being subsequently used as a receptacle for 
 honey. At first only workers are produced and they at once relieve the 
 queen of the duties of collecting nectar and pollen, caring for the young, 
 etc. The workers are of different sizes, the smaller ones being nurses 
 or builders and the larger ones foragers — the kind commonly seen out of 
 doors. In the latter part of summer both males and females are pro- 
 duced, but when severe frost arrives, the old queen, the workers and the 
 males succumb, leaving only the young queens to survive the winter. 
 
 Social Wasps 
 
 The Social Wasps constitute the family Vespidas, of which we have 
 three genera, namely, Vespa, Polistes and Polybia, the last genus being 
 represented by a single Californian species. 
 
 Vespa.— Some species of Vespa, as V. maculata, make a nest which 
 consists of several tiers of cells protected by an envelope (Fig. 288), at- 
 taching the nest frequently to a tree; other species, as germanica and 
 vulgaris, make a nest underground. The paper of which the nests are 
 
288 ENTOMOLOGY 
 
 composed is manufactured from weather-worn shreds of wood, which 
 are torn off by the mandibles and then masticated with a secreted fluid 
 which cements the paper and makes it waterproof. 
 
 A solitary queen founds the colony in spring; she starts the nest, 
 lays eggs, feeds the young and brings forth the first workers; these then 
 relieve her — continue the building operations, collect food, nurse the 
 young; in short, assume the burden of the labor. In the latter part of 
 summer, fertile males and females appear and pairing occurs. Though 
 the statement has often been made that only the young queens survive 
 
 ^^ 
 
 Fig. 288. — Nest of wasp, Vespa macidata. A, outer aspect; B, with envelope cut away to 
 show combs. Greatly reduced. 
 
 the winter, there is some reason to believe that not only the queens but 
 also males and workers may hibernate successfully in the nest. 
 
 The larvae are fed at first, by regurgitation, upon the sugary nectar 
 of flowers and the juices of fruits, and later upon more substantial food, 
 such as the softer parts of caterpillars, flies, bees, etc., reduced to a pulp 
 by mastication; occasionally wasps steal honey from bees. 
 
 The workers, as is usual among social Hymenoptera, are modified 
 females, incapable of reproduction as a rule, though the distinction be- 
 tween worker and queen is not nearly so sharp among wasps as it is 
 among bees. Worker eggs are said to be parthenogenetic and to pro- 
 duce only males. The males, unhke those of the honey bee, are active 
 laborers in the colony. In the tropics there are wasps that form per- 
 manent colonies, store honey and swarm, after the manner of honeybees. 
 
 Polistes.— The preceding description of Vespa applies equally well 
 to our several species of Polistes, except that the nest of Polistes is a 
 
INTERRELATIONS OF INSECTS 289 
 
 single comb hanging by a pedicel and without a protecting envelope. 
 Miss Enteman, who has carefully studied the habits of Polistes, finds 
 that the larva spins a lining as well as a cap for its cell, by means of a 
 fluid from the mouth, and that the adults emerge after a pupal period of 
 three weeks, males and females appearing (in the vicinity of Chicago) 
 in the latter part of August and early in September.' 
 
 Ants 
 
 The habits of ants have engaged the serious attention of some of the 
 most sagacious students of the phenomena of life. Any species of ant 
 presents innumerable problems to the thoughtful investigator and about 
 five thousand species, subspecies and varieties of ants have been 
 described. 
 
 A large part of our knowledge of the habits of these remarkable 
 insects has been obtained by the use of artificial formicaries, which are 
 easily constructed and have yielded important results in the hands of 
 Lubbock, Forel, Janet, Wasmann, Fielde, Wheeler and other well- 
 known students of ants. We have an important comprehensive volume 
 on these insects by Wheeler. 
 
 Castes. — In a colony of ants three kinds of individuals are produced 
 as a rule: males, females and workers, the last being sexually imperfect 
 females. 
 
 The males and females swarm into the air for a nuptial flight, after 
 which the males die, but the females shed their wings and enter upon a 
 new and prolific existence, which may last for many years; a queen of 
 Lasius niger was kept alive by Lubbock for nine years, and one oi Formica 
 fusca, fifteen years, and then its death was due to an accident. 
 
 The workers live from one to seven years, according to the same 
 authority. They constitute the vast majority in any colony and are the 
 familar forms that so often command attention by their industry and 
 pertinacity. In some species certain of the workers are known as 
 soldiers; these may be recognized by their larger head and mandibles. 
 
 Pol3miorphism. — Ants and termites surpass all other insects in 
 respect to the number of forms under which a single species may occur. 
 In some species of ants several types of workers exist; these are distin- 
 guished by structural peculiarities of one kind or another, which 
 possibly indicate special functions, for the most part as yet unas- 
 certained. Furthermore, the sexual individuals are not necessarily 
 winged; some or all of them may be wingless, especially the females. 
 
290 ENTOMOLOGY 
 
 These wingless males and females are termed ergatoid, on account of 
 their resemblance to workers. 
 
 As to how these various forms are produced, very little is known. 
 Probably, as among bees, workers and queens are produced from the 
 same kind of eggs, which have been fertilized, and the differences 
 between worker and queen and between workers themselves may be due 
 to the quality and quantity of the food that is supplied to the larvae 
 by their nurses. As in bees, the parthenogenetic eggs laid by abnormal 
 workers may produce males, as Forel, Lubbock and Miss Fielde have 
 found; or they may produce normal workers, as Reichenbach and Mrs. 
 A. B. Comstock have found to be the case in Lasius niger. Wheeler 
 points out the possibility of the inheritance of worker characters through 
 the male offspring of workers. 
 
 Larvae. — The numerous eggs laid by one or more queens are taken 
 in charge by the young workers, through whose assiduous care the help- 
 less larvae are carried to maturity. The nurses feed the larvae from their 
 own mouths, clean the larvae, and carry them from one place to another 
 in order to secure the optimum conditions of temperature, moisture, etc. 
 When a nest is broken open, the workers seize the larvae and pupae and 
 hurry into some dark place. The pupa is either naked or else enclosed 
 in a cocoon, spun by the larva. 
 
 Nests. — The species of the tropical genus Eciton do not make nests 
 but occupy temporarily any suitable retreat which they may happen to 
 find in the course of their wanderings. Ants in general know how to 
 utilize all sorts of existing cavities as nests; they make use of crevices 
 in rocks and under stones or bark, the holes made by bark-beetles, hollow 
 stems or roots, plant-galls, fruits, etc. The extraordinary "ant-plants" 
 have already received special consideration. 
 
 Very many ants excavate their nests in the ground ; after a rain these 
 ants are especially industrious in the improvement of the nest, pressing 
 the wet earth into the walls of the galleries and adding probably a se- 
 creted fluid which acts as a cement; stones and sticks are often worked 
 into the walls of a nest and the mounds of ants are frequently fashioned 
 about blades of grass or growing herbage of whatever kind. The sub- 
 terranean galleries are often complex labyrinths; frequently there are 
 long underground passages extending out in all directions, sometimes 
 to aphid-infested roots of plants or, as in the case of the leaf-cutting 
 ants of the tropics, to trees which are destined to be attacked; special 
 chambers are set apart for the storage of food and others for eggs, larvae 
 or pupae. 
 
INTERRELATIONS OF INSECTS 29I 
 
 Often a nest is excavated under a stone. As Forel observes, the 
 stone warms speedily under the rays of the sun, and in damp or cool 
 weather the ants are always in the highest story of the nest as soon as 
 the sun's warmth begins to penetrate the soil, while they go below as 
 soon as the sun disappears or when its heat becomes too strong. They 
 select stones that are neither too large nor too small to regulate the tem- 
 perature well, while other ants attain the same object by making the 
 nest under sheltering herbage or by making a mound with a hard 
 cemented roof. 
 
 The well-known ant-hills may consist simply of excavated particles 
 of soil or else, as in the huge mounds of Formica exsectoides,mz,ycontdi\n 
 labyrinthine passages in addition to those underground. The mounds 
 of this species are elaborate structures which may last a man's lifetime 
 at least. F. exsectoides is accustomed to form new colonies in connec- 
 tion with the parent nest; McCook found in the Alleghanies no less than 
 1,600 nests, forming a single enormous community with hundreds of 
 millions of inhabitants, hostile to all other colonies of ants, even those 
 of the same species. This ant covers its mound with twigs, dead leaves, 
 grass and all sorts of foreign material, and is said to close the exits of the 
 nest with bits of wood at night and in rainy weather, removing them in 
 the morning or when the weather becomes favorable. 
 
 As Forel says [translation]: "The chief feature of ant architecture, 
 in contradistinction to that of the bees and the wasps, is its irregularity 
 and want of uniformity — that is to say, adaptability, or the capacity of 
 making all the surroundings and incidents subserve the purpose of at- 
 taining the greatest possible economy of space and time and the greatest 
 possible comfort. For instance, the same species will live in the Alps 
 under stones which absorb the rays of the sun; in a forest it will live in. 
 warm, decayed trunks of trees; in a rich meadow it will live in high, 
 conical mounds of earth." Some species construct peculiar pasteboard 
 nests, as Lasius fuliginosus of Europe and tropical species of Cremasto- 
 gaster; and others spin silk to fasten leaves together, as Polyrhachis of 
 India and (Ecophylla of tropical Asia and tropical Africa, the silk being 
 probably a salivary secretion, according to Forel. 
 
 Habits in General. — The habits of ants are an inexhaustible and 
 ever-fascinating subject of study to the naturalist, and well repay the 
 most critical observation. While each species has its characteristic 
 habits, ants in general have many customs in common. 
 
 Thus ants of one colony exhibit, as a rule, a pronounced hostiHty. 
 toward ants of any other colony, even one of the same species, but 
 
292 ENTOMOLOGY 
 
 recognize and spare members of their own colony, even after many 
 months of separation and though the colony may number half a million 
 individuals. This recognition is effected by means of an odor, dis- 
 tinctive of the colony and apparently inheritable. When an ant is 
 washed and then restored to its fellows, it is treated at first as an intru- 
 der and may even be killed. The same is true when the ant has been 
 smeared with juices from the bodies of alien ants. According to Miss 
 Fielde, workers of colony A, smeared with the juices from crushed ants 
 of colony B and then placed in colony B are received amicably, but at 
 once set about to destroy their hosts, Uke "wolves in sheep's clothing." 
 These statements apply only to workers, however, for alien larvae and 
 pupae are frequently captured and reared by ants, and Miss Fielde 
 states that kings of one colony of Stenamma when introduced into 
 another colony are even cordially received. 
 
 Some of the most careful students of the habits of ants agree that 
 these insects can communicate with one another. An ant discovers a 
 supply of food, returns toward the nest, meets a fellow worker, the two 
 stroke antennae and then both start back to the food; before long other 
 members of the colony swarm to the prize. It has been thought that 
 the odor of the food or some other odor, left by the first ant, serves as a 
 trail for the other ants to follow. Bethe, indeed, infers from his ex- 
 periments that this phenomenon is purely mechanical and involves no 
 psychical qualities on the part of the ants. His own experiments, how- 
 ever, show that one ant can inform another by means of an odor as to 
 the whereabouts of food — which is certainly one form of communication. 
 
 Ants avoid sunlight as a rule but prefer rays of lower refrangi- 
 bility to those of higher. Upon exposing ants to the colors of the spec- 
 trum, as transmitted through glasses of different colors, Lubbock found 
 that they congregated in greatest numbers under the red glass and that 
 the numbers diminished regularly from the red to the violet end of the 
 spectrum, there being very few individuals under the violet glass. 
 
 Miss Fielde, experimenting with queens, workers and young of 
 Stenamma fulvum piceum in an artificial nest, covered half the nest with 
 orange glass and half with violet. "The ants removed hastily from 
 under the violet as often as an interchange of the panes was made, once 
 or twice a day, for about twenty days. Thereafter they became indif- 
 ferent to the violet rays." "The plasticity of the ants is remarkably 
 shown in their gradually learning to stay where they were never disturbed 
 by me, under rays from which their instincts at first withdrew them." 
 
 Ants are sensitive not only to the different colors of the spectrum 
 
INTERRELATIONS OF INSECTS 293 
 
 but also to the ultra-violet rays, which produce no appreciable effect 
 on the human retina (though they induce chemical changes) . If obliged 
 to choose between the two, ants prefer violet to ultra-violet rays, as 
 Lubbock found. If, however, the ultra-violet rays are intercepted, by 
 means of a screen of sulphate of quinine or bisulphide of carbon, the ants 
 then collect under the screen in preference to under the violet rays. 
 
 From lack of experience we can form no adequate idea as to the range 
 of sensation in ants or other insects. Ants can taste substances that we 
 cannot, and vice versa. They show no response to sounds of human 
 contrivance, yet many of them possess stridulating organs and organs 
 that are doubtless auditory; whence it may be inferred that ants can 
 communicate with one another by means of sounds. In rare instances 
 the stridulation of an ant can impress the human ear, as in a species of 
 Atta mentioned by Sharp. 
 
 Experiments show that ants, as well as bees and wasps, find their 
 way back to the nest, not by a mysterious "sense of direction," but by 
 remembering the details of the surroundings, and in the case of ants, by 
 means of an odor left along the trail. 
 
 In studying the habits of ants, the greatest care must be exercised in 
 order to discriminate between actions that may be regarded as purely 
 instinctive and those that may indicate some degree of intelligence. If 
 any insects show signs of intelligence, the social Hymenoptera do; but 
 in the study of this recondite subject, false conclusions can be avoided 
 only by observation and experimentation of the most critical kind. 
 
 Hunting Ants.^ — Some ants, as Formica fusca, live by the chase, 
 hunting their prey singly. The African "driver ants " {Anomma arcens) , 
 although bhnd, hunt in immense droves, consuming all the animal refuse 
 in their way, devouring all the insects they meet, and not hesitating to 
 attack all kinds of vertebrates; these ants ransack houses from time to 
 time and clear them of all vermin, though they themselves are a great 
 nuisance to the householder. The Brazilian species of Eciton (Fig. 290, 
 jB, C) have similar habits and are likewise blind, or else have but a single 
 lens on each side of the. head. These insects hunt in armies of hundreds 
 of thousands, to the terror of every animate thing they come across* 
 They have no permanent abode, but now and then appropriate some 
 convenient hole for the purpose of raising a new brood of marauders. 
 
 Slave-making Ants.— It is a fact that some ants make slaves of 
 other species. Formica sanguinea, for example, will attack a colony of 
 Formica fusca, kill its active members in spite of their determined re- 
 sistance, kidnap the larvae and pupae and carry them home, where the 
 
294 
 
 ENTOMOLOGY 
 
 captives receive every care, and at length, as imagines, serve their mas- 
 ters as faithfully as they would serve their own species. In the Alle- 
 ghanies, according to McCook, colonies of F.fusca occur where there are 
 no "red ants" {F. sanguinea) , but are hard to find where the enslaving 
 species occurs. 
 
 Although F. sanguinea can exist very well without slaves, Polyergus 
 rufescens, of Europe, is notoriously dependent upon their services, it 
 being doubtful whether it is capable of feeding itself. This species is 
 powerful as a warrior, but its mandibles are of little use, except to pierce 
 the head of an adversary. Strongylonotus is still more helpless, while 
 Aner gates (also of Europe) is said to depend absolutely upon its slaves. 
 
 Polyergus lucidus occurs in the AUeghanies, where the colonies of this 
 species, according to McCook, contain large numbers of the workers of 
 Formica schaufussi. The masters are good fighters but do no other 
 work, and have not been seen to feed themselves, though they may often 
 be seen feeding from the mouths of their slaves. 
 
 Honey Ants.— Among ants in general, the workers that stay in the 
 
 Pig. 289.- 
 
 -Honey ants, Myrmecocyslus melliger, clinging to the roof of their chamber. 
 About natural size. — After McCook. 
 
 nest receive food from the mouths of the foragers — a custom which has 
 led to the extraordinary conditions found in the "honey ants," in which 
 certain of the workers sacrifice their own activity in order to act as liviilg 
 reservoirs of food (repletes) for the benefit of the other members of the 
 colony. This remarkable habit has arisen independently, in different 
 genera of ants, in North America, Australia and South Africa, as Lub- 
 bock observes. 
 
INTERRELATIONS OF INSECTS 295 
 
 The honey ant whose habits are best known, through the studies of 
 McCook and others, is Myrmecocystus melliger, of Mexico, New Mexico 
 and southern Colorado. In this species some of the workers hang slug- 
 gishly from the roof of their little dome-like chamber, several inches 
 underground, and act as permanent receptacles for the so-called honey, 
 which is a transparent sugary exudation from certain oak-galls; it is 
 gathered at night by the foraging workers and regurgitated to the 
 mouths of the "honey-bearers," whose crops at length become dis- 
 tended with honey to such an extent that the insects (Fig. 289) look 
 like so many little translucent grapes or good-sized currants. This 
 stored food is in all probability drawn upon by the other ants when 
 necessary. 
 
 Leaf-cutting Ants. — The most dangerous foes to vegetation in 
 tropical America are the several species of AUa (Fig. 290, A). Living 
 
 Fig. 290. — A, leaf -cutting ant, Alia cephaloies. B, wandering ant, Eciton drepanophorum; 
 C, Eciton omnivorum. Natural size. — After Shipley. 
 
 in enormous colonies and capable of stripping a tree of its leaves 
 in a few hours, these formidable ants are the despair of the planter; 
 where they are abundant it becomes impossible to grow the orange, 
 coffee, mango and many other plants. These ants dig an extensive 
 underground nest, piling the excavated earth into a mound, sometimes 
 thirty or forty feet in diameter, and making paths in various directions 
 from the nest for access to the plants of the vicinity; Belt often found 
 these ants at work half a mile from their nest; they attack flowers, 
 fruits and seeds, but chiefly leaves. Each ant, by laboring four or five 
 minutes, bites out a more or less circular fragment of a leaf (Fig. 291) 
 and carries it home, or else drops it for another worker to carry; and 
 two strings of ants may be seen, one carrying their leafy burdens toward 
 the nest, the other returning for more plunder. 
 
 The use made of these leaves has been the subject of much discus- 
 sion. Belt found the true explanation, but it remained for Moller to 
 investigate the subject so thoroughly as to leave no room for doubt. 
 The ants grow a fungus upon these leaves and use it as food. The bits 
 of leaves are kneaded into a pulpy, spongy mass, upon which the 
 
296 
 
 ENTOMOLOGY 
 
 fungus at length appears. The food for the sake of which the ants 
 carry on their complex operations consists of the knobbed ends of 
 fungus threads (Fig. 292), and these bodies, rich in fluid, form the most 
 important, if not the sole food of the leaf-cutting ants. By assiduously 
 weeding out all foreign organisms the ants obtain a pure culture of the 
 
 fungus, and by pruning the fungus 
 they keep it in the vegetative con- 
 dition and prevent its fructification; 
 under exceptional circumstances, 
 nevertheless, the fungus develops 
 aerial organs of fructification of the 
 
 Fig. 291. — A, B, cuts made Fig. 292. — Fungus clumps {Roziles 
 
 in Cuphea leaves in four or five gongylophora) cultivated by ants of the 
 
 minutes by Atta discigera; genus A Ha. Greatly magnified. — After 
 
 natural size. C, Atta dis- Moller. 
 
 cigera transporting severed 
 fragments of leaves; reduced. — 
 After Moller. 
 
 agaricine type, but this species (Rozites gongylophora) has never been 
 found outside of ants' nests. The pecuHar clubbed threads were 
 produced by Moller in artificial cultures and are not spores, but prod- 
 ucts of cultivation. Other ants are known to cultivate other kinds 
 of fungi for similar purposes. 
 
 McCook has found a leaf-cutting ant {Atta fervens) in Texas, and 
 mentions that it cuts circular pieces out of leaves of chiefly the live-oak, 
 these being dropped to the ground and taken to the nest by another 
 set of workers. He records an underground tunnel of Atta fervens 
 which extended 448 feet from the nest and then opened into a path 185 
 feet in length; the tunnel was 18 inches below the surface on an average, 
 though occasionally as deep as 6 feet, and the entire route led with 
 remarkable precision to a tree which was being defoHated. 
 
INTEREELATIONS OF INSECTS 297 
 
 The same observer has given also a brief account of a leaf-cutting ant 
 that lives in New Jersey. This species {Trachymyrmex septentrionalis) 
 cuts the needle-like leaves of seedling pines into little pieces, which are 
 carried to the nest. Two columns of workers may be seen, one com- 
 posed of individuals returning to the nest, each with a piece of pine 
 needle, the other of outgoing workers. The nest is a simple structure, 
 extending some seven inches underground and ending in a chamber in 
 which are several small pulpy balls, consisting probably of masticated 
 leaves. Further studies upon our own leaf-cutting ants, modeled after 
 the admirable studies of Moller, are much to be desired. 
 
 Harvesting Ants. — Lubbock observes that some ants collect the 
 seeds of violets and grasses and preserve them carefully for some purpose 
 as yet unknown. From such a beginning as this may have arisen the 
 extraordinary habits of the agricultural, or harvesting, ants, of which 
 some twenty species are known from various parts of the world. 
 
 The Texas species Pogonomyrmex barbatus, studied by Lincecum 
 and by McCook, clears away the herbage around its nest (even plants 
 several feet high and as thick as a man's thumb) and levels the ground, 
 forming a disk often lo or 12 and sometimes 15 to 20 feet in diameter, 
 from which radiating paths are made, from 60 to 300 feet in length. 
 The ants go back and forth along these roads, carrying to the nest seeds 
 which they have collected from the ground or else have cut from plants ; 
 these seeds are stored in "granaries" several feet underground and are 
 eventually used as food. The ants prefer the seeds of a grass, Aristida 
 oligantha, but the oft-repeated statement that they sow the seeds of this 
 "ant-rice," guard it and weed it, is denied by Wheeler. 
 
 Notwithstanding the elaborate studies of McCook upon this subject, 
 there still remain not a few essential questions to be answered. 
 
 Myrmecophilism. — To add to the complexity of ant-life, the nests 
 of ants, when at all extensive, are frequented by a great variety of other 
 arthropods, which on account of their association with ants are termed 
 myrmecophiles. Most of* these are insects, of which Wasmann has 
 catalogued 1,200 species, but not a few are spiders, mites, crustaceans, 
 etc. Though the diverse relations between myrmecophiles and ants 
 are but partially understood, these aliens may for convenience be con- 
 sidered under five groM^?>: captives^ guests, visitors, intruders dind parasites. 
 
 Captives. — Besides enslaving other species, as already mentioned, 
 ants make use of aphids and some coccids for the sake of their palatable 
 products. The attendance of ants upon colonies of plant lice is a com- 
 mon occurrence and one that repays careful observation. With the 
 
298 ENTOMOLOGY 
 
 aid of a hand-lens, one may see the ants hastening about among the 
 plant lice and patting them nervously with the antennae until at length 
 some aphid responds by emitting from the end of the abdomen a glisten- 
 ing drop of watery fluid, which the ant snatches. This fluid, contrary 
 to prevalent accounts, is not furnished by the so-called honey-tubes of 
 the aphid, but comes from the alimentary canal; the " honey- tubes " are 
 glandular indeed, but are probably repellent in function. In some 
 instances ants give much care to their aphids, for example covering them 
 with sheds of mud, which are reached through covered passageways. 
 More than this, however, some ants actually collect aphid eggs and pre- 
 serve them over winter as carefully as they do their own eggs. In one 
 such instance Lubbock found that the aphids upon hatching, after six 
 months, were brought out by the ants and placed upon young shoots of 
 the English daisy, their proper food plant. In our own country, as 
 Forbes has discovered, the eggs of the corn root louse {Aphis maidira- 
 dicis) are collected in autumn by ants (especially of the genus Lasius) 
 and stored in the underground nests. In winter the eggs are taken to 
 the deepest parts of the nest, and on bright spring days they are brought 
 up and even scattered about temporarily in the sunshine; while if a nest 
 is opened, the ants carry off the aphid eggs as they would their own. 
 In spring the ants tunnel to the roots of pigeon grass and smar tweed, 
 seize the aphids and carry them to these roots, and later to the roots of 
 Indian corn. Throughout the year the ants exercise supervision over 
 these aphids; occasionally, as Forbes says, an ant seizes a winged louse 
 in the field and carries it down out of sight, and in one such instance it 
 appeared that the wings had been gnawed away near the body, as if to 
 prevent the escape of the louse. Similar relations exist also between 
 ants and some species of scale insects. 
 
 Guests. — Though Aphididae and Coccidae are able almost always to 
 live without the help of ants, there are some insects which have never 
 been found outside the nests of ants. Most of these insect guests are 
 beetles, notably Staphylinidae and Pselaphidae. The rove-beetles make 
 themselves useful by devouring refuse organic matter, and these scav- 
 engers are unmolested by the ants with which they live. A few myrme- 
 cophilous beetles furnish their hosts with a much-coveted secretion and 
 receive every attention from the ants, which clean these valuable beetles 
 and even feed them mouth to mouth, as the ants feed one another. 
 Lomechusa (Fig. 293) is one of these favored guests, as it has abdominal 
 tufts of hairs from which the ants secure a secreted fluid. Atemeles 
 (Fig. 294) is another; it solicits and obtains food from the mouth of a 
 
INTERRELATIONS OF INSECTS 
 
 299 
 
 foraging ant as if it were an ant itself. In the Alleghanies, Atemeles 
 cava occurs in the nests of Formica rufa, and is much prized by this ant 
 on account of the fluid which the beetle secretes from glandular hairs 
 on the sides of the abdomen. 
 
 The beetle Claviger has at the base of each elytron a tuft of hairs, 
 
 Fig. 293. — Lomechusa strumosa being freed of mites by Dinarda dentata. — After Wasmann. 
 
 Fig. 294. — Atemeles emarginatus being fed by an ant, Myrmica scabrinodis. — After 
 
 Wasmann. 
 
 which the ants lick persistently. This beetle is blind and appears to be 
 incapable of feeding itself; for when deprived of ant-assistance it dies, 
 even though surrounded by food. These cases of symbiosis, or mutual 
 benefit, are well authenticated. 
 
 Visitors.— Many myrmecophilous insects are not restricted to ants' 
 nests, but are free to enter or to leave. This is true of such Staphylinidae 
 as visit formicaries simply for shelter or to feed upon detritus, and these 
 visitors are treated with indifference by the ants. 
 
300 
 
 ENTOMOLOGY 
 
 Intruders. — Not so, however, with species that are inimical to the 
 interests of the ants, such as many species of StaphyUnidae and His- 
 teridae, which steal food from the ants, kill them or devour their larvae 
 or pupae at every opportunity. The ants are hostile to these marauders, 
 though the latter often escape through their agihty or else rely upon 
 their armor for protection. Quedius brevis and Myrmedonia, as Schwarz 
 observes, are soft-bodied forms which remain beside the walls of the gal- 
 leries or near the entrance of a nest and attack solitary ants; while 
 Hetcerius, which mixes with the ants, is protected by its hard and smooth 
 covering, under which the legs and antennae can be withdrawn. Such 
 an enemy is an unavoidable evil from the standpoint of an ant. 
 
 Fig. 295. — Atelura formicaria stealing food from a pair of ants. — After Janet. 
 
 Janet has described the amusing way in which an audacious species 
 of Atelura steals food from the very mouths of ants, As is well known, 
 ants are accustomed to feed one another from mouth to mouth. When 
 the foragers, filled with honey or other food, return to the nest, they are 
 solicited for food by those that have remained at home; as a forager and 
 a beggar stand head to head, the former disgorges small drops of food, 
 which are seized by the latter. While a pair of ants are engaged in this 
 performance (Fig. 295), and a drop of honey is being passed, the Atelura 
 rushes in, grabs the drop and hurries away. As might be expected, 
 these interlopers are constantly being chased by their victims from one 
 corner of the nest to another. 
 
 Parasites.^-Nematode worms occupy the pharyngeal glands of ants; 
 larvae of Stylops inhabit their bodies; more than thirty kinds of mites 
 attach themselves to the heads or feet of ants; while Chalcididae and 
 Proctotrypidae parasitize ants' eggs. 
 
INTERRELATIONS OF INSECTS 3OI 
 
 Origin of the Social Habit. — Wheeler regards "trophallaxis," 
 meaning exchange of nourishment, as the source of the social habit in 
 wasps, ants, and termites; though admitting that the phenomenon has 
 not been observed in the social bees. He says: "If we confine our 
 attention largely to the ants, I believe it can be shown that trophallaxis, 
 originally developed as a mutual trophic relation between the mother 
 insect and her larval brood, has expanded with the growth of the 
 colony like an ever-widening vortex till it involves, first, all the adults 
 as well as the brood and therefore the entire colony; second, a great 
 number of species of ahen insects that have managed to get a foothold 
 in the nest as scavengers, praedators or parasites (symphily); third, 
 alien social insects — i.e., other species of ants (social parasitism); 
 fourth, alien insects that live outside the nest and are ''milked" by 
 the ants (trophobiosis) ; and, fifth, certain plants which are visited or 
 sometimes partly inhabited by the ants (phytophily)." 
 
CHAPTER XI 
 
 INSECT BEHAVIOR 
 
 The subject of insect behavior will be considered under three heads ; 
 (i) Tropisms, (2) Instinct, (3) IntelHgence. 
 
 I. Tropisms 
 
 Environmental influences, such as light, temperature or moisture, 
 may control the direction of locomotion of an organism by determining 
 the orientation of its body. The reaction of the organism under these 
 circumstances is known as a tropic, or tactic, reaction. A moth, for ex- 
 ample, flies toward a flame — is positively phototropic; a cockroach, on 
 the contrary, avoids the Ught — is negatively phototropic. A plant turns 
 toward the sun — in other words, is positively heliotropic. 
 
 An insect flies toward the Ught as inevitably and as mechanically as 
 a plant turns toward the sun; indeed, the two phenomena are funda- 
 mentally the same. Some students prefer, however, to use the term 
 taxis for bodily movements of motile organisms, and the term tropism 
 for turning movements of fixed organisms. 
 
 The study of tropic reactions has already illuminated the entire 
 subject of the behavior of organisms and placed it on a rational basis, 
 and the complex tropisms of insects offer a fresh and large field to the 
 investigator. 
 
 Chemotropism. — Positive and negative chemotropism, as Wheeler 
 observes, "are among the most potent factors in the Uves of insects." 
 Insects are affected positively or negatively by such substances as can 
 affect their end-organs of smell or taste. Positive chemotropism 
 enables many insects to find their food or their mates; and negative 
 chemotropism enables them to avoid injurious substances. This 
 negative reaction on the part of other organisms is made use of also by 
 such insects as emit repellent odors. 
 
 A maggot orients its body with reference to a source of food and then 
 moves toward the food just as mechanically as a moth flies to a flame. 
 The maggot, as Loeb maintains, is influenced chemically by the radiat- 
 ing diffusion from a piece of meat, and follows a line of diffusion to the 
 
 302 
 
INSECT BEHAVIOR 303 
 
 center of diffusion in much the same way that a moth follows a ray of 
 light to its source. In both cases a stimulus affects muscular tissue; 
 the animal orients its body until the muscular tension is symmetrically 
 distributed, and then locomotion brings the animal to the source of the 
 stimulus, whether it be food or light. 
 
 The remarkable "instinctive" action of the fly in laying her eggs on 
 meat is due, according to Loeb, simply to the fact that both the fly and 
 the maggot have the same kind of positive chemotropism. Similarly 
 also in the case of such butterflies or other insects as lay their eggs on a 
 special kind of plant. It is certain that "neither experience nor voHtion 
 plays any part in these processes." 
 
 W. M. Barrows determined experimentally that the well-known 
 pomace fly, Drosophila ampelophila, is positively chemotropic to amyl 
 alcohol, ethyl alcohol, acetic acid, lactic acid and other chemical sub- 
 stances, all of which occur in fermenting fruits. The fly finds its food, 
 not by sight, but by smell, and when this sense is lost it reaches its food 
 only by accident. The olfactory sense organs that are concerned with 
 finding food are located in the third or terminal segment of the antenna. 
 When one antenna is lost and the other antenna is stimulated by food 
 odor, circus movements are carried out in such a way as to prove that 
 the fly orients normally by an unequal stimulation of the antennae. 
 Drosophila, when stimulated by a weak food odor, first shows random 
 movements, i.e., it attempts to find the food by the method of trial and 
 error, but as the fly passes into an area of greater stimulation, these 
 movements give way to a direct orientation. 
 
 Hydrotropism. — Wheeler observed that beetles of the genera Hali- 
 plus and Hydroporus were positively hydrotropic; that when released on 
 the shore from a bunch of water plants, they scrambled toward the lake, 
 twenty feet away. Collectors take advantage of the negative hydro- 
 tropism of Bembidion, Elaphrus, Omophron and other shore-dwelling 
 beetles by splashing the water upon the dry bank, when the beetles leave 
 their places of concealment and are easily caught. 
 
 It is well known that after a rain ants carry their young out into the 
 sunshine, though when the upper parts of the nest become too dry, the 
 ants transfer their eggs, larvae and pupae to lower and moister galleries. 
 In these instances, however, we have to deal with thermotropism as well 
 as hydrotropism. 
 
 Thigmotropism. — Negative thigmotropism (stereotropism) as dis- 
 played in the withdrawal from contact, is a common phenomenon 
 among animals, from Protozoa to Vertebrata, and is often conducive 
 
304 
 
 ENTOMOLOGY 
 
 to the safety of an organism; though the negative response occurs 
 none the less, whether it is to prove useful or not, and occurs as auto- 
 matically as the collapse of a sensitive plant at a touch. 
 
 Positive thigmotropism is less common, though nevertheless wide- 
 spread among animals. Protozoa and Infusoria cling to solid bodies 
 and become aggregated about them. Cockroaches squeeze themselves 
 into crevices until their bodies come into close contact with surrounding 
 surfaces. A moth, Pyrophila (Amphipyra) pyramidoides, is accustomed 
 to squeeze into crevices under loose bark or elsewhere, though this habit, 
 though doubtless protective, is not performed/or the purpose of self-con- 
 cealment. That this is not a case of negative phototropism, it was 
 proved by Loeb, who wrote -."Iplaced some of these animals in a box, one- 
 half of which was covered with a non- transparent body, the other half with 
 glass. I covered the bottom of the box with small glass plates which 
 rested on small blocks, and were raised just enough from the bottom to 
 allow an Amphipyra to get under them. Then the Amphipyra collected 
 under the little glass plates, where their bodies were in contact with 
 solid bodies on every side, not in the dark corner where they would 
 have been concealed from their enemies. They even did this when in so 
 doing they were exposed to direct sunlight. This reaction also occurred 
 when the whole box was dark. It was then impossible for anything 
 but the stereotropic [thigmotropic] stimuli to produce the reaction." 
 
 Among the water-striders, Gerridae, thigmotropism is strongly in 
 evidence at the inception of and during the hibernation period. The 
 gerrids hibernate in large groups or clusters under dead leaves, in holes 
 in banks of streams, under logs, etc., with their bodies in close contact 
 with the substratum. The acts of crawling into and remaining in such 
 places are evidently due to the contact stimuH that impinge on them at 
 such times (C. F. C. Riley). 
 
 Rheotropism. — Fishes swimming or heading directly against a cur- 
 rent of water illustrate positive rheotropism. When facing the current, 
 the resistance of the water is symmetrically distributed on the body of 
 the animal and is met by symmetrical muscular action, in the most eco- 
 nomical manner. Many aquatic insects offer such examples of rheo- 
 tropism, either positive or negative. 
 
 E. P. Lyon gives, however, a different explanation. He found that 
 fishes orient themselves just as well when they are put into a closed 
 glass bottle, which is dragged through the water, although in this case 
 they are not under the influence of any friction from the current. When 
 the bottle is not moved the fishes swim in any direction inside the 
 
INSECT BEHAVIOR 305 
 
 bottle. It is obviously the motion of the retina images of the objects 
 on the bank of the brook which causes the "rheotropic" orientation of 
 fishes. When driven backward by the current or when dragged back- 
 ward in a bottle through the water, the objects on the bank of the river 
 seem to move in the opposite direction. The animal being compelled 
 to keep the same object fixed, an apparent forward motion of the fixed 
 object changes the muscles of the fins in such a sense as to cause the 
 animal to follow the fixed object automatically. When such rheotropic 
 fishes were kept in an aquarium and a white sheet of paper with black 
 stripes was moved constantly in front of the aquarium the fishes ori- 
 ented themselves against the direction in which the paper and its 
 stripes moved. The phenomenon was more marked in young than in 
 older specimens. All the phenomena of rheotropism ceased in the dark 
 or when the fishes were blind. (J. Loeb.) 
 
 Anemotropism. — Various flies orient the body with reference to the 
 direction of the wind. Wheeler observed swarms of the male of Bibio 
 alhipennis poising in the air, with all the flies headed directly toward the 
 gentle wind that was blowing. If the wind shifted, the insects at once 
 changed their position so as again to face to windward; a strong wind, 
 however, blew them to the ground. The males of an anthomyiid 
 {Ophyra leucostoma), according to the same naturalist, hover in swarms 
 in the shade for hours at a time; if the breeze subsides they lose their 
 definite orientation, but if it is renewed they face the wind with mihtary 
 precision. In Syrphidae, he finds, either males or females are positively 
 anemotropic. Midges of the genus Chironomus, which on summer days 
 dance in swarms for hours over the same spot, orient themselves to 
 every passing breeze. So also in the case of Empididas, which Wheeler 
 has observed swarming in one spot every day for no less than two weeks, 
 possibly on account of "some odor emanating from the soil and attract- 
 ing and arresting the flies as they emerged from their pupas." 
 
 The Rocky Mountain locusts "move with the wind and when the 
 air-current is feeble are headed away from its source;" when the wind is 
 strong, however, they turn their heads toward it. 
 
 Anemotropism and rheotropism are closely allied phenomena. As 
 Wheeler says, "The poising fly orients itself to the wind in the same way 
 as the swimming fish heads upstream," adjusting itself to a gaseous 
 instead of a liquid current. "In both cases the organism naturally 
 assumes the position in which the pressure exerted on its surface is sym- 
 metrically distributed and can be overcome by a perfectly symmetrical 
 action of the musculature of the right and left halves of the body." 
 
3o6 
 
 ENTOMOLOGY 
 
 Geotropism.- — Gravity frequently determines the orientation and 
 direction of locomotion of an animal. A freshly emerged moth hangs 
 with the abdomen downward and remains in this position until the 
 wings have expanded. Certain dolichopodid flies found on the bark 
 of trees "rest or walk with the long axis of the body perpendicular to 
 the earth and parallel with the long axis of the trunk of the tree and the 
 head pointing upwards. • When disturbed they fly off, but very soon 
 alight nearer the earth and again walk upward." (Wheeler.) Cocci- 
 nellidas (lady beetles) and cockroaches are also negatively geotropic. 
 
 The latter insects, as Loeb 
 has observed, tend to leave 
 a horizontal surface but 
 come to rest on a surface 
 that is vertical or as nearly 
 so as possible. 
 
 Wheeler says, " Geotro- 
 pic as well as anemotropic 
 orientation is not altered 
 for the sake of response to 
 light. Even if the insect 
 be strongly heliotropic, as 
 is the case inmost Diptera, 
 it orients itself to the wind 
 or to gravity no matter 
 whence the light may fall." 
 Experiments by W. H. 
 
 Fig. 296. — yl , tracks made on paper by a larva of Cole shoW that the pomace 
 
 Lucilia casar moving out of a spot of ink under the n t-w .7-7 .7 
 
 influence of light; a and B show respectively the first AY' i^rOSOpHlla ampelO- 
 
 and second directions of the light. jB, tracks made in -hfiHa when creeoinff 
 
 the dark.— After Pouchet. r j ^ F a> 
 
 reacts negatively to grav- 
 ity, to a centrifugal force which is equal to or sUghtly greater than 
 gravity, and to air currents without regard to other stimuli. Gravity 
 is, then, a kinetic as well as a directive stimulus. The stimuli caus- 
 ing these reactions are probably received by the sensory nerves of the 
 leg muscles. (Cole.) . 
 
 Phototropism.— It is a matter of common observation that house 
 flies, butterflies, bees and many other diurnal insects fly toward the 
 light; and that cockroaches and bedbugs avoid the light. These are 
 familiar examples of phototropism {heliotropism) or the ''control of the 
 direction of locomotion by light." The phototropic response is 
 
INSECT BEHAVIOR 307 
 
 either positive or negative according as the organism moves, respec- 
 tively, toward or away from the source of light. Maggots of Lucilia 
 ccesar and of many other flies are negatively phototropic as a rule (Fig. 
 296, A), but in the absence of light (other directive stimuH being 
 excluded, of course) wander about indifferently (Fig. 296, B). 
 
 Do the different rays of the spectrum differ in phototropic power? 
 This question has occurred to many investigators, who have found that, 
 in general, the rays of shorter wave length, as violet or blue, are more 
 effective than those of longer wave length, as yellow or red; the latter in 
 fact acting like darkness. Ants avoid violet rays as they would avoid 
 direct sunlight, but carry on their operations under yellowish red Hght 
 as they would in darkness. Miss Fielde has made use of this fact in 
 studying the habits of ants, by using as a cover for her artificial formi- 
 caries an orange-red sheet of glass such as the photographer uses for his 
 dark room. Though ants avoid violet rays, they prefer them to ultra- 
 violet rays, as Lubbock found. 
 
 These responses to light are inevitable on the part of the organism, 
 whether they are beneficial or harmful, and it is now becoming recog- 
 nized that the reactions of both plants and animals to light are funda- 
 mentally the same. 
 
 Phototaxis and Photopathy. — A phototropic organism, if bilater- 
 ally symmetrical, orients itself with the head directly toward or else 
 directly away from the source of light and moves toward or away from 
 the light, as the case may be. In either event the long axis of the 
 organism becomes parallel with the rays of light. Now a ray of light is 
 ever diminishing in intensity from its source, and it would seem that 
 differences of intensity along the paths of light rays determine the orien- 
 tation and consequent direction of locomotion of the organism. Some 
 investigators, however, distinguish between the effects of intensity of 
 light and those of its direction. Thus by ingeniously contrived experi- 
 ments, it has been found, apparently, that Protista (Strasburger), 
 Daphnia (Davenport and Cannon) and the caterpillars of Porthesia 
 (Loeb) move toward a source of light even while, in so doing, they are 
 passing into regions of less intensity of illumination. For this migration 
 as determined by the direction of the light rays, the term phototaxis is by 
 some authors (as Davenport) reserved. Usually, however, the 
 direction of locomotion does depend on differences of intensity, without 
 regard to the direction whence the light comes. This "migration 
 towards a region of greater or less intensity of light" has been termed 
 photopathy, and organisms are said to be photophil or photophob, accord- 
 
308 ENTOMOLOGY 
 
 ing as they move, respectively, toward or away from a more intensely 
 illuminated area. 
 
 Verworn and others maintain, however, that differences of intensity 
 are sufficient to account for all phototropic phenomena. 
 
 Optimum Intensity. — It has been found that there is a certain 
 optimum degree of light, differing according to the organism, toward 
 which the organism will move, from either a region of greater illumina- 
 tion or one of less. The organism appears to be attuned to a "certain 
 range of intensity." This attunement is used by Davenport to explain 
 apparent anomalies between the response to light of a butterfly and 
 that of a moth. Butterflies are positively phototropic to sunlight and 
 most moths are negatively so. Why, then, do moths fly toward a lamp 
 or an electric light? The answer is given that the moth is positively 
 phototropic up to a certain intensity of light, at which it becomes nega- 
 tively phototropic. "Butterflies are attuned to a high intensity of 
 light,. moths to a low intensity; so that bright sunlight, which calls 
 forth the one, causes the other to retreat. On the other hand, a light 
 like that of a candle, so weak as not to stimulate a butterfly, produces a 
 marked response in the moth." (Davenport.) 
 
 The circhng of moths and other insects about a Hght is a matter of 
 common observation, an explanation for which has been given by Loeb. 
 Loeb says, "If a moth be struck by the light on one side, those muscles 
 which turn the head toward the light become more active than those of 
 the opposite side, and correspondingly the head of the animal is turned 
 toward the source of light. As soon as the head of the animal has this 
 orientation and the median-plane (or plane of symmetry) comes into the 
 direction of the rays of light, the symmetrical points of the surface of the 
 body are struck by the rays of light at the same angle. The intensity 
 of light is the same on both sides, and there is no reason why the animal 
 should turn to the right or left, away from the direction of the rays of 
 light. Thus it is led to the source of the light. Animals that move 
 rapidly (like the moth) get into the flame before the heat of the flame has 
 time to check them in their flight. Animals that move slowly are 
 affected by the increasing heat as they approach the flame; the high 
 temperature checks their progressive movement and they walk or fly 
 slowly about the flame." As Loeb insists, the moth "does not fly into 
 the flame out of 'curiosity,' neither is it 'attracted' by the light; it is 
 only oriented by it and in such a manner that its median-plane is 
 brought into the direction of the rays and its head directed toward the 
 
INSECT BEHAVIOR 309 
 
 source of light. In consequence of this orientation its progressive 
 movements must lead it to the source of light." 
 
 Factors Influencing Phototropism. — The response of an organism 
 to light is influenced by previous exposure to light, by temperature, 
 moisture, nutrition and other factors, all of which have to be taken into 
 account in experiments on phototropism. 
 
 Loeb found that larvae of the brown-tail moth, Euproctis chrysor- 
 rhcea, driven by the warm sunshine out of the nest in which they have 
 hibernated, crawl upward to the tips of branches and feed upon the 
 buds and new leaves. This self-preservative "instinct" is purely a 
 response to light. The caterpillars are positively phototropic, and as 
 the horizontal components of the surrounding light neutralize each 
 other, only the light from above is effective as a stimulus to orientation. 
 After feeding, however, the larvae are no longer positively phototropic 
 and crawl downward; in other words, they are positively phototropic 
 only so long as they are unfed. Here the kind of phototropism is 
 dependent upon nutrition. 
 
 Phototropism may be overruled by chemotropism and influenced by 
 conditions of metabolism, as Parker found for the butterfly Vanessa 
 antiopa. In his words: Vanessa antiopa, in bright sunlight, comes to 
 rest with the head away from the source of light, that is, it is negatively 
 phototropic, when the surface on which it settles is not perpendicular 
 or very nearly perpendicular to the direction of the sun's rays. When, 
 however, this surface is'perpendicular to the sun's rays the insect settles 
 without reference to the direction of the rays. When feeding or near 
 food [such as running sap] the butterflies do not respond phototropically. 
 
 This negative phototropism is seen only in intense sunlight and after 
 the butterfly has been on the wing, i.e., after a certain state of metab- 
 olism has been established. 
 
 V. antiopa creeps and flies toward a source of light, that is, it is 
 positively phototropic in its locomotor responses. Positive photo- 
 tropism also occurs in intense sunKght, and is not dependent upon any 
 particular phase of metabolism. 
 
 Both negative and positive phototropism in this species are inde- 
 pendent of the "heat rays" of sunlight. 
 
 The position assumed in negative phototropism exposes the color 
 patterns of the wings to fullest illumination, and probably has to do 
 with bringing the sexes together during the breeding season. 
 
 To these may be added other important conclusions of Parker's; 
 
3IO ENTOMOLOGY 
 
 No light reactions are obtained from the butterfly when shadows are 
 thrown upon any part of the body except the head. When one eye is 
 painted black the butterfly creeps or flies in circles ("circus move- 
 ments") with the unaffected eye always toward the center. When both 
 eyes are painted black all phototropic responses cease and the insect fldes 
 upward. Butterflies with normal eyes liberated in a perfectly dark room 
 come to rest near the ceiling. _ This upward flight in both cases is due 
 to negative geotropism, not to phototropic activity. 
 
 V. antiopa does not discriminate between lights of greater or less 
 intensity provided they are all of at least moderate intensity and of 
 approximately equal size. V. antiopa does discriminate between light 
 derived from a large luminous area and that from a small one, even when 
 the hght from these two sources is of equal intensity as it falls on the 
 animal. These butterflies usually fly toward the larger areas of light. 
 This species remains in flight near the ground because it reacts positively 
 to large patches of bright sunlight rather than to small ones, even 
 though the latter, as in the case of the sun, may be much more 
 intense. 
 
 V. antiopa retreats at night and emerges in the morning, not 
 so much because of light differences, as because of temperature 
 changes. On warm days it will, however, become quiet or active, 
 without retreating, depending upon a sudden decrease or increase of light. 
 
 The maggots of the muscid Phormia regina are, as the author has 
 observed, negatively phototropic until full grown, when they become 
 positively phototropic for an hour or less, leave the decaying matter in 
 which they have developed and wriggle along the ground toward the 
 sun; or if the sunhght is diffused by clouds, wander about aimlessly, 
 but at length bury themselves in the ground to pupate. Here the 
 positive phototropism just before pupation is adaptive. 
 
 The swarming of the honey bee is likewise a case of periodic positive 
 phototropism, as Kellogg has observed. 
 
 Winged ants of both sexes are strongly positively phototropic when 
 they swarm from the ground for the nuptial flight. After mating, 
 however, the female becomes negatively phototropic and positively 
 thigmo tropic; enters the ground, sheds her wings, and enters upon a 
 subterranean existence, during which she is intensely positively thigmo- 
 tropic. In connection with this subject, it is a significant fact that the 
 pomace fly, Drosophila, loses its phototropism when its wings are 
 removed artificially. 
 
 In autumn, gravid females of the mosquito, Culex pipiens, become 
 
INSECT BEHAVIOR 
 
 Strongly negatively phototropic and seek dark hibernation quarters, in 
 spite of warm temperatures that may prevail. If hibernating in a 
 warm place the mosquito becomes positively thigmotropic, and loses 
 its phototropism, prolonged exposure to strong lights producing no 
 response, though the insect responds actively to mechanical stimuli. It 
 is also negatively geotropic, as it always assumes a position with the 
 long axis of the body perpendicular to the earth and the head pointing 
 upward. (H. B. Weiss.) 
 
 Though adaptive in their results, these phototropic reactions can 
 scarcely be said to be performed on account of their usefulness. They 
 are performed anyway, and may result harmfully, as when they lead 
 a moth into a flame or, to take a more natural example, when they 
 expose an insect to its enemies. 
 
 Phototropism and thermotropism, either together or singly, as 
 Wheeler suggests, may explain the up and down migration of insects in 
 vegetation. "On cold, cloudy days few insects are taken because they 
 lurk quietly near the surface of the soil and about the roots of the vegeta- 
 tion, but with an increase in warmth and Hght they move upwards 
 along the stems and leaves of the plants, and, if the day be warm and 
 sunny, escape into the air." 
 
 F. Payne bred sixty-nine successive generations of the pomace fly, 
 Drosophila ampelophila in the dark without any resultant effect upon 
 either the eyes or the phototropism of the flies. 
 
 Drosophila is usually positively phototropic, but R. S. McEwen 
 obtained a mutant which is not phototropic; this character being 
 "linked" with a characteristic "tan" color. 
 
 Muscle Tension Theory. — Experiments by Professor S. J. Holmes 
 with water scorpions (Ranatra) showed that when the insect is illuminated 
 from the right side the legs on the right side are flexed and those of the left 
 side are extended, with a resultant locomotion toward the light. These 
 and other experiments "leave no doubt that the primary effects of light 
 consist in changes in the tension of muscles." (Loeb.) The muscle tone 
 is dependent upon the intensity of the light. If a positively phototropic 
 insect is illuminated from one side only it turns toward the light until the 
 muscle tension is equal on the two sides of the body; then locomotion is 
 inevitably toward the source of light. The stimulus is received through 
 the eyes. 
 
 Artificial Heliotropic Machine.— As illustrating the purely 
 mechanical nature of the response to light, the artificial heliotropic 
 machine, as described by Loeb, may be referred to. Briefly, this 
 
312 ENTOMOLOGY 
 
 electrically-operated machine, invented by Mr. John Hays Hammond, 
 Jr., is a box containing the mechanism and mounted on three wheels. 
 Two of these are geared to a driving motor and the third, on the rear 
 end, can be turned by means of electro-magnets in a horizontal plane. 
 A pair of five-inch condensing lenses on the front end look hke large 
 eyes. If a portable electric Hght, as a hand flashhght, be turned on 
 in front of the machine this will immediately move toward the light and 
 will follow the light all around the room in complex manoeuvers at a 
 speed of about three feet per second. Upon shading or switching 
 off the light the "dog," as it is called, can be stopped at once, but will 
 resume its uncanny movements as soon as the light reaches the "eyes" 
 of the machine in sufficient intensity. The orientation mechanism 
 possesses two selenium cells, one behind each "eye," which when influ- 
 enced by light effect the control of sensitive relays, analogous to the nerv- 
 ous system of a moth. These relays operate electro-magnetic switches, 
 which control the driving motors and the steering wheel. 
 
 The principle of this mechanism has been applied to the "Hammond 
 dirigible torpedo." 
 
 Thermotropism. — Ants are strongly thermotropic; they carry their 
 eggs, larvae and pupae from a cooler to a warmer place or vice versa, 
 and thus secure optimum conditions of temperature. Caterpillars and 
 cockroaches migrate to regions of optimum temperature. 
 
 In thermotropism it appears that the direction of heat rays has 
 little or no effect as compared with differences of intensity. 
 
 Tropisms in General. — Other kinds of tropisms are known, for 
 example, tonotropism, or the control of the direction of locomotion 
 by density, and electrotropism {galvanotropism) ; not to mention any 
 more. 
 
 All these phenomena are responses of protoplasm to definite stimuli 
 and are almost as inevitable as the response of a needle to a magnet. 
 
 The tropisms of the lower organisms have been experimented upon 
 by many skilled investigators, whose results furnish a broad basis for 
 the study of the subject in the higher animals. Even in the simplest 
 organisms, behavior is the resultant effect of several or many stimuli 
 acting at once, and the precise effect of each stimulus can be ascertained 
 only by the most guarded kind of experimentation; while in the higher 
 animals, with their complex organization, including speciahzed sense 
 organs, the study of behavior becomes intricate and cannot be carried 
 on intelligently without an extensive knowledge of the behavior of uni- 
 cellular organisms. The properties of protoplasm are the key to the 
 
INSECT BEHAVIOR 313 
 
 behavior of organisms. Furthermore, the study of tropic reactions is 
 complicated by the fact that they are due not only to external stimuli, 
 but also to Httle-understood internal stimuli, arising from unknown 
 conditions of the alimentary canal, muscles, reproductive organs, etc. 
 
 A recognized property of protoplasm is that of adaptation, as mani- 
 fested in the acclimatization of protoplasm to untoward conditions 
 of temperature, hght, contact and other stimuH; and this adaptation to 
 unusual conditions may take place without the aid of natural selection. 
 
 A tropic reaction occurs, whether it is to prove useful to the organism 
 or not. Thus a lady-bird beetle walks upward, on a branch, on a fence, 
 on one's finger. It walks upward as far as possible and then flies into 
 the air. If it happens to reach the tip of a twig and finds aphids there, 
 the beetle stops and feeds upon them. This adaptive result is in a sense 
 incidental. Yet, upon the whole, tropic reactions are wonderfully adap- 
 tive in their results. Here natural selection is of special value as afford- 
 ing an explanation of the phenomena. 
 
 As Loeb and Davenport have insisted, the mechanical reactions to 
 gravity, light, heat and other influences determine the behavior of the 
 organism. 
 
 2. Instinct 
 
 Insects are eminently instinctive; though their automatic behavior 
 is often so remarkably successful as to appear rational, instead of purely 
 instinctive. 
 
 A satisfactory definition of "instinct" seems to be impossible, 
 though some of the characteristics of instinctive behavior are quite 
 evident. 
 
 Instinct, as distinguished from reason, attains adaptive ends without 
 prevision and without experience. For example, a butterfly selects a 
 particular species of plant upon which to lay her eggs. Caterpillars of 
 the same species construct the same kind of nest, though so isolated from 
 one another as to exclude the possibility of imitation. Every caterpillar 
 that pupates accomplishes the intricate process after the manner of its 
 kind, without the aid of experience. 
 
 Instinctive actions belong to the reflex type — they consist of co-or- 
 dinated reflex acts. A complex instinctive action is a chain, each link 
 of which is a simple reflex act. In fact, no sharp line can be drawn 
 between reflexive and instinctive actions. 
 
 Basis of Instinct.— Reflex acts, the elements from which instinctive 
 actions are compounded, are the inevitable responses of particular organs 
 
314 ENTOMOLOGY 
 
 to appropriate stimuli, and involve no volition. The presence of an 
 organ normally implies the ability to use it. The newly born butterfly 
 needs no practice preliminary to flight. The process of stinging is 
 entirely reflex; a decapitated wasp retains the power to sting, directing its 
 weapon toward any part of the body that is irritated; and a freshly 
 emerged wasp, without any practice, performs the stinging movements 
 with greatest precision. 
 
 As Whitman observes, the roots of instincts are to be sought in the 
 constitutional activities of protoplasm. 
 
 Apparent Rationality. — The ostensible rationality of behavior 
 among insects, as was said, often leads one to attribute intelligence to 
 them, even when there is no evidence of its existence. As an illustra- 
 tion, many plant-eating beetles, when disturbed, habitually drop to the 
 ground and may escape detection by remaining immovable. We 
 cannot, however, believe that these insects "feign death" with any con- 
 sciousness of the benefit thus to be derived. This act, widespread 
 among animals in general, is instinctive, or reflex, as Whitman maintains, 
 being at the same time, one of the simplest, most advantageous and 
 deeply seated of all instinctive performances. 
 
 Take the many cases in which an insect lays her eggs upon only one 
 species of plant. The philenor butterfly hunts out Aristolochia, which 
 she cannot taste, in order to serve larvae, of whose existence she can have 
 no foreknowledge. Oviposition is here an instinctive act, really a 
 chemotropism, which is not performed until it is evoked by some sort 
 of stimulus — probably an olfactory one — from a particular kind of plant. 
 
 Stimuli. — Some determinate sensory stimulus is, indeed, the neces- 
 sary incentive to any reflex act. The first movements of a larva within 
 the egg-shell are doubtless due to a sensation, probably one of tem- 
 perature. Simple contact with the egg-shell is probably sufficient to 
 stimulate the jaws to work, and the caterpillar eats its way out; yet it 
 cannot foresee that its biting is to result in its liberation. Nor, later on, 
 when voraciously devouring leaves, can the caterpillar be supposed to 
 know that it is storing up a reserve supply of food for the distant period 
 of pupation and the subsequent imaginal stage. The ends of these 
 reflex actions are proximate and not ultimate, except from the stand- 
 point of higher intelhgence. 
 
 Just as simple reflexes link together to form an instinctive action, so 
 may instincts themselves combine. The complex behavior of a solitary 
 wasp is a chain of instincts, as the Peckhams have shown. All the opera- 
 tions of making the nest, stinging the prey, carrying it to the nest, etc.. 
 
INSECT BEHAVIOR 315 
 
 are performed as a rule in a definite, predicable sequence, and even a 
 slight interference with the normal sequence disconcerts the insect. 
 Just as the performance of one reflex act may serve as the stimulus for 
 the next reflex in order, so the completion of one instinctive action may 
 be in part the stimulus for the next one. 
 
 Modification of Instincts. — An action can be regarded as purely 
 instinctive in its initial performance only, because every subsequent 
 performance may have been modified by experience; in other words, 
 habits may have been forming and fixing, so that the results of instinct 
 become blended with those of experience. Thus the first flight of a 
 dragon fly is instinctive and erratic, but later efforts, aided by experience, 
 are well under control. 
 
 When once shaped by experience, reflex or instinctive actions tend 
 to become intense habits. Thus, certain caterpillars, having eaten all 
 the available leaves of a special kind, will almost invariably die rather 
 than adopt a new food plant, whereas larvae of the same species will eat- 
 a strange plant if it is offered to them at birth. An act is strengthened 
 in each repetition by the influence of habit, to the increasing exclusion 
 of other possible modes of action. Many a caterpillar, having eaten its 
 way out of the egg-shell, does not stop eating, but consumes the remain- 
 der of the shell — a reflex act, started by a stimulus of contact against the 
 jaws and continued until the cessation of the stimulus, unless some 
 stronger stimulus should intervene. It has been said that the larva eats 
 the remains of the shell because they might betray its presence to its 
 enemies. Whether this is true or not, to assume conscious foresight of 
 such a result on the part of an inexperienced caterpillar is worse than 
 unnecessary. 
 
 With insects, as with other animals, many instincts are transitory; 
 even when partially fixed by habit, they are replaceable by stronger 
 instincts. Thus the gregarious habit of larvae is finally overpowered by 
 a propensity to wander, which does not mature, however, until the 
 approach of the transformation period. The reproductive instinct is 
 another of those impulses that do not ripen until a certain age in the 
 individual. 
 
 Inflexibility of Instincts. — Broadly speaking, instinctive actions 
 lack individuality — are performed in the same way by every individual 
 of the species. The solitary wasps of the same species are remarkably 
 consistent in architecture, in the selection of a special kind of prey, in 
 the way they sting it, carry it to the nest and dispose of it; all these 
 operations, moreover, are performed in a sequence that is characteristic 
 
3l6 ENTOMOLOGY 
 
 of the species. Examples of this so-called inflexibility of instinct are 
 so omnipresent, indeed, that insect behavior as a whole is admitted to 
 be instinctive, or automatic. Insects are capable of an immense num- 
 ber of reflex impulses, ready to act singly or in intricate correlation, 
 upon the requisite stimuli from the environment. 
 
 To normal conditions of the environment, the behavior of an insect 
 is accurately adjusted; but in the face of abnormal circumstances 
 demanding the exercise of judgment, most insects are helpless. The 
 speciahzation to one kind of food, though usually advantageous, is fatal 
 if the supply becomes insufiicient and the larva is unable to adopt 
 another f ood . A species of Sphex habitually drags its grasshopper victim 
 by one antenna. Fabre cut off both antennae and then found that the 
 wasp, after vain efforts to secure its customary hold, abandoned the 
 prey. Under such unaccustomed conditions, insects often show a sur- 
 prising stupidity, capable as they are amid ordinary circumstances. 
 
 Flexibility of Instincts. — Notwithstanding such examples, the 
 common assertion that instincts are absolutely "blind," or inflexible, is 
 incorrect. Instinctive acts are not mechanically invariable, though 
 their variations are so inconspicuous as frequently to escape casual 
 observation. A precise observer can detect individual variations in the 
 performance of any instinctive act — variations analogous to those of 
 structure. 
 
 To take extreme examples, the Peckhams found that an occasional 
 queen of Polistes fusca would occupy a comb of the previous year, 
 instead of building a new one ; and that an individual of Pompilus mar- 
 ginatus, instead of hiding her captured spider in a hole or under a lump 
 of earth as usual, hung it up in the fork of a purslane plant. They 
 observed also that one Ammophila, in order to pound down the earth 
 over her nest, actually used a stone, held between the mandibles (Fig. 
 297). 
 
 This performance, which has been witnessed also by Professor 
 Williston and a few other observers, illustrates the flexibihty of in- 
 stinctive action, and has been cited as an instance of adaptability, or 
 intelligence. It can not be supposed, however, that the insect is 
 conscious of the efficiency of a stone as a tool. The performance may be 
 an accident. If one observes an Ammophila at work he will notice that 
 she not only pounds down the earth with her head, but also lifts and 
 lays aside small stones with her mandibles. Possibly she now and then 
 chances to begin the pounding movement before she has happened to 
 release a stone from her jaws. 
 
INSECT BEHAVIOR 317 
 
 Even the despotic power of habit may be overborne by individual 
 adaptability. Among caterpillars that have exhausted their customary 
 food, there are often a few that will adopt a new food plant and survive, 
 leaving their more conservative fellows to starve. 
 
 As Darwin himself held, the doctrine of natural selection is applicable 
 to instincts as well as structures. All reflex acts are to some extent 
 variable. Disadvantageous reflexes or combinations of reflexes elimi- 
 nate themselves, while advantageous ones persist and accumulate. 
 
 Indeed, structures and instincts must frequently have evolved hand 
 in hand. The remarkable protective resemblance of the Kallima butter- 
 
 FiG. 297. — Ammophila urnaria using a stone to pound down the earth over her nest. 
 Greatly enlarged. — After Peckham, from Bull. Wisconsin Geol. and Nat. Hist. Survey. 
 
 fly would be useless, did not the insect instinctively rest among dead 
 leaves of the appropriate kind. 
 
 Origin of Instinct. — There are two leading theories as to the origin 
 of instinct. Lamarck, Romanes and their followers have regarded in- 
 stinct as inherited habit; have supposed that instincts have originated 
 by the relegation to the reflex type of actions that at first were rational, 
 and that instincts represent the accumulated results of ancestral experi- 
 ence. This habit theory, however, has little to support it, and assumes 
 the inheritance of acquired characters — which has not been proved. 
 
 The selection theory of Darwin, Weismann, Morgan and others has 
 much in its favor. It regards reflex acts as primitive, as the raw 
 material from which natural selection, as the chief factor, has effected 
 those combinations that are termed instincts. 
 
3l8 ENTOMOLOGY 
 
 Instincts and Tropisms. — We have already emphasized the fact 
 that an instinct is a reflex act or a combination of reflex acts. The same 
 fact may now be stated in these words: an instinct is a tropism or a 
 combination of tropisms. The more important of these tropisms have 
 been considered. Whenever possible it is better to discard the ambigu- 
 ous term instinct in favor of such more precise terms as phototropism, 
 geotropism, etc.; though the term instinct remains useful as applied to an 
 action that is the resultant of several tropic responses. 
 
 The modern student of instincts aims to resolve them into their 
 component reflexes and to determine as precisely as possible the influ- 
 ence of each reflex component. Thanks to the labors of a great number 
 of skilled investigators, we are no longer satisfied to class an action as 
 "instinctive" and then dismiss it from thought; for we are now in a 
 position to analyze the action, and may hope to explain it eventually 
 in terms of the physical and chemical properties of protoplasm. 
 
 3. Intelligence 
 
 Though manifestly dominant, pure instinct fails to account for all 
 insect behavior. The abihty of an insect to profit by experience indi- 
 cates some degree of intelligence. 
 
 Take, for example, the precision with which bees or wasps find their 
 way back to the nest. This is no longer to be accounted for on the as- 
 sumption of a mysterious "sense of direction," for there is the best of 
 evidence for believing that it depends upon the recognition of surround- 
 ing objects. When leaving the nest for the first time, these insects make 
 "locality studies," which are often elaborate. Referring to a digger- 
 wasp, Sphex ichneumonea, the Peckhams write: "At last, the nest dug, 
 she was ready to go out and seek for her store of provision and now came 
 a most thorough and systematic study of the surroundings. The nests 
 that had been made and then deserted had been left without any 
 circling. Evidently she was conscious of the difference and meant, 
 now, to take all necessary precautions against losing her way. She 
 flew in and out among the plants first in narrow circles near the surface 
 of the ground, and now in wider and wider ones as she rose higher in the 
 air, until at last she took a straight line and disappeared in the distance. 
 The diagram [Fig. 298, A] gives a tracing of her first study preparatory 
 to departure. Very often after one thorough study of the topography 
 of her home has been made, a wasp goes away a second time with much 
 less circling or with none at all. The second diagram [Fig. 298, B] gives 
 a fair illustration of one of these more hasty departures. , 
 
INSECT BEHAVIOR 
 
 319 
 
 "If the examination of the objects about the nest makes no impres- 
 sion upon the wasp, or if it is not remembered, she ought not to be 
 inconvenienced nor thrown of! her track when weeds and stones are 
 removed and the surface of the ground is smoothed over; but this is 
 just what happens. Aporus fasciatus entirely lost her way when we 
 broke off the leaf that covered her nest, but found it without trouble 
 when the missing object was replaced. All the species of Cerceris were 
 extremely annoyed if we placed any new object near their nesting-places. 
 Our Ammophila refused to make use of her burrow after we had drawn 
 
 Fig. 298. — Locality studies made by a wasp, Sphex ichneumonea. A, a thorough study; 
 B, a hasty study; «, nest. — After Peckham, from Bull. Wisconsin Geol. and Nat. Hist. 
 Survey. 
 
 some deep Hnes in the dust before it. The same annoyance is exhibited 
 when there is any change made near the spot upon which the prey of 
 the wasp, whatever it may be, is deposited temporarily." 
 
 If we take, as one criterion of inteUigence, the power to choose be- 
 tween alternatives, then insects are more inteUigent than is generally 
 admitted. The control of locomotion, the selection of prey, and the 
 avoidance of enemies, as results of experience, indicate powers of dis- 
 crimination. The power of intercommunication, conceded to exist 
 among social Hymenoptera, implies some degree of intelligence. 
 
 If instinct is bhnd, or mechanical, with no adjustment of means to 
 ends, then a pronounced individuality of action must signify something 
 more than instinct. In regard to a female Pompilus scelestus, which had 
 dragged a large spider nearly to her nest, the Peckhams observe: 
 
320 
 
 ENTOMOLOGY 
 
 "presently she went to look at her nest and seemed to be struck with a 
 thought that had already occurred to us — that it was decidedly too 
 small to hold the spider. Back she went for another survey of her 
 bulky victim, measured it with her eye, without touching it, drew her 
 conclusions, and at once returned to the nest and began to make it larger. 
 We have several times seen wasps enlarge their holes when a trial had 
 demonstrated that the spider would not go in, but this seemed a remark- 
 ably intelligent use of the comparative faculty." 
 
 From the standpoint of pure instinct, indeed, much of the behavior 
 of the solitary wasps is inexplicable; while the actions of the social 
 Hymenoptera have led some of the most critical students to ascribe 
 intelligence to these insects. The activities of the harvesting ants, the 
 miHtary or the slave-holding species, are of such a nature that the 
 possibility of education by experience and instruction is strong, to say 
 the least. In fact, Forel has maintained that a young ant is actually 
 trained to its domestic duties by its older companions. 
 
 In his scholarly volume, Ants, Wheeler shows that these insects 
 have the ability tcr profit by experience, as exhibited in their foraging 
 and homing operations, the recollection of nest-mates and aliens, 
 communication, imitation and co-operation; and that they have 
 memory in the general sense of the word, but that they have memory 
 images only as the result of sensory stimulation, and are unable to call 
 them up at will, much less to refer them to the absent or to the past. 
 "If this moderate estimate of the memory of ants be correct, it follows 
 that they must be incapable of reasoning — of 'focusing the wherefore,' 
 to use Lloyd Morgan's expression, for a mere association of sense impres- 
 sions is not deducing conclusions from premises." (Wheeler.) 
 
 It is extremely difl&cult, if not impossible, however, to draw the line 
 between instinct and intelUgence; and in doubtful cases there is a gen- 
 eral tendency to exaggerate the importance of intelligence rather than 
 that of instinct. For example, the well-known discrimination on the part 
 of ants between members of their own colony and those of other colonies, 
 even of the same species, would seem to imply intelligent recognition. 
 This recognition is due, however, to a characteristic odor, which 
 is derived from the mother of the community. An ant after being washed 
 receives hostile treatment from others in its own colony; while an alien 
 ant after being smeared with the juices of hostile ants is treated by the 
 latter as a friend. 
 
 Each instance of apparent intelligence must be examined impartially 
 on its own merits. At present it may be said that, while most of the 
 
INSECT BEHAVIOR 32I 
 
 behavior of insects is purely instinctive, there is some reason to believe 
 that at least gleams of intelligence appear in the most speciahzed 
 Hymenoptera. 
 
 Lack of Rationality.- — However intelligent the social Hymenoptera 
 may be in their way, they show no signs of the power of abstract reasoning. 
 Even ants, according to the experiments of Lubbock, display profound 
 stupidity in the face of novel emergencies from which they might 
 extricate themselves by abstract reasoning of the simplest kind. The 
 thoughts of an ant or bee seem to be limited to simple associations of 
 concrete things. Miss Enteman observed a Polistes worker which 
 gnawed a piece out of the side of a dead larva of its own kind and, turn- 
 ing, actually offered it as food to the mouth of the same larva. In 
 another instance a larva was attacked and killed, and then offered a 
 piece of its own body. 
 
 Such examples as these emphasize the strength of the reflex factor in 
 the behavior of insects. Indeed, the basis of all behavior is being sought 
 in the reactions of protoplasm to external stimuli. Possibly even mem- 
 ory, consciousness and other attributes of intelhgence will eventually be 
 reduced to this basis, improbable as it may now seem. • 
 
CHAPTER XII 
 
 DISTRIBUTION 
 
 I. Geographical 
 
 Importance of Dispersion. — Dispersion enables species to miti- 
 gate the intense competition and the rigid selection that result from 
 crowded numbers; hence the tendency to disperse, being self -preserva- 
 tive, has become universal. Some species habitually emigrate in pro- 
 digious numbers: the African migratory locust, the Rocky Mountain 
 locust, and the milkweed butterfly, which annually leaves the Northern 
 states for the South in immense swarms, in autumn, and in the follow- 
 ing spring straggles back to the North. Vanessa cardui occasionally 
 migrates in immense numbers, as do also Fieri s, some dragon flies and 
 some beetles, notably CoccinelHdae. 
 
 Wide Distribution of Insects. — Insects have been found in almost 
 every latitude and altitude explored by man. Butterflies and mos- 
 quitoes occur beyond the polar circle, the former in Lat. 83° N., the 
 latter in Lat. 72° N., and a species of Emesa closely aUied to our common 
 E. longipes is recorded by Whymper from an altitude of 16,500 ft. in 
 Ecuador, where, according to the same traveler, Orthoptera occur at 
 16.000 ft., Pieris xanthodice ranges above 15,000 ft., and dragon flies, 
 Hymenoptera and scorpions reach a height of 12,000 ft., while twenty- 
 nine species of Lepidoptera range upward of 7,300 ft. A very few 
 species of insects inhabit salt water, Halobates being found far at sea; 
 some kinds live in arid regions and a few even in hot springs, while 
 caves furnish many pecuhar species. In short, insects are the most 
 widely distributed of all animals, excepting Protozoa and possibly 
 Mollusca. 
 
 While all the large orders of insects are world-wide in distribution, 
 the most richly distributed are Coleoptera, Thysanura and Collembola, 
 the last two feeding usually upon minute particles of organic matter in 
 the soil and being remarkably tolerant of extremes of temperature. 
 The four chief families of butterflies occur the world over, as do several 
 families of beetles. Of species that are essentially cosmopoHtan we may 
 mention the coWemholsm Folsofnia fimetaria, and the butterflies Vanessa 
 cardui and Anosia plexippus, while among beetles no less than one hun- 
 
 322 
 
DISTRIBUTION 323 
 
 dred species are cosmopolitan or subcosmopolitan, including Tenehrio 
 molitor, Silvanus surinamensis, Dermestes lardarius, Attagenus piceus 
 and Calandra oryza. The coccinellid genus Scymnus occurs in North 
 America, Europe, Hawaii, Galapagos Islands and New Zealand, and 
 Anohium and Hydrobius are distributed as widely. The huge noctuid, 
 Erebus odora, occurring in Brazil on the lowlands, and in Ecuador at an 
 altitude of 10,000 ft., finds its way up into the United States and even 
 into Canada. The chinch bug and many other Central American forms 
 also spread far northward, as described beyond. 
 
 Means of Dispersal. — This exceptional range of insects is due to 
 their exceptional natural advantages for dispersal, chief among which 
 are the power of flight and the ability to be carried by the wind. The 
 migratory locust, Schistocerca peregrina, has been found on the wing five 
 hundred miles east of South America. The home of the genus, accord- 
 ing to Scudder, is Mexico and Central America, where 23 species are 
 found; 20 occurring in South America, including the Galapagos Islands, 
 II in the United States and 6 in the West Indies; and there is every 
 reason to believe that S. peregrina — the biblical locust and the only 
 representative of its genus in Africa — crossed over from South America, 
 where it is found indeed at present. Darwin and others have recorded 
 many instances of insects being taken alive far at sea; Trimen mentions 
 moths and longicorn beetles as occurring 230 miles west of the African 
 coast and Sphinx convolvulus as flying aboard ship 420 miles out. In 
 these instances the insects have usually been assisted or carried by 
 strong winds, particularly the trade-winds, and oceanic islands have 
 undoubtedly been colonized in this way. On land, Webster has found 
 that the direction in which the Hessian fly spreads is determined largely 
 by the prevailing winds at the time when these delicate insects are on 
 the wing, and that the San Jose scale insect spreads far more rapidly 
 with the prevailing winds than against them, the wind carrying the 
 larvae as if they were so many particles of dust. The pernicious buffalo- 
 gnat of the South emerges from the waters of the bayous and may be 
 carried on a strong wind to appear suddenly in enormous numbers 
 twenty miles distant from its breeding place. Mosquitoes are dis- 
 tributed locally by Hght breezes, but chng to the herbage during strong 
 winds. 
 
 Ocean currents may carry eggs, larvae or adults on vegetable drift 
 to new places thousands of miles away. Thus the Gulf Stream annually 
 transports thousands of tropical insects to the shores of Great Britain, 
 where they do not survive, however. 
 
324 ENTOMOLOGY 
 
 Fresh-water streams convey incalculable numbers of insects in all 
 stages; and insects as a whole are very tenacious of life, being able to 
 withstand prolonged immersion in water, and even freezing, in many 
 instances, while they can hve for a long time without food. 
 
 The universal process, of soil-denudation must aid the diffusion of 
 insects, slowly but constantly. 
 
 Birds and mammals disseminate various insects in one way or 
 another, while the agency of man is, of course, highly important. In- 
 tentionally, he has spread such useful species as the honey bee, the silk- 
 worm and certain useful parasites; incidentally he has distributed the 
 San Jose scale, Colorado potato beetle, gipsy moth and many other 
 pests. 
 
 Barriers. — The most important of the mechanical barriers which 
 limit the spread of terrestrial species is evidently the sea. Mountain 
 ranges retard distribution more or less successfully, though a species 
 may spread along one side of a range and sooner or later pass through a 
 break or else around one end. Mountain chains act as barriers, 
 however, chiefly because they present unendurable conditions of 
 climate and vegetation. For the same reason deserts are highly effect- 
 ive barriers. Indeed the most important checks upon distribution are 
 those of climate, and of cUmatal factors temperature is the most power- 
 ful. Tropical species cannot, as a rule, survive and reproduce in 
 regions of frost; most of the tropical species which have entered the 
 United States are restricted to its narrow tropical belts (Plate IV). 
 The stages of an insect are frequently so accurately adjusted to par- 
 ticular climatal conditions that an unfamiliar climate deranges the life 
 cycle. Thus many Southern butterflies find their way every year to 
 the Northern states, only to perish without reproducing their kind. 
 Insects are, nevertheless, more adaptable than most other animals in 
 respect to climate, and frequently follow their food plants into new 
 climates, as in the case of the harlequin cabbage bug, which has pushed 
 north from the tropics to Missouri, southern Ilhnois and Indiana. 
 
 Humidity ranks next to temperature in the importance of its 
 influence upon the distribution of organisms, but in the case of animals 
 acts for the most part indirectly, by its effects upon vegetation. Thus 
 the effectiveness of an arid region as a barrier is due chiefly to the lack of 
 vegetation in consequence of the lack of moisture. Excessive moisture, 
 on the other hand, may act as a barrier. The Rocky Mountain locust, 
 which formerly migrated eastward in immense swarms, succumbed in the 
 moist valley of the Mississippi; the chinch bug is never seriously injur- 
 
DISTRIBUTION 325 
 
 ous in wet years. Moisture checks the development of these and other 
 insects in ways as yet unascertained; possibly it acts indirectly by favor- 
 ing the growth of fungus diseases, to which insects are much subject. 
 
 The absence of proper food is more effective than climate, as a direct 
 check upon the spread of an animal; food itself being, of course, de- 
 pendent ultimately upon climatal factors and soil. Many insects, being 
 confined to a single food plant, can not exist long where this plant does 
 not occur ; but they will follow the plant, as was just said, into new 
 climates; thus Anosia plexippus is following the milkweed over the 
 world. The butterfly Euphydryas phaeton is remarkably local in its 
 occurrence, being limited to swamps where its chief food plant {Chelone 
 glabra) grows ; and Epidemia epixanthe is similarly restricted to cranberry 
 bogs. 
 
 Former Highways of Distribution. — Many facts of distribution 
 which are inexplicable under the present conditions of topography and 
 climate become intelHgible in the Hght of geological history. The 
 marked similarity between the fauna of Europe and that of North 
 America means community of origin; and though the Arctic zone now 
 interposes as a barrier, there was once an opportunity for free dispersion 
 when, in the early Pleistocene or late Pliocene, a land connection existed 
 between Asia and North America and a warm climate prevailed 
 throughout what is now the Arctic region. 
 
 The extraordinary isolation of the butterfly CEneis semidea on moun- 
 tain summits in New Hampshire and Colorado (particularly Mt. 
 Washington, N. H., and Pikes Peak, Col.) is explained by glacial geology. 
 The ancestors of this species, it is thought, were driven southward be- 
 fore an advancing ice-sheet and then foflowed it back as it retreated 
 northward, adapted as they were to a rigorously cold cKmate. Some 
 of those ancestors presumably followed the melting ice up the mountain 
 sides, until they found themselves stranded on the summits. Other 
 individuals, undiverted from the lowlands, followed the retreating glacier 
 into the far north; and at present there occurs throughout Labrador a 
 species of CEneis which differs but sHghtly from its lonely ally of the 
 mountain tops. 
 
 Glaciation undoubtedly had a profound effect upon the fauna and 
 flora of North America. "With the slow southward advance of the ice, 
 animals were crowded southward; with its recession they advanced 
 again northward to reoccupy the desolated region, until now it has long 
 been repopulated, either with the direct descendants of its former in- 
 habitants or with such limitations to the integrity of the fauna as this 
 
326 ENTOMOLOGY 
 
 interruption of local life may have caused." (Scudder.) Probably 
 many species were exterminated and many others became greatly modi- 
 fied, though little is known as to the relationship of the present fauna to 
 the preglacial fauna. "The glacial cold still lingers over the northern 
 part of this continent and our present animals are only a remnant of 
 the rich fauna that existed in former ages, when the magnolia and the 
 sassafras thrived in Greenland." 
 
 Island Faunae. — The abihty of insects to surmount barriers, under 
 favorable circumstances, is strikingly shown in the colonization of 
 oceanic islands. Not a few insects, including Vanessa cardui, have 
 found their way to the isolated island of St. Helena. In the Madeira 
 Islands, according to Wollaston, there are 580 species of Coleoptera, of 
 which 314 are known to occur in Europe, while all the rest are closely 
 allied to European forms. Subtracting 120 species as having been intro- 
 duced probably or possibly through the agency of man, there remain 
 194 that have been introduced by "natural" means. The rest, 266 
 species, are endemic, though akin to European species. 
 
 The scanty insect fauna of the Galapagos Islands includes twenty 
 species of Orthoptera, which have been studied by Scudder and by Snod- 
 grass. Five of these are cosmopolitan cockroaches, doubtless intro- 
 duced commercially, and the remaining fifteen are all "distinctly South 
 and Central American in their affinities." Three of these fifteen are 
 strong-winged species which doubtless arrived by flight from the neigh- 
 boring mainland; indeed, Scudder records a Schistocerca {S. exsul) as 
 having been taken at sea two hundred miles off the west coast of South 
 America, or nearly half way to the Galapagos Islands. Thirteen of the 
 fifteen are endemic, and five are apterous or subapterous, while a sixth 
 has an apterous female. Apterous insects, noticeably common on 
 wind-swept oceanic islands, may have been carried thither on drift- 
 wood, though it is more likely that the apterous condition arose on the 
 islands, where the better-winged and more venturesome individuals may 
 .have been constantly swept out to sea and drowned, leaving the more 
 feeble-winged and less venturesome individuals behind, to reproduce 
 their own life-saving peculiarities. 
 
 The Coleoptera of the Hawaiian Islands, studied by Dr. Sharp, num- 
 ber 428 species, representing 38 famihes, and "are mostly small or very 
 minute insects," the few large forms being non-endemic, with little or 
 no doubt; 352 species are at present known only from this archipelago. 
 Dr. Sharp distinguishes three elements in the fauna: "first, species that 
 have been introduced, in all probabiUty comparatively recently, by arti- 
 
DISTRIBUTION 327 
 
 ficial means, such as with provisions, stores, building timber, ballast, or 
 growing plants; many of these species are nearly cosmopolitan. Second, 
 species that have arrived in the islands, and have become more or less 
 completely naturalized; they are most of them known to be wood- or 
 bark-beetles, but some that are not so may have come with the earth 
 adhering to the roots of floating trees; a few, such as the Dytiscidae, or 
 water beetles, may possibly have been introduced by. violent winds. 
 Third, after making every allowance for introduction by these artificial 
 and natural methods, there still remains a large portion standing out 
 in striking contrast with the others, which we are justified in considering 
 strictly endemic or autochthonous." Among the introduced genera are 
 Coccinella, Dermestes, Aphodius, Buprestis, Ptinus and Ceramhyx. The 
 immigrant longicorns appear to have been derived "from the nearest 
 lands in various directions" — the Phihppine Islands, tropical America 
 and the Polynesian Islands — and the same conclusion will probably be 
 found to hold for the other immigrants, when their general distribution 
 shall have been suj6&ciently studied. The endemic species number 214, 
 or exactly half the total number of species, and are distributed among 9 
 families, as follows: 
 
 Families. Species. Genera. Endemic 
 
 Genera. 
 
 Carabidae 51 7 7 
 
 Staphylinidae 19 3 i 
 
 Nitidulidae 38 2 i 
 
 Elateridae 7 i i 
 
 Ptinidas (Anobiini) 19 3 3 
 
 Cioidae 19 i o 
 
 Aglycj'deridse 30 i i 
 
 Curculionidae (Cossonini) 21 3 3 
 
 Cerambjxidae 10 i i 
 
 Sharp writes: "I think it may be looked on as certain that these 
 islands are the home of a large number of peculiar species not at present 
 existing elsewhere, and if so it follows that either they must have existed 
 formerly elsewhere and migrated to the islands, and since have become 
 extinct in their original homes, or that they must have been produced 
 within the islands. This last seems the simpler and more probable sup- 
 position, and it appears highly probable that there has been a large 
 amount of endemic evolution within the limits of these isolated islands." 
 
 The parasitic Hymenoptera of Hawaii, according to Ashmead, num- 
 ber 14 families, 69 genera and 128 species; only eleven genera are en- 
 demic and most of the other genera are represented in nearly all the 
 
328 ENTOMOLOGY 
 
 known faunae of the earth. Ashmead concurs in the view that the 
 Hawaiian fauna was originally derived from the Australasian fauna — 
 the view held by all the specialists who have studied Hawaiian insects. 
 
 Geographical Varieties. — Darwin found that wide-ranging species 
 are as a rule highly variable. The cosmopolitan butterfly Vanessa 
 cardui presents striking variations in different parts of the earth, largely 
 on account of climatal differences, as is indicated by the temperature 
 experiments of several investigators. Standfuss exposed German pupae 
 of this insect to cold, and obtained thereby a dark variety such as occurs 
 in Lapland; and by the influence of warmth, obtained a very pale form 
 such as occurs normally in the tropics only. Our Cyaniris pseudargi- 
 olus, which ranges from Alaska into Mexico and from the Pacific to the 
 Atlantic, exhibits many geographical varieties, some of which are 
 clearly due to temperature, as experiments have shown. 
 
 Geographical isolation is often followed by changes in the specific 
 characters of an organism, as witness the endemic species and varieties 
 of oceanic islands. Even in the same archipelago, the different islands 
 may be characterized by different varieties of one and the same species, 
 or even by different but closely allied species of the same genus. Thus 
 Darwin and Alexander Agassiz found that in the Galapagos Islands each 
 island had its own species of Tropidurus (a lizard) and had only one 
 species, with almost no exceptions. The same phenomenon occurs in 
 the two Galapagan species of Schistocerca — S. melanocera and 5", 
 literosa. In melanocera, as Scudder discovered, ''Three or four distinct 
 types are becoming gradually differentiated on the eight [now ten] 
 islands from which they are known." Snodgrass, who has made 
 important additions to Scudder's account, says, in regard to the two 
 species, "The specimens from the different islands show striking though, 
 in most cases, slight differences distinguishing the individuals of each 
 island as a race, from those inhabiting any other island. There are 
 two exceptions. Abingdon and Bindloe have the same form, and Albe- 
 marle supports at least two races." Each of these two species presents 
 no less than five racial types, to which distinctive names have been 
 applied. Though the relationships and evolution of these races have 
 been ably discussed by Snodgrass, definite conclusions upon these 
 subjects are still needed. 
 
 Faiinal Realms. — The general distribution of hfe is such that 
 naturalists divide the earth into several realms, each of which has its 
 characteristic fauna and flora. As to the precise boundaries of these 
 faunal realms, zoologists do not all agree, owing chiefly to the fact that 
 
DISTRIBUTION 331 
 
 faunfe overlap one another to such an extent as to render their exact 
 separation more or less arbitrary. Five realms, at least, are generally 
 recognized: Holarctic, Neotropical, Ethiopian, Oriental and Australian 
 (Plate III). 
 
 The Holarctic realm comprises the whole of Europe, Northern 
 Africa as far south as the Sahara, Asia down to the Himalayas, and 
 North America down to Mexico. Though the faunae of all these areas 
 are fundamentally alike (as Merriam and other authorities maintain), 
 it is often convenient to divide the Holarctic into two parts: the 
 Palcearctic, including Europe and most of temperate Asia, being limited 
 roughly by the Tropic of Cancer; and the Nearctic, occupying almost 
 the entire continent of North America, including Greenland. The 
 northern portion of the Holarctic realm forms a circumpolar belt with a 
 remarkably homogeneous fauna and flora; therefore some authors 
 distinguish an Arctic realm, limited by the isotherm of 32°, which marks 
 very closely the tree-limit. 
 
 The boreal insects of Eurasia and North America are strikingly 
 alike. Dr. Hamilton has catalogued almost six hundred species of 
 beetles as being holarctic in distribution; five hundred of these are com- 
 mon to Europe, Asia and North America, and the remainder are known 
 to occur in North America and also in Europe or Asia ; one hundred are 
 cosmopohtan or sub-cosmopoHtan, to be sure, but fifty of these are 
 probably holarctic in origin, for example — Dermestes lardarius (larder 
 beetle) and Tenebrio molitor (meal-worm). Of butterflies, out of some 
 two hundred and fifty species that are found in the United States east 
 of the Rocky Mountains, scarcely more than a dozen occur also in the 
 old world. North of the United States, however, as Scudder finds, no 
 fewer than thirteen genera are represented in the old world by the same 
 or by allied species. 
 
 The Neotropical realm embraces South America, Central America, 
 the West Indies and the coasts of Mexico; Mexico being for the most 
 part a transition tract between the Neotropical and the Nearctic. The 
 richest butterfly fauna in the world is found in tropical South America. 
 To this region are restricted, almost without exception, the Euploeinae 
 and Lemoniinae and over ninety-nine per cent, of the Libytheinae; here 
 the Heliconiida; and Papilionidse attain their highest development, as 
 do also the Cerambycidae, or longicorn beetles. 
 
 The Ethiopian realm consists of Africa south of the Sahara, Southern 
 Arabia and Madagascar; though some prefer to regard Madagascar as 
 a distinct realm, the Lemurian. According to Wallace, the Ethiopian 
 
^3^ 
 
 ENTOMOLOGY 
 
 realm has seventy-five peculiar genera of Carabidae and is marvelously 
 rich in Cetoniidas and Lycaenidae. 
 
 The Oriental realm includes India, Ceylon, Tropical China, and the 
 Western Malay Islands. In the richness of its insect fauna, this realm 
 vies with the Neotropical.' Danaidae and Papilionidae are abundant, 
 while the genus Morpho is represented by some forty species; of Cole- 
 optera, Buprestidae are important andLucanidae especially so. 
 
 The Australian realm embodies Austraha, New Zealand, the Eastern 
 Malay Islands and Polynesia. Buprestidae are here represented by 
 forty-seven genera, of which twenty are peculiar; against this showing, 
 the Oriental has forty-one genera and the Neotropical thirty-nine (Wal- 
 lace). Strong affinities are said to exist between the Australian and 
 Neotropical insect faunae. 
 
 Life Zones of North America. — Merriam, the chief authority upon 
 the subject, says: "The continent of North America may be divided. 
 
 ■^^ 
 
 tSfS^ 
 
 v^ 
 
 ^^ 
 
 \^ 
 
 /^^ 
 
 Fig. 299. — Distribution of Erynnis mani- 
 toba, a butterfly restricted to subarctic and 
 subalpine regions. — After Scudder. 
 
 Fig. 300.— Distribution in the United 
 States of Eudamus proteus, primarily a trop- 
 ical butterfly. — After Scudder. 
 
 according to the distribution of its animals and plants, into three 
 primary transcontinental regions — Boreal, Austral and Tropical." 
 (Plate IV). 
 
 The Boreal region covers the northern part of the continent to about 
 the northern boundary of the United States and continues southward 
 along the higher portions of the mountain ranges. This region is 
 divided into three transcontinental zones: (i) the Arctic- Alpine, lying 
 above the limits of tree growth, in latitude or altitude; (2) the Hudso- 
 nian, comprising the northern part of the great transcontinental conifer- 
 ous forest and the upper timbered slopes of the highest mountains of the 
 United States and Mexico; (3) the Canadian, covering theremainder of 
 the Boreal region. The butterfly Erynnis manitoha (Fig. 299) is strictly 
 boreal in distribution. 
 
Plate IV. 
 
DISTRIBUTION 335 
 
 The Austral region "covers the whole of the United States and 
 Mexico, except the Boreal mountains and the Tropical lowlands." It 
 comprises three transcontinental belts: (i) the Transition zone, in 
 which the Boreal and the Austral overlap; (2) the Upper Austral; (3) 
 the Lower Austral. The butterfly Eudamus proteus (Fig. 300) is re- 
 stricted, generally speaking, to the Tropical region and the warmer and 
 more humid portions of the Austral. 
 
 The Tropical region covers the southern extremity of Florida and 
 of Lower California, most of Central America and a narrow strip along 
 the two coasts of Mexico, the western strip extending up into California 
 and Arizona. 
 
 These divisions are based primarily upon the distribution of mam- 
 mals, birds and plants, and the three primary divisions serve almost 
 equally well for insects also. In regard to the zones, however, not so 
 much can be said^ — for insects are to a high degree independent of minor 
 differences of climate. Many instances of this are given beyond. 
 
 The insect fauna of the United States is upon the whole a hetero- 
 geneous assemblage of species derived from several sources, and the 
 foreign element of this fauna we shall consider at some length. 
 
 Paths of Diffusion in North America. — It may be laid down as a 
 general rule that every species tends to spread in all directions and does 
 so spread until its further progress is prevented, in one way or another. 
 The paths along which a species spreads are determined, then, by the 
 absence of barriers. The diffusion of insects in our own country has 
 received much attention from entomologists, especially in the case of 
 such insects as are important from an economic standpoint. The ac- 
 cessions to our insect fauna have arrived chiefly from Asia, Central and 
 South America, and Europe. 
 
 Webster, our foremost student of this subject, to whom the author 
 is indebted for most of his facts, names four paths along which insects 
 have made their way into the United States: (i) Northwest — Northern 
 Asia into Alaska and thence south and east; (2) Southwest — Central 
 America through Mexico ; (3) Southeast— West Indies into Florida ; (4) 
 Eastern — from Europe, commercially. 
 
 Northwest.^ — The northern parts of Europe, Asia and North America 
 have in common very many identical or closely allied species, whose 
 distribution is accounted for if, as geologists assure us, Asia and North 
 America were once connected, at a time when a subtropical climate 
 prevailed within the Arctic Circle; in fact, the distribution is scarcely 
 explicable upon any other theory. Curiously enough, the trend of 
 
33(> 
 
 ENTOMOLOGY 
 
 diffusion seems to have been from Asia into North America and rarely 
 the reverse, so far as can be inferred. 
 
 The lady-beetle, Coccinella quinquenotata, occurring in Siberia and 
 Alaska, has spread to Hudson Bay, Greenland, Kansas, Utah, CaHfornia 
 and Mexico; while C. sanguinea, well known in Europe and Asia, ranges 
 from Alaska to Patagonia ; and Ceratomegilla fuscilahris from Vancouver 
 and Canada to Chile. About six hundred species of beetles are holarctic 
 in distribution, as was mentioned. Some of them inhabit different 
 climatal regions in different parts of their range; thus Lina lapponica in 
 the Old World "occurs only in the high north and on high mountain 
 ranges, whereas in North America it extends to the extreme southern 
 portion of the country," being widely diffused over the lowlands 
 (Schwarz). Similarly, Silpha lapponica is strictly arctic in Europe, but 
 is distributed over most of North America ;5i/^/m opaca, on the contrary, 
 is common all over Europe, but is strictly arctic in North America. 
 Silpha atrata, common throughout Europe and western Siberia, was 
 introduced into North America, but failed to estabhsh itself. 
 
 Southwest. — Very many species have come to us from Central 
 America and even from South America. South America appears to be 
 the home of the genus Halisidota, according to Webster, who has traced 
 several of our North American species as offshoots of South American 
 forms. Many of our species may be traced back to Yucatan. H. cinc- 
 tipes ranges from South America to Texas and Florida; H. tessellaris 
 has spread northward from Central America and now occurs over the 
 middle and eastern United States, while a form closely like tessellaris 
 ranges from Argentina to Costa Rica; H. carycs follows tessellaris, and 
 appears to have branched in Central America, giving off E. agassizii, 
 which extends northward into CaHfornia. Similarly in the case of the 
 Colorado potato beetle {Leptinotarsa decemlineata) and its relatives. 
 According to Tower, the parent form, L. undecimlineata, seems to have 
 arisen in the northern part of South America, to have migrated north- 
 ward and, in the diversified Mexican region, to have spHt into several 
 racial varieties. The parent form grades into L. multilineata of the 
 Mexican table lands, which in ttirn, in the northern part of the Mexican 
 plateau, passes imperceptibly into L. decemlineata, which last species has 
 spread northward along the eastern slope of the western highlands, west 
 of the arid region. In the lower part of the Mexican region the parent 
 form may be traced into L.juncta, which has spread along the low humid 
 Gulf Coast, up the Mississippi valley to southern Illinois, and along the 
 Gulf Coast and up the Atlantic coast to Maryland, Delaware and New 
 
DISTRIBUTION 337 
 
 Jersey. In general, the mountains of Central America and Mexico and 
 the plateau of Mexico have been barriers to the northward spread of 
 many species, which have reached the United States by passing to the 
 east or to the west of these barriers, in the former case skirting the Gulf 
 of Mexico and spreading northward along the Mississippi valley or along 
 the Atlantic coast, in the latter event traveling along the Pacific coast 
 to California and other Western states. Not a few species, however, 
 have made their way from the Mexican plateau into New Mexico and 
 Arizona ; this is true of many Sphingidae. The butterfly A nosia berenice 
 ranges from South America into New Mexico, Arizona and Colorado; 
 while many of the Libytheidae have entered Arizona and neighboring 
 states from Mexico. The chrysomeHd genus Diabrotica is almost ex- 
 clusively confined to the western hemisphere and its home is clearly in 
 South America, where no fewer than 367 species are found. About 100 
 species occur in Venezuela and Colombia, "of which 11 extend into 
 Guatemala, 8 into Mexico, and i into the United States." We have 18 
 species of Diabrotica, almost all of which can be traced back to Mexico, 
 and several of them — as the common D. longicornis — to Central 
 America. "The common Dynastes tityus occurs from Brazil through 
 Central America and Mexico, and in the United States from Texas to 
 Illinois and east to southern New York and New England." Erebus 
 odora ranges from Ecuador and Brazil to Colorado, Illinois, Ohio, New 
 England and into Canada, though it is not known to breed in North 
 America, being in fact a rare visitor in our northern states. 
 
 Southeast. — Many South American species have made their way 
 into southern and western Florida by way of the West Indies, while 
 some subtropical species have reached Florida probably by following 
 around the Gulf coast. The semitropical insect fauna of southern and 
 southwestern Florida, including about 300 specimens of Coleoptera, 
 according to Schwarz, is entirely of West Indian and Central American 
 origin, the species having been introduced with their food plants, chiefly 
 by the Gulf Stream, but also by flight, as in the case of Sphingidae. 
 Ninety-five species of Hemiptera collected in extreme southern Florida 
 by Schwarz and studied by Uhler are distinctly Central American and 
 West Indian in their affinities. Indeed Uhler is inclined to beheve that 
 the principal portion of the Hemiptera of the United States has been 
 derived from the region of Central America and Mexico. 
 
 Eastern.— On the Atlantic coast are many European species of 
 insects which have arrived through the agency of man. Most of them 
 have not as yet passed the Appalachian mountain system, but some 
 
338 ENTOMOLOGY 
 
 have worked their way inland. Thus the common cabbage butterfly 
 {Pieris m/>«), first noticed in Quebec about i860, was found in the north- 
 ern parts of Maine, New Hampshire and Vermont five or six years later, 
 was established in those states by 1867, entered New York in 1868 and 
 then Ohio. Aphodius fossor followed much the same course from New 
 York into northeastern Ohio, as did also the asparagus beetle {Crioceris 
 asparagi), the clover leaf weevil {Hyper a punctata), the clover root 
 borer {Hylastinus obscurus) and other species. In short, as Webster has 
 pointed out. New York offers a natural gateway through which species 
 introduced from Europe spread westward, passing either to the north 
 or to the south of Lake Erie. 
 
 Inland Distribution. — Pieris rapce, the spread of which in North 
 America has been thoroughly traced by Scudder, reached northern New 
 York in 1868 (as above), but appears to have been independently intro- 
 duced into New Jersey in 1868, whence it reached eastern New York 
 again in 1870; it was seen in northeastern Ohio in 1873, Chicago 1875, 
 Iowa 1878, Minnesota 1880, Colorado 1886, and has extended as far 
 south as northern Florida, but is apparently unable to make its way 
 down into the peninsula. 
 
 The asparagus beetle, Crioceris asparagi, another native of Europe, 
 became conspicuous in Long Island in 1856, spread southward to 
 Virginia and westward to Ohio, where it was taken in 1886; it is fre- 
 quent now in Illinois and Wisconsin and is known in Colorado and 
 California. This insect, as Howard observes, flies readily, and may 
 be introduced commercially in the egg or larval stage on bunches of 
 asparagus. 
 
 The clover leaf weevil, Hypera punctata, common over Europe and 
 most of Asia, was found in Canada some seventy years ago, has spread 
 into Mississippi, Texas, Utah and Idaho, and is present on the Pacific 
 coast also. 
 
 The lesser clover leaf weevil, Phytonomus nigrirostris, introduced 
 from Europe into the United States, has spread steadily westward and 
 has now reached Illinois, where it has been common since 1919. 
 
 Cryptorhynchus lapathi, a beetle destructive to willows and poplars, 
 and common in Europe, Siberia and Japan, was found in New Jersey in 
 1882 and in New York in 1896, though known for many years previously 
 in Massachusetts. It became noticeable in Ohio in 1901, and is steadily 
 extending its ravages, being known now in Minnesota. 
 
 From Colorado the well-known potato beetle {Leptinotarsa decem- 
 lineata) has worked eastward since 1840, reaching the Atlantic coast, 
 
DISTRIBUTION 339 
 
 and has even made its way several times into Great Britain, only to 
 be stamped out with commendable energy. The box-elder bug {Lep- 
 tocoris trivittatus) is similarly working eastward, having now reached 
 Ohio. Formerly the Rocky Mountain locust periodically migrated east- 
 ward, but always met a check in the moist valley of the Mississippi. 
 
 The chinch bug {Blissus leucopterus), the distribution of which has 
 been traced by Webster, has spread from Central America and Mexico 
 northward along the Gulf coast into the United States, following three 
 paths: (i) along the Atlantic coast to Cape Breton; (2) along the 
 ]\Iississippi valley and northward into Manitoba; (3) along the western 
 coast of Central America and Mexico into Cahfornia and other Western 
 states. Everywhere this insect has found wild grasses upon which to 
 feed, but has readily forsaken these for cultivated grasses upon 
 occasion. 
 
 Every year some of the southern butterflies reach the Northern states, 
 where they die without finding a food plant, or else maintain a precari- 
 ous existence. Thus Iphiclides ajax occasionally reaches Massachusetts 
 as a visitor and a visitor only; Lartias philenor, however, finds a limited 
 amount of food in the cultivated Aristolochia. P. thoas, one of the pests 
 of the orange tree in the South, is highly prized as a rarity by New Eng- 
 land collectors and is able to perpetuate itself in the Middle States on the 
 prickly ash (Xanthoxylum). The strong- winged grasshopper, Schisto- 
 cerca americand, belonging to a genus the center of whose dispersion is 
 tropical ; America, ranges freely over the interior of North x\merica, 
 sometimes in great swarms, and its nymphs are able to survive in 
 moderate numbers in the southern parts of Illinois, Ohio and other 
 states of as high latitude, while the adults occasionally reach Ontario, 
 Canada. 
 
 Many species are now so widely distributed that their former paths 
 of -diffusion can no longer be ascertained. The army worm {Cirphis 
 unipuncta), feeding on grasses, and occurring all over the United States 
 south of Lat. 45° 23' N., is found also in Central America, throughout 
 South America, and in Europe, Africa, Japan, China, India, etc.; in 
 short, it occurs in all except the coldest parts of the earth, and where it 
 originated no one knows. 
 
 Determination of Centers of Dispersal. — In accounting for the 
 present distribution of fife, naturalists employ several kinds of evidence. 
 Adams recognizes ten criteria, aside from palaeontological evidence, for 
 determining centers of dispersal: 
 
 I. Location of greatest dififerentiation of a type. 
 
340 ENTOMOLOGY 
 
 2. Location of dominance or great abundance of individuals. 
 
 3. Location of synthetic or closely related forms (Allen). 
 
 4. Location of maximum size of individuals (Ridgway-AUen) . 
 
 5. Location of greatest productiveness and its relative stability, 
 in crops (Hyde). 
 
 6. Continuity and convergence of lines of dispersal. 
 
 7. Location of least dependence upon a restricted habitat. 
 
 8. Continuity and directness of individual variations or modifica- 
 tions radiating from the center of origin along the highways of dispersal. 
 
 9. Direction indicated by biogeographical affinities. 
 
 10. Direction indicated by the annual migration routes, in birds 
 (Palmen). 
 
 2. Geological 
 
 Means of Fossilization. — Abundant as insects are at present, they 
 are comparatively rare as fossils, the fossil species forming but one per 
 cent, of the total number of described species of insects. The absence 
 of insect remains in sedimentary rocks of marine origin is explained by 
 the fact that almost no insects inhabit salt water; and terrestrial forms 
 in general are ill-adapted for fossihzation. The hosts of insects that die 
 each year leave remarkably few traces in the soil, owing perhaps, in 
 great measure, to the dissolution of chitin in the presence of moisture. 
 
 Most of the fossil insects that are known have been found in vege- 
 table accumulations such as coal, peat and lignite, or else in ancient 
 fresh-water basins, where the insects were probably drowned and 
 rapidly imbedded. At present, enormous numbers of insects are 
 sometimes cast upon the shores of our great lakes — a phenomenon which 
 helps to explain the profusion of fossil forms in some of the ancient 
 lake basins. 
 
 Insects in rich variety have been preserved in amber, the fossilized 
 resin of coniferous trees. This substance, as it exuded, must have en- 
 tangled and enveloped insect visitors just as it does at present. Many 
 of these amber insects are exquisitely preserved, as if sealed in glass. 
 Copal, a transparent, amber-like resin from various tropical trees, par- 
 ticularly Leguminosae, has also yielded many interesting insects. 
 
 Ill-adapted as insects are by organization and habit for the com- 
 moner methods of fossilization, the number of fossil species already 
 described is no fewer than three thousand. 
 
 Localities for Fossil Insects.^ — The Devonian of New Brunswick 
 has furnished a few forms, found near St. John, in a small ledge that 
 
DISTRIBUTION 34I 
 
 outcrops between tide-marks; these forms, though few, are of extraor- 
 dinary interest, as will be seen. 
 
 For Carboniferous species, Commentry in France is a noted locality, 
 through the admirable researches of Brongniart, who described from 
 there 97 species of 48 genera, representing 12 families or higher groups, 
 10 of which are regarded as extinct; without including many hundred 
 specimens of cockroaches which he found but did not study. In this 
 country many species have been found in the coal fields of Illinois, 
 Nova Scotia, Rhode Island, Pennsylvania and Ohio. 
 
 Many fine fossils of the Jurassic period have been found in the litho- 
 graphic limestones of Bavaria; 143 species from the Lias — four fifths of 
 them beetles — were studied by Heer. 
 
 The Tertiary period has furnished the majority of fossil specimens. 
 To the Oligocene belong the amber insects, of which 900 species are 
 known from Baltic amber alone, and to the same epoch are ascribed the 
 deposits of Florissant and White River in Colorado and of Green River, 
 Wyoming. These localities — the richest in the world — have been made 
 famous by the monumental works of Scudder. At Florissant there is an 
 extinct lake, in the bed of which, entombed in shales derived from vol- 
 canic sand and ash, the remains of insects are found in astonishing pro- 
 fusion. For Miocene forms, of which 1,550 European species are 
 known, the QEningen beds of Bavaria are celebrated as having furnished 
 844 species, described by the illustrious Heer. 
 
 Pleistocene species are supplied by the peats of France and Europe, 
 the lignites of Bavaria, and the interglacial clays of Switzerland and 
 Ontario, Canada. 
 
 Silurian and Devonian. — The oldest fossil insect known consists of 
 a single hemipterous wing, Protocimex, from 
 the Lower Silurian of Sweden. Next in age 
 comes a wing, PalaoUaUina (Fig. 301), of 
 doubtful position,^ from the Middle Silurian 
 of France. Following these are six specimens fig. 301.— Paiaobiattina 
 
 of as many remarkable species from the Devon- gfotS'iAR?^'^^ size.-After 
 ian shales of New Brunswick. The specimens, 
 
 to be sure, are nothing but broken wings, yet these few fragments, 
 interpreted by Dr. Scudder, are rich in meaning. All are neuropteroid, 
 but they cannot be classified satisfactorily with recent forms on account 
 of being highly synthetic in structure. Thus Platephemera antiqua (Fig. 
 
 * There is some evidence, it should be said, that this species is not an insect. Handlirsch 
 denies also that Protocimex is an insect. 
 
342 
 
 ENTOMOLOGY 
 
 302), though essentially a May fly of gigantic proportions (spreading 
 probably 135 mm.), has an odonate type of reticulation; while Xenoneura 
 (Fig. 303) combines characters which are now distributed among Ephe- 
 meridas, Sialidas, Rhaphidiidae, Coniopterygidas, and other families, 
 besides being in many respects unique. These Devonian forms attained 
 huge dimensions as compared with their recent representatives; Gere- 
 phemera, for example, had an estimated expanse of 175 millimeters. 
 
 Fig. 302. — Platephemera antiqua, natural size. — After Scudder. 
 
 Fig. 303. — Xenoneura antiquorum, five times natural size. — After Scudder. 
 
 Carboniferous. — The Carboniferous age, with its luxuriant vegeta- 
 tion, is marked by the appearance of insects in great number and variety, 
 still restricted, however, to the more generaHzed orders. The domi- 
 nance of cockroaches in the Carboniferous is especially noteworthy, no 
 fewer than 200 Palaeozoic species being known from Europe and North 
 America. These ancient roaches (Fig. 304) differed from their modern 
 descendants in the similarity of the two pairs of wings, which were alike 
 in form, size, transparency and general neuration, with six principal 
 nervures in each wing; while in recent cockroaches the front wings have 
 become tegmina, with certain of the veins always blended together, 
 though the hind wings have retained their primitive characteristics with 
 a few modifications, such as the expansion of the anal area. Carboni- 
 ferous cockroaches furthermore exhibit ovipositors, straight, slender, 
 and half as long again as the abdomen — organs which do not exist in 
 recent species. 
 
DISTRffiUTION 
 
 343 
 
 Lithomantis (Fig. 305), a remarkable form from Scotland, possessed 
 in addition to its four large neuropteroid wings, a pair of prothoracic 
 
 Fig. 304. — Eloblatlina ma- Fig. 305. — Lithomantis carbonarius, showing protho- 
 
 zona, a Carboniferous cock- racic appendages. Two thirds natural size. — After WooD- 
 roach from Illinois. Twice ward. 
 natural size. — After Scudder 
 in Miall and Denny. 
 
 Fig. 306. — Stenodictya lobata, showing wing-like appendages of prothorax and abdomen. 
 Natural size. — After Handlirsch. 
 
 wing-like appendages which, provided they may be regarded as homolo- 
 gous with wings, represent a third pair, either atrophied or undeveloped 
 
344 ENTOMOLOGY 
 
 — a condition which is never found today, unless the patagia of Lepidop- 
 tera represent wings, which is unhkely. 
 
 Stenodidya lohata (Fig. 306) described by Brongniart from the 
 Upper Carboniferous of Commentry, France, also bears prothoracic 
 "wings" and, in addition, eight pairs of abdominal wing-like or gill-like 
 appendages. No fewer than five families of Palaeozoic insects are 
 represented by specimens having prothoracic wings. 
 
 From the rich deposits of Commentry, Brongniart has described 
 several forms of striking interest. Dictyoneura is a Carboniferous genus 
 
 Fig. 307. — Eugereon bockingi. Three quarters natural size. — After Dohrn. 
 
 with neuropteroid wings and an orthopteroid body, having, in common 
 with several contemporary genera, strong isopteran affinities. Coryda- 
 loides scudderi, a phasmid, has an alar expanse of twenty-eight inches. 
 The Carboniferous prototypes of our Odonata were gigantic beside their 
 modern descendants, one of them {Meganeura) having a spread of more 
 than two feet; they were more generalized in structure than recent 
 Odonata, presenting a much simpler type of neuration and less differen- 
 tiation of the segments of the thorax. The Carboniferous precursors of 
 our May flies attained a high development in number and variety; in 
 fact, the Ephemeridae, like the Blattidae, achieved their maximum 
 development ages ago, when they attained an importance strongly con- 
 trasting with their present meager representation. 
 
 The Permian has supplied a remarkable genus Eugereon (Fig. 307) 
 
DISTRIBUTION 345 
 
 with hemipterous mouth parts associated with filiform antennaj and 
 orthopteroid wings. The earliest unquestionable traces of insects with 
 an indirect metamorphosis are found in the Permian of Bohemia, in 
 the shape of caddis-worm cases. 
 
 Triassic. — Triassic cockroaches present interesting stages in the 
 evolution of their family. Through these Mesozoic species the con- 
 tinuity between Palaeozoic and recent cockroaches is clearly established 
 — which can be said of no other insects; and in fact of no other animals, 
 the only comparable cases being those of the horse and the moUuscan 
 genus Planorhis. In the Triassic period occur the first fossils that can be 
 referred indisputably to Coleoptera and Hymenoptera, the latter order 
 being represented first, as it happens, by some of its most specialized 
 members, namely ants. 
 
 Jurassic. — At length, in the Jurassic, all the large orders except Lep- 
 idoptera occur; Diptera appear for the first time, and Odonata are rep- 
 resented by many well-preserved specimens, while the Liassic 
 Coleoptera studied by Heer number over one hundred species. The 
 Cretaceous has yielded but few insects, as might be expected. 
 
 Tertiary. — In the rich Tertiary deposits all orders of insects occur. 
 Baltic amber has yielded Collembola, some remarkable Psocidae, many 
 Diptera, and ants in abundance. Of 844 species taken from the noted 
 Miocene beds of OEningen, nearly one half were Coleoptera, followed by 
 neuropteroid forms (seventeen per cent.) and Hymenoptera (fourteen 
 per cent.) ; ants were twice as numerous in species as they are at present . 
 in Europe. Almost half the known species of fossil insects have been 
 described from the Miocene of Europe. To the Miocene belongs -the 
 indusial limestone of Auvergne, France, where extensive beds — in some 
 places two or three meters deep — consist for the most part of the cal- 
 cified larval cases of caddis flies. 
 
 At Florissant, as contrasted with Q^ningenby Scudder, Hymenoptera 
 constitute 4.0 per cent, of the specimens, owing chiefly to the predomi- 
 nance of ants; Diptera follow with 30 per cent, and then Coleoptera with 
 13 per cent. Modern famihes are represented in great profusion. The 
 material from Florissant and neighboring locahties includes a Lepisma, 
 fifteen species of Psocidae, more than thirty species of Aphididae, and 
 more than one hundred species of Elateridae, while the Rhynchophora 
 number 193 species as against 150 species from the Tertiary of Europe. 
 Tipulidae are abundant and exquisitely preserved, while Bibionidae, as 
 compared with their present numbers, are surprisingly common. Nu- 
 merous masses of eggs occur, undoubtedly sialid and closely like those of 
 
346 ENTOMOLOGY 
 
 Corydalis. Sialid characters, indeed, appear in the oldest fossils known, 
 and are strongly manifest throughout the fossil series, though among 
 recent insects Sialidae occupy only a subordinate place. Strange to say, 
 few aquatic insects have been found in this ancient lake basin. 
 
 Fossil butterflies are among the greatest rarities, only seventeen 
 
 being known; yet Florissant has 
 contributed eight of these, a few of 
 which are marvelously well pre- 
 served (Fig. 308), as appears from 
 Scudder's figures. Two of the 
 Florissant specimens belong to 
 Libytheinae, a group now scantily 
 represented, though widely distri- 
 buted over the earth. The group 
 is structurally an archaic one, and 
 Fig. 308. — Prodryas persephone, a fossil its recent members (forming only 
 
 butterfly from Colorado. Natural size. — •1.1 1 i.i r .-i •, m i 
 
 After ScuDDER. One eight-hundredth of the described 
 
 species of butterflies) are doubtless 
 relicts. 
 
 Taken as a whole, the insect facies of Tertiary times was apparently 
 much the same as at present. The Florissant fauna and flora indicate, 
 however, a former climate in Colorado as warm as the present climate 
 of Georgia. 
 
 Quaternary. — The interglacial clays of Toronto, Ontario, have yielded 
 fragments of the skeletons of beetles to the extent of several hundred 
 specimens, about one third of which (chiefly elytra) were sufficiently 
 complete or characteristic to be identified by Dr. Scudder, who found in 
 all 76 species of beetles, representing 8 families, chiefly Carabidae and 
 Staphylinidae. All these interglacial beetles are referable to recent 
 genera, but none of them to recent species, though the differences 
 between the interglacial species and their recent alHes are very slight. 
 As a whole, these species "indicate a climate closely resembling that of 
 
 Ontario to-day, or perhaps a sHghtly colder one One cannot 
 
 fail, also, to notice that a large number of the allies of the interglacial 
 forms are recorded from the Pacific coast." (Scudder.) The writer, 
 who has studied these specimens, has been impressed most by their 
 Hkeness to modern species. It is indeed remarkable that so little 
 specific differentiation has occurred in these beetles since the inter- 
 glacial epoch — certainly ten thousand and possibly two to three hundred 
 thousand years ago. 
 
DISTRIBUTION 347 
 
 General Conclusions. — Unfortunately, the earliest fossils with 
 which we are acquainted shed much less light upon the subject of insect 
 phylogeny than one might expect. The few Devonian forms, though 
 synthetic indeed as compared with their modern allies, are at the same 
 time highly organized, or far from primitive, and their ancestors have 
 been obliterated. 
 
 The general plan of wing structure, as Scudder finds, has remained 
 unaltered from the earliest times, though the Devonian specimens 
 exhibit many peculiarities of venation, in which respect some of them are 
 more specialized than their nearest living allies, while none of them 
 have much special relation to Carboniferous forms. 
 
 Carboniferous insects are more nearly related to recent forms than are 
 the Devonian species, but present a number of significant generalized 
 features. Generally speaking, the thoracic segments were similar and 
 unconsolidated, and the two pairs of diaphanous wings were alike in 
 every respect — in groups that have since developed tegmina and dis- 
 similar thoracic segments. The Carboniferous precursors of our cock- 
 roaches, phasmids and May flies have been mentioned. Palasozoic 
 insects were grouped by Scudder into a single order, Palaeodictyoptera, on 
 account of their synthetic organization, though other authors have tried 
 to distribute them among the modern orders. This disagreement will 
 continue until, with increasing knowledge, our classification becomes 
 less arbitrary and more natural. 
 
 Mesozoic insects are interesting chiefly as evolutionary links, 
 notably so in the case of cockroaches — the only insects whose ancestry 
 is continuously traceable. In this era the large families became differen- 
 tiated out. 
 
 Most of the Tertiary species are referable to recent genera, peculiar 
 famihes being highly exceptional, while all the Quaternary species 
 belong to recent genera. 
 
 Hemiptera appear in the Silurian; Neuroptera (in the old sense) in 
 the Devonian; Thysanura and Orthoptera, Carboniferous; Coleoptera 
 and Hymenoptera, Triassic; Diptera, Jurassic; and Lepidoptera not 
 until the Tertiary. 
 
 Since Scudder's day, considerable additions to the knowledge of our 
 fossfl insects have been made by Professor T. D. A. Cockerell and 
 by Professor H. F. Wickham. 
 
 A comprehensive and richly illustrated account of fossil insects is 
 given by Handlirsch in his great work. Die fossilen Insekten. 
 
CHAPTER XIII 
 
 INSECT ECOLOGY 
 
 Ecology is the physiology of organisms in relation to environment. 
 It is the physiology of entire organisms rather than of organs. It deals 
 with, the reactions of organisms to the conditions of their existence, 
 including the modification of these reactions in relation to changes of 
 environment. 
 
 Though its subject matter is primarily animals and plants, ecology 
 is based upon all the sciences, and cannot be pursued most precisely 
 without the aid of some mathematics. 
 
 Insect life in its omnipresence and diversity affords countless illus- 
 trations of ecological principles, under which innumerable isolated 
 observations fall into organization. 
 
 The qualitative study of the subject is simply a matter of accurate 
 and thorough observation and correct inference, with the aid of the 
 simplest kind of experimentation. Even in quantitative investigation, 
 the ecological principles may be brought out with the use of such 
 inexpensive means as thermometers, ice-boxes, weather maps, etc. 
 For the most refined work, however, elaborate appliances for controlling 
 ecological factors are often necessary. 
 
 It should be remembered that the study of insects alone gives only 
 a partial understanding of ecology, with an imperfect perspective of 
 the subject. 
 
 The ecology of individuals is known as Autecology; that of com- 
 munities, as Synecology. 
 
 I. Conditions of Terrestrial Existence 
 I. Soil 
 
 The edaphic conditions of existence (those relating to the soil) are 
 the same for animals and plants, but are utiHzed in different ways by 
 these organisms. Plants can utilize inorganic constituents of the soil 
 as food, but animals can not. All the food of animals, with such 
 exceptions as water and salt, is derived in the last analysis from plants. 
 
 Structure. — The retention of water by the soil depends largely upon 
 the size of the soil particles; soil of small particles holding more water 
 
 348 
 
INSECT FXOLOGY 349 
 
 than one of large particles. Water evaporates more rapidly from 
 coarse soils than from fine ones, but in loose soils the more rapid evapora- 
 tion from the surface forms an aerated "mulch" which retards further 
 evaporation. The different capacities of different soils for absorbing 
 or retaining moisture affects insects indirectly by its effects on vegetation, 
 or may affect them directly. The compactness of loose soils varies with 
 the amount of water present, which is of importance to burrowing insects. 
 A good example of this is seen in the sandy beach of a lake, when the 
 sand wet by waves becomes firm; the water evaporates rapidly, however, 
 until the sand is dry again, in proportion to its nearness to the surface. 
 In such sand, with frequent alternations from wet to dry, insects do not 
 live; though some forms, as tiger beetles and beetles of the genus 
 Bembidion, burrow in the sand a little farther back from the shore, 
 where the fluctuations in the water content are not so great. 
 
 In a loose soil white grubs or wireworms go easily and rapidly from 
 one plant to another. Tiger beetles and ants need soil of a consistence 
 which will maintain the burrows after they are made. Caterpillars, 
 grubs, etc., about to pupate, can not burrow in soil that is too hard, and 
 frequently avoid also soil that is too loose. The bollworm if unable to 
 dig into hard baked soil will enter cracks in the soil. Some grasshoppers, 
 on the other hand, prefer hard-packed soil in which to lay their eggs. 
 In making their pupal cells in the ground, larvae press the surrounding 
 soil into a compact wall, often adding a cementing fluid which is fre- 
 quently waterproof. The bollworm, or corn ear worm, lines its burrow 
 with silk. 
 
 A soil of loose texture faciHtates the emergence of adult insects. 
 If the soil is too hard they may not be able to emerge until it has been 
 softened by rain. Plowing and roUing the soil of a stubble field in 
 summer is known to prevent the exit of Hessian flies. 
 
 The depth to which insects burrow in the ground depends upon the 
 physical nature of the soil, and temperature and moisture as well. 
 
 Chemical Conditions. — In addition to oxygen, carbon dioxide 
 and nitrogen, the soil contains other gases and various chemical com- 
 pounds, some of which are essential to plant life and therefore indirectly 
 to the welfare of animals. The character of the vegetation as determined 
 by the acidity or alkalinity of the soil affects the character of the insect 
 fauna. The acid water of bogs is directly unfavorable to insect life, 
 but is favorable to the growth of peculiar plants which are selected as 
 food by certain insects. In New Jersey, Mr. H. Bird, by acidulating 
 soil with an artificial bog water made with the extract of hemlock used 
 
350 ENTOMOLOGY 
 
 for tanning leather, succeeded in growing the pitcher plant, Sarracenia 
 purpurea, and in raising thereon a species of rare moth, Papaipema 
 appassionata, known for thirty years only by a unique type in the 
 British Museum. 
 
 Plants of alkaline desert soils have their characteristic insect fauna. 
 
 Air.- — The oxygen content of subterranean air is important directly 
 for respiration; indirectly for its effects on vegetation. Aeration of the 
 soil is essential to subterranean life. In too compact a soil insects 
 suffer from lack of oxygen and excess of carbon dioxide, and may 
 experience also the effects of excessive evaporation and mechanical 
 difficulties in burrowing. 
 
 Water. — For their welfare, soil insects must have neither too much 
 nor too httle water. They may be drowned by gravitational water, 
 which acts also by fiUing the air spaces around soil particles. Sub- 
 mersion was used effectively in France against the destructive Phyl- 
 loxera of the grape. Capillary water is, on the contrary, favorable to 
 the insect life until it evaporates to excess. As with terrestrial insects, 
 the vital effects of water and temperature are produced through 
 evaporation, in relation to which soil forms exhibit various adaptations. 
 As the soil dries, ants dig deeper. The depth of pupal chambers, 
 their compact waterproofed walls, and the air space around the pupa, 
 and the closing of the entrance to the burrow, all tend to protect the 
 pupa from undue loss of bodily moisture. 
 
 With the tiger beetles, the amount of moisture determines whether 
 eggs are to be laid, and their number if laid; eggs being absent in dry 
 soil (Shelford). 
 
 Temperature.— There are great differences in the temperatures of 
 different soils, from dry sands to moist shaded humus. Temperature 
 and moisture determine largely the character of the flora and of the 
 accompanying fauna. The greater the depth of soil the lower the tem- 
 perature as a rule. Ants and other insects will dig deeper to avoid heat 
 as well as dryness. Ants often find suitable conditions of temperature 
 and moisture under stones or logs. 
 
 In the case of insects that are said to be killed by heat, the mortality 
 is due primarily to evaporation and secondarily to the coagulation of the 
 protoplasm; perhaps also to ultra-violet rays. 
 
 Physiographic Conditions. — As environmental factors there must 
 be considered also the nature of the surface of the soil as regards exposure 
 or cover, the slope of the soil, and the altitude at which it is found. 
 All these things affect the fauna. Angle of slope has an effect in 
 
INSECT ECOLOGY 35 I 
 
 determining the presence or absence of oviposition burrows of tiger 
 beetles, and the presence, absence, or number of eggs laid (Shelf ord). 
 
 Nutriment. — The food of soil insects may be roots or stems of 
 plants, dead animal or vegetable matter, other insects or other animals. 
 Some insects are parasitic on burrowing mammals. Many ants derive 
 part of their nourishment from the root-sucking aphids or coccids 
 which they attend. Ants and termites sustain diverse relations as 
 regards food with various other insects and other arthropods that live 
 in their nests. Some species that burrow near the surface, as tiger 
 beetles and ant-lions, capture their prey from the surface of the ground. 
 
 Soil that contains no organic matter, as pure quartz sand, is food 
 for no insect. Some larvae, as white grubs and wireworms, that subsist 
 primarily on roots of plants, can if necessary thrive for many months on 
 a diet of soil alone, but only because of the organic matter that it 
 contains. 
 
 Interactions. — The subject of interactions in the soil environment 
 can only be touched upon here. The character of the soil itself is 
 changed by the plants and animals that inhabit it. Thus burrowing 
 animals, as worms, crawfishes, insects, moles, mice, many larger 
 mammals, etc., alter the distribution and the physical and chemical 
 composition of the soil. Bacteria and fungi play important parts. 
 The soil is not fully effective in protecting its insect inhabitants from 
 predaceous and parasitic enemies among other insects, and soil insects 
 are themselves food for many birds, mammals, and other of the larger 
 animals. 
 
 2. Atmosphere 
 
 The most conspicuous effect of hght is its directive effect on locomo- 
 tion. This phenomenon is discussed in another chapter (p. 306), 
 where it is shown that insects react either positively or negatively to 
 light, are often attuned to definite ranges of light intensity, and react 
 differently to hght of different wave lengths. The results of photo- 
 tropism are often incidentally adaptive. As examples, the positive 
 reaction may take insects to their food, cause the nuptial flight of ants 
 or termites, or the swarming of bees; while the negative response may 
 lead insects into places of concealment, pupation, or hibernation. 
 Structures and functions are correlated with the presence or the absence 
 of light; for example, those of the eyes. Insects that Kve in darkness, 
 as boring species, subterranean forms, and cave insects, exhibit special 
 
352 ENTOMOLOGY 
 
 modifications in relation to the absence of light that are mentioned in 
 other parts of this book. 
 
 Growth.- — In nature the effects of light on growth are bound up 
 with those of temperature. The temperature of the air varies with 
 light {insolation, or exposure to the sun's rays) . Cloudy summer days 
 are cooler than sunny days. Cloudy winter days are warmer. (Shel- 
 ford.) Light affects the rate of growth, or more precisely, some wave 
 lengths are more effective than others. Beclard reared larvae of the 
 flesh-fly, Musca carnivora, from the eggs, under glass bells of different 
 colors. The largest larvae were found under violet or blue; the smallest 
 under green; the colors producing their effects in the following order: 
 violet, blue, red, yellow, white, green. Under violet the larvas were 
 three-quarters greater than under green. Green rays retarded growth, 
 as did also white light. (C. B. Davenport.) 
 
 Activity. — Sunshine, aside from temperatures, unless they are 
 extreme, has a stimulating effect on reproduction and other activities 
 in flies (Bishopp, Dove, Parman) ; and this is true probably for most 
 diurnal insects. On cloudy days the boll weevil and most other 
 insects as well are less active than on clear days, without regard to 
 temperature. 
 
 Exposure to hot sunshine kills pupae of the bollworm, plum curculio 
 and other forms. This result is due primarily to heat with evaporation, 
 but possibly the ultra-violet rays also exert some influence. 
 
 Sleep.- — Whatever the temperature may be, insects go to sleep when 
 ■ night falls, and do so during the daytime if clouds diminish the sunlight 
 beyond a certain point which varies for different species. If it becomes 
 very cloudy, the mourning-cloak, Vanessa antiopa, seeks some crevice 
 and goes to sleep, but is quickly aroused, however, by returning sun- 
 shine. The sleep of insects doubtless has the same physiological 
 results as that of other animals. 
 
 "A few species seem to choose protectively colored situations, and 
 others select sites which are in various ways protective. Some which 
 are solitary by day are gregarious at night, and some insects sleep with 
 all the regularity of a theoretical modern infant, while others of a more 
 unsystematic life snatch a wink when they can. " (P. Rau and N. Rau.) 
 
 Temperature 
 
 Temperature Limits. — It goes without saying that the life-processes 
 and the activities of every animal or plant are confined within a certain 
 range of temperature, outside of which the organism cannot exist. 
 
INSECT ECOLOGY 353 
 
 This range is different for different species, for the same species in differ- 
 ent seasons or places, and is different even for different individuals of 
 the same species under apparently equal conditions, and for different 
 stages in the growth or development of the same individual. The 
 temperature-range is affected by food, moisture, evaporation, and 
 several other factors. 
 
 Growth and development proceed most rapidly in a certain optimum 
 range of temperature, within which there is, at least theoretically, an 
 optimum degree of temperature. At and above a certain degree of 
 high temperature heat-rigor sets in, and may or may not be fatal to an 
 organism, according to the duration of the exposure to the temperature. 
 This maximimi temperature has as its upper limit the uUramaximum, 
 at which the organism dies at once, probably because of the coagulation 
 of proteids in the protoplasm. At a certain degree of low temperature, 
 cold-rigor takes place; the point at which it occurs being near the freez- 
 ing point, on account of the fluid content of protoplasm. Below this 
 minimum is an ultraminimum temperature, at which the organism dies. 
 
 The following examples of temperature-limits are from Davenport's 
 Experimental Morphology. 
 
 Insect Maximum Ultramaximum 
 
 Springtail, Podiira similata 27° C. 36.0° C, 
 
 Mosquito, Culex pipiens 40° C. 
 
 Larva of fly, Musca vomitoria , 42 . 5° C. 
 
 Pupa of fly, Musca vomitoria 43 . 7° C. 
 
 Silkworm, Bombyx mori 42 . 5° C. 
 
 Back-swimmer, Notoneda 45 . 0° C. 
 
 It should be noted that the Podura (near Achorutes) has a thin 
 integument, and can not live in a dry atmosphere. The pupa of the 
 fly is protected somewhat by its puparium, and the back-swimmer by 
 a fairly thick integument. 
 
 Insect Ultraminimum 
 
 Honey bee, Apis mellifera — i . 5° C. 
 
 House fly, Musca domestica — 5 . 0° C. 
 
 Larva of cockchafer, Melolontha — 15 .0° C. 
 
 Adult cockchafer, Melolontha — 18 . 0° C. 
 
 Davenport notes that the large size and thick covering of the beetle, 
 Melolontha prevent the rapid loss of heat. 
 
 Activity in Relation to Temperature. — The range of activity of the 
 adult cotton boll weevil lies between 56° F. and 95° F. From 95° to 
 122° is the range of aestivation, within which the beetles are inactive. 
 From 122° to 140° (soil temperature) is an upper range of fatal tem- 
 
 23 
 
354 ENTOMOLOGY 
 
 peratures, in which the weevil dies in 15 minutes to i second, according 
 to the temperature, 140° being the maximum fatal temperature. 
 
 In the descending scale of temperature, there is a range between 56° 
 to 24° within which the beetles hibernate. Below 24° is the lower range 
 of fatal temperatures, with 7° as the minimum fatal temperature. As 
 the hmits of these ranges vary with moisture and other factors, these 
 ranges, as given by Hunter and Pierce (191 2) are necessarily approxima- 
 tions; but they serve to illustrate the fact that such ranges exist, and 
 are accurate for the particular conditions under which they were made. 
 
 It may be mentioned that Hunter and Pierce found that the winter 
 cold is, on the average, almost twice as effective as summer heat in 
 kilhng the beetle; which has several times been greatly reduced in 
 numbers by early freezes in the South. 
 
 High temperatures are more favorable to the activities of insects 
 than to those of human beings. The temperature range of activity 
 varies with different species. 
 
 The effect of temperature upon the locomotor activity of the boll 
 weevil was tested by Dr. A. W. Morrill, who found that as the tem- 
 perature was gradually raised the activity of the weevils increased up 
 to 105° F. At 95° the beetles were very active; at 86° they began to 
 lose their activity; and at 37° all movement ceased. Out of doors, 
 weevil activity began and ceased at about 75°; feeding continuing at 
 lower temperatures than oviposition. 
 
 The number of daily feeding punctures of the weevil was found to be 
 greatest at about 80° F., as was also the number of eggs laid. (Hunter 
 and Hinds.) 
 
 The curve representing the average number of eggs deposited daily 
 by the alfalfa weevil, Phytonomus posticus, follows the curve of the mean 
 daily temperature in all its major fluctuations, the highest record 
 (twenty-six eggs) occurring on the day (May 18) with the highest mean 
 temperature (72° F.) of any day previous to June 6. (T. H. Parks.) 
 
 By stimulating the activities of insects, high temperatures diminish 
 the longevity. Thus a worker honey bee that hibernates may live for 
 six or seven months, but an active worker in summer lives only five or 
 six weeks. 
 
 Other things being equal, the longevity of insects in general is 
 lengthened by a decrease in temperature and shortened by an increase 
 (when these temperatures are between about 42° and 72° F.) ; the differ- 
 ence in longevity of a species at different temperatures corresponding 
 roughly to the difference in temperature. (J. P. Baumberger.) 
 
INSECT ECOLOGY 
 
 355 
 
 Development in General.^The effects of temperature on the 
 development of insects are known in a qualitative way, and considerable 
 progress has been made in the quantitative study of the subject. At 
 a certain degree of low temperature during development an insect 
 becomes physiologically inactive, or dormant, without being killed, 
 and may resume activity when the temperature rises. This point 
 is termed the threshold of development {critical point, developmental 
 zero). Temperatures above this point that are conducive to develop- 
 ment are termed effective temperatures, and in ascertaining the number 
 of temperature units requisite to development, all temperatures below 
 the threshold of development are disregarded. The effects of high 
 temperatures in accelerating development, and of low temperatures in 
 retarding development, are known to all who have raised butterflies 
 or moths from pupae. 
 
 The theory used to be that the entire development of an insect, 
 from the time the egg is laid until the adult emerges, requires a fixed 
 number of effective degrees of temperature; the same being true also 
 for any stage of the insect, as egg, larva or pupa; that the entire develop- 
 ment, or any phase of the development, will not be completed until a 
 definite number of temperature units have been experienced, whether 
 the time required be long or short. The number expressing the total 
 temperature, or temperature constant, is obtained by multiplying the 
 mean daily temperature by the number of days required for the develop- 
 ment. Needless to say, the effects of temperature are obscured by 
 those of humidity, light, and several other influences in nature, and 
 become evident only under the exact conditions of experimentation. 
 
 For the development of the boll weevil, Hunter and Hinds (1905) 
 give the following summary: 
 
 
 Average 
 
 Average 1 
 
 Total 
 
 1 Total 
 
 period 
 
 effective 
 
 effective 
 
 Stage 
 
 observations 
 
 for stage, 
 
 temperature, 
 
 temperature, 
 
 
 
 Days 
 
 °F. 
 
 °F. 
 
 Egg 616 
 
 4.0 
 
 34-0 
 
 136.0 
 
 Larva 313 
 
 9.8 
 
 32.2 
 
 315-6 
 
 Pupa 530 
 
 S-S 
 
 33-2 
 
 182.6 
 
 Total development, sum of stages i , 459 
 
 193 
 
 32.9 
 
 634.2 
 
 Observations on entire period of 
 
 
 
 
 development 887 
 
 19.6 
 
 32.2 
 
 632.0 
 
 temperati 
 
356 ENTOMOLOGY 
 
 Exact experimental studies of the effects of temperature, moisture, 
 and other conditions have undoubtedly an important economic bearing. 
 For example: it was found, from experiments made by Professor. T. J. 
 Headlee in Manhattan, Kansas, that the cycle of the codUng moth 
 required an average of 39 days with an average of 1,006 degrees of 
 effective temperature (temperatures above the threshold of develop- 
 ment, given at that time as about 50° F.). With as exact a knowledge 
 of the other factors, particularly moisture, one ought to be able, with 
 the aid of weather reports, to foretell when a given brood of the cod- 
 ling moth will appear; which would evidently be of advantage to 
 fruit-growers. 
 
 The subject is, however, not so simple as it was thought to be. 
 Sanderson (1908, 1910), who has given a useful discussion of this sub- 
 ject, showed "that upon purely theoretical grounds there could be 
 no uniform accumulation of temperature or 'thermal constant' for the 
 various stages of insect growth, but that the relation of temperature to 
 growth phenomena was probably different for each species and might 
 be expressed by a curve, the abscissas of which represent degrees of 
 temperature and the ordinates represent the time factor. The impor- 
 tance of considering the so-called law of the velocity of chemical reaction 
 as influenced by temperature was pointed out and it was shown that the 
 velocity of reaction varies at different temperatures. It was shown 
 that both the so-called thermal constant and coefficient of velocity 
 increase as the temperature is lowered from the optimum of the species, 
 and that the curve for each species and phase of growth or activity of 
 that species must be plotted before the influence of temperature can be 
 exactly stated." Sanderson defined the " thermal constant" for insects 
 as "that accumulation of mean daily temperature above the 'critical 
 point' of the species, which will cause it to emerge from hibernation or 
 to transform from any given stage." (i)There is no uniform minimum 
 above which the temperature may be accumulated as effective, but this 
 varies with each species and phase of growth; (2) there is no "thermal 
 constant" as far as a mere accumulation of temperatures is concerned; 
 and (3) the velocity of reaction varies according to the range of tem- 
 peratures (Sanderson) . To illustrate the first of these three statements, 
 Sanderson cites the green-bug, Toxoptera graminum, which, as Hunter 
 and Glenn showed, begins to develop at 1.65° C, while its parasite, 
 Lysiphlebus tritici, shows no activity below about 4° or 5° C. For the 
 bollworm the point of cold rigor is about 10° C. In regard to the second 
 statement, Sanderson adds: "It is evident that any accumulation of 
 
INSECT ECOLOGY 357 
 
 temperature to secure a thermal or physiological constant cannot be 
 based on a mere addition where variable temperatures are involved, for 
 it is evident that every degree has a different value in relation to the 
 time factor. Thus as the mean temperature rises with the advance of 
 the season both the time for the pupal stage and the total accumulated 
 temperature for the pupal stage of the codhng moth decrease with the 
 advancing season. Though a fairly constant 'total effective tem- 
 perature' for any given phase of an insect's hfe or activity may be 
 secured for the summer months when there is a fairly constant mean 
 temperature, such an accumulation will have no meaning in regard 
 to the same phenomena in spring and fall when the temperatures are 
 more variable. If we wish to be exact, we must secure the temperature 
 curve for the species, based on the observation of a considerable num- 
 ber of individuals kept at different constant temperatures, or possibly 
 better at temperatures having a diurnal variation with constant maxi- 
 mum and minimum, and with fairly constant moisture conditions." 
 
 Krogh on Temperature-velocity.— The results obtained by Krogh, 
 which differ in some respects from those of other investigators, are 
 regarded as highly important. He finds that the temperature-velocity 
 curve expressing the rate at which segmentation takes place in frog's 
 eggs is, between 7° and 20.7°, a straight line. "An increase in tem- 
 perature between these limits produces a proportional increase in the 
 velocity with which the processes in the egg leading up to segmentation 
 take place. Below 7° the curve deviates from the straight line and the 
 reaction takes place more rapidly than one would expect from the 
 results obtained at higher temperatures. At the lowest temperature, 
 where the development certainly is no longer normal the curve turns 
 downward once more." 
 
 "The relation between the temperatures and the velocity of embry- 
 onic development is algebraic over a range of temperatures which 
 corresponds approximately to that at which normal development can 
 take place, and the curve representing the relation is consequently a 
 straight Hne." The velocity of embryonic development is a linear 
 function of the temperature. 
 
 In regard to the relation between temperature and the later stages of 
 development of the frog, Krogh says: "Between the temperatures 12° 
 and 25° the increment in velocity of the embryonic development of the 
 frog is therefore proportional to the temperature increment, but below 
 12° the development is more rapid than one would expect from the 
 formula." 
 
358 ENTOMOLOGY 
 
 Concerning the time of incubation of the eggs of a water beetle, 
 Acilius sulcatus, Krogh found that "when the reciprocal values of the 
 hatching times at the three temperatures are plotted against the tem- 
 peratures, they are found to lie in a straight line." (See also Krogh's 
 results on Pupal Development, p. 359.) 
 
 From all that has been said, then, it appears that there is a threshold 
 of development, which varies for different species and under different 
 conditions of existence, and that there is such a thing as an accumulation 
 of effective temperatures, or thermal constant. This constant is lim- 
 ited, however, to a certain range of temperature, below which growth or 
 development is faster than the constant requires, and above which it is 
 slower. This fact has an economic consequence; for basing predictions 
 upon the thermal constant alone, the spring brood of the codHng moth 
 or other insect would appear earlier than would be expected, and the 
 autumn brood later. 
 
 Reproduction. — Among plant lice parthenogenesis (reproduction 
 without fertilization) is apparently continuous and uninterrupted under 
 favorable environmental conditions; amphigony (reproduction by fertili- 
 zation) occurring only under the influence of low temperatures and, 
 as certain authors claim, inadequate food supply. Aphids in tropical 
 and other warm climates appear to have the tendency to reproduce 
 exclusively by parthenogenesis. The same condition apparently obtains 
 among greenhouse aphids in temperate climates. Aphids in colder 
 climates undergo heterogony (reproduction both by parthenogenesis 
 and amphigony) as an adaptation to adverse environmental conditions. 
 In certain species, the appearance of the amphigonous generation seems 
 to be a rhythmic process, which continues to occur at definite cyclical 
 intervals for some time after the influence of low temperature has been 
 eliminated. (L. B. Uichanco.) 
 
 Incubation. — The length of the egg period varies greatly according 
 to surrounding conditions, chiefly those of temperature. First brood 
 eggs of the codHng moth in Michigan hatched at outdoor temperatures 
 in 4 to 10 days, average 8 days, at an average mean temperature of 
 about 67.6° F.; eggs not hatching readily, however, during extremely 
 dry weather. (A. G. Hammar.) 
 
 In regard to the eggs of this species, C. B. Simpson says: " (i) Under 
 a low temperature the length of the egg stage is longer than at high 
 temperatures. (2) Under normal field conditions a small difference 
 in temperature causes but Httle change in the length of the stage. (3) 
 
INSECT ECOLOGY 359 
 
 The eggs are not in the same stage of maturity at the time of oviposition, 
 as at 24° F. we have from 9 to i8 days as the length of the stage." 
 
 As regards the threshold of development, Sanderson found that eggs 
 of the meal worm, Tenehrio molitor> failed to hatch at 9° or 10° C. but 
 hatched at 12° C. 
 
 The time from the deposition of the eggs to hatching of the chinch 
 bug' is variable, being longer if temperature is low, or shorter if high. 
 Thus first brood eggs (June) with an average mean temperature of 73° F. 
 hatch, in 17.3 days; and second brood eggs (August) at 76.58° F. in 11.45 
 days; the average for both broods being 14.4 days (Headlee and 
 McCoUoch). 
 
 Larval Development. — The discussion already given of growth and 
 development in relation to temperature applies of course to the larval 
 stage as well as to all other stages of development. 
 
 Larvae of the cotton boll weevil in squares developed in 7 days at 
 an average mean temperature of 75° F.; the total of effective tem- 
 peratures being 280 degrees F. (Hunter and Hinds.) 
 
 The bollworm, or corn ear worm, developed in 21 days at an average 
 mean temperature of 77° F.; the total of effective temperatures being 
 617 degrees F. (Quaintance and Brues.) 
 
 In these experiments it was assumed, as was formerly customary, 
 that only temperatures above 43° F. were effective for growth; this is 
 known to be a mistake. A small percentage of boll worms survive 
 a temperature of 34° F. ; but larvae subjected to temperatures somewhat 
 below freezing for one to two days are killed outright. 
 
 A constant temperature of 90° F. prevents the development of the 
 plant louse. Aphis avence; the optimum temperature for the production 
 of the wingless agamic forms being about 65° F. (H. E. Ewing.) 
 
 Warmth and dryness are favorable to the development of species 
 of "thrips" (Thysanoptera) and of the "red spider," a well known 
 mite that injures plants, especially in greenhouses. 
 
 Molting. — In the walking-stick, Diapheroirtera Jemorata, a low tem- 
 perature lengthens, while a high temperature shortens, on an average, 
 the interval between molts. A low temperature has a tendency to 
 decrease the number of molts, while a high temperature increases the 
 number. (H. H. P. and H. C. Severin.) 
 
 Pupal Development. — Krogh found that the extremely simple 
 relation (already described) between temperature and the velocity of 
 embryonic development held good also for the changes taking place 
 during the pupal life of the meal worm, Tenehrio molitor. He says: 
 
360 ENTOMOLOGY 
 
 (i) "The relation between the temperature and the velocity of pupal 
 development in Tenehrio cannot be expressed in terms of Van't Hoff's 
 formula, but between 18.5° and 28° the relation is algebraic and the curve 
 representing it is a straight line. (2) Beyond these hmits the curve 
 is not straight, but bends upwards at the lower temperature and down- 
 wards at the higher. Normal development is still possible at tempera- 
 tures between 15° (13.5°) and 2,^,°. (3) In the metaboHc activity of the 
 chrysalides of Tenehrio three stages are recognizable, corresponding 
 roughly to periods of disintegration of larval tissues, comparative rest 
 and formation of imago tissues. The metaboHsm in the tissue disin- 
 tegration period is practically of the same intensity as in the tissue for- 
 mation period. (4) The total amount of CO2 produced during the pupal 
 life is the same at all the temperatures examined (2i°-33°). There is 
 no optimum temperature with regard to metabolism. The relation be- 
 tween the temperature and the average CO2 production per hour 
 follows the same curve as that found for the velocity of development. " 
 
 Sanderson found that pupae of the meal worm, Tenehrio molitor, 
 failed to transform at 9° or 10° C. but transformed at 12° C; and that 
 pupae of the codling moth underwent little development below 55° F. 
 As a rule, the length of the pupal period is rapidly shortened by 
 increase of temperature. In Michigan, in spring, pupae of the codling 
 moth developed in an average of 18.4 days at an average mean tempera- 
 ture of 66° F. (A. G. Hammar.) The boll weevil in summer had a pupal 
 period of 5.1 days at an average mean temperature of 74.3° F. (Hunter 
 and Pierce.) 
 
 Life Cycle. — The total hfe cycle of the boll weevil, as obtained by 
 adding egg, larval, and pupal periods, was found to be 17.65 days, at 
 an average mean temperature of,77.8° F.; or an average of effective 
 temperaturesof 34.8 degrees; the total of effective temperatures being 
 614.2 degrees. As found by continuous observations on the same indi- 
 viduals, the life cycle was 17.7 days, with average mean temperature 76.9° 
 F.; average of effective temperatures 33.9 degrees, and total of effective 
 temperatures 600 degrees. (Hunter and Hinds.) Here, again, 43° F. 
 was assumed to be the " zero of development." 
 
 Acclimatization. — A few insects have become adapted to survive and 
 thrive under extremely high temperatures. Larvae of a fly, Stratiamys, 
 have been found in a hot spring in Colorado with a temperature of 69° C. 
 A water beetle in India was found in a warm spring at 44.4° C. Few 
 organisms, however, resist temperatures over 45° C. (Dr. C. B. Daven- 
 port.) Probably in successive generations of the ancestors of these forms 
 
INSECT ECOLOGY 361 
 
 there were some individuals that could endure a little more heat than 
 the others, and gradually a resistant strain of a species was built up. 
 
 Hibernation. — Temperature manifestly bears an important relation 
 to hibernation, the phenomenon of passing the winter in seclusion, 
 usually in a quiescent or inactive condition. The stimulus leading to 
 hibernation is usually decreased temperature in autumn. Thus the 
 cotton boll weevil begins to hibernate with the decrease in mean average 
 temperature to about 55°. (Hinds and Yothers.) Low temperature is 
 not always, however, the immediate incentive to hibernation. The 
 codling moth larva begins to hibernate before the temperature falls 
 and before food fails. The woolly bear caterpillars {Isia isabella) show 
 great regularity in the date at which they stop feeding, under con- 
 ditions of high temperature, different degrees of relative humidity, 
 and an abundance of fresh food. (Baumberger.) Mosquitoes begin to 
 hibernate before cold weather sets in. Among other influences there 
 may be a "tendency" to hibernate in many species. 
 
 The period of hibernation is prolonged by low temperatures. The 
 emergence of Cecropia moths from their cocoons may be delayed for 
 more than one year by placing the cocoons in cold storage with the 
 temperature a little above the freezing point. 
 
 Warm periods during winter may arouse insects to more or less 
 activity. It is commonly thought by collectors that a uniformly 
 cold winter is more favorable to a subsequent abundance of insect life 
 than a winter interrupted by mild spells. 
 
 Some insects do not awaken easily from the condition of hibernation, 
 while others respond readily to an increase of temperature. Examples 
 of the latter kind are the pomace flies {Drosophila), the house fly {Musca 
 domeslica) and other flies, and cockroaches. 
 
 The temperature requisite to emergence varies with the species. 
 The boll weevil, in hibernation by the time of the first hard frost, con- 
 tinues to hibernate until the mean average temperature has been for 
 some time above 65° F. (Hunter and Hinds.) In the case of the brown- 
 tail moth 34° F. is the threshold above which the temperature accumu- 
 lates in determining the time of emergence of the caterpillars from their 
 winter nests. (Sanderson.) 
 
 According to J. P. Baumberger, insects hibernate as (i) adults, 
 when their food habits are such that oviposition can take place on the 
 proper food at the earliest warm weather; (2) as larvae, when protected 
 from the cold and thus able to continue feeding to the latest date pos- 
 sible; (3) as pupae or eggs, because they are nonfeeding resistant stages. 
 
362 ENTOMOLOGY 
 
 , Many examples of adaptation in relation to winter conditions will 
 suggest themselves. Insects when about to hibernate seek shelter or 
 construct shelter, or both. They may simply crawl into existing 
 crevices or holes, as in the ground or in plants, under stones, logs, loose 
 bark, dead leaves, among stems or roots of plants, or may burrow into 
 the ground or into Hving or dead plants; or may miake cocoons or silken 
 nests or earthen cells, in which protection is afforded by surrounding air- 
 spaces. A curious situation for hibernation is that of back-swimmers 
 (Notonecta) , which have been found clustered in small cavities in thick 
 ice. Hibernating insects protect themselves more or less successfully 
 from such adverse inifluences as sudden changes of temperature, excess 
 of moisture or of dryness, invasion by fungi and bacteria, and from 
 attacks by other insects or by birds or mammals. 
 
 There are, however, many examples of unsuccessful hibernation. 
 Exceptionally low temperatures occasionally exterminate the boll weevil 
 in. certain areas, the mortality being increased by excessive rainfall. 
 Concerning the caterpillars of the brown-tail moth in their winter nests, 
 Sanderson says that where nests of average size containing 300-400 
 larvae were subjected to —24° F. or lower, from 72 to 100 per cent, of 
 the larvae were killed, but that in large nests from the same locaHty only 
 57 per cent, were killed; the larvae in the outer parts of the nests dying 
 first. 
 
 Following a period of subnormal temperatures in the state of 
 Washington, 1919, examinations were made of larvae of the codHng moth 
 under bark or burlap bands. It was found that wherever the minimum 
 temperature had been lower than —25° F. all larvag were killed. On 
 higher ground, where the minimum temperatures ranged from —20° to 
 — 25°, 80 to 90 per cent, of the larvae were killed. On still higher 
 ground, with minimum temperatures of —15° to —20°, the mortality 
 was approximately 70 per cent. One interesting fact noted was that 
 frequently, on tearing away the burlap band, one or two living larvae 
 would be found in the midst of a number of dead ones. It seems impos- 
 sible, in these cases, that the living larvae had any more protection than 
 the others. They must simply have had more vitality. (E. J. New- 
 comer.) 
 
 Distribution. — Minimum temperatures exert an important influence 
 in hmiting the northern distribution of insects, according to Sanderson, 
 from whose article on the subject the following extracts have been taken. 
 In New Hampshire (January, 1907) most of the hibernating caterpillars 
 of the brown-tail moth (excepting those in large nests) were killed off by 
 
INSECT ECOLOGY 363 
 
 a temperature of — 24° F. and below. The northern Hmit of the San 
 Jose scale insect corresponds approximately with the average annual 
 minimum isotherm of —15° F. This species dies out in central Wis- 
 consin and cannot survive in Minnesota. The wide-ranging cotton 
 bollworm, or corn ear worm, does not winter in Minnesota and no records 
 of injury occur in Montana, Wyoming or the Dakotas. The harlequin 
 cabbage bug maintains a foothold in the latitude of Long Island, 
 southern Ohio and southern Illinois, but has been unable to extend 
 its permanent range farther north on account of being killed off by cold 
 during hibernation. 
 
 A blanket of snow may offset the effects of minimum temperatures, 
 as with the striped cucumber beetle, which hibernates in the soil, the 
 codling moth, which passes the winter as a caterpillar in a cocoon under 
 bark, the scale insects, and many other species. 
 
 Occasional periods of extremely low temperature, occurring at 
 long intervals, are temporary checks upon the distribution, but the 
 exact northern limits of distribution depend rather upon the average 
 minimum temperature. 
 
 Pressure 
 
 From the few observations that have been made upon the subject it 
 appears that insects are sensitive to variations in atmospheric pressure, 
 as birds and mammals, including man, are said to be. Atmospheric 
 pressure as correlated with humidity affects animals indirectly through 
 its effects on evaporation. Thus high pressure with low humidity 
 means increased evaporation, and vice versa. 
 
 The following extracts are from an interesting article by D. C. Par- 
 man on the effect of storm phenomena on insect activity. 
 
 With a rapidly falling barometer several species of flies (Muscidae) 
 first become nervously active and then go into a state of partial coma, 
 in which state they are more subject to the action of other destructive 
 agencies, diseases probably included. The decrease in the number of 
 flies is quite appreciable after a severe tropical storm. 
 
 The adults of the fly Chrysomyia macellaria apparently will not chill 
 and die under the effect of a rising barometer as under a lowering baro- 
 metric pressure. 
 
 Insects attracted to hghts are more active during high barometric 
 periods and especially while the barometer is rising. 
 
 Bred adult Diptera tend to emerge on periods of rising barometer. 
 
364 ENTOMOLOGY 
 
 The hea\y emergences apparently always have been during periods of 
 high barometric pressure. Trappings and observations indicate that 
 muscoid Diptera are most abundant during long periods with slight 
 variations in barometric pressure, provided, of course, temperature, 
 humidity and rainfall are favorable. 
 
 Migration of the butterfly, Hypatus bachmani was observed during 
 the summer and fall of 19 16 to take place after storms, which indicates 
 that the flights were during high barometric pressure. 
 
 Moisture 
 
 Moisture ranks with temperature as a highly essential condition of 
 existence. Moisture affects terrestrial animals most vitally through 
 evaporation, which will be considered beyond. Here we may state 
 the effects of moisture without special reference to evaporation, but it 
 should be borne in mind that, in most of the phenomena discussed, 
 evaporation is an important factor. 
 
 Metabolism. — "Water plays a part in growth second in importance 
 to no other agent, so that in its absence growth cannot occur. As the 
 quantity is increased, growth is increased until an optimum is reached. 
 The amount imbibed does not, however, depend directly upon the 
 amount available, but rather upon the needs and habits of the 
 species." (Dr. C. B. Davenport.) 
 
 I. There is an optimum moisture for insect development. 2. This 
 optimum is not the same for different species. 3. The moisture which 
 may hasten the development of one species may retard the develop- 
 ment of another. (Bachmetjew.) Headlee adds that the rate of 
 metabolism in certain actively feeding insects with an abundant supply 
 of succulent food is not affected by large differences in atmospheric 
 moisture. He found that the green-bug, Toxoptera graminum, required 
 six days to pass from birth to maturity under a constant temperature of 
 80° F. and relative humidities of 37, 50, 70, 80 and 100 per cent. Pro- 
 fessor Headlee found also that, with the angoumois grain moth and the 
 bean weevil (i) increase in atmospheric humidity means increase in 
 speed of metabolism as measured by length of Ufe cycle; (2) the optimum 
 per cent, of atmospheric humidity is the highest which will not encour- 
 age a heavy growth of fungi; (3) 100 per cent, atmospheric humidity 
 destroys by encouraging the growth of fungi, and low atmospheric mois- 
 ture destroys directly — probably by the extraction of water; (4) while 
 the egg stage of the bean weevil, at least, is most sensitive to the effect 
 
INSECT ECOLOGY 365 
 
 of low atmospheric humidity, other stages are unfavorably affected; 
 (5) low atmospheric moisture might be developed into an efficient in- 
 secticide for certain species of stored grain insects. 
 
 Eclosion. — Moisture frequently determines the time of eclosion, 
 or the emergence of an insect from the pupa. Hessian flies do not 
 emerge from the puparia in dry weather, but issue in abundance after 
 rainfall in the proper season. When bred indoors, the flies do not 
 emerge from dry soil, even though the temperature be favorable, but 
 emerge shortly when the soil is moistened. 
 
 Activity. — Wet weather lessens the activities of insects exposed to 
 it. There are some exceptions, however. Larvae of the midges, Itoni- 
 didae, are all very sensitive to the presence of moisture, to which they 
 react positively. Larvae of the clover seed midge emerge from the clo- 
 ver heads usually in damp weather and often in large numbers when the 
 plants are wet with rain. Even when full grown and contracted in 
 readiness to form the puparium, they revive and move about if mois- 
 tened with water. 
 
 Oviposition. — It has been found that with the house fly, when 
 temperatures are high or moderately high, increased humidity hastens 
 egg-laying. This may be partially due to the effect of humidity on 
 the food and breeding substances — keeping them moist and attractive. 
 (Bishopp, Dove, Parman.) 
 
 Mortality.— Changes in relative humidity produce striking changes 
 in the mortality of Drosophila, the mortality increasing with a decrease 
 of humidity, the optimum humidity being loo per cent. The effects 
 of low humidity on mortality are most marked with very youngpupae, 
 whose covering permits a rapid evaporation of body moisture. After 
 a few hours, when integumental changes making evaporation more 
 difficult have set in, the eft'ects of low humidity are correspondingly 
 decreased. (A. Elwyn.) 
 
 Hibernation. — As a preparation for hibernation, the water content 
 of an organism is frequently reduced; as also in seeds or spores. Thus 
 the Colorado potato beetle loses about 30 per cent, of its gross weight 
 through the loss of water, which enables it to withstand a lower freezing 
 point and higher temperatures than if the protoplasm were not thus 
 condensed. (Tower.) As Sanderson notes, the time of emergence from 
 hibernation is controlled by moisture conditions as well as temperature, 
 or independent of temperature. Tower kept potato beetles for eight- 
 een months at a high temperature, but with a dry atmosphere, and 
 they emerged as soon as normal moisture conditions were produced. 
 
366 ■ ENTOMOLOGY 
 
 -Estivation. — In the case of the potato beetle, hibernation and (esti- 
 vation, or the condition of dormancy in summer, are practically the same 
 as regards the Hfe history of the insect, according to Tower. In the 
 tropics, where there is no hibernation, aestivation occurs over the dry 
 season. Though aestivation is associated mainly with heat, relative 
 humidity is also a factor, and "undoubtedly has the most important 
 influence upon the time of emergence of forms in aestivation during 
 the summer or in arid regions. (Sanderson.) During intense heat (95° 
 to 122° F.) the boll weevil aestivates temporarily on the ground under 
 protecting objects. 
 
 Drought. — ^Drought accompanies heat and affects animals and 
 plants through evaporation. It affects them directly, by desiccation; 
 or indirectly, by drying out the food plants or other food substances; 
 as with larvae of the boll weevil or the house fly. The range of dryness 
 within which insects can exist varies greatly with different species. 
 The chinch bug, unlike the Hessian fly, thrives in hot dry summers; 
 and species that inhabit arid regions are exceptionally resistant to 
 conditions of drought. 
 
 Precipitation. — Rainfall is direct or indirect in its influence on the 
 life and activities of insects. Eggs of the cotton boll worm are destroyed 
 in immense numbers by the mechanical force of the rain during violent 
 storms. The combined effects of rain, wind, and sandy particles 
 washed against the plants removes many eggs . (Quaintance and B rues .) 
 Young larvae of the bollworm feeding on corn early in the spring are 
 often washed down by rain and submerged for considerable periods. 
 Of twenty newly hatched larvae submerged for seventeen hours, all 
 but four survived the immersion. Larger larvae cannot stand such 
 long periods, but when dropped into water become stupefied after a few 
 minutes. Pupae could not withstand twenty-four hours' submergence 
 in rain water at normal summer temperatures, but at a temperature of 
 from 50° to 60° F. they were unharmed by from four to six days' 
 submergence. (Quaintance and Brues.) In the case of the cotton boll 
 weevil, a pupa survived an immersion of six hours; and 60 per cent, of 
 adults, one of fifteen hours. Ten adults were floated for one hun- 
 dred and twelve hours, after which only one was dead, but only two 
 were normal; after floating for only twenty-five hours, however, six of 
 the ten were normal. The floating of adults and infested squares ex- 
 plains the appearance of weevils in great numbers along high-water 
 line immediately after a flood. (Hunter and Hinds.) 
 
 Rains favor weevil increase in several ways. Frequent rains in- 
 
INSECT ECOLOGY 367 
 
 crease the growth of the plant and lead to the production of a larger 
 number of squares which may become infested. Driving rains knock 
 off infested squares, and by softening and moistening the food hasten 
 the development of the larvas within. Squares which are already upon 
 the ground are protected during rainy weather from sunshine and dry- 
 ing. Rain hinders the enemies of the weevil far more than it does the 
 development of the weevils themselves. On the other hand, it seems 
 probable that as many of the hibernating weevils perish from frequent 
 wetting as from exposure to the cold. (Hunter and Hinds.) 
 
 Frequent heavy rains in spring reduce greatly the numbers of 
 immature chinch bugs. 
 
 Moisture increases the mortality of insects indirectly by favoring 
 the growth of parasitic fungi or bacteria. Thus, in moist weather 
 chinch bugs may be almost exterminated by the fungus Sporotrichum, 
 as described with other examples in a preceding chapter. (See 
 page 218.) 
 
 This chinch bug fungus will not grow in a relative humidity of 90 
 per cent, or less, but will remain dormant in the spore stage for an indefi- 
 nite period (more than eighteen months, in dryness.) The fungus can 
 hardly have too much moisture in a state of nature; dashing and wash- 
 ing rains serving merely to distribute it. (Headlee and McColloch.) 
 
 Composition 
 
 The fact that animals require oxygen for respiration, and give off 
 carbon dioxide, while plants utihze carbon dioxide and set free oxygen, 
 need only be alluded to. 
 
 The chief constituents of air are oxygen, nitrogen, carbon dioxide, 
 water-vapor in varying amounts, with small quantities of gaseous 
 ammonia and hydrogen dioxide, and extremely small amounts of argon. 
 The organic matters present, as bacteria, spores of fungi, pollen grains, 
 etc., are highly important biologically. 
 
 In atmospheric air there are very nearly three parts of nitrogen to 
 one part of oxygen, whether by volume or by weight; with slight varia- 
 tions in these proportions. 
 
 The carbon dioxide is present in relatively small quantity, about 
 three parts in ten thousand, the proportion varying according to the 
 locality and season; being greater in cities than in the country; in sum- 
 mer than in winter; in warm climates than in cold; in lower altitudes than 
 in higher; and "greatest near the ground where decomposition is taking 
 place." 
 
368 entomology 
 
 Movement 
 
 The movement of air is physiologically important in affecting the 
 rate of evaporation from the bodies of animals. With other conditions 
 constant, the rate of evaporation is proportional to the strength of 
 the air-current. 
 
 The directive effect of currents of air (anemotropism) has been dis- 
 cussed (page 305). Some insects turn away from currents of air be- 
 cause of increased evaporation. (Shelford.) 
 
 Winds are highly effective agents in the distribution of insects. 
 To what has been said on this subject (page 323) these remarks may be 
 added. 
 
 In the case of the cotton boll weevil, "prevaihng winds frequently 
 cause the majority of the insects to follow one course." (Hunter and 
 Pierce.) 
 
 The natural spread of the gipsy moth is accomplished chiefly by 
 means of winds, acting on the hairy first-stage larvae. (A. F. Burgess.) 
 
 Hessian flies are often carried two miles, in an uninjured condition, 
 by strong winds. One female must have been carried five miles. (J. W. 
 McColloch.) These flies may be borne by winds with a velocity of 
 twenty-five miles or more per hour; mosquitoes, on the other hand, 
 cling to herbage near the ground during strong winds, but are conveyed 
 many miles by gentle breezes. 
 
 The green-bug, Toxoptera graminum, and many other plant lice 
 are widely distributed, as winged viviparous females, by the wind. 
 "If the temperature be below the point of activity for the species, 
 it is very clear that the velocity of the wind would have no effect what- 
 ever upon the diffusion of the insect. The conditions necessary, then, 
 for the wind to exert its greatest influence will be a decreasing food 
 supply for the insect under a temperature considerably above that 
 actually necessary for its activity, with numbers not seriously reduced 
 by parasites; under these conditions, many species of aphids are known 
 to be carried about in immense numbers by the winds." (Webster and 
 Phillips.) 
 
 Electricity 
 
 Electric currents have a directive effect on animals {electrotropism, 
 galvanotropism) but the conditions under which this effect is obtained 
 are artificial, and may or may not be paralleled in nature. 
 
 Atmospheric electricity, the effects of which vary with variations 
 
INSECT ECOLOGY 369 
 
 in Other conditions of the atmosphere (Shelford), doubtless exerts 
 some influence on the activities of insects and other animals, but in 
 regard to this subject little is known. 
 
 In the hterature there are observations of the effects of electrical 
 storms on insects, but these effects are results of several influences 
 operating in combination (as temperature, moisture, pressure, light, 
 and wind and rain, acting mechanically) ; and possible effects of elec- 
 tricity alone are not distinguishable. 
 
 Evaporation 
 
 Evaporation depends upon air-temperature, pressure, relative 
 humidity, air-movement and, indirectly, light. The amount of evapo- 
 ration expresses the total effect of these factors. The evaporating power 
 of the air is "by far the best index of physical conditions surrounding 
 animals wholly or partly exposed to the atmosphere. " (Shelford.) The 
 rate of evaporation is directly correlated with temperature and illu- 
 mination, but most closely correlated with relative humidity. (Yapp.) 
 
 In the experimental study of evaporation Livingston's atmometer 
 is usually employed. This consists essentially of a cup of porous clay 
 which is filled with water, that is replaced as it evaporates, from a 
 reservoir of water. The amount of evaporation is easily measured by 
 the amount of water necessary to restore the water in the reservoir 
 to its original level. 
 
 Few precise studies have been made upon the effects of evaporation 
 on insects, though many have been made with man and other warm- 
 blooded animals. 
 
 Metabolism in Relation to Evaporation. — "Metabolism results 
 in heat, and the temperatures of the bodies of animals both warm and 
 cold blooded, is nearly always higher than the surrounding medium, at 
 least during activity. The surrounding conditions may be stated as 
 usually acting on metaboHsm, etc., as follows: (a) A moist cold atmos- 
 phere (very low evaporation) causes body temperature to fall more 
 rapidly than a dry cold one at the same temperature, because of the more 
 rapid conduction of heat. Such a fall in temperature decreases metab- 
 olism of cold blooded animals, and increases metabolism of warm blooded 
 animals within their capacity for heat regulation. In a dry cold atmos- 
 phere the heat loss is less pronounced because of the less rapid conduc- 
 tion of heat, (b) In a dry warm atmosphere (high evaporation) rapid 
 evaporation keeps down the peripheral temperature, and prevents death 
 from over-heating and destructive metabolism in cold blooded animals. 
 
370 ENTOMOLOGY 
 
 and makes possible body temperature regulation and thus prevents 
 heat stroke and death in warm blooded animals. In a moist warm 
 atmosphere, death and heat stroke occur because of lack of evaporation 
 and lack of peripheral cooling in the case of warm blooded animals 
 even when the surrounding temperature is at or below the normal body 
 temperature, (c) Wind movement (which increases evaporation) 
 increases radiation of body heat and of heat due to insolation. It 
 increases evaporation and further cools the body, thus within certain 
 limits increasing the metabolism of warm blooded animals and de- 
 creasing it in cold blooded animals, (d) Decrease of pressure increases 
 evaporation and radiation both of which lower the temperature of 
 animal bodies and influence metabolism. 
 
 "Conditions which withdraw water from organisms (evaporation 
 as influenced by various factors) influence irritabihty, activity and 
 length of life history. Thus Hennings found that low humidity in- 
 creased insect metabolism and Sanderson found that in dry air the 
 optimum temperature of the growth of insects was lower than in moist 
 air. Factors probably operate with reference to an optimum." 
 (Shelford.) 
 
 Professor Headlee raised bean weevils, Bruchus oUectus, from the 
 eggs at a constant temperature of 80° F., but with various degrees of 
 atmospheric moisture, from less than i per cent, to approximately 100 
 per cent. The optimum relative humidity was found to lie between 
 80 and 89 per cent. At 89.7 and 100 fungi developed and greatly re- 
 duced the numbers of the insects. Comparatively few individuals 
 reached maturity in an atmospheric moisture of 25 per cent, and none 
 in one of less than i per cent. 
 
 Burger, as reported by Shelford, studied the water relations of 
 the meal worm, Tenebrio molitor when kept in dry air and fed on bran 
 which had been dried at 105° C. He believed that the animals were in 
 essentially absolute dryness. Here they lived for weeks, but lost 
 weight. He found, however, that the per cent, of water in the animals 
 remained practically the same until after death and came to the conclu- 
 sion that the insect larvae could not use their food to produce water and 
 so the living substance itself was used. No doubt the food taken pro- 
 duced water but this was not sufficient in quantity. The most important 
 fact brought out was that the per cent, of water remained about the 
 same in spite of the extreme dryness and rapid loss of moisture. 
 
 Reactions." — Professor Shelford, who studied experimentally the 
 behavior of various animals under different rates of evaporation, found 
 
INSECT ECOLOGY 37 I 
 
 that in dry air (evaporation 0.06 cc. per hour) running beetles of the 
 genus Pterostichus were very sensitive, exhibiting a preference for 
 moist air. Digger wasps, Microhemhex, were sHghtly positive to dry 
 air, their chief reaction being digging, which took place in medium and 
 moist air but not in the dry. A tiger beetle, Cicindela, gave a nega- 
 tive reaction to air evaporating 3.6 cc. per hour, and a positive reaction 
 to air evaporating 1.56 cc. per hour. 
 
 Shelford studied also the influence of rapidly flowing and of warm 
 air in increasing evaporation. All the animals that he studied could be 
 killed by loss of water, when other conditions remained favorable to 
 their existence. The smaller animals died from loss of water much 
 more quickly than the larger, the surface being greater in proportion to 
 the volume in the smaller animals. The animals died after a smaller 
 amount of evaporation when the rate was slow than when it was more 
 rapid. The most remarkable fact brought out was that the animals died 
 more quickly from evaporation due to rapid movement of air than due 
 to dryness. 
 
 With a total evaporation of 31.0 cc. in a dry atmosphere Pterostichus 
 died in twenty-two hours. 
 
 The Pterostichus referred to came from under leaves on the ground 
 in a dense forest — a moist habitat; and Microhemhex is a resident of 
 dry open sand areas. ' 
 
 Hatching. — With fertile eggs of plant lice {Aphis avence and A. 
 pomi) air of high moisture content is more favorable to hatching than 
 air having a lower moisture content. The moisture content of the air 
 influences the evaporation from the eggs, determines the percentage of 
 hatching, and probably influences the rate of splitting of the outer 
 layer of the egg shell. (A. Peterson.) 
 
 Nymphs of walking-sticks, Phasmidae, frequently fail to extract 
 themselves from the egg shell, owing to dryness at the time of hatching. 
 Most of them succeed in escaping, however, if supplied with moisture. 
 In this instance evaporation has the mechanical effect of causing the 
 appendages or the abdomen to adhere to the amniotic membrane. (H. 
 P. and H. C. Severin.) 
 
 Life Cycle. — The length of the life cycle is often influenced greatly 
 by evaporation as determined by temperature and relative humidity. 
 With the Hessian fly, high temperature and low humidity lengthen the 
 cycle. In a dry atmosphere the eggs shrivel; in periods of drought 
 most of the puparia dry out and die. High temperature with high 
 humidity, however, does not retard the development, and is not fatal. 
 
372 ENTOMOLOGY 
 
 Low temperatures lengthen the cycle and may be fatal to prepupal 
 stages. Low humidity also increases the length of the cycle, and if 
 extreme is fatal in all stages of development. (Headlee.) 
 
 Eclosion. — Every one who has had experience in raising moths 
 from pupse knows that the pupae must have a certain amount of 
 moisture or they will dry out and die. Out of doors the rainfall sup- 
 plies the requisite moisture, but even there pupae may succumb to too 
 much or too little moisture. 
 
 Moths and butterflies upon emerging from the pupa can not expand 
 their wings if the air is too dry, on account of the rapid evaporation of 
 moisture from the wings. Indoors the moisture must be supplied if 
 necessary. It has often been observed that moths emerge from cocoons 
 in greater numbers on damp days. In dry weather many insects emerge 
 at night, when the relative humidity is higher than in the daytime. 
 This incidentally protects the helpless. insect from its diurnal enemies. 
 
 Adaptations. — Many thin-skinned larvae, as those of the house fly 
 and the plum curculio, that live in a moist environment of decaying 
 substance, die quickly if subjected to a dry atmosphere, when the tem- 
 perature alone is not sufificiently high to kill them. On the other hand, 
 larvae with a thick integument, like the meal worm, resist evaporation 
 more successfully. 
 
 An immense number of dipterous larvae, those of the Hessian fly 
 and the house fly, for example, when full grown retain the larval skin 
 instead of shedding it; this skin drying and hardening to form a pupa- 
 rium, which retards evaporation from the developing pupa within. An 
 unusually hot dry summer will, however, kill most of the puparia of 
 the Hessian fly, excepting such as may be protected by their depth in 
 the soil. 
 
 Some of our large silkworms smear the inner surface of the cocoon 
 with a waterproof gum or varnish which undoubtedly prevents the un- 
 due esca;pe of water from the enclosed pupa. 
 
 Larvae that burrow into the ground (for example many caterpillars 
 and maggots, white grubs, larvae of the plum curculio, Colorado potato 
 beetle, and numerous others) and make earthen cells in which to pupate, 
 secure thereby protection from evaporation as well as from other 
 influences. Larvae of the late fall brood of the bollworm (corn ear 
 worm) dig much deeper than those pupating earlier in the season. 
 (Quaintance and Brues.) 
 
 The beetles of the subfamily Eleodinae (Tenebrionidae) that are 
 characteristic of arid and semi-arid regions, have a thick integument and 
 
INSECT ECOLOGY 373 
 
 are quite at home in the desert. The integument is possibly no thicker 
 than in other tenebrionids, but having a thick skin to begin with, these 
 forms have found a suitable environment and have thrived in arid 
 places. 
 
 3. Food Relations 
 
 As regards its kind and quantity, food is, needless to say, a most 
 important condition of existence. Examples of food habits have been 
 given (page 212); here should be mentioned some of the more essential 
 facts concerning food as an ecological factor. 
 
 Classification of Food Habits. — According to the nature of their 
 food, most insects may be classified as follows: pantophagous (omnivo- 
 rous); phytophagous (plant-eating, referring usually to the flowering 
 plants); monophagous (with a single food plant); oligophagous (with 
 several definitely fixed food plants) ; polyphagous (feeding indiscrimi- 
 nately on many plants); sarcophagous (carnivorous); har pacta phagous 
 (predatory) ; entomophagous (parasitic on insects) ; saprophagous (feed- 
 ing on decaying substances) ; necrophagous (feeding on dead animals) ; 
 coprophagous (eating excrementitious material) ; mycetophagous (feeding 
 on fungi) ; microphagous (on micro-organisms, as bacteria, yeasts, etc.) . 
 
 Not all these categories will be considered here, but a few of them 
 need special mention. 
 
 Microphaga. — The pomace flies (Drosophila) famous as subjects of 
 investigation by geneticists, feed naturally in fermenting fruits, where 
 they find nourishment, not in the products of fermentation, but chiefly 
 in the yeasts that cause the fermentation. On sterilized glucose-agar 
 the larvae cannot grow unless yeast is added; and a medium of yeast 
 nucleo-protein, sugars and inorganic salts is a complete food for this 
 insect. (Loeb and Northrop, Baumberger.) 
 
 Sarcophaga. — Dipterous larvae that normally feed on decaying 
 animal tissue were raised from eggs to adults on a diet of banana and 
 yeast-agar, by Baumberger, who says that we must consider the 
 probabiUty that all decaying or fermenting substrata are merely the 
 media on which fungous or bacterial food of insects is growing. 
 
 Coprophaga. — ^Larvae of the house fly were raised on bran mash 
 containing a heavy growth of molds. Sections through these larvae 
 showed a complete absence of all material except bacteria, fungous 
 spores, and yeast cells in the digestive tract. It appears probable that 
 the larvae feed on micro-organisms, and are associated with them in the 
 same manner as that of Drosophila and yeasts. (Baumberger.) 
 
374 ENTOMOLOGY 
 
 Mycetophaga. — Many, though not all, of the fungus flies (Myceto- 
 philidae) feed on fungi. Larvae of a species of Sciara that feeds in woody 
 tissue were found to contain in the digestive tract fungous mycelia 
 along with considerable woody material. Larvae of the same species 
 were reared on a medium of bran-agar, which they soon infected with 
 molds, upon which they were subsequently observed to feed. The 
 wood is merely the substratum in which the food material develops. 
 (Baumberger.) 
 
 The ambrosia beetles, of which there are many species, make their 
 tunnels in damp wood of weak or dead trees. Their food is not wood, 
 however, but a fungous growth which develops rapidly on the walls of 
 the galleries — so rapidly often as to choke the galleries and kill their 
 inmates. The fungus begins its growth on a bed of chips which the 
 female prepares, and on which she lays eggs. The fresh tender growth 
 of the fungus is food for both larvae and beetles, but only the latter can 
 eat the older growth. "Different species of fungi are associated with 
 different species of beetles, and these associations are constant for the 
 same species in spite of changes of host plants." (Baumberger.) 
 
 In connection with this subject the elaborate fungus-gardens of 
 leaf-cutting ants and of termites should be recalled (page 295). 
 
 Selection of Food. — Insects find food for themselves or for their 
 future larvae by means of the senses of (i) smell, the most widespread 
 method; (2) taste, as with butterflies, pomace flies, flesh flies and other 
 forms that feed as adults; (3) vision, as with dragon flies, which after 
 capturing their prey test it, however, and reject portions unsuitable as 
 food; also bees, which can discriminate between flowers of different 
 colors. 
 
 Brues adds, in his paper on this subject, that the selection of food 
 plants by Lepidoptera depends also on (i) "Some attribute of the plant, 
 perhaps an odor but far less pronounced to our own senses than those 
 mentioned above. Species restricted to plants like Leguminosae or 
 Violaceae may be considered in this category. Undoubtedly there is 
 some attribute of such plants which insects can recognize in a general 
 way and not as a specific characteristic of some single plant species or 
 genus. (2) A similarity in the immediate environment or general form 
 of the food plant. The effect of something of this sort is seen particu- 
 larly in oligophagous and also polyphagous caterpillars feeding mainly 
 on trees or shrubs, such as the gipsy moth, Cecropia moth, etc., and those 
 of certain species like some of the Arctiid moths that feed upon a great 
 variety of low plants. (3) Apparently chance associations that have 
 
INSECT ECOLOGY 375 
 
 become fixed, whereby diverse plants are utilized by oligophagous 
 species." 
 
 The selection of food by means of its odor is simply a case of positive 
 chemotropism (see page 302), a blind reaction to a chemical substance. 
 Pomace flies, which feed on and lay their eggs in fermenting fruits, are 
 positively chemotropic to weak percentages of certain alcohols and 
 acetic acid, which are products of fermentation. House flies are stimu- 
 lated to oviposition by ammonium carbonate, with its odor like that of 
 manure. The cabbage butterfly is induced to lay eggs by mustard 
 oils, which occur naturally in its usual food plants, Cruciferae. 
 
 Growth. — Other things equal, the length of the larval stage depends 
 upon the kind, condition, and amount of food. With the house fly, it 
 is primarily temperature and moisture that determine the rate of devel- 
 opment; but with an average temperature of about 21° C, the maggots 
 develop in. horse manure in fourteen to twenty days, and on a diet of 
 bananas, in twenty-seven days. At the same temperature, the rate of 
 development is directly proportional to the condition of the food as 
 regards moisture. Dry conditions may retard development five or six 
 weeks, tend to produce flies of subnormal size, or may be fatal. (C. G. 
 Hewitt.) 
 
 If the mother insect lays her eggs in a considerable supply of food 
 substance, as happens usually in the case of the house fly, pomace fly, 
 carrion beetles, dung beetles, and many other insects, the development 
 of the larva is assured, so far as the amount of food is concerned. The 
 quantity of food present becomes important, however, for insects that 
 are restricted to one kind of food plant, or to a food of low nutritive 
 value. The nutritive content of wood is small, and wood-boring cater- 
 pillars and grubs frequently require long periods for their growth, even 
 several years (Cerambycid^) ; though less time is needed if the larvae, 
 like those of the peach tree borers and the flat-headed apple borer, 
 feed largely on the inner bark, which is more nutritive than the 
 wood. 
 
 Size. — Under-nourished larvae produce small adults, as might be 
 expected. The size of boll weevils depends upon the abundance of the 
 food supply and also upon the nature of the food. The smallest weevils 
 develop from squares which are very small, and which fall very soon 
 after the egg is deposited ; the largest, from bolls which grow to maturity. 
 In bolls the food supply is most abundant, and the period of larval 
 development is several times as long as it is in squares. (Hunter and 
 Pierce.) 
 
376 ENTOMOLOGY 
 
 Reproduction.^ — It goes without saying that constant feeding is 
 necessary in the case of long-Uved proHfic females, such as queen bees, 
 ants, or termites. 
 
 With plant lice, it has long been known that the drying up of the 
 food plant causes the appearance of large numbers of winged, or migrant 
 females. In experiments with the pea louse, Macrosiphum pisi, it 
 was found that the subjection of parthenogenetic (reproducing without 
 fertilization) females to periods of partial starvation induced the produc- 
 tion of winged offspring from the wingless mothers. These winged 
 young would otherwise have been wingless, as check experiments 
 showed. (L. H. Gregory.) 
 
 In regard to the relation of food to the production of the males and 
 oviparous (egg-laying) females of plant lice, not much seems to be 
 definitely known. 
 
 Fecundity. — The kind and amount of food influence fecundity. If 
 female boll weevils are fed on leaves alone, eggs do not develop; while 
 a diet of squares leads to the development of eggs in about four days. 
 More eggs are laid when squares are abundant than when they are few. 
 (Hunter and Pierce.) 
 
 Guyenot found that pomace flies {Drosophila) reared from aseptic 
 larvae on sterile potato (without yeast) did not produce offspring. The 
 flies themselves, if fed on potato alone, were much less prolific than when 
 fed on potato and yeast. 
 
 Oviposition. — With many adult insects feeding is not necessary for 
 oviposition; in fact the mouth parts are often rudimentary, as in some 
 of the moths. Such insects owe their activity to the presence of a 
 supply of food stored up by the larva. Other insects, however, must 
 feed in order to lay. eggs; the queen honey bee, for example. 
 
 Adults of Pteromalus puparum, a parasite of the cabbage butterfly, 
 Pieris rapee, if kept without food for three days, attempt to oviposit 
 but are physically unable to do so. If then fed, however, with honey- 
 water or with blood from punctured chrysalides (their natural food), 
 they succeed in drilling into the chrysalides of their hosts. When 
 supplied with fresh pupae one of these females may feed and lay eggs 
 for three weeks; and if given honey-water also, for two months. 
 (S. B. Doten.) 
 
 Sex-determination.— One of the most plausible of the theories of 
 sex-determination has been that high nutrition produces females and low 
 nutrition, males. In raising moths or butterflies from caterpillars 
 males and females occur in about equal numbers, as a rule. If, however. 
 
INSECT ECOLOGY 377 
 
 the caterpillars are almost starved, some will die, and there will result 
 many more male adults than female. Dr. C. V. Riley explained this 
 long ago, by pointing out the fact that female caterpillars require a 
 longer time for growth than males (having sometimes one more molt 
 than the males); so that conditions of starvation would kill chiefly 
 female caterpillars, that had not completed their growth, and affect 
 male caterpillars less. T. H. Morgan, in a discussion of the subject, 
 adopts this view, and points out the fact that the sex of the caterpillar 
 is determined before the egg is laid; furthermore, that an excess of food 
 does not cause an excess of females. 
 
 Longevity. — The duration of life is evidently related to food. 
 Insects cannot live long, if active, without food; and activity is corre- 
 lated with the amount of food utilized. 
 
 Females live longer than males, with some exceptions, particularly 
 if they have not laid their eggs, and frequently, possess an ample supply 
 of reserve food accumulated by the larva, as in the case of many moths, 
 particularly such as do not themselves feed as adults (silkworm moth) . 
 
 With cotton boll weevils after emergence from hibernation, unfed 
 beetles of both sexes were found to live ten days, and fed beetles, 
 twenty-five days. (Hinds and Yothers.) 
 
 A queen honey bee, constantly fed with highly nutritious food, 
 may live more than four years; a queen ant, fifteen years (one instance). 
 On the other hand, the Hessian fly, which does not feed and has 
 little reserve nutriment, lives only from one day (males) to four days 
 (females) . 
 
 A remarkable instance of longevity under starvation conditions is 
 given by J. E. Wodsedalek. Finding that larvae of the common museum 
 beetle, Trogoderma tarsale, would live a long time without food, molting 
 meanwhile but not eating the cast skins, he tested their longevity by 
 keeping them individually in glass vials without food. The larvae 
 gradually decreased in size to almost their length at hatching, but were 
 surprisingly tenacious of Hfe. Newly hatched larvae that had never 
 eaten lived four months without food; quarter-grown larvae, fourteen 
 months; half -grown larvae, three years; three-quarters-grown larvae, 
 four years; and full grown individuals, from four years to five years, 
 one month and twenty-nine days (one larva). If stunted specimens 
 were given food they began to grow again, and could again be reduced 
 in size by a second period of starvation. By alternate periods of feasting 
 and fasting, larvae were three times brought to their maximum size 
 and three times reduced to the minimum size. 
 
378 ENTOMOLOGY 
 
 Hibernation. — Food is of minor importance as an incentive to hiber- 
 nation. Codling moth caterpillars, woolly bears {Isia isahella) and 
 many other insects enter hibernation before there is any failure of the 
 food supply. 
 
 Insects which feed on evergreen trees are not as rhythmical in 
 their hibernation as those which feed on deciduous trees. (Pictet, 
 Baumberger.) 
 
 Some larvae are full-fed upon entering hibernation (codHng moth) ; 
 while others are not (brown- tail moth). Emergence from hibernation 
 depends immediately upon temperature, but it is possible that hunger 
 also is a stimulus to the renewal of activity. 
 
 As metabolism is at its minimum in hibernating insects, their food 
 requirement is similarly small. 
 
 Coloration. — Food, as regards kind and condition, often affects 
 coloration, particularly pigmental coloration (see page 176). 
 
 In the cotton boll weevil the color becomes darker with age; conse- 
 quently, hibernated individuals are the darkest found; but food also 
 influences the color. The smaller the size of the weevil, the darker 
 brown is its color; the largest weevils are light yellowish brown. The 
 principal reason for the variation, in the opinion of Dr. W. E. Hinds, 
 lies in the degree of development of the minute, hair-like scales, which 
 are much more prominently developed in the large than in the small 
 specimens, although the color of old specimens is often changed by, the 
 abrasion of the scales. These scales are yellow in color, while the ground 
 color of the integument bearing them is a dark brown or reddish brown. 
 The development of the scales appears to take place mostly after the 
 adult weevils have become quite dark in color, but before the chitin 
 becomes fully hardened. They seem, therefore, to be, to a certain 
 extent, an aftergrowth which depends upon the surplus food supply 
 remaining after the development of the essential parts of the weevil 
 structure. (Hunter and Pierce.) 
 
 Food Relations in General. — A phytophagous species which is 
 limited to one species of food plant frequently dies out in a locality 
 from having consumed or fatally weakened all its food plants (the but- 
 terfly L. philenor, on Aristolochia, in the North). 
 
 Evidently, a species which has many kinds of food plants has an 
 advantage (gipsy moth, grasshoppers, army worm, etc.). 
 
 The quantity of food present becomes important for an insect that 
 is restricted to a single species of plant. It may be a plant that is 
 
INSECT ECOLOGY 379 
 
 always abundant, like the pawpaw, to which the Ajax butterfly is 
 confined; or it may not be. 
 
 In a state of nature, if food plants of one species are scattered among 
 other plants, their insect enemies do not become injurious; but in a 
 state of nature, if many plants of one species grow together, insects may 
 injure them (in forests, for example). Where man grows one kind of 
 plant over a large area, insect enemies flourish (Hessian fly, chinch bug, 
 cotton boll weevil, codling moth, etc.). 
 
 The same relations exist between parasites or predators and their 
 hosts. A parasitic species of insect that is limited to one species of host 
 will die if it destroys all the individuals of the host species. The 
 successful parasites (as Ichneumonidae, Chalcididae, and Braconidai) 
 are those that have available immense numbers of a single species of 
 host, or a large number of species as hosts. 
 
 Most predaceous insects, however, feed indifferently on almost any 
 species of insects that they can overcome, and of ten do not limit them- 
 selves to insects for food; therefore their numbers are not affected by the 
 absence of this or that species of possible victim. 
 
 These food relations form a most important factor in the interactions 
 of organisms, the subject next to be considered. 
 
 4. BiOTic Conditions 
 
 The animals and plants of a region form a vast complex, in which 
 every organism affects every other, directly or indirectly, and is in turn 
 affected by all the others. Furthermore, all the organisms are influenced 
 by their environment, and in turn affect the character of the environ- 
 ment itself more or less. All the organisms are bound up with one 
 another in an intricate network of interactions which the mind can only 
 partially comprehend. 
 
 Interactions. — As a familiar illustration of these interactions, take 
 the case of any common plant louse and the extensive society, or conso- 
 cies, which it dominates. 
 
 To begin with, the numbers of aphids depend greatly upon inorganic 
 influences, as heat or cold, dryness or moisture; evaporation being 
 important. Aphids are often blown off their plants, or washed off by 
 rains, and killed mechanically. When they are abundant, many are 
 squeezed to death between branches that are blown against each other. 
 Bacteria and fungi destroy the lice. The fungus, Empusa aphidis, is 
 the most important enemy, for in damp weather it can almost extermi- 
 
38o 
 
 ENTOMOLOGY 
 
 nate plant lice locally. Weather conditions may render the plants 
 unfit for food, or may prevent the eggs from hatching. In short, 
 aphids are affected for good or ill by all the influences that act upon 
 their food plants. 
 
 Enemies are abundant. Many kinds of spiders and a few kinds of 
 mites kill the Hce. The EngHsh sparrow eats the pea louse voraciously, 
 and the chickadee in winter consumes enormous numbers of aphid eggs. 
 Most of the enemies are, however, other insects. Here are lists of the 
 insects known to affect, directly or indirectly, the common pea louse, 
 or clover louse, Macrosiphum pisi. 
 
 Predators^ 
 
 CoccinellidcR (lady beetles) 
 Ceratomegilla fuscilabris 
 Hippodamia tredecimpunctata 
 Hippodamia parenthesis 
 Hippodamia glacialis 
 Hippodamia convergens 
 Coccinella novemnotata 
 Cycloneda sanguinea 
 Adalia bipunctata 
 Chilocorus bivulnerus 
 
 SyrphidcB (flower flies) 
 
 Ocyptamus fuscipennis 
 Platychirus quadratus 
 Syrphus americanus 
 Syrphus ribesii 
 Allograpta obliqua 
 Mesogramma marginata 
 Mesogramma polita 
 Sphaerophoria cylindrica 
 
 ChrysopidcB (lace-wings) 
 Chrysopa oculata 
 Chrysopa rufilabris 
 Chrysopa plorabunda 
 
 Gryllida (tree-crickets) 
 (Ecanthus confluens 
 
 Pentalomidce (stink bugs) 
 Podisus maculiventris 
 Euschistus variolarius 
 
 Anthocoridce. (flower bugs) 
 Triphleps insidiosus 
 
 CantharidcB (cantharids) 
 Podabrus rugulosus 
 Podabrus tomentosus 
 
 Ilonididce (gall gnats) 
 
 Aphidoletes meridionalis 
 
 IchneumonidcB (ichneumons) 
 Praon simulans 
 Trioxys cerasaphis 
 Aphidius fletcheri 
 
 Parasites 
 
 Aphidius washingtonensis 
 
 Aphidius rosse 
 Miscogasteridce (miscogasterids) 
 
 Megorismus fletcheri 
 
 The species of the preceding list feed directly on the pea louse. 
 Those of the following list affect the louse indirectly, by feeding on the 
 preceding species or on one another. 
 
 1 Additional details in regard to all these insects will be found in Bull. 111. Agr. Exp. 
 Sta., No. 134, and Bull. U. S. Dept. Agr., No. 276. 
 
INSECT ECOLOGY 38 I 
 
 Affecting M. pisi Indirectly 
 Braconida (braconids) 
 
 Perilitiis americanus, parasitic on the beetles, Ceralomegilla fuscilahris and Coccinella 
 novemnotata. 
 
 Bassus Icetotorius, a parasite bred from larvjc and pupa; of Allograpla obliqua and five 
 other species of Syrphidce. 
 Figitidce (figitids) 
 
 Sohnaspis hyalinus, a parasite from larvae of M esogramma polila. 
 Pteromalidcc (pteromalids) 
 
 Pachynenron syrphi, a parasite of Bassus Icetotorius. 
 EncyrtidcB (encyrtids) 
 
 Encyrlus mesograptcB, a parasite from larvae of M esogramma polita. 
 Chalcididce (chalcids) 
 
 Isocratus vulgaris, a parasite of Bassus Icetotorius. 
 Proctotry pidce (proctotrypids) 
 
 Telenomus podisi, a parasite of the eggs of Podisus and Euschislus. 
 
 A few examples will illustrate the intricacy of the interrelations of 
 these insects that are dominated by Macrosiphum pisi. 
 
 M. pisi is preyed upon by lady beetles, the pupae of which are sucked 
 by the stink bugs, the eggs of which are parasitized by a proctotrypid. 
 
 M. pisi is food for larvae of flower flies, the larvae and pupae of which 
 are parasitized by a braconid, which is itself parasitized by a pteromahd 
 and a chalcid. 
 
 M. pisi is destroyed by larvae of flower flies, the larvae of which are 
 attacked by stink bugs, while the adults are eaten by robber flies, toads, 
 and various birds, as the kingbird, flicker andphoebe. 
 
 Thus forty species of insects are known to be vitally concerned with 
 the pea louse. There should be added the mite, Rhyncholophus parvus, 
 which feeds on the louse. 
 
 The writer has found more than two hundred species of insects in a 
 field of red clover. All these have some influence on the pea louse 
 (clover louse) and on each other; though the influence is often remote in 
 its effects and practically insignificant. The scavenger insects on the 
 ground, and collembolans etc., in the soil, feeding on organic matter, 
 affect the texture and composition of the soil and consequently the 
 plant. Without considering earthworms, moles, mice, birds and many 
 other animal factors that might be thought of, we shall mention insects 
 orfly. The bees that pollenize the flowers, and the various insects that 
 destroy the roots, stems, leaves or flowers, all affect indirectly the louse. 
 As illustrating interactions, though it is of no practical consequence, 
 we may say that the yield of clover seed depends slightly upon the struc- 
 ture of the milkweed flower; for flower flies whose larvae destroy plant 
 
382 ENTOMOLOGY 
 
 lice are sometimes fatally entangled in the flowers of milkweed. We 
 might even go farther, and implicate all the factors that control milk- 
 weed; and so on indefinitely. Such speculation is not altogether profit- 
 less, if one bears in mind the fact that only the more immediate 
 influences are of any practical importance, and that the effect of one 
 factor may be increased, diminished, or neutralized by that of another. 
 
 Every one of the insects or other animals that affect the clover 
 louse directly or indirectly, is itself the center of a little world of inter- 
 actions. Though we cannot follow all these interactions, their total 
 effect at any given time is expressed by the existing number of individ- 
 uals of each of the species involved; which measures also the success of 
 each species from its own point of view, so to speak. 
 
 Equilibrium.— It is not surprising, then, that species fluctuate in num- 
 ber of individuals. The presence or absence, or increase or decrease, 
 of one influence may affect many other factors, and disturb preexist- 
 ing relations. This is seen in the case of the rapid multiplication of 
 the gipsy moth and the San Jose scale insect, when introduced into 
 this country without their natural enemies. 
 
 Evidently there is actually no such thing as a "balance of nature," 
 a true equilibrium; on the contrary there is continual fluctuation 
 within wider or narrower limits. The so-called equilibrium is simply 
 a condition of relatively small fluctuation. Under conditions of 
 nature, animals and plants approximate a condition of stability, or 
 fluctuation within comparatively narrow limits, to the benefit of all 
 concerned. Under artificial conditions, however, as when man grows 
 one kind of plant over a large area, the insects of the plant multiply 
 rapidly. Man is able to remedy such disturbances of the "order of 
 nature" in proportion to his knowledge of the factors concerned, espe- 
 cially of their relative importance. He has unwisely introduced the 
 English sparrow to subdue caterpillars; but has wisely imported and 
 propagated the native enemies of the fluted scale, the gipsy moth, and 
 other pests. 
 
 II. Conditions or Aquatic Existence 
 
 The fundamental physiological requirements are the same for 
 aquatic as for terrestrial animals, but these conditions are often met in 
 different ways in the two groups. Though insects may broadly be 
 divided into these two groups, there are many kinds whose environment 
 is intermediate between water and land, and many forms are aquatic 
 in their immature stages and terrestrial as adults. 
 
INSECT ECOLOGY 383 
 
 I. Chemical Conditions 
 
 Animals cannot exist in water that does not contain certain 
 gases and chemical compounds in solution. 
 
 Gases. — Oxygen is a necessity, and most aquatic animals select 
 water with a high oxygen content. In air dissolved in water the pro- 
 portion of oxygen to nitrogen is much larger than it is in atmospheric 
 air ; because oxygen is more soluble in water than nitrogen. The oxygen 
 content of the water is more variable than that of the atmosphere. 
 The importance of the oxygen factor is indicated by the many elaborate 
 adaptations for respiration displayed by aquatic insects. 
 
 Carbon dioxide given off by animals during respiration, acts in 
 small quantities as a stimulation to respiration, and in large amounts 
 as a narcotic capable of fatal effects. Aquatic animals react nega- 
 tively to even a small increase of carbon dioxide. This is due to the 
 increase in hydrogen-ion concentration which it causes. Since a large 
 amount of dissolved carbon dioxide is commonly accompanied by a 
 low oxygen content as well as other important factors, the hydrogen-ion 
 concentration of waters of low alkalinity is probably the best single 
 index of the suitability of the water for animals. (Shelf ord.) 
 
 "Nitrogen has little effect upon animals except when present in 
 excess." (Shelford.) 
 
 "Oxygen and nitrogen go into solution from the atmosphere and 
 oxygen is also produced by green plants. The other gases are produced 
 chiefly by organisms as excretory and decomposition products." 
 (Shelford.) 
 
 Chemical Compounds.^ — Carbonates, sulphates, and chlorides of 
 magnesium, calcium, and sodium, and salts of potassium, iron, and 
 silicon are practically always present in solution in water, and their 
 presence in definite proportions is essential to the life of the animals. 
 (Shelford.) Sodium chloride, or common salt, is unfavorable to insect 
 life. Almost no insects live in the ocean (see p. 170). In fact, if an 
 insect larva be taken from a brook and put in a brackish pool it will 
 actually lose water through its skin ; it will partly dry up. (F. E. Lutz.) 
 Flies of the genus Ephydra are, however exceptional in this respect. 
 Two species of these "salt-flies" are abundant in Great Salt Lake, the 
 salinity of which is greater than that of the ocean. The flies and pupa- 
 ria sometimes occur in inconceivable numbers, the latter forming large 
 brown patches on the water or windrows on the shore. The larvae, 
 which feed on an alga, are active even when the water evaporates 
 
384 ENTOMOLOGY ^ 
 
 down until covered with a crust of salt. (J. M. Aldrich.) Not a few 
 insects live in brackish water, however; some of them occurring also 
 in fresh water; as the nymphs of certain dragon flies, which inhabit also 
 salt, sulphurous, or slightly alkaline ponds in the West. (R. C. Osburn.) 
 A few Hemiptera of fresh- water occur also in brackish water or in water 
 strongly impregnated with various mineral salts. (H. G. Barber.) 
 Several species of mosquitoes confine themselves for breeding purposes 
 to salt marshes, where A'edes sollicitans is always the most abundant 
 and is found in practically all the temporary pools uninhabited by fish. 
 (J. A. Grossbeck.) 
 
 Larvae of the malaria mosquitoes {Anopheles) also develop in 
 brackish water. The salt marsh mosquito {Aedes sollicitans) was 
 found to develop in water so strongly polluted with acid waste from a 
 "guano factory" that all other animal life appeared to be extinct. 
 (S. F. Hildebrand.) 
 
 Water containing certain acids, as the humic acids of peat bogs, is 
 deleterious to insect life. 
 
 .2. Physical Conditions 
 
 Circtilation. — "The distribution of dissolved salts and gases is 
 dependent upon the circulation of the water, as their diffusion is too 
 slow to keep them evenly distributed. The circulation of water in 
 streams is probably such as to keep all dissolved gases and salts about 
 equally distributed. The water of streams has been found to be 
 supersaturated with oxygen. Oxygen is taken up by the water near the 
 surface. Nitrogen and carbon dioxide are produced especially near the 
 bottom, and if the water did not circulate they would be too abundant 
 in some places and deficient in others for animals to Uve. " (Shelf ord.) 
 
 The flowing or splashing of water increases the oxygen content. 
 Larvae such as the hellgrammite, those of black-flies (Simulium) and 
 of some caddis flies (as Hydropsyche) require well-aerated water, and 
 are found always in moving water, often in strong currents. They 
 occur in flowing water not primarily on account of its greater oxygen 
 content, however, but because, as Shelford has shown, such animals 
 orient themselves toward a strong current of water (positive rheotaxis) 
 and move against the current. Furthermore, they are positively thig- 
 motactic and show a strong preference for hard surfaces, as those of 
 large stones; with an avoidance of sand; the members of a rapids 
 community differing from those of a pool community in this respect. 
 
INSECT ECOLOGY 385 
 
 Hydropsyche reacts positively to the direction of light, though indifferent 
 to its intensity; but some other members of the rapids community, as 
 hellgrammites and burrowing caddis worms, avoid light. 
 
 "Current is an important factor of aquatic environments which 
 finds its terrestrial counterpart in winds. That it is a very important 
 factor is shown by the numerous devices aquatic insects have to keep 
 their position, and it varies from nothing in puddles to the rush of 
 Niagara." (F.E.Lutz.) Larvae of the black-flies are fastened to stones 
 or other objects; some caddis worms anchor their cases securely; beetles 
 of the family Elmidae cling with their claws tightly to submerged objects. 
 With caddis flies of the family Hydropsychidae, which live in swift 
 streams, the instantaneous emergence of the adult as soon as the pupa 
 reaches the surface prevents the fly from being swept away. (C. E. 
 Sleight.) 
 
 Temperature. — Temperature is of great indirect importance in the 
 control of the distribution of life in water. (Shelford.) It is "more 
 constant in aquatic environments than in terrestrial, although it is 
 somewhat variable from place to place and month to month. In the 
 summer, a spring hole is cooler than a rainwater puddle and the opposite 
 is apt to be true in the winter. In general, a running stream is apt to 
 be cooler in summer than a stagnant one. In the spring a deep pond is 
 generally cooler than a shallow one, and the opposite is true in the 
 autumn. But aquatic insects are never subject to the sharp daily 
 fluctuations of temperature that most of their terrestrial relatives must 
 bear, and even the annual range of temperature variations is slight. " 
 (F. E. Lutz.) Such differences as there are have, however, an influence 
 on aquatic life. Temperature affects activities of various kinds, as 
 locomotion and oviposition; may determine the length of the egg- 
 period; or may act in other ways. 
 
 Light. — Light controls distribution and activities. Its intensity 
 decreases rapidly, particularly that of the orange and red rays, with the 
 depth of the water. Aquatic insects, like terrestrial, react either posi- 
 tively or negatively to the directive action of light {phototropism, p. 
 306). Some of them frequent shaded or dark places, while others, as 
 the whirHgig-beetles {Gyrinidce) and the water-striders {Gerrida) are 
 at home on the surface of the water in the strongest sunlight. 
 
 Pressure. — Pressure in water increases with depth, at the rate of 
 about one atmosphere for each thirty-three feet (Shelford) . Its effects 
 on aquatic insects are for the most part indirect; the pressure affecting 
 other conditions of existence. 
 
 25 
 
386 ENTOMOLOGY 
 
 Depth. — Depth is mostly important indirectly, on account of its 
 influence on other conditions, such as circulation, temperature, light, 
 and pressure; but is in itself a determining condition in some instances. 
 Thus such larvae of horse-flies (Tabanidae) as have a posterior res- 
 piratory tube bearing the spiracles must have shallow water, where the 
 spiracles can be raised to the surface; though sometimes these larvae 
 are found in moist earth where there is no standing water. (R. C. 
 Osburn.) 
 
 Bottom. — "The character of materials and topography of the 
 bottom are very important to animals living on the bottom, but it has 
 its effect also on free swimming animals as a determining factor in the 
 amount of sediment. The kind of bottom is important because many 
 animals are dependent upon sohd objects for attachment and are absent 
 from bottoms made up of fine materials. Others must burrow into 
 mud or creep on sand and gravel. " (Shelford.) 
 
 Most Dytiscidae prefer clean live water, being averse to very muddy 
 bottoms. (J. D. Sherman.) On the other hand, nymphs of various dra- 
 gon flies bury themselves in the mud. Some of the caddis worms prefer 
 a clear sandy bottom; others, a bottom with slime, or one with sticks, 
 dead leaves or other debris. 
 
 Vegetation. — It goes without saying that vegetation, in its amount 
 and kind, is extremely important as a condition of aquatic existence. 
 The green plants give off oxygen. Plants are used for shelter, escape 
 from enemies, as places in which to wait for the prey (dragon fly 
 nymphs, Zaitha), as surfaces for locomotion (non-swimming larvae 
 of diving beetles, whirligig beetles and others) , especially as a means of 
 reaching the surface for air or for the transformation (dragonfly nymphs, 
 etc.). Eggs may be laid on the plants (electric light bugs, back-swim- 
 mers. May flies, caddis flies, etc.) or inserted into plant tissues (diving 
 beetles, water scorpions). 
 
 3. Food Conditions 
 
 The small beetles of the family HalipHdae are said to feed on algae. 
 The water-scavenger beetles (Hydrophilidae) feed mostly on decaying 
 vegetable matter, but are sometimes carnivorous, and some ofjthe 
 adults will eat green vegetation. The diving beetles (Dytiscidae) 
 are carnivorous; the whirhgig beetles (Gyrinidae) feed on small insects 
 found on the surface of the water. The water-striders (Gerridae) 
 capture disabled or living insects for food; the water boatmen (Corix- 
 
INSECT ECOLOGY 387 
 
 idae) are predaceous. Nymphs of dragon flies are predaceous, catching 
 other insects by means of their peculiar extensile lower lip, and even 
 young fishes, tadpoles and smaller nymphs of their own kind. (R. C. 
 Osburn.) Most caddis worms are plant-eating, but some are insectiv- 
 orous, as Hydropsyche, which catches its victims in the nets that it 
 spreads in swift currents. May fly nymphs are carnivorous, or feed on 
 plants or mud. Additional examples of food habits are given on p. 165. 
 
 4. BiOTic Conditions 
 
 Aquatic animals and plants, like terrestrial, form a vast complex of 
 organisms that interact upon one another in innumerable ways and are 
 acted upon by the environment; but the interactions are different to the 
 extent that the aquatic environment differs from the terrestrial. As 
 a whole, the physical and chemical conditions of existence are more 
 uniform in water th^n on land. Furthermore, the number of species 
 concerned is fewer; thus aquatic insects form only 3 per cent, of all 
 insects. As regards food supply, the truism that its diminution lessens 
 the numbers of the animals dependent upon it, applies of course, as with 
 terrestrial forms. Aquatic insects are, however, much less specialized 
 than terrestrial as regards food habits. Thus the plant-eating species 
 are seldom limited to one species of plant, therefore can always find 
 food, even though there are fewer species of aquatic plants than of 
 terrestrial. The great majority of aquatic insects are, however, carniv- 
 orous, and many are omnivorous, and rarely suffer from lack of food. 
 Though the predaceous habit is highly developed among aquatic 
 insects, the parasitic habit has developed almost entirely among terres- 
 trial forms; and aquatic insects, while actually in the water, are practi- 
 cally free from the attacks of parasitic insects. 
 
 On the whole, the interrelations of aquatic forms, though incon- 
 ceivably complex, are less extensive than those of terrestrial species. 
 
 The so-called equilibrium or "balance of nature" is maintained,, 
 which is, as on land, a condition of continual fluctuation within rela- 
 tively narrow limits; with a smaller range of fluctuation in the aquatic 
 environment. 
 
 Ill . Environmental Factors in General 
 
 The important factors of the environment have been considered 
 individually. In nature they do not operate singly, however, and by 
 
388 ENTOMOLOGY 
 
 simple observation, unaided by experimentation, one cannot disen- 
 tangle the effects of one factor from those of others acting with it. 
 The environment is a complex of many interdependent factors. 
 
 The factors control one another, but those that are more immediate 
 in their operation are controlled by the larger influences of physiography 
 and vegetation. 
 
 Physiography .^ — "In streams, current and oxygen content are 
 determined very largely by physiographic conditions. Current is a 
 function of volume of water and slope of stream bed. Oxygen content 
 is largely determined by the rate of flow, and therefore is influenced by 
 physiography. In lakes, oxygen content is determined by the depth, 
 the temperature, and winds — physiographic factors are again important. 
 On land, moisture and light are in a measure controlled by physio- 
 graphic features. Slope and direction of facing profoundly affect 
 vegetation, moisture, and light." (Shelford.) 
 
 Siirface Materials and Vegetation.^" Materials for abode are 
 largely the surface soil or rock or the vegetation. Surface soil or rock 
 influences the moisture. Both moisture and surface materials influ- 
 ence the kind and amount of vegetation. All are interdependent. 
 
 "Physiographic features change with time. Erosion changes the 
 gradient of streams, the width of valleys, the steepness of valley walls 
 and cliffs, the ground- water level, etc. The weathering of rock is a 
 process familiar to all. It is the aggregate of processes by which the 
 coarse' and hard or massive materials are reduced to clay and soil. 
 This requires time. 
 
 "The fact that vegetation grows upon the so-called sterile, coarse, 
 rough-surface materials, usually scattered or ephemeral at first, but 
 increasing in denseness with each generation, is also familiar. Plants 
 add organic matter to the soil. This organic matter holds the water 
 so that moisture increases and plants may increase. With such changes 
 it is obvious that an area of sterile soil will support more animals as 
 time goes on, than at the outset, when the conditions were such that 
 only a few hardy species could live. Here again, then, time is the 
 important factor in determining the change of the area, so as to be 
 suitable for more species (because more species are adapted to live in 
 the resulting than in the initial conditions) . The length of time which 
 has elapsed since a given set of surface and physiographic conditions 
 became exposed to the atmosphere is very important in governing the 
 number, kind, and distribution of animals in a given area." (Shelford.) 
 
INSECT ECOLOGY 389 
 
 IV. Classification of Environments 
 
 The distinction must be made between climatic environmental 
 complexes and local complexes. "The climate, and such features as 
 types of vegetation covering large areas, e.g., steppe, deciduous forest, 
 etc., are commonly regarded as climatic. Opposed to these, and lying 
 within them, are the local conditions, such as streams, lakes, soils, 
 exposure, etc., which are only indirectly dependent upon climate." 
 (Shelford.) 
 
 The classification of animal environments is based upon vegetation, 
 physiography, or both. Where vegetation exists, animal communities 
 are referred to the plant communities which form their environments. 
 (Plate V.) 
 
 The simple and natural classification of plant communities recom- 
 mended by Livingston and Shreve is illustrated as follows: 
 
 "The extensive areas such as the sagebrush plains of the Great 
 Basin, the grasslands of Nebraska and Kansas, or the pine forests of 
 the Atlantic Coastal Plain are designated sls formations . The smaller 
 and less markedly differentiated areas within a formation are designated 
 as associations, as, for example, the forests of shortleaf pine in New 
 Jersey, those of loblolly pine in Maryland and Virginia, and those of 
 longleaf pine in the Gulf States, all lying within the Coastal Plain 
 formation. The smallest units of vegetation are [sometimes] termed 
 societies, and these are of small area and represent portions of the associa- 
 tion in which a definite aggregation of species is to be found." (Living- 
 ston and Shreve.) 
 
 An outline of the content of animal ecology prepared by a committee 
 of the Ecological Society of America, in 1920, contains the following 
 useful synopsis. 
 
 Distribution of Communities 
 I. Land communities. 
 
 (a) Forests with broad thin leaves. 
 
 1. Continuously moist and evergreen. 
 
 (a) Uniformly warm, affording habitats in six or more strata. (Tropical 
 
 rain forests.) 
 (6) With cool season. (Temperate rain forests.) 
 
 2. Intermittently dry or cold, and deciduous. 
 
 (a) Warm with distinct dry season. (Tropical deciduous forest.) 
 
 (b) With cold winter, little winter shelter. (Temperate deciduous forest.) 
 
 (b) Communities of evergreen forests of narrow, thick leaves. 
 
 1. Moist conifer forest with little undergrowth. 
 
 2. Rainy conifer forest with shrub undergrowth. 
 5. Open, arid, conifer forest. 
 
390 ENTOMOLOGY 
 
 (c) Communities of sav^anna and grassland. 
 
 1. Tropical savanna (dry season) affording habitats in groves, thickets, forest 
 
 margins and grasslands. 
 
 2. Tropical steppe; large herds of mammals. 
 
 3. Temperate savanna; habitats in groves, thickets, forest margins and 
 
 grasslands. 
 
 4. Temperate steppe with cold or dry winters and usually large herds of 
 
 mammals. 
 
 5. Arid, broken, bush-covered steppe with small herds of mammals. 
 
 ((f) Communities of winter rain (forests with broad thick leaves) e.g., California 
 
 semi-desert, 
 (e) Communities of desert and semi-desert. 
 
 1. Grass, cactus, tree semi-desert with grazing mammals (e.g., South Texas 
 
 semi-desert); succulent semi-desert; shrub-covered semi-desert. 
 
 2. Extreme desert without large diurnal mammals. 
 (/) Arctic and Alpine lands. 
 
 1. Tundra. 
 
 2. Alpine meadows. / 
 
 3. Ice fields. 
 
 2. Communities of waters and shores. 
 
 (a) Communities of the sea (Marine). 
 
 1. Communities of the open sea (Pelagic). 
 
 (a) Mid-oceanic communities. 
 
 (b) Oceanic island communities. 
 
 (c) Sargassum communities. 
 
 (d) Coastal oceanic communities. 
 
 2. Communities of the sea bottom (Benthic). 
 
 3. Littoral communities. 
 
 (a) Communities of eroding shores; subdivisions based on exposure, 
 bottom material and latitude. 
 
 (fi) Communities of depositing shores; subdivisions as above plus vegeta- 
 tion. 
 
 (c) Special communities: coral; tidepools; kelp. 
 
 3. Communities of the sea shores. Animals feeding in the sea and breeding on the land, 
 
 or vice versa. Classification based on climate. 
 
 4. Communities of the fresh waters. 
 
 (c) Communities of still waters. Subdivisions based on size, depth and vegetation; 
 littoral, pelagic, benthic. 
 
 (b) Communities of turbulent waters. Sbdivisions based on character of water 
 movement. 
 
 (c) Swamps, marshes, etc. 
 
 Ecology finds its distinctive field of study in communities and 
 succession. These important subjects can not, however, be adequately 
 presented from an entomological viewpoint alone. Furthermore, little 
 has been published on the subject as regards insects. The most that 
 can be done here is to illustrate the subject by naming some of the better 
 known insects as being characteristic of a few typical environments, 
 and to add occasional remarks on adaptation in relation to habitat. 
 
Plate V. 
 
 €01 Bli 
 
INSECT ECOLOGY 395 
 
 V. Communities 
 
 In a given habitat the fauna and flora together constitute a biota. 
 The term fauna is generally used in connection with classification or 
 geographical distribution, as is also the term flora. In reference to 
 ecological relations, however, the animals or plants of a given habitat 
 constitute a community. 
 
 As animals and plants, according to their structural resemblances or 
 differences, fall into species, genera, families, orders, etc., so do animal 
 or plant communities, according to their ecological likenesses or unlike- 
 nesses, fall into mores, consocies, strata, associations, and formations; 
 each of these orders being inclusive of the preceding kind; there the 
 resemblance ends. The animals of a community agree in their reactions 
 to the factors that they encounter. If they meet environmental influ- 
 ences in the same way, they are said to be ecologically similar; if they 
 meet the same influences in different ways, they are ecologically equiva- 
 lent. Thus a caterpillar that meets low temperature by making a co- 
 coon, and one that gets the same result by digging into the ground, 
 are ecologically equivalent. Animals select their habitats, probably by 
 trial and error; and their behavior becomes adjusted to the surrounding 
 conditions. (Shelf ord.) ' ' The habitat is the mold into which the organ- 
 ism fits. Since habitats are different, animal communities occupying 
 different habitats are physiologically different. Communities are sys- 
 tems of correlated working parts." (Shelford.) 
 
 ''Mores are groups of organisms in full agreement as to physiological 
 life histories as shown by the details of habitat preference, time of 
 reproduction, reactions to physical factors of the environments, etc. 
 The organisms constituting a mores usually belong to a single species 
 but may include more than one species. 
 
 "Consocies are groups of mores usually dominated by one or two of 
 the mores concerned and in agreement as to the main features of habitat 
 preference, reaction to physical factors, time of reproduction, etc. 
 Example: the prairie aphid consocies. The aphids dominate a group of 
 organisms which for the most part prey upon them, as, for instance, 
 certain species of lacewing, lady beetles, syrphus-flies, etc. 
 
 "Strata are groups of consocies (and animals not so grouped) occupy- 
 ing the recognizable vertical divisions of a uniform area. Strata are in 
 agreement as to material for abode and general physical conditions but 
 in less detail than the consocies which constitute them. 
 
 "For example, a forest-animal community is clearly divisible into 
 
394 ENTOMOLOGY 
 
 the subterranean-ground stratum, the field stratum (zone of the tops 
 of the herbaceous vegetation), the shrub stratum (zone of the tops of 
 the dominant shrubs), the /ou'erZ/'gestratum (zone of the shaded branches 
 of the trees), and the upper tree stratum. A given animal is classified 
 primarily with the stratum in which it breeds, as being most impor- 
 tant to it, and secondarily with the stratum in which it feeds, etc., as in 
 many cases most important to other animals. The migration of ani- 
 mals from one stratum to another makes the division lines difficult to 
 draw in some cases. Still, the recognition of strata is essential but a 
 rigid classification undesirable. Consocies boring into the wood of 
 living trees probably should be considered as consocies relatively 
 independent of stratification phenomena. 
 
 ^^Associations are groups of strata uniform over a considerable area. 
 The majority of mores, consocies, and strata are different in different 
 associations. A minority of strata may be similar. The term is 
 applied in particular to stages of formation development of this ranking. 
 The unity of associations is dependent upon the migration of the 
 same individual and the same mores from one stratum to another at 
 different times of day or at different periods of their life histories. 
 Migration is far more frequent from stratum to stratum than from one 
 association to another. 
 
 "Formations are groups of physiologically similar associations. 
 Formations differ from one another in all strata, no two being closely 
 similar. The number of species common to two formations is usually 
 small (e.g., 5 per cent.). Migrations of individuals from one formation 
 to another are relatively rare." (Shelford.) 
 
 VI. Examples of Insect Communities 
 
 The article by A. G. Vestal, from which the following extracts are 
 taken, though limited to a single group of insects, the grasshoppers, 
 is a good example of how entomological field observations may be 
 organized on an ecological basis. The observations were made at 
 Douglas Lake. Michigan. 
 
 Community-relations of Grasshoppers 
 
 Northeastern Conifer Formation.— r//w/a Association. — Cedar and 
 peat bog. Melanoplus islandicus the only species. 
 
 Aspen Association. — In treeless parts, M. angustipennis is the 
 common species. M. luridus is found sparingly in scattered aspen 
 
INSECT ECOLOGY 395 
 
 growths. Scirtetica marmorata occurs usually on or near the hchen- 
 covered surfaces. 
 
 Eastern Deciduous Forest Formation. — Herbaceous Associations. — 
 Hot dry clearings. Grasshoppers are numerous both in individuals and 
 in species. In order of abundance: Melanoplus atlanis, Camnula 
 pellucida, Dissosteira Carolina (Carolina locust), etc. 
 
 Thicket and Bramble Associations. — :M. bivittatus occasional on 
 shrubs. M. atlanis and others occur on the ground. 
 
 Local Associations. — Dry Beach. — Pure sand, dry and shifting, 
 with full exposure to sun and wind. Here are several species of grass- 
 hoppers, which occur also in other habitats. Trimerotropis maritima 
 (the seaside grasshopper, p. 196) is, however, limited to this habitat, 
 and has the same brownish color as the sand. 
 
 Marsh Associations. — Several species of grasshoppers are found in 
 the tall, rather close, sedge or grass growths. Stenobothris curtipennis 
 is the characteristic grasshopper of littoral situations. 
 
 Ruderal Associations. — Dry Grassland. — Waste places, dry pastures, 
 abandoned fields, roadsides, etc. In order of importance: M. atlanis, 
 Camnula pellucida, M. bivittatus, Dissosteira Carolina, Arphia pseudo- 
 nietana. All these species, with the possible exception of the last, are 
 more abundant in ruderal than in native vegetation. 
 
 Sparsely Vegetated or Bare Soil. — The CEdipodinae normally rest on 
 bare soil and oviposit in it. Bare soil as a habitat is, however, not 
 sufficient; nearby vegetation is necessary. Grasshoppers are rare on 
 extensive areas of bare soil, except at the borders. They are conspicu- 
 ous on bare places, but are more abundant in the interspaces between 
 plants, in open growths. The Carolina locust, Dissosteira Carolina, is 
 the most familiar species of bare soil, though other species have the 
 same habitat. 
 
 Meadow Associations. — Variable in character. In a bluegrass- white 
 clover meadow, M. atlanis and Stenobothris curtipennis are of about equal 
 abundance. The red-legged locust, M . femur-rubrum is more abundant 
 than these in such places, in some localities. The differential locust, 
 M. dijferentialis , is typical in meadow habitats. 
 
 1. Grasshoppers are more abundant, in species and in individuals, 
 in herbaceous or grassland habitats than in forest, and more abundant 
 in dry than in moist or wet situations. 
 
 2. Certain species are much more restricted than others in range of 
 habitats, and in accompanying range of toleration of physical and 
 vegetational factors of the environment. 
 
396 ENTOMOLOGY 
 
 3. Although a species may be found over several associations, it is 
 more abundant in one, or two, of these, than in others. Certain activi- 
 ties take place in more restricted habitats; chief of these restricted 
 activities is the laying of eggs. 
 
 4. No two plant associations have identical grasshopper assemblages. 
 
 5. No two grasshopper species have identical habitat-preferences. 
 It should be said that these scanty excerpts give no idea of the scope 
 
 of Vestal's article; most important in which are the ecological generaliza- 
 tions. 
 
 Mr. A. P. Morse, authority on Orthoptera, has paid particular atten- 
 tion to the subjects of distribution and adaptation. His data were given 
 according to life zones and habitats, but are rearranged here as follows. 
 
 Shores of Seas and Lakes. — Bare sands, hot and dry. Ground 
 Stratum. The seaside locust, Trimerotropis maritima, found along the 
 Atlantic coast from Maine to North Carolina, and inland about the 
 Great Lakes, is a characteristic arenicolous (sand-dwelling) species, 
 which varies in color from gray to brown, in harmony with its local 
 habitat (see p. 196). 
 
 Salt Marshes and Vegetation Bordering Brackish Waters. — Moist 
 Soil. Ground and Herbaceous Strata. Orphulella olivacea, occurring 
 along the Atlantic coast from Connecticut to Florida and Texas; the 
 only halophilous (inhabiting salty soil) locust of the Eastern States. 
 
 Semi-Arid Areas. — Hot and Dry. Herbaceous and Shrub Strata. 
 Eesperotettix pratensis, ranging from Mexico and Texas to Washington, 
 and California to Indiana; occurring also in the Southeastern States a- 
 mid conditions much resembling those of its habitats in the arid West; 
 for example along the Gulf shore of Florida, among the xerophytic 
 (inhabiting hot, dry places) strand vegetation. 
 
 Temperate Savanna and Grassland Formation.— Heihsiceons Stratum. 
 Orphulella picturata and Melanoplus bispinosus are common on the 
 prairies west of the Mississippi. In damp grassy fields the red-legged 
 locust, Melanoplus femur-rubrum, is common; in dry grassy fields, M. 
 atlanis. On ruderal dry grasslands are species of Arphia, Syrbula, etc. 
 On bare soil, hot and dry, are the Carolina locust, Dissosteira Carolina, 
 and Trimerotropis citrina. On the moist banks of streams, M. femora- 
 tus. On moist soil of sandy loam, or the banks or beds of freshwater 
 streams, somewhat exposed, are the grouse locusts, Tetriginae, some of 
 which feed sometimes on humus. On bunch-grass in fields or openings 
 in the forest is Eesperotettix brevipennis, limited to this plant. 
 
 Temperate Deciduous Forest Formation. — In the undergrowth is Mela- 
 
INSECT ECOLOGY 397 
 
 noplus strumosus. On bare or lichen-crusted rock occurs Trimerotropis 
 saxatilis (see page 197), which occupied that station before the forest 
 came. 
 
 Adaptations. — "Brachypterism (the short-winged condition) in 
 locusts is a more complete adaptation to a leaping mode of progression 
 brought about by life in situations where flight is difficult or impracti- 
 cable, and consequently disadvantageous. That this is the true ex- 
 planation is indicated by the habits and haunts of the majority of the 
 flightless species (sylvan surroundings or tangled undergrowth wherever 
 found); by their distribution locally, horizontally, and vertically; and 
 by the equally characteristic habits, haunts, and distribution of macrop- 
 terous (long- winged) species as inhabitants of the open field, desert, or 
 savanna. 
 
 "The advantages of progression by fiight^dispersal widely and 
 easily effected, often aided by the wind, ease of escape from many ene- 
 mies, etc., and the superiority of this mode in open lands — are evident 
 to all. On the other hand, long wings and locomotion by flight are 
 disadvantageous amid dense underbrush, where a leaping mode of 
 progression has decided advantages. Organs unused or disadvanta- 
 geous tend to dwindle and disappear; hence the loss of wings. 
 
 "It is found that Orthoptera frequenting habitats involving passage 
 over open spaces of considerable extent, such as fields, between trees in 
 forests, and bushes or thickets in deserts, are usually long-winged, flying 
 species; and others dwelling in an environment of more or less dense, 
 intricate, interlacing vegetal growth, be it sub-alpine or sub-tropical, 
 in forest or swamp — or in burrows, crevices, etc., — in short, in stations 
 where wings are not needed or are at a disadvantage, are very generally 
 apterous (wingless) or brachypterous (short-winged). 
 
 "Brachypterism, therefore, appears to be largely not so much a case 
 of natural selection through the agency of the wind as an adaptation in 
 structure to habits. The fact that the heavier-bodied female is more 
 frequently or completely brachypterous than the male and that the teg- 
 mina in the latter sex when used as musical organs are retained in a 
 less degenerate condition (even when entirely useless in flight) , confirms 
 this explanation of brachypterism." (A. P. Morse.) 
 
 Communities of Streams 
 
 From Shelf ord's notable volume. Animal Communities in Temperate 
 North America, we may take, from the wealth of data given, examples of 
 common insects representing the various communities of streams. 
 
398 ENTOMOLOGY 
 
 Intermittent Stream Communities. Temporary rapids consocies. — 
 The larva of the black-fly, Siniulium, found in the smallest trickle of 
 water. Nymphs of May flies, as the stream grows a little larger. No 
 permanent aquatic residents, however, in these temporary streams. 
 The temporary residents may fail to transform if the water dries out too 
 soon. Temporary pool consocies. — -Somewhat more permanent. Insects 
 that belong primarily to stagnant ponds make their appearance. 
 Permanent pool communities. — A practically permanent fauna. Water 
 striders, back-swimmers, water boatmen, etc. are common. Dragon fly 
 nymphs, diving beetles, crane fly larvae, and many other insects. 
 
 Spring Brook Associations. — In streams fed by springs. On the 
 stones, larvae of the black-fly, Simulium, and the caddis fly, Hydropsyche. 
 Under the stones, nymphs of May flies and larvae of flies and midges 
 {Chironomus, Dixa). 
 
 Swift-stream Commimities. Hydropsyche or Rapids Formation. — 
 Three ecologically equivalent modes of life, each meeting the current in 
 a different way. These are (i) clinging to stones in the current, (2) 
 avoiding the current by creeping under stones, (3) self-maintenance by 
 strong swimming powers. Upper surface of stones (stratum i) : 
 black-fly larvae, hanging from stones to which they are attached by 
 means of a sucker at the posterior end of the body. Caddis worms, 
 Hydropsyche, in cases made of pebbles; with a net for catching floating 
 food. Among the stones (stratum 2) : miscellaneous insects, also of the 
 following stratum. Under the stones (stratum 3) : May fly nymphs, 
 larvae of midges, Chironomus, and of horse flies, Tabanus. Stone fly 
 nymphs, Perlidae, with flattened bodies. Larvae of the parnid beetle 
 Psephenus. Caddis worms, Helicopsyche. Nymphs of the damsel 
 fly, Calopteryx, if vegetation is present. Sandy and gravelly bottom forma- 
 tion (pools). — Bloodworms, Chironomus. The burrowing dragon fly 
 nymph, Gomphus exilis, a burrowing May fly nymph, caddis worms. 
 
 Sandy Bottomed Streams.- — With shifting bottom, the animals 
 present being those which belong to moderately swift water. Brook 
 beetles, Parnidae, attached to the few scattered plants. On logs and 
 roots, many Parnidae; predaceous diving beetles, Dytiscidae, hiding in 
 the crevices; a few caddis worms, Hydropsyche; the little dytiscid, 
 Hydroporus mellitus, which buries itself in the sand. 
 
 Sluggish Stream Commimities. Sand and Silt Bottom Formations. — 
 Bloodworms, Chironomidas ; green midge larvae, Chironomidae ; occa- 
 sional caddis worms, Hydropsyche; a burrowing May fly nymph, 
 Hexagenia. Formation of the Vegetation. — A densely rooted vegetation. 
 
INSECT ECOLOGY 399 
 
 as in ponds. Large numbers of diverse insects, rnany of which come 
 to the surface for air, both in the adult and the young stages. Water 
 scorpions, Ranatra; creeping water bugs, Pelocoris femoratus; small water 
 bug, Zaitha fluminea; water boatmen, Corixa; predaceous diving beetles, 
 Dytiscidae; water scavenger beetles, Hydrophilida;. The gilled aquatic 
 insects are the May fly nymphs, Ccenis and Callihcetis; damsel fly 
 nymphs, Ischnura verticalis; diagon fly nymphs, ^^schnidae and 
 Libellulidaj; these utilizing the vegetation as resting-places or clinging- 
 places, or as a means of creeping to the surface to transform. 
 
 Tension Lines. — Margins of bodies of water, swamps and marshes, 
 and temporary ponds are on the border line between land and water. 
 The classification of the communities of such tension lines of overlapping 
 environments is often diflicult. (Shelford.) 
 
 Along the margins of young ponds and lakes is an area which is 
 characterized by being made up of wet sand or mud which is submerged 
 at high water and moist at other times. Here we find springtails 
 (especially Poc^wm aquatica), shore bugs (Saldidae), many tiger beetles 
 (Cicindelidae) and numerous small flies. The ground beetle {Bemhidion 
 cannula) and numerous scavengers (Staphylinidas, Histeridae, etc.) 
 are common because the beach is often strewn with dead animals which 
 have floated ashore. (Shelford.) 
 
 In Shelf ord's Animal Communities there are extended accounts of 
 communities of streams, lakes, ponds, prairies, and forests. 
 
 Community Relations in New Mexico 
 
 The notes that follow on the insect ecology of New Mexico are taken 
 from an interesting report by Professor J. R. Watson. They are 
 here arranged under four of Livingston's vegetational areas. 
 
 Northern Mesophytic Evergreen Forest Formation. Douglas 
 Spruce Association. — Poor in insect life. Some thirty species listed. The 
 carpenter ant, Camponotus pennsylvanicus , is common here and in the 
 yellow pine association, but was not seen outside of the mountains. 
 The butterfly, Grapta zephyrus, is also limited to these two associations. 
 The familiar mourning cloak butterfly, Vanessa antiopa, is present. 
 Yellow Pine Association.- — About fifty species of insects listed. Machi- 
 lis sp. The hemipteron Oncometopia lateralis is confined to this asso- 
 ciation. Circotettix undulatus is very rare outside of this association; 
 it makes the loudest noise of any grasshopper in the region. Another 
 locust, Arphia acta, noteworthy for its loud crackling noise, is common, 
 and descends into the cedar association. 
 
400 ENTOMOLOGY 
 
 Western Xerophytic Evergreen Forest Formation.— A dwarf and 
 open form of semi-forest that characterizes the edges of the preceding 
 formation. Pinon Association.- — The locust, Trimerotropis cyanea, is 
 especially at home here. The hemipteron, Perihalus limbolarius, is 
 very abundant on blossoms of Yucca. The skipper butterfly Epargyreus 
 tityrus seems to belong here. Cedar Association. — The tarantula killer, 
 Pepsis formosa, is particularly abundant here. On milkweed, which is 
 more abundant here than elsewhere, is the cerambycid beetle, Tetraopes 
 iemoratus, and the hemipteron, LygcBUs turcicus. 
 
 Desert-grassland Transition Formation. — Intermediate between 
 the Grasslands to the east and the Desert regions to the west. Opuntia 
 arborescens Society.— Several insect species are quite characteristic of 
 this society. The nitidulid beetle, Carpophilus pallipennis, eats the 
 pollen and petals of the Opuntia and every blossom commonly shows 
 from a dozen to a hundred or more individuals. The peculiar ceram- 
 bycid beetle, Presmis pocularis, and the next insect are chiefly respon- 
 sible for weakening and kilHng the cactus plants. The beetle apparently 
 never leaves the plant, and its wings are degenerate. The female is 
 usually seen carrying her much smaller mate. The larvae bore in the tis- 
 sues of the plant. The cicada, Cacama valvata, is very abundant on the 
 tree cactus, but, unlike the last, also occurs on the prickly pears. The 
 loud calls of the males are heard on every hand when the sun is shining. 
 But let a cloud obscure the sky for a moment and all is hushed. The 
 larvae feed on the roots of the cactus. Shortgrass Association. — The mesa 
 grasshopper, Trimerotropis vinculata is extremely numerous, ascending 
 even into the yellow pine association. It is very variable in color and 
 the variations have a very definite relation to that of the ground around 
 them, being very light on sandy soil, mottled on pebbly hills and darker 
 among the pines where there is more vegetation. The species migrates 
 in large numbers when the rains cease and the grasses on which it feeds 
 dry out. Many species of insects inhabit the mesa. Here lives the 
 harvesting ant, Pogonomyrmex occidentalis (see page 297). It is well 
 known that these ants bring their stores of grain out to air occasionally. 
 Professor Watson relates that "One somewhat windy day in September, 
 a hill was visited in which part of the ants were busily engaged in 
 bringing out the grain to air and others were as busily engaged in 
 carrying it back again. One ant would drop a grain and at once start 
 back without a load into the hill for another, whereupon the grain 
 would be at once seized by another ant and carried back into the gran- 
 ary. It is possible that this treatment is what the grain needed but it 
 
INSECT ECOLOGY 4OI 
 
 looked to the interested observer like a serious disagreement in the 
 colony as to where that grain should be, a case illustrating the limita- 
 tions of instinct in developing 'team work.' " 
 
 Large centipedes, Scolopendra, are quite common, often entering 
 houses and being much feared; though their bite is by no means as 
 serious as represented. The whip-scorpion, Thelyphonus, "is rarely 
 met with on the mesa. Though probably poisonous, its bite is also 
 grossly exaggerated in popular belief. " (Watson.) Tarantulas, Lycosa, 
 "are somewhat more common than the last but much less so than the 
 centipedes. Their bite is more serious than any of the above, but still 
 not dangerous to most people." (Watson.) 
 
 Rio Grande Semi-desert Formation. — Hot and dry. Gutierrezia 
 Association. — The big clumsy sand-cricket, Stenopelmalus fasciatus, 
 is common under stones, etc. Several species of the tenebrionid sub- 
 family Eleodinae are characteristic. One of these beetles, Eleodes 
 longicollis, when held, can squirt an ill-smelling fluid to a distance of 
 eight inches. The large black tenebrionid beetles, Eusattus convexus, 
 "form a very large and characteristic feature of the fauna of this region. 
 They are true children of the desert. Their elytra are grown together 
 and to their backs, an adaptation to the fierce sand storms of the mesa. 
 These wind storms drifting sand and gravel with them are a source of 
 grave danger to the fauna of the region, even to man himself. The 
 author has several times been caught out on the mesa when one struck 
 the region with its usual suddenness and has stopped to observe the 
 behavior of the animals. The prairie horned larks sought the shelter 
 of the friendly arroyo banks. (The author has picked up these birds 
 on the mesa during one of these storms. They were so exhausted by the 
 buffeting that they had received that they made no effort to escape.) 
 The digger wasps climbed into the Gutierrezia bushes and hung on for 
 dear life with all of their feet wrapped about the stem, an attitude that 
 they also assume during a shower; the snout beetles on the other hand 
 backed down off the Gutierrezia and sought shelter in the ground; the 
 woolly bears and other caterpillars curled up under the shelter of tufts 
 of grass; most of the lizards sought their holes as did the harvester 
 ants; but these Tenebrionidae went about their business as usual entirely 
 oblivious, apparently, of the storm. Their heavy bodies kept them 
 from being blown away and their heavy coat of chitin (it is hardly 
 possible to force a heavy insect pin through some species) defied the drift- 
 ing wind. In their disposition not to be too particular as to what they 
 eat they again show that they are true children of the desert. Anything 
 
402 ENTOMOLOGY 
 
 from the tender green seedling leaves of a Hoflfmanseggia to a dead 
 member of their own species is good. They collect in large numbers 
 about the carcass of a dead mammal. They will come out from their 
 winter quarters under the rosettes of Yucca and other sheltered places 
 any time in winter if it is as warm as 60° F. They have been taken by 
 the author on January 15. On the other hand they seem somewhat 
 to shun the hottest hours of the day in summer, being then much more 
 noticeable toward sunset." (J. R. Watson.) 
 
 In the shallow depressions or "draw" in the mesa above the place 
 where a definite arroyo develops, there is found a society of which 
 certain quick-growing annual grasses are most conspicuous. "Here 
 and here only have I ever found this big, nearly wingless, 'lubberly 
 locust ' (Brachystola magna) , a good illustration of an insect restricted 
 to a very limited habitat. " (Watson.) The grasshopper, Heliastus 
 aridus, is particularly abundant in these arroyos, where its mottled 
 colors agree perfectly with the gravelly surface. 
 
 Chrysothamnus Association. — Occupying such rapidly eroding and 
 hence unstable situations as the dissected edge of the mesa and the 
 higher gravelly parts of the valley of the Rio Grande, this is the most 
 xerophytic (inhabiting hot dry places) of the associations. The charac- 
 teristic tenebrionid beetle, Cysteodemus wislizeni, is very common in 
 colonies, which are spread over much ground. The ambush bug, 
 Phymata erosa fasciata is very abundant; it is almost perfectly concealed 
 in yellow blossoms, as those of golden rod, where it occurs more com- 
 monly than in white blossoms. The clear-winged moth, Calesesia 
 coccinea, is exceedingly abundant on Hymenopappus during the third 
 week in May; its conspicuous colors blending perfectly with those of the 
 blossoms of this plant. The insect disappears by the first of June. 
 The magnificent noctuid moth, Erebus odora, is occasionally taken. 
 
 The sand dunes are entirely barren of vegetation and of insect life 
 except for a species of digger-wasp, Bembex, which here finds conditions 
 favorable for its colonies. "All the specimens of the scorpion {Buthus) 
 that I have seen have come from this association. Its sting is, to 
 most people, not nearly as serious as it is represented to be. Persons 
 that have experienced it say that for a short time only is the pain more 
 severe than that resulting from the sting of a hornet and that it does 
 not last as long. " (Watson.) In the Croton Society the short-winged, 
 tricolored, or "barber-pole" grasshopper, Dactylotum pictum, occurs 
 wherever its food plant, Croton texensis, occurs in sufficient abundance. 
 The walking-stick, Diapheromera femorata, is present also. It is, of 
 
INSECT ECOLOGY 403 
 
 course, perfectly harmless, but is charged by the natives with causing 
 the death of many a poor horse. 
 
 In the "Valley" insects are abundant in number of species and of 
 individuals; but the term valley does not signify much, ecologically, 
 since it may mean anything from mud flats to desert. On the mesa, 
 dragon flies range five or six miles from any possible breeding place, 
 but the feebler damsel flies never fly far from home. The harlequin 
 cabbage bug is sometimes abundant on Cleome and on cabbage sprouts, 
 but does not seem to be a very serious pest, possibly because it prefers 
 the Cleome. The squash bug, Anasa tristis, is very abundant on culti- 
 vated squashes, and . commonly hibernates under yucca stems miles 
 from any cultivated fields. The well-known Carolina locust, Dis- 
 sosteira Carolina, which in the East frequents the driest of situations, 
 in New Mexico clings very closely to the moist valleys, like other eastern 
 forms (as tiger beetles) that occur also in New Mexico. In both east 
 and west, however, the species frequents places of about the same degree 
 of humidity. In the Alkaline Meadow Society, the lesser migratory 
 locust, Melanoplus atlanis, occurs in the more moist situations, and 
 damages alfalfa in the valleys. The red-legged locust is common, 
 inhabiting somewhat drier situations than the last species. Mosquitoes, 
 Culex pipiens, breed in countless millions in the ponds that form in the 
 valley whenever the Rio Grande is high, usually in May and June. All 
 the mosquitoes seen on the mesa come from the valley; sometimes they 
 are five miles from any possible breeding place. They are carried by a 
 gentle breeze, but a brisk breeze causes them to seek shelter low down 
 among the herbage and not to venture forth. 
 
 The following species, of wide distribution and not characteristic of 
 any particular formation, are of interest as occurring in New Mexico, 
 because they are some of the most familiar insects of more eastern states 
 under quite different climatal conditions. Coleoptera. — The metallic 
 leaf-beetle, Chrysochus auratus, occurs on Apocynum as usual, but at an 
 altitude sometimes of ten to eleven thousand feet. Euphoria inda 
 occurs from the valley up to the yellow pine association and doubtless 
 higher. The lady-beetle, Hippodamia convergens, is abundant every- 
 where from the tops of the highest mountains to the lowest parts of 
 New Mexico. Lepidoptera. — Colias eury theme, is common in the moun- 
 tains and in the valley wherever there is damp soil, but is absent from 
 the mesa. The checkered white, Pieris protodice, is found from the 
 valley to the spruce association. The painted lady, Pyrameis cardui, is 
 abundant wherever the thistle grows; and more abundant up in the 
 
404 ENTOMOLOGY 
 
 blue spruce association than anywhere else. Hymenoptera. — The social 
 wasp, Polistes variatus, nests fronii the valley of the Rio Grande up into 
 the spruce forest at eight thousand feet. The pigeon Tremex, T. columba, 
 is equally abundant in the cottonwoods of the valley and in the Douglas 
 spruce of the mountains. Hemiptera. — Gerris remigis, the well known 
 water strider of eastern states, is found on all suitable ponds and streams 
 in both valley and mountains. The plant-feeding bug, Lygus pratensis, 
 is as ubiquitous here as it is elsewhere in the United States. 
 
 VII. Succession 
 
 "Succession is no doubt one of the most important and widespread 
 of the phenomena discovered by the ecologists up to the present time. 
 Simply stated, it means that on a given fixed area organisms succeed one 
 another, because of changes in conditions. These changes make 
 impossible the continued existence of the forms present at any given 
 time; with the death or migration of such forms, others adapted to the 
 changed conditions occupy the area, whenever such adapted forms are 
 available. The changes referred to result from physical or biological 
 causes, or combinations of the two. It is probable that the causes of 
 the changes are frequently complex combinations of various factors. 
 
 "We have among the physical causes changes in climate and changes 
 in topography. All degradation of land is a cause of succession. Such 
 geological processes are well understood and treated in textbooks on 
 geology and physiography. 
 
 "The biological causes of succession lie chiefly in the fact that organ- 
 isms frequently so affect their environment that neither they themselves 
 nor their offspring can continue to Uve at the point where they are now 
 living. Every organism adds certain poisonous substances to its 
 surroundings, and takes away certain substances needed by itself. It 
 frequently thus so changes conditions that its offspring cannot Hve and 
 grow to maturity in the same locality as the parents. However, by 
 these same processes it prepares the way for other organisms which can 
 live and grow in the conditions thus produced." (Shelf ord.) 
 
 "The general growth or evolution of environmental conditions 
 and the communities which belong to them are included under succes- 
 sion. The word succession is used in three distinct senses. We speak 
 of (a) geological succession, (b) seasonal succession, and (c) ecological 
 succession." (Shelford.) 
 
 Geological. — "Geological succession is primarily a succession of 
 species throughout a period or periods of geological time. It is due 
 
INSECT ECOLOGY 405 
 
 mainly to the dying-out of one set of species and the evolution of 
 others which take their places, or in some cases to migration." 
 (Shelford.) 
 
 Many species of insects owe their present distribution primarily to 
 the phenomena of the glacial epoch. An excellent example of this is 
 the White Mountain butterfly (page 325). In Arkansas mountains, 
 the "elevation is not sufficient to provide true boreal conditions, but 
 does modify the temperature so that certain species, abundant at the 
 north, and forced southward during the glacial epoch, have been enabled 
 to exist in this latitude till the present time. Such are the grasshoppers 
 Tettix hancocki, Chloealtis conspersa, and Melanoplus fasciatus." 
 (Morse.) 
 
 "The chief biological importance of the Southeastern United States, 
 comprising Virginia, North and South Carolina, Georgia, Florida, 
 Alabama, eastern Tennessee, and West Virginia, is connected with two 
 facts: First, this region served during the Glacial Epoch as a refuge for 
 boreal forms of life which had been pushed southward by the climatal 
 conditions of the Ice Age, and at the close of that period it became the 
 center of dispersal whence these forms were able to restock the opening 
 country at the north. Second, during this later period its lowland 
 plains served, and probably continue to serve, as a highway of dispersal 
 for austral forms entering the country from the south and southwest, 
 many of which have penetrated far into the heavily glaciated region of 
 the Northern States." (Morse.) 
 
 Seasonal. — "Seasonal succession is the succession of species or 
 stages in the life histories of species over a given locality, due to heredi- 
 tary and environic differences in the life histories (time of appearance) 
 of species living there. " (Shelford.) "Successful species are those that 
 fit wJc the seasonal rhythm with respect to physical conditions, 
 food, and numerous o'-^r reiatiorxS. " (Shelford.) 
 
 Many examples of seasonal succession among insects will occur 
 to the student of insect life. The seasonal succession of insects is 
 frequently correlated with that of plants. The cycle of an insect may 
 be adjusted to that of a plant upon which it depends. 
 
 Thus "the Membracidae or tree hoppers are celebrated for the 
 wonderful variety and complexity of their adaptations to their food 
 plants. . . . The tree hoppers of the genus Telamona, for example, 
 feed very largely on the sap of the trees and mainly on the tender 
 growing twigs. They find optimum conditions for such feeding only 
 during the comparatively short period in which the tree is making its 
 
4o6 ENTOMOLOGY 
 
 growth. They also must find a location and deposit their eggs while 
 the wood is still soft and tender; otherwise they will be unable to 
 penetrate to a sufficient depth to protect the eggs from predaceous and 
 parasitic insects. The result is that we find that they, with a possible 
 exception, pass the winter in the egg .stage and have a single annual 
 generation. ... A striking adaptation to a special period in a plant's 
 growth is shown in the life cycle of Micrutalis calva, the little shining 
 black seed-like tree hopper. The nymphs are found between the 
 branches of the blossom head of the Ironweed, Vernonia. This purple 
 flower appears only in the fall, so that the single generation of nymphs 
 comes on over 70 days later than its relative that lives in the tree. 
 
 "In the case of Ceresa bubalis (the Buffalo tree hopper) and its 
 vegetation-feeding allies the need of haste is not so great as their food 
 plants, Composites, Legumes and others, grow all summer, so we find 
 the nymphal period both longer and later and the adults extending into 
 the fall." (E.D.Bali.) 
 
 The time of appearance of the locust borer, Cyllene robinice, in the 
 fall coincides with that of the flowers of golden rod, on which the beetles 
 feed; the coloration of the beetles being protective, as Prof. H. Garman 
 has observed in Kentucky. 
 
 Ecological.— " Ecological succession of animals is succession of 
 mores over a given locality as conditions change. If species have rela- 
 tively fixed mores we have succession of species. When mores are 
 flexible we may have the same species remaining throughout, with 
 changes in mores. " (Shelford.) 
 
 A few examples, from Shelf ord's Vegetation and the Control of Land 
 Animal Communities, will serve to illustrate this kind of succession. 
 
 The stages of forest development are marked by the dominance of 
 certain species of trees which succeed one another in a rather definite 
 order. On the sand areas at the head of Lake Michigan, the sequence 
 is as follows (Cowles). i. Cottonwood Stage. Near the lake shore, 
 with the sand more or less shifting and rarely with more than a trace of 
 humus. 2. Pine Stage. With stable sand, considerably blackened by 
 humus, except in blowouts. 2>- ^^<^(^k Oak Stage. With the sand much 
 darkened by humus and locally covered with a dry moss or with dead 
 leaves; grasses and a shrubby undergrowth occur. 4. Red Oak Stage. 
 Ground with a carpet of leaves and humus; with a well marked shrubby 
 and herbaceous growth. Red oak, black oak, and white oak; often 
 hickory also. 5. Beech Stage. The mineral soil is covered with a 
 thick layer of leaves and humus. Fewer species of trees than in the 
 
INSECT ECOLOGY 
 
 407 
 
 preceding stage, but a greater number of species of small shrubs, with 
 a smaller number of individual shrubs. The trees close the overhead 
 spaces and make a dense shade, while the lower forest is open. Beech 
 and sugar maple are characteristic. These five stages are linked 
 together by transitional stages. 
 
 Of the many species tabulated by Shelford, the tiger beetles and 
 grasshoppers may be selected to illustrate succession in relation to forest 
 development. The tiger beetles, Cicindela, breed in the subterranean 
 stratum and feed in the ground stratum. 
 
 Tiger Beetles of Forest Succession (Shelford) 
 In these tables C signifies common; F, few; P, present 
 
 Stage I 
 Cottonwood 
 
 Pine 
 
 Black Oak 
 
 Red Oak- 
 Hickory 
 
 5 
 Beech 
 
 C. hpida 
 
 C formosa generosa. . 
 C. sculellaris lecontei. 
 C. sex guttata 
 
 With the tiger beetles the character of the soil, as regards suitability 
 for oviposition, is the chief factor that determines the presence or 
 absence of this or that species. C. sexguttata, which comes in with the 
 white oak- red oak- hickory forest, lays its eggs under loose leaves or in 
 little irregularities in the ground, which contain a little humus and are 
 slightly shaded; it is rare, however, in very shady situations, such as 
 those of the beech and maple forest. 
 
 Of the orthoptera named in the following table, numbers i to 6 
 breed in the subterranean stratum and feed in the ground stratum; 
 6 feeds also in the vegetation strata; 7 breeds in the ground stratum, 
 feeds in the herbaceous; 8 and 9 breed and feed in the herbaceous; 
 10 and II breed and feed in the tree stratum; 12 breeds and feeds in 
 the subterranean-ground stratum; and 13 in the ground stratum. 
 
 The table indicates that the successive changes in vegetation are 
 accompanied by corresponding changes in the character of the orthop- 
 teran fauna. Other insects or other animals also illustrate the same 
 phenomenon of ecological succession. During the successive vegeta- 
 tional stages the numbers of a species increase until optimum conditions 
 of habitat are attained, and thereafter decrease. 
 
4o8 
 
 ENTOMOLOGY 
 Orthoptera or Forest Succession (Shelford) 
 
 Stage I 
 Cottonwood 
 
 1-2 
 
 2 
 
 Pine 
 
 2-3 
 
 3 
 Black Oak 
 
 4 
 Red Oak- 
 Hickory 
 
 P 
 
 
 
 
 
 c 
 
 C 
 
 C 
 
 
 
 P 
 
 P 
 
 
 
 
 c 
 
 c 
 
 C 
 
 
 
 c 
 
 c 
 
 c 
 
 
 
 c 
 
 c 
 
 C 
 
 C 
 
 F 
 C 
 
 C 
 
 F 
 C 
 
 5 
 Beech 
 
 1. Seaside locust, Trimerotropis 
 
 marilima 
 
 2. Long-homed grasshopper, Psi- 
 
 nidia fenesiralis 
 
 3. Sand locust, Agenotettix are- 
 
 nosus 
 
 4. Mottled sand locust, Spharage- 
 
 mon ivyotningarum 
 
 5. Migratory locust, Melanoplus 
 
 atlanis 
 
 6. Locust, Melanoplus angusli- 
 
 pennis 
 
 7- Sprinkled locust, Chloeallis con- 
 sPersa 
 
 8. Texas grasshopper, Scudderia 
 
 texensis 
 
 9. Tree cricket, Oecanthus fasciatus 
 10. Tree cricket, Oecanthus angusti- 
 
 pennis 
 
 ri. Katydid, Cyrtophyllus perspicil- 
 
 latus 
 
 f2. Camel cricket, Ceuihophilus. . . . 
 [3. Locust, Melanoplus islandicus.. . 
 
 Some species of insects do not appear until the Black Oak stage, and 
 others not until the Red Oak-Hickory or the Beech-Maple stage. 
 
 The causes of animal succession and the control of animal com- 
 munities are discussed by Shelford, who draws these conclusions, among 
 others. 
 
 "The development of forest on sand or other mineral soil is accom- 
 panied by an almost complete change of animal species and probably 
 by a complete change of animal mores. 
 
 "Forest development is accompanied by marked changes in soil 
 and physical factors; animal distribution is more closely correlated 
 with differences in physical factors than with species of plants. 
 
 "Succession of all the animals of the forest communities under 
 consideration is comparable in principle to that in ppnds. Succession 
 is due to an increment of changes in conditions produced by the plants 
 and animals living at a given point. Animals through their effect 
 upon the soil play an important though minor part in the process. 
 
 "The various animal species are arranged in these communities in 
 an orderly fashion and the dominating animal mores are correlated 
 with the dominating conditions. 
 
 "Taxonomic (structural) species usually have distinct mores. 
 
INSECT ECOLOGY 409 
 
 though the same species often has different mores under different 
 conditions, and different species may have the same mores. Species 
 and mores are therefore not synonymous. 
 
 "Ecology considers together mores that are alike or similar in 
 their larger characters." 
 
CHAPTER XIV 
 
 INSECTS IN RELATION TO MAN 
 
 A great many insects, eminently successful from their own stand- 
 point, so to speak, nevertheless interfere seriously with the interests of 
 man. On the other hand, many insects are directly or indirectly so 
 useful to man that their services form no small compensation for the 
 damage done by other species. 
 
 Injurious Insects.- — Insects destroy cultivated plants, infest do- 
 mestic animals, injure food, manufactured articles, etc., and molest or 
 harm man himself. 
 
 The cultivation of a plant in great quantity offers an unusual oppor- 
 tunity for the increase of its insect inhabitants. The number of species 
 affecting one kind of plant — to say nothing of the number of individuals 
 — is often great. Thus about 200 species attack Indian corn, 50 of 
 them doing notable injury; 200 affect clover, directly or indirectly; and 
 400 the apple; while the oaks harbor probably 1,000 species. 
 
 The average annual loss through the cotton worm, i860 to 1874, was 
 $15,000,000, according to Packard; the loss from the Rocky Mountain 
 locust, in 1874, in Iowa, Missouri, Kansas and Nebraska, $40,000,000 
 (Thomas) ; and the total loss from this pest, 1874 to 1877; $200,000,000. 
 The loss through the chinch bug, in 1864, was $73,000,0000 in Illinois 
 alone, as estimated by Riley. The ravages of the Hessian fly, fluted 
 scale, San Jose scale, gipsy moth and cotton boll weevil need only be 
 mentioned. 
 
 At times, an insect has been the source of a national calamity, as was 
 the case for forty years in France, when Phylloxera threatened to ex- 
 terminate the vine. In Africa the migratory locust is an unmitigated 
 evil. 
 
 Probably at least ten per cent, of every crop is lost through the at- 
 tacks of insects, though the loss is often so constant as to escape obser- 
 vation. Regarded as a direct tax of ten cents upon the dollar, however, 
 this loss becomes impressive. Webster says: "It costs the American 
 farmer more to feed his insect foes than it does to educate his children." 
 The average annual damage done by insects to crops in the United 
 States was conservatively estimated by Walsh and Riley to be $300,000,- 
 
 410 
 
INSECTS IN RELATION TO MAN 4II 
 
 000 — or about $50 for each farm. "A recent estimate by experts put the 
 yearly loss from forest insect depredations at not less than $100,000,000. 
 The common schools of the country cost in 1902 the sum of $235,000,000, 
 and all higher institutions of learning cost less than $50,000,000, making 
 the total cost of education in the United States considerably less than 
 the farmers lost from insect ravages. Thus it would be within the 
 statistical truth to make a still more starthng statement than Webster's, 
 and say that it costs American farmers more to feed their insect foes 
 than it does to maintain the whole system of education for everybody's 
 children. 
 
 "Furthermore, the yearly losses from insect ravages aggregate 
 nearly twice as much as it costs to maintain our army and navy; more 
 than twice the loss by fire ; twice the capital invested in manufacturing 
 agricultural implements ; and nearly three times the estimated value of the 
 products of all the fruit orchards, vineyards, and small fruit farms in the 
 country." (Slingerland.) 
 
 Though most of the parasites of domestic animals are merely annoy- 
 ing, some inflict serious or even fatal injury, as has been said. The 
 gad flies persecute horses and cattle; the maggots of a bot fly grow in 
 the frontal sinuses of sheep, causing vertigo and often death; another 
 bot fly develops in the stomach of the horse, enfeebling the animal. 
 The worst of the bot flies, however, is Hypoderma lineata, the ox-warble, 
 which not only impairs the beef but damages the hide by its perforations ; 
 the loss from this insect for one period of six months (Chicago, 1889) was 
 conservatively estimated as $3,336,565, of which $667,513 represented 
 the injury to hides. 
 
 All sorts of foodstuffs are attacked by insects, particularly cereals; 
 clothing, especially of wool, fur or feathers; also furniture and hundreds 
 of other useful articles. 
 
 As carriers of disease germs, insects are of vital importance toman, 
 as we have shown. 
 
 Beneficial Insects.— The vast benefits derived from insects are too 
 often overlooked, for the reason that they are often so unobvious as 
 .compared with the injuries done by other species. Insects are useful 
 as checks upon noxious insects and plants, as pollenizers of flowers, as 
 scavengers, as sources of human clothing, food, etc., and as food for 
 birds and fishes. 
 
 Almost every insect is subject to the attacks of other insects, pre- 
 daceous or parasitic — to say nothing of its many other enemies — and 
 but for this a single species of insect might soon overrun the earth. 
 
412 ENTOMOLOGY 
 
 There are only too many illustrations of the tremendous spread of an 
 insect in the absence of its accustomed natural enemies. One of these 
 examples is that of the gipsy moth, artificially introduced into Massa- 
 chusetts from Europe; another is the fluted scale, transported from 
 Australia to Cahfornia. Some conception of the vast restricting influ- 
 ence of one species upon another may be gained from the fact that the 
 fluted scale was practically exterminated in California as the result of 
 the importation from Australia of one of its natural enemies, a lady-bird 
 beetle known as Novius cardinalis. The plant lice, though of un- 
 paralleled fecundity, are ordinarily held in check by a host of enemies 
 
 (P- 379)- 
 
 An astonishingly large number of parasites may develop in the body 
 of a single individual; thus over 3,000 specimens of a hymenopterous 
 parasite {Copidosoma truncatellum) were reared by Giard from a single 
 Plusia caterpillar. 
 
 Parasites themselves are frequently parasitized, this phenomenon of 
 hyperparasitism being of considerable economic importance. A bene- 
 ficial primary parasite may be overpowered by a secondary parasite, 
 evidently to the indirect disadvantage of man, while the influence of a 
 tertiary parasite would be beneficial again. Now parasites of the third 
 order occur and probably of the fourth order, as appears from Howard's 
 studies, which we have already summarized. Moreover, parasites of all 
 degrees are attacked by predaceous insects, birds, bacteria, fungi, etc. 
 The control of one insect by another becomes, then, a subject of extreme 
 intricacy. 
 
 Insects render an important, though commonly unnoticed, service 
 to man in checking the growth of weeds. Indeed, insects exercise a vast 
 influence upon vegetation in general. A conspicuous alteration in the 
 vegetation has followed the invasions of the Rocky Mountain locust, 
 as Riley has said; many plants before unnoticed have grown in profu- 
 sion and many common kinds have attained an unusual luxuriance. 
 
 As agents in the cross pollination of flowers, insects are eminently 
 important. Darwin and his followers have proved beyond question 
 that as a rule cross pollination is indispensable to the continued vitaHty 
 of flowering plants; that repeated close pollination impairs their vigor 
 to the point of extermination. Without the visits of bees and other 
 insects our fruit trees would yield Httle or nothing, and the fruit grower 
 owes these helpers a debt which is too often overlooked. 
 
 As scavengers, insects are of inestimable benefit, consuming as they 
 do in incalculable quantity all kinds of dead and decaying animal and 
 
INSECTS TN RELATION TO MAN 413 
 
 vegetable matter. This function of insects is most noticeable in the 
 tropics, where the ants, in particular, eradicate tons of decomposing 
 matter that man lazily neglects. 
 
 Of insects that are directly useful to man, the silkworms and the 
 several species of honey bees are the most important. Silk is most 
 valuable as a textile material, but has minor uses. Some of the best 
 fishing lines are made of silk; and the best "leaders"- — long, tapering, 
 strong, and practically invisible in the water — are the silk glands them- 
 selves, after being stretched and dried. These leaders are imported 
 from the Mediterranean region, but may easily be made from the glands 
 of our large native silkworms, such as the Cecropia. 
 
 Though honey as a food is not as indispensable to us as it was to the 
 ancients, immense quantities of it are produced annually, and the 
 demand for it is usually greater than the supply. Beeswax has more 
 uses than one might suppose. One of its chief uses is for the manufac- 
 ture of comb ''foundation" for bee hives. Beeswax, though rivaled by 
 paraffin and ceresin, is better than these for some purposes. It is used 
 in poHshes for furniture, floors, carriages, automobiles, shoes and other 
 leather articles, and steel tools; as a coating for shoemaker's thread and 
 for steel nails; as an ingredient of some varnishes; for the insulation of 
 electric wires, etc.; for church candles; salves and cosmetics; in sealing 
 wax and grafting wax; by sculptors for making models; by dentists for 
 taking impressions; and was anciently used on writing tablets. 
 
 Lac, commonly used as sheUac and for lacquer and other resistant 
 varnishes, is yielded by several species of scale insects, but chiefly 
 Tachardia lacca, which is abundant in many parts of India on a variety 
 of plants (Zizyphus, Acacia, Butea, etc.). The lac is a resinous secre- 
 tion, produced abundantly by the female, and forming with the exuviae a 
 protective covering over her body. 
 
 A coccid that produces considerable quantities of lac occurs in 
 Arizona on Larrea mexicana. 
 
 Several coccids of the genus Ceroplastes, in India and China, produce 
 white wax, which is highly valued for some purposes but has been 
 replaced by paraffin for other uses. 
 
 The brilliant crimson pigment of the lac-insect of India is extracted 
 and known to artists as "lake." 
 
 The cochineal insect, Dactylopius coccus, is indigenous to Mexico, 
 but has been transported with its food plant, the prickly pear, to Spain, 
 India, and elsewhere. From the dried bodies of the females, carmine is 
 extracted. The cochineal industry, which dates back to the time of the 
 
414 ENTOMOLOGY 
 
 Aztecs, attained an immense development until some fifty years ago, 
 when it began to decline with the discovery of aniline dyes. Even at 
 present, however, there is a constant demand for cochineal, which is used 
 for coloring confectionery, fabrics, inks, and druggists' preparations. 
 
 The cottony cochineal insect, Dactylopius confusus, ranges through- 
 out the cactus region of the United States, and contains the same crim- 
 son fluid as its ally. 
 
 The Greeks and Romans obtained a red dye from species of Kertnes 
 living on an oak. Galls of Cynipidae were once important as a source 
 of ink. 
 
 As articles of human food, some insects are highly nutritious, but 
 are appreciated chiefly by savages. Not exclusively, however, for the 
 "manna" of bibHcal times was almost certainly the honey-dew from a 
 coccid. It is still used by Arabs as food under the name of "man." 
 The flavor of the large black carpenter ants, Camponotus, which can be 
 scooped up with the hands in large numbers, appeals to some who would 
 resent being called savages. White grubs, available in any desirable 
 quantity, are said to make an excellent salad, high in protein content. 
 Used in connection with corn they furnish almost a balanced ration for 
 hogs. 
 
 The red Indians formerly used many kinds of insects as food. 
 Especially dehcious was a bushel of grasshoppers roasted in a hole in 
 the ground. After all, the grasshopper is more attractive in appearance 
 and more refined in its choice of food than the much-esteemed lobster. 
 The Pah Utes of Utah eke out an existence on dried caterpillars, and 
 annually flock from far and near to harvest the salt-fly of the salt lakes. 
 The puparia of these flies {Ephydra hians) are washed up on the shore in 
 such enormous numbers that they can be collected by hundreds of 
 bushels. After the dirt is removed and the puparium shelled off, the 
 pupa, which is rather large, supplies a food which is said to be not un- 
 pleasant to the taste (Aldrich). 
 
 According to Dr. Aldrich, the Indians in the vicinity of Mono Lake, 
 California, collect for food the caterpiUars of the saturniid moth, 
 Coloradia pandora, from a species of pine tree. The great event of 
 gathering the crop comes, unfortunately, only every other year; as the 
 insect has a two-year cycle and only one brood. The Indians dig a 
 trench around a tree, making the outer wall of the trench vertical; then 
 beat the caterpiUars off the branches and collect them in the trench. 
 The dried caterpillars are a great delicacy to the Indians. Aldrich 
 says they taste like linseed oil. 
 
INSECTS IN RELATION TO MAN 415 
 
 Water-boatmen {Corixa) and their eggs are used as food in Mexico, 
 and are said to have a fine flavor. In Australia the Bugong moth 
 occurs in millions in certain localities, and the moth itself was formerly 
 an important article of food with the aborigines (Sharp). The bush- 
 men of Australia find that the clay of termite mounds makes a solid 
 meal; and hill tribes of India eat the termites, which have a flavor like 
 that of almonds. In Africa the migratory locust has been eaten since 
 history began. 
 
 The wise fisherman knows that certain kinds of insects are excellent 
 bait for fishes, especially at certain seasons. The better known of these 
 insects are grub worms, grasshoppers and hellgrammites. 
 
 A few insects have medicinal properties. Coccids of the genus 
 Kermes that live on an oak in the Mediterranean region yield a medic- 
 inal syrup. Another coccid, Llaveia axinus, of Mexico, produces a 
 peculiar substance known as axin. This is used as an external medic- 
 inal application, and is of considerable value as a varnish. (Sharp.) 
 Our native blister beetles and oil beetles possess a blistering or vesicant 
 property, which is due to the presence of cantharidin in their blood. 
 The crushed bodies of a Mediterranean species are still used medically 
 under the name of Spanish fly. In China medicinal properties are 
 ascribed to many different kinds of insects. 
 
 The use of insects as ornaments must not be forgotten. Beetles 
 with metallic colors or with iridescence, like the diamond beetle of 
 Brazil, are made up into jewelry. A coccid, Margarodes formicarium, 
 of the West Indies, found in the soil, where it lives on roots of plants and 
 is often plowed up, resembles a pearl, and is strung into necklaces, etc. 
 (Comstock.) The cucujo beetles (Pyrophorus) of tropical America 
 are the most brilhantly luminous of insects. They are used for orna- 
 mental display and are said to be serviceable as candles. Their diffused 
 light is pleasing in its quality, and it is reported that "the smallest 
 print may be read by moving one of these insects along the lines." 
 
 The showy butterflies, moths, and beetles, mounted for purposes of 
 display, are familiar to all. 
 
 In Japan a "fire-box" to hold a charcoal fire is made from a section 
 of a log, placed on end. For this purpose a log is frequently selected 
 on account of its natural ornamentation made by the engraver beetles; 
 or a screen may be made of wood that is carved with tunnels made by 
 termites. 
 
 The unimportant use of insects as playthings need only be alluded 
 to. In the south, children amuse themselves by attaching the green June 
 
41 6 ENTOMOLOGY 
 
 bugs to threads and letting them fly about. In China crickets are 
 matched against each other in fighting contests. 
 
 Many other examples of insects beneficial, more or less, to man 
 could be given if space permitted. 
 
 Doubtless many of us have now and then kept crickets or katydids in 
 cages because we liked to hear them sing; or have put fire flies in bottles 
 to watch them glow. 
 
 The Japanese, with a national appreciation of nature which is 
 foreign to this country, are accustomed to do these things. Crickets 
 and katydids are sold on the streets, at prices equivalent to two to 
 fifteen cents each, much as flowers are sold here. 
 
 As they have a cherry blossom season, they have also a fire fly 
 season, when it is the common custom to make visits to the country to 
 procure fire flies. Special trains are even run for these excursions. 
 
 Annually the people of Gifu collect many thousands of fire flies, 
 which are sent to Tokyo and on a certain night are liberated for the 
 enjoyment of the emperor. 
 
 As objects of scientific investigation insects are important, as no 
 entomologist will deny. They are even economically important in this 
 respect, for some of the principles of heredity, applicable to the breeding 
 of domesticated animals, have been worked out with the aid of insects, 
 particularly the pomace flies, Drosophila. 
 
 Introduction and Spread of Injurious Insects. — Many of our worst 
 insect pests were brought accidentally from Europe, notably the 
 Hessian fly, wheat midge, codling moth (probably), gipsy moth, 
 brown-tail moth, European corn borer, elm leaf beetle, leopard moth, 
 woolly apple aphid, cabbage butterfly, cabbage aphis, clover leaf 
 beetle, clover root borer, asparagus beetle, imported currant worm and 
 many cutworms; though few American species have obtained a foothold 
 in Europe, one of the few being the dreaded Phylloxera, which appeared 
 in France in 1863. 
 
 The gipsy moth (Porthetria dispar) , a native of Europe, where it is 
 at times a serious pest, was Uberated in eastern Massachusetts in 1868, 
 and has spread over the eastern half of the state and into New Hamp- 
 shire, Maine and Connecticut, in spite of all efforts to control it. Small 
 infestations occur also in New York and Pennsylvania, and in July, 
 1920, a colony was found in New Jersey, where at present (1922) 410 
 square miles are infested. The cost of controlling this omnivorous pest 
 is enormous (see beyond). "The amount expended by the Bureau in 
 the campaign against the Gipsy Moth, including the appropriation for 
 
INSECTS IN RELATION TO MAN 
 
 417 
 
 the current fiscal year, is $4,650,000. " (Dr. L. O. Howard, March 28, 
 1922.) 
 
 The brown-tail moth {Euprociis chrysorrkcea) is a native of the Old 
 World " where it is found from Algiers on the South to Sweden on the North 
 and from England on the West to the Himalaya Moutains on the 
 East. Over most of this area it is recognized as a pest of orchards and 
 forests. " (Dr. W. E. Britton.) This moth was accidentally introduced 
 into eastern Massachusetts on nursery stock, and first attracted the 
 attention of entomologists in 1897, since when it has spread over most 
 of Massachusetts and New Hampshire, into Vermont, Maine, Nova 
 Scotia and New Brunswick, over all of Rhode Island, half of Connecti- 
 cut, and into New York. The brown-tail moth has accompanied the 
 gipsy moth in its work of destruction. 
 
 The brown-tail moth spreads locally by means of flight, mostly; 
 but may be carried great distances commercially, on shipments of young 
 trees bearing young caterpillars in their winter nests. The first nests 
 found in Connecticut came on fruit tree seedlings imported in 1909 
 from a French nursery. (Britton.) The pest has several times reached 
 nurseries in Illinois on young trees from Belgium and France, but has 
 each time been eradicated by the state inspection service before it 
 could spread from the nurseries. In 192 1 the federal inspectors inter- 
 cepted nests of the brown-tail moth on forty-two shipments from 
 France, and egg masses of the gipsy moth on one shipment. 
 
 These two pests have been fought most vigorously but are not yet 
 under complete control. It is worth while to give here an account of 
 the expenditures made up to date (April 5, 1922) in the fight against 
 the gipsy moth and the brown-tail moth. Mr. A. F. Burgess, who is in 
 charge of the work, has kindly furnished these figures. 
 Expenditures by Infested States 
 (Federal Funds Not Included) 
 
 States 
 
 Expenditures 
 
 From 
 
 beginning 
 
 of work to — 
 
 Expenditures 
 by towns, in- 
 dividuals, etc. 
 
 Totals 
 
 Connecticut 
 
 Maine 
 
 Massachusetts 
 
 New Hampshire 
 
 Rhode Island 
 
 183,715-55 Dec. I, 1921 
 435,000.00 do 
 5,137,000.00 do 
 
 186,500.00 Sept. 30, 1921 
 179,600.00 Dec. 31, 1921 
 24,409.72 do 
 161,883.73 do 
 175,000.00 do 
 
 229.50 
 180,000.00 
 9,126,927.97 
 No record 
 
 20 , 000 . 00 
 No record 
 
 25,000.00 
 No record 
 No record 
 
 183,945.05 
 615,000.00 
 14,263,927.97 
 186,500.00 
 199,600.00 
 
 Vermont 
 
 New Jersey 
 
 24,409.72 
 186,883.73 
 
 New York 
 
 175,000.00 
 
 Pennsylvania 
 
 600 . 00 
 
 do 
 
 600.00 
 
 
 $6 , 483 , 709 . 00 
 
 $9,352, 157.47 $15,835,866.47 
 
4l8 ENTOMOLOGY 
 
 Add to this the amount supplied by the Federal Government, and 
 the total is more than twenty million dollars. 
 
 The San Jose scale insect {Aspidiotus perniciosus) , a native of North 
 China, was introduced into the San Jose valley, California, about 1870, 
 probably upon the flowering Chinese peach, became seriously destruc- 
 tive there in 1873, was carried across the continent to New Jersey in 
 1886 or 1887 on plum stock, and thence distributed directly to several 
 other states upon nursery stock. At present the San Jose scale is a 
 permanent menace to horticulture throughout the United States, and is 
 being checked or subdued only by the vigorous and continuous work of 
 ojQ&cial entomologists, acting under special legislation. This pernicious 
 insect occurs also in Japan, Hawaii, Australia and Chile. 
 
 The Mexican cotton boll weevil {Anthonomus grandis), which is 
 found throughout Mexico and in Guatemala, Costa Rica and western 
 Cuba, crossed the Rio Grande river and appeared in Brownsville, 
 Texas, about 1892. It either flew across the river or was carried across 
 in seed cotton. Since then it has extended its range every year until in 
 1921 it had practically "reached the limit of cotton cultivation." 
 
 The beetle hibernates and lays its eggs in the squares or bolls of 
 cotton; these are injured both by the larva feeding within and by the 
 beetles, whose feeding-punctures destroy the bolls and cause them to 
 drop. The annual loss from the weevil is far in excess of $200,000,000. 
 The pest has now been thoroughly studied by the Bureau of Entomology, 
 and the adoption of the control methods recommended by the Bureau 
 enables cotton to be grown at a fair profit; though the days of "bumper 
 crops" have gone. 
 
 The European corn borer {Pyrausta nubilalis), long known in Europe 
 as a pest of corn, hemp, hops and millet, was discovered near Boston, 
 Massachusetts, in 191 6, having been introduced probably in hemp sent to 
 a cordage factory, or in broom corn. In 1919 the borer was found to 
 be infesting four hundred square miles in the vicinity of Schenectady, 
 New York, having arrived possibly in bales of broom corn from Austria. 
 In 1920 the insect had established itself in an area of nineteen hundred 
 square miles in eastern Massachusetts, southern New Hampshire, and 
 New York, and appeared in Ontario, Canada. The borer feeds not only 
 on cultivated plants but also on a great variety of weeds. Energetic 
 efforts are being made to prevent this destructive insect from spreading 
 westward into the corn belt. 
 
 The green Japanese beetle {Popillia japonica), which in its native 
 home is not an important pest, was discovered in New Jersey in August , 
 
INSECTS IN RELATION TO MAN 419 
 
 1 91 6, and in Pennsylvania in 1920. It came from Japan probably as 
 grubs in soil about the roots of iris or azalea plants, but brought none of 
 its native enemies with it, and spread rapidly in its new environment. 
 In 192 1 it occupied two hundred and thirteen square miles in New 
 Jersey and fifty-seven in Pennsylvania. 
 
 The injury is done mostly by the beetles, which skeletonize the leaves 
 of trees and shrubs, both wild and cultivated, destroy ripening fruits, 
 and have a longer list of food plants than the brown-tail moth. 
 
 Extensive operations against the beetle are being conducted by the 
 Bureau of Entomology in co-operation with the Departments of Agri- 
 culture of New Jersey and Pennsylvania. 
 
 The elm leaf beetle {Galerucella luteola), notorious in southern 
 Europe as a defoliator of elm trees, entered Maryland about 1837, 
 spread along the coast as far as southern New Hampshire, and has made 
 its way into New York, Ohio and Kentucky, killing off thousands of 
 fine old elms on its way. The only eft"ective means of controlling this 
 beetle seems to be an arsenical spray. 
 
 The leopard moth {Zeuzera pyrina) , another European species acci- 
 dentally introduced into New Jersey some time before 1879, spread north 
 into Massachusetts, assisting the elm leaf beetle in its injurious activity. 
 The leopard moth is not confined to elms, however, though it injures 
 chiefly elms and silver maples, but attacks more than eighty kinds of 
 trees and shrubs, and affects fruit trees as well as shade trees. The cater- 
 pillar does not feed on the leaves but bores into the branches, which 
 become weakened as a result and are broken off by the wind. 
 
 The pink bollworm {Pectinophora gossypiella) , a cotton pest which is 
 probably a native of southern Asia and occurs also in Africa, Hawaii 
 and Brazil, entered Mexico and was recently introduced into Texas. 
 This serious pest is now being eradicated by the Department of Agri- 
 culture, at an annual expense of about half a million dollars. 
 
 An insect often passes readily from a wild plant to a nearly related 
 cultivated species. Thus the Colorado potato beetle passed from the 
 wild species Solarium rostratum to the introduced species, Solanum 
 tuberosum, the potato. Many of our fruit-tree insects feed upon wild, as 
 well as cultivated, species of Rosaceae; the peach borer, a native of this 
 country, probably fed originally upon wild plum or wild cherry. Many 
 of the common scarabaeid larvae known as 'white grubs " are native to 
 prairie sod, and attack the roots of various cultivated grasses, including 
 corn, and those of strawberry, potato and other plants. The chinch 
 bug fed originally upon native grasses, but is equally at home on cul- 
 
420 ENTOMOLOGY 
 
 tivated species, particularly millet, Hungarian grass, rice, wheat, 
 barley, rye and corn. In fact, the worst corn insects, such as the chinch 
 bug, wireworms, white grubs and cutworms, are species derived from 
 wild grasses. 
 
 Even in the absence of cultivated plants their insect pests continue 
 to sustain themselves upon wild plants, as a rule; the larva of the 
 codling moth, for example, is very common in wild apples and wild 
 haws. 
 
 The Economic Entomologist. — To mitigate the tremendous dam- 
 age done by insects, the individual cultivator is almost helpless without 
 expert advice, and the immense agricultural interests of this country 
 have necessitated the development of the economic entomologist, the 
 value of whose services is universally appreciated by the intelligent. 
 
 Almost every State now has one or more economic entomologists, 
 responsible to the State or else to a State Experiment Station, while the 
 general Government attends to general entomological needs in the most 
 comprehensive and thorough manner. 
 
 "It is the special object of the economic entomologist," says Dr. 
 Forbes, "to investigate the conditions under which these enormous 
 losses of the food and labor of the country occur, and to determine, first, 
 whether any of them are in any degree preventable; second, if so, how 
 they are to be prevented with the least possible cost of labor and money; 
 and, third, to estimate as exactly as possible the expenses of such pre- 
 vention, or to furnish the data for such an estimate, in order that each 
 may determine for himself what is for his interest in every case arising. 
 
 "The subject matter of this science is not insects alone, nor plants 
 alone, nor farming alone. One may be a most excellent entomologist 
 or botanist, or he may have the whole theory and practice of agriculture 
 at his tongue's end, and at his fingers' ends as well, and yet be without 
 knowledge or resources when brought face to face with a new practical 
 problem in economic entomology. The subject is essentially that of 
 the relations of these things to each other; of insect to plant and of plant 
 to insect, and of both these to the purposes and operations of the farm, 
 and it involves some knowledge of all of them. 
 
 "As far as the entomological part of the subject is concerned, the 
 chief requisites are a familiar acquaintance with the common injurious 
 insects, and especially a thorough knowledge of their life histories, to- 
 gether with practical familiarity with methods of entomological study 
 and research. The life histories of insects lie at the foundation of the 
 whole subject of economic entomology; and constitute, in fact, the 
 
INSECTS IN RELATION TO MAN 42 1 
 
 principal part of the science; for until these are clearly and completely 
 made out for any given injurious species, we cannot possibly tell when, 
 where or how to strike it at its weakest point. 
 
 "But besides this, we must also know the conditions favorable and 
 unfavorable to it; the enemies which prey upon it, whether bird or insect 
 or plant parasite; the diseases to which it is subject, and the effects 
 of the various changes of weather and season. We should make, in fact, 
 a thorough study of it in relation to the whole system of things by which 
 it is affected. Without this we shall often be exposed to needless alarm 
 and expense, perhaps, in fighting by artificial remedies, an insect already 
 in process of rapid extinction by natural causes; perhaps giving up in 
 despair just at the time when the natural checks upon its career are about 
 to lend their powerful aid to its suppression. We may even, for lack 
 of this knowledge, destroy our best friends under the supposition that 
 they are the authors of the mischief which they are really exerting 
 themselves to prevent. In addition to this knowledge of the relations 
 of our farm pests to what we may call the natural conditions of their life, 
 we must know how our own artificial farming operations affect them, 
 which of our methods of culture stimulate their increase, and which, if 
 any, may help to keep it down. And we must also learn where strictly 
 artificial measures can be used to advantage to destroy them. 
 
 "For the life histories of insects, close, accurate and continuous 
 observation is of course necessary; and each species studied must be fol- 
 lowed not only through its periods of destructive abundance, when it 
 attracts general attention, but through its times of scarcity as well, and 
 season after season, and year after year. 
 
 "The observations thus made must of course be collected, collated 
 and most cautiously generahzed, with constant reference to the con- 
 ditions under which they were made. No part of the work requires 
 more care than this. 
 
 "This work becomes still more difficult and intricate when we pass 
 from the simple life histories of insects to a study of the natural checks 
 upon their increase. Here hundreds and even thousands of dissections 
 of insectivorous birds and predaceous insects are necessary, and a care- 
 ful microscopic study of their food, followed by summaries and tables 
 of the principal results, a tedious and laborious undertaking, a specialty 
 in itself, requiring its special methods and its special knowledge of the 
 structures of insects and plants, since these must be recognized in frag- 
 ments, while the ordinary student sees them only entire. 
 
 "If we would understand the relations of season and weather to the 
 
42 2 ENTOMOLOGY 
 
 abundance of injurious insects, we are led up to the science of meteor- 
 ology; and if we undertake to master the obscure subject of their diseases, 
 especially those of epidemic or contagious character, we shall find use 
 for the highest skill of the microscopist, and the best instruments of 
 microscopic research. 
 
 "All these investigations are preliminary to the practical part of our 
 subject. What shall the farmer do to protect his crops? To answer 
 this question, besides the studies just mentioned, much careful experi- 
 ment is necessary. All practical methods of fighting the injurious insects 
 must be tried — first on a small scale, and under conditions which the 
 experimenter can control completely, and then on the larger scale of 
 actual practice; and these experiments must be repeated under varying 
 circumstances, until we are sure that all chances of mistake or of acci- 
 dental coincidence are removed. The whole subject of artificial remedies 
 for insect depredations, whether topical applications or special modes of 
 culture, must be gone over critically in this way. So many of the so- 
 called experiments upon which current statements relating to the value 
 of remedies and preventives are based have been made by persons 
 unused to investigation, ignorant of the habits and the transformations 
 of the insects treated, without skill or training in the estimation of evi- 
 dence, and failing to understand the importance of verification, that the 
 whole subject is honeycombed with blunders. Popular remedies for 
 insect injuries have, in fact, scarcely more value, as a rule, than popular 
 remedies for disease. 
 
 "Observation, record, generalization, experiment, verification — 
 these are the processes necessary for the mastery of the subject, and 
 they are the principal and ordinary processes of all scientific research." 
 
 The official economic entomologist uses every means to reach the 
 public for whose benefit he works. Bulletins, circulars and reports, 
 embodying most serviceable information, are distributed freely where 
 they will do the most good, and timely advice is disseminated through 
 newspapers and agricultural journals. An immense amount of corre- 
 spondence is carried on with individual seekers for help, and personal 
 influence is exerted in visits to infested localities and by addresses before 
 agricultural meetings. Special emergencies often tax every resource 
 of the official entomologist, especially if he is hampered by inadequate 
 legislative provision for his work. Too often the public, disregarding 
 the prophetic voice of the expert, refuses to "close the door until the 
 horse is stolen." 
 
 Aside from these emergencies, such as outbreaks of the Rocky Moun- 
 
INSECTS IN RELATION TO MAN 423 
 
 tain locust, chinch bug, Hessian fly, San Jose scale and others, the State 
 or Experiment Station entomologist has his hands full in any State of 
 agricultural importance; in fact, can scarcely discharge his duties prop- 
 erly without the aid of a corps of competent assistants. 
 
 This chapter would be incomplete without some mention of the 
 progress of economic entomology in this country, especially since 
 America is pre-eminently the home of the science. The history of the 
 science is largely the history of the State and Government entomologists, 
 for the following account of whose work we are indebted chiefly to the 
 writings of Dr. Howard, to which the reader is referred for additional 
 details as well as for a comprehensive review of the status of economic 
 entomology in foreign countries. 
 
 Massachusetts. — Dr. Thaddeus W. Harris, though preceded as a 
 writer upon economic entomology by William D. Peck, was our pioneer 
 official entomologist — official simply in the sense that his classic volume 
 was prepared and published at the expense of the state of Massachu- 
 setts, first (1841) as a "Report" and later as a "Treatise." The 
 splendid Flint edition (1862), entitled "A Treatise on Some of the 
 Insects Injurious to Vegetation," is still "the vade mecum of the working 
 entomologist who resides in the northeastern section of the country." 
 
 Dr. Alpheus S. Packard gave the state three short but useful reports 
 from 1871 to 1873. 
 
 As entomologist to the Hatch Experiment Station of the Massachu- 
 setts Agricultural College, Prof. Charles H. Fernald issued important 
 bulletins upon injurious insects, and published in collaboration 
 with Edward H. Forbush a notable volume upon the gipsy moth. 
 
 New York. — Dr. Asa Fitch, appointed in 1854 by the New York State 
 Agricultural Society, under the authorization of the legislature, was the 
 first entomologist to be officially commissioned by any state. His 
 fourteen reports (1855 to 1872) embody the results of a large amount of 
 painstaking investigation. 
 
 In 188 1 Dr. James A. Lintner became state entomologist of New 
 York. Highly competent for his chosen work, Lintner made every 
 eft'ort to further the cause of economic entomology, and his thirteen 
 reports, accurate, thorough and extremely serviceable, rank among the 
 best. Lintner has had a most able successor in Dr. E. P. Felt, who is 
 continuing the work with exceptional vigor and the most careful regard 
 for the entomological welfare of the state. Felt has published at this 
 writing thirty-eight bulletins (including twenty-one annual reports), 
 besides important papers on forest and shade-tree insects, and has 
 
424 ENTOMOLOGY 
 
 directed the preparation by Needham and his associates of three notable 
 volumes on aquatic insects. 
 
 The Cornell University Agricultural Experiment Station, established 
 in 1879, has issued many valuable publications upon injurious insects, 
 written by the master-hand of Professor Comstock or else under his 
 influence. The studies of Comstock and Slingerland were always made 
 in the most conscientious spirit and their bulletins — original, thorough 
 and practical — are models of what such works should be. 
 
 More recently, Prof. C. R. Crosby and Prof. G. W. Herrick, of Cor- 
 nell, have published important contributions to economic entomology. 
 
 The Geneva station has issued many excellent entomological 
 bulletins, the results of investigations by V. H. Lowe, F. A. Sirrine, 
 H. E. Hodgkiss, P. J. Parrott, and W. J. Schoene. 
 
 Illinois. — Mr. Benjamin D. Walsh, engaged in 1867 by the lUinois 
 State Horticultural Society, published in 1868, as acting state entomolo- 
 gist, a report in the interests of horticulture — an accurate and 
 altogether excellent piece of original work. Like many other economic 
 entomologists he was a prolific writer for the agricultural press and his 
 contributions, numbering about four hundred, were in the highest degree 
 scientific and practical. 
 
 Walsh was succeeded by Dr. William LeBaron, who published (187 1 
 to 1874) four able reports of great practical value. In the words of Dr. 
 Howard, "He records in his first report the first successful experiment 
 in the transportation of parasites of an injurious species from one locality 
 to another, and in his second report recommended the use of Paris green 
 against the canker worm on apple trees, the legitimate outcome from 
 which has been the extensive use of the same substance against the 
 codling moth, which may safely be called one of the great discoveries 
 in economic entomology of late years." 
 
 Following LeBaron as state entomologist. Rev. Cyrus Thomas and 
 his assistants, G. H. French and D. W. Coquillett, produced a creditable 
 series of six reports (1875 to 1880) as part of a projected manual of the 
 economic entomology of Illinois. 
 
 In 1882 Prof. S. A. Forbes was appointed state entomologist. His 
 reports and bulletins, based upon the labors of an able corps of assist- 
 ants, are among the best that have been produced. Of the eighteen 
 reports issued by Dr. Forbes, those dealing with the chinch bug, San 
 Jose scale, corn insects and sugar beet insects are especially noteworthy. 
 
 The oflEice of state entomologist was discontinued in 191 7, without, 
 however, any interruption of the entomological work, which is now 
 
INSECTS IN RELATION TO MAX 425 
 
 carried on by Dr. Forbes, as director of the Natural History Survey, 
 with W. P.- Flint as chief entomologist. 
 
 Missouri. — Appointed in 1868, Prof. Charles V. Riley published 
 (1869 to 1877) nine reports as state entomologist. To quote Dr. How- 
 ard. "They are monuments to the state of Missouri, and more especially 
 to the man who wrote them. They are original, practical and scientific. 
 . . . They may be said to have formed the basis for the new economic 
 entomology of the world." Riley's subsequent work will presently be 
 spoken of. 
 
 Minnesota. — The reports that Dr. O. Lugger issued in Minnesota, 
 though compiled for the most part, contain much serviceable informa- 
 tion, presented in a popularly attractive manner. Following Lugger, 
 F. L. Washburn published several useful reports. The present state 
 entomologist is Prof. A. G. Ruggles. 
 
 New Jersey. — New Jersey has long been active and progressive in 
 state entomological work. Dr. J. B. Smith, state entomologist from 
 1894 until his death in 1912. was a most energetic investigator and 
 prolific writer of useful bulletins and reports. He was succeeded by Dr. 
 T. J. Headlee, well known for his work in Kansas. 
 
 Connecticut. — Dr. W. E. Britton has published twenty reports as 
 state entomologist. These are of a high degree of excellence, are well 
 illustrated, and are most useful treatises on the injurious insects of 
 the state. 
 
 Maine. — Dr. C. H. Fernald and Prof. F. L. Harvey formerly 
 rendered entomological service to the state of Maine. The work is now 
 in the efficient hands of Dr. Edith M. Patch, an authority on Aphididae, 
 who has made a reputation for the state by her excellent publications 
 and those of her co-workers. 
 
 California. — The progressive spirit of California has been carried 
 into the entomological work of the state. Many excellent investiga- 
 tions, chiefly upon insects affecting citrus plants and the grape, and 
 upon means of control, have been made by Prof. C. W. Woodworth, 
 Prof. W. B. Herms, Prof. H. J. Quayle, and Prof. E. O. Essig. 
 
 Ohio. — F. M. Webster became known as one of the leading investiga- 
 tors in economic entomology by his work in Ohio. Since then Prof. 
 H. A. Gossard and J. S. Houser have made important contributions to 
 the literature of economic entomology. 
 
 Kansas. — Manhattan, Kansas, is a well-known center of entomolog- 
 ical activity, from which have appeared many important publications on 
 economic entomology. Prof. G. A. Dean, Dr. J. H. Merrill, and Dr. 
 
426 ENTOMOLOGY 
 
 R. C. Smith, with their efficient assistants, are carrying on the work 
 there. At the University of Kansas, Prof. S. J. Hunter is in charge of 
 entomological work. 
 
 Iowa. — At Ames, Iowa, Prof. H. E. Summers was formerly state 
 entomologist, followed by R. L. Webster as acting state entomologist, 
 who was succeeded by Dr. E. D. Ball, now Director of Research of 
 the U. S. Department of Agriculture. All these men, with Dr. C. P. 
 Gillette (now of Colorado) and Prof. Herbert Osborn (now of Ohio), 
 have greatly aided entomological progress by their studies. 
 
 Other States. — The states just mentioned are those in which 
 economic entomology has long been encouraged and developed. In 
 almost all the other states, however, the value of the science is at present 
 appreciated. In the following states the work of the entomologists who 
 are named has been especially noteworthy. Alabama: Dr. W. E. Hinds. 
 Delaware: Prof. E. D. Sanderson. Prof. C. 0. Houghton. Florida: 
 Prof. P. H. Rolfs. Prof. H. A. Gossard. Idaho: Prof. J. M. Aldrich. 
 Indiana: Prof. W. S. Blatchley. Prof. J. J. Davis. Kentucky: Prof. 
 H. Garman. Louisiana: Prof. H. A. Morgan. Wilmon Newell. 
 Maryland: W. G. Johnson. Prof. T. B. Symons. Massachusetts: 
 Prof. C. H. Fernald. Prof. H. T. Fernald. Michigan: Prof. A. J. Cook. 
 Prof. R. H. Pettitt. Mississippi: Prof. G. W. Herrick. Prof. R. W. 
 Harned. Missouri: Prof. J. M. Stedman. Montana: Prof. R. A. 
 Cooley. Nebraska: Prof. L. Bruner. Prof. M. H. Swenk. Nevada: 
 Prof. S. B. Doten. New Hampshire: Dr. C. M. Weed. Prof. E. D. 
 Sanderson. Prof. W. C. O'Kane. New Mexico: Prof. C. H. T. 
 Townsend. Prof. T. D. A. Cockerell. North Carolina: Prof. F. 
 Sherman, Jr. Oregon: Dr. A. B. Cordley. South Carolina: Prof. A. F. 
 Conradi. Tennessee: Dr. H. A. Morgan. Washington: Prof. A. L. 
 Melander. West Virginia: Dr. A. D. Hopkins. Prof. L. M. Peairs. 
 
 State Experiment Stations.^The organization of State Agri- 
 cultural Experiment Stations in 1888, under the Hatch Act, gave 
 economic entomology an additional impetus. At present at least one 
 experiment station is in operation in every state and territory; there 
 being stations in Alaska, Hawaii, Porto Rico, Virgin Islands, and 
 Guam. These stations, often in connection with state agricultural 
 colleges, maintain altogether more than two hundred workers in en- 
 tomology, and have issued a great number of bulletins upon injurious 
 insects. These publications are extremely valuable as a means of dis- 
 seminating entomological information, and most of them are based 
 upon the investigations of their authors. 
 
INSECTS IN RELATION TO MAN 427 
 
 While these workers have been conspicuously active in the publica- 
 tion of their investigations, there are many other station entomologists 
 and state entomologists who devote themselves entirely to the practical 
 application of entomological knowledge, and whose work in this respect 
 is highly important, even though its influence does not extend beyond 
 the limits of the state. 
 
 The U. S. Entomological Commission. — This commission, founded 
 under a special Act of Congress in 1877 ^o investigate the Rocky Moun- 
 tain locust, consisted of Dr. C. V. Riley, Dr. A. S. Packard and Rev. 
 Cyrus Thomas, remained in existence until 188 1, and pubHshed'five 
 reports and seven bulletins, all of lasting value. The first two reports 
 form a most elaborate monograph of the Rocky Mountain locust; the 
 third report includes important work upon the army worm and the 
 canker worm; the fourth, written by Riley, is an admirable volume on 
 the cotton worm and boll worm; and the fifth, by Packard, is a useful 
 treatise on forest and shade-tree insects. 
 
 The U. S. Department of Agriculture.- — The first entomological 
 expert appointed under the general government was Townend Glover, 
 in 1854. He issued a large number of reports (1863-1877), which ''are 
 storehouses of interesting and important facts which are too little used 
 by the working entomologists of to-day," as Howard says. Glover 
 prepared, moreover, a most elaborate series of illustrations of North 
 American insects, at an enormous expense of labor, out of all proportion, 
 however, to the practical value of his undertaking. 
 
 Glover was succeeded in 1878 by Riley, whose achievements have 
 aroused international admiration. He resigned in a year, after writing 
 a report, and was succeeded by Prof. Comstock, who held office for two 
 years, during which he wrote two important volumes (published re- 
 spectively in 1880 and 1881) dealing especially with cotton, orange and 
 scale insects. His work on scale insects laid the foundation for all our 
 subsequent investigation of the subject. 
 
 Riley, assuming the office of government entomologist, published up 
 to 1894, "12 annual reports, 31 bulletins, 2 special reports, 6 volumes of 
 the periodical bulletin Insect Life and a large number of circulars of 
 information." During his vigorous and enterprising administration 
 economic entomology took an immense step in advance. The life 
 histories of injurious insects were studied with extreme care and many 
 valuable improvements in insecticides and insecticide machinery were 
 made. One of the notable successes of Dr. Riley and his co-workers, 
 which has attracted an exceptional amount of public attention, was the 
 
428 ENTOMOLOGY 
 
 practical extermination of the fluted scale {Icerya purchasi), which 
 threatened to put an end to the cultivation of citrus trees in California. 
 This disaster was averted by the importation from Australia, in 1888, of 
 a native enemy of the scale, namely the lady-bird beetle Novius ( Vedalia) 
 cardinalis, which, in less than eighteen months after its introduction 
 into California, subjugated the noxious scale insect. The United States 
 has since sent Novius to South Africa, Egypt and Portugal with similar 
 beneficial results. 
 
 The Department of Agriculture succeeded in starting a new and im- 
 portant industry in California — the culture of the Smyrna fig. The 
 superior flavor of this variety is due to the presence of ripe seeds, in other 
 words, to fertilization, and for this it is necessary for pollen of the wild 
 fig, or ''caprifig," to be transferred to the flowers of the Smyrna fig. 
 Normally this pollination, or *' caprification," is dependent upon the serv- 
 ices of a minute chalcid, Blastophaga grossorum, which develops in the 
 gall-like flowers of the caprifig. The female insect, which in this excep- 
 tional instance is winged while the male is not, emerges from the gall 
 covered with pollen, enters the young flowers of the Smyrna fig to ovi- 
 posit, and incidentally pollenizes them. 
 
 After many discouraging attempts, Blastophaga, imported from 
 Algeria, was established in California, and the new industry has devel- 
 oped rapidly. 
 
 Based upon the foundation laid by Riley, the work of the Bureau 
 of Entomology has steadily progressed, under the leadership of Dr. 
 Leland 0. Howard. With a comprehensive and firm grasp of his sub- 
 ject, alert to discover and develop new possibilities, energetic and 
 resourceful in management. Dr. Howard has brought the government 
 work in applied entomology to its present position of commanding 
 importance. Admirably organized, the Bureau now (1922) requires 
 the services of 460 employes, 386 of whom are directly engaged in 
 scientific work. 
 
 In the magnitude and importance of its contributions to economic 
 entomology the Bureau is unapproached by any other organization. 
 
 The Bureau of Entomology has always secured the services of the 
 best entomologists avaflable, and its staff of experts includes many of 
 the leading entomologists of the world. Those in charge of the work 
 are as follows: Dr. L. O. Howard, entomologist and chief of bureau. 
 C. L. Marlatt, entomologist and assistant chief of bureau. W. D. 
 Hunter, southern field crop insect investigations. W. R. Walton, 
 cereal and forage insect investigations. Prof. A. L. Quaintance, decidu- 
 
INSECTS IN RELATION TO MAN 429 
 
 ous-fruit insect investigations, tropical and subtropical fruit insect 
 investigations. C. L. Marlatt, investigations of the Mediterranean 
 and other fruit flies. Dr. F. H. Chittenden, truck-crop insect investiga- 
 tions. E. A.. Back, stored-product insect investigations. Dr. A. D. 
 Hopkins, forest insect investigations. Dr. L. O. Howard, W. D. Hun- 
 ter, and J. L. Webb, investigations of insects affecting the health of 
 man and animals. Dr. E. F. Phillips, investigations in bee culture. 
 A. F. Burgess, gipsy moth and brown-tail moth investigations. 
 
 The U. S. Department of Agriculture publishes annually a List of 
 Workers in Subjects Pertaining to Agriculture, which contains the names 
 of all the entomological workers in the Department of Agriculture, in 
 State Agricultural Colleges and in Experiment Stations. 
 
 Canada. — The development of economic entomology in Canada 
 was due largely to the efforts of Dr. James Fletcher, of the Dominion 
 Experimental Farms, Ottawa, whose annual reports and other writings 
 were of exceptional value. His work was furthered in every way by 
 the "eminent director of the experimental farms system. Dr. William 
 Saunders, himself a pioneer in economic entomology in Canada and the 
 author of one of the most valuable treatises upon the subject that has 
 ever been published in America." Dr. Fletcher was Government ento- 
 mologist from 1884 until his death, in 1908. Dr. C. Gordon Hewitt, 
 who was appointed Dominion entomologist in 1909, made in ten years a 
 brilliant record in public service. His remarkable work was cut short 
 by his death in February, 1920. In October, 1920, Arthur Gibson was 
 made Dominion entomologist. He is well fitted by ability and experience 
 to maintain the standard of excellence set by his eminent predecessors. 
 
 Outside of the government work, entomology in Canada centers 
 around the Entomological Society of Ontario, whose excellent publica- 
 tions, sustained by the government, are of great scientific and educa- 
 tional importance. In addition to its annual reports, this society 
 issues the Canadian Entomologist, one of the leading serials of its 
 kind, edited for many years by its founder, the Rev. C. J. S. Bethune, 
 whose devoted services have been appreciated by every entomologist. 
 
 The Association of Official Economic Entomologists.— Organ- 
 ized in 1889 by a few energetic workers, this association has had a rapid 
 and healthy growth and now numbers among its members all the leading 
 economic entomologists of America and a large number of foreign work- 
 ers. The annual meetings of the association impart a vigorous stimulus 
 to the individual worker and tend to promote a well-balanced develop- 
 ment of the science of economic entomology. 
 
LITERATURE 
 
 The literature on entomological subjects now numbers about 150,000 titles. The 
 works listed below have been selected chiefly on account of their general usefulness and 
 accessibility. Works incidentally containing important bibliographies of their special 
 subjects are designated each by an asterisk — *. 
 
 BIBLIOGRAPHICAL WORKS 
 
 Hagen, H. A. Bibliotheca Entomologica. 2 vols. Leipzig, 186 2- 1863. Covers the entire 
 literature of entomology up to 1862, 
 
 Englemann, W. Bibliotheca Historico-Naturalis. i vol. Leipzig, 1846. Literature 
 1 700-1846. 
 
 Carus, J. v., and Englemann, W. Bibliotheca Zoologica. 2 vols. Leipzig, 186 1. Litera- 
 ture, I 846-1 860. 
 
 Taschenberg, O. Bibliotheca Zoologica. 5 vols. Leipzig, 1887-1899. Vols. 2 and 3, 
 entomological literature, 1861-1880. 
 
 The Zoological Record. London. Annually since vol. for 1864. 
 
 Catalogue of Scientific Papers, Royal Society. London. Since 1868. 
 
 Zoologischer Anzeiger. Leipzig. Fortnightly since 1878. Bibliographica Zoologica, 
 annual volumes since 1896. 
 
 Concilium Bibliographictmi. Zurich. Card catalogue of current zoological literature 
 since 1896. 
 
 Archiv fiir Naturgeschichte. Berlin. Annual summaries since 1835. 
 
 Journal of the Royal Microscopical Society. London. Summaries of the most important 
 works, beginning 1878. 
 
 Zoologischer Jahresbericht. Leipzig. Yearly summaries of literature since 1879. 
 
 Zoologisches Centralblatt. Leipzig. Reviews of more important literature since 1895. 
 
 Psyche. Cambridge, Mass. Records of American literature. Also earlier records, 
 beginning 1874. 
 
 Entomological News. — Philadelphia, 1890 to date. Records of current literature. 
 
 BibUography of the more important contributions to American Economic Entomology. 
 8 parts. Pts. 1-5 by S. Henshaw; pts. 6-8 by N. Banks. 1318 pp. Washington, 
 1889-1905. 
 
 Banks, N. 1917. Index to the Literature of American Economic Entomology. Jan. i, 
 1905 to Dec. 31, 1914. 5 + 323 pp. Amer. Assoc. Econ. Ent. Melrose Highlands, 
 Mass. 
 
 Colcord, M. 1921. Index II to the Literature of American Economic Entomology. Jan. 
 1, 1915 to Dec. 21, 1919. 4 + 388 pp. Amer. Assoc. Econ. Ent. Melrose High- 
 lands, Mass. 
 
 Review of Applied Entomology. 1913 to date. Series A: Agricultural. Series B : Medical 
 and Veterinary. Imperial Bureau of Entomology. London. Dulau & Co., Ltd. 
 Reviews of current literature. 
 
 Catalogue of Scientific Serials, 1633-1876. S. H. Scudder. Cambridge, Mass. Harvard 
 University, 1879. 
 
 A Catalogue of Scientific and Technical Periodicals, 1665-1895. H. C. Bolton. Wash- 
 ington, Smithsonian Institution, 1897. 
 430 
 
LITERATURE 43 1 
 
 A List of Works on North American Entomology. N. Banks. Bull. U. S. Dept. Agric, 
 Bur. Ent., no. 81 (n.s.), 120 pp. Washington, 1910. 
 
 GENER.\L ENTOMOLOGY 
 
 Kirby, W., and Spence, W. 1822-26. An Introduction to Entomology. 4 vols. 36 + 
 
 2413 pp., 30 pis. London. 
 Burmeister, H. 1832-55. Handbuch der Entomologie. 2 vols. 28 + 1746 pp., 16 taf. 
 Trans, of Band i : 1836. W. E. Shuckard. A Manual of Entomology. 12 + 
 654 pp., 32 pis. London. 
 Westwood, J. O. 1839-40. An Introduction to the Modern Classification of Insects. 
 
 2 vols. 23 + 620 pp., 133 figs. London. 
 Graber, V. 1877-79. Die Insekten. 2 vols. 8 + 1008 pp., 404 figs. MUnchen. 
 Miall, L. C, and Denny, A. 1886. The Structure and Life-History of the Cockroach. 
 
 6 + 224 pp., 125 figs. London, Lovell Reeve & Co.; Leeds, R. Jackson. 
 Comstock, J. H. 1888. An Introduction to Entomology. 4 + 234 pp., 201 figs. Ithaca, 
 
 N. Y. 
 Kolbe, H. J. 1889-93. Einfuhrung in die Kenntnis der Insekten. 12 + 709 pp., 324 figs. 
 
 Berlin. F. Diimmler.* 
 Packard, A. S. 1889. Guide to the Study of Insects. Ed. 9. 12 + 715 pp., 668 figs., 
 
 15 pis. New York. Henry Holt & Co. 
 Hyatt, A., and Arms, J. M. 1890. Insecta. 23 + 300 pp., 13 pis., 223 figs. Boston. 
 
 D. C. Heath & Co.* 
 Kirby, W. F. 1892. Elementary Text-Book of Entomology. Ed. 2. 8 -t- 281 pp., 87 pis. 
 
 London. Swan Sonnenschein & Co. 
 Comstock, J. H. and A. B. 1895. A Manual for the Study of Insects. 7 + 701 pp., 
 
 797 figs., 6 pis. Ithaca, N. Y. Comstock Pub. Co. 
 Sharp, D. 1895, 1901. Insects. Cambr. Nat. Hist., vols. 5, 6. 12 -f 1130 pp., 618 figs. 
 
 London and New York. Macmillan & Co.* 
 Comstock, J. H. 1897, 1901. Insect Life. 6 -|- 349 PP-, 18 pis., 296 figs. New York. 
 
 D. Appleton & Co. 
 Packard, A. S. 1898. A Text-Book of Entomology. 17 -f 729 pp., 654 figs. New York 
 
 and London. The Macmillan Co.* 
 Carpenter, G. H. 1899. Insects; their Structure and Life. 11 + 404 pp., 184 figs. 
 
 London. J. M. Dent & Co.* 
 Packard, A. S. 1899. Entomology for Beginners. Ed. 3. 16 -f 367 pp., 273 figs. New 
 
 York. Henry Holt & Co.* 
 Howard, L. O. 1901. The Insect Book. 27 -|- 429 pp., 48 pis., 264 figs. New York. 
 
 Doubleday, Page & Co. 
 Hxmter, S.J. 1902. Elementary Studies in Insect Life. 18 -f 344 pp., 234 figs. Topeka. 
 
 Crane & Co. 
 Henneguy, L. F. 1904. Les Insectes. Morphologic, Reproduction, Embryogenie. 
 
 18 4- 804 pp., 622 figs., 4 pis. Paris. Masson et Cie. Contains more than two 
 
 thousand references.* 
 Kellogg, V. L. 1905. American Insects. 7 + 674 pp., 13 pis., 812 figs. New York. 
 
 Henry Holt & Co. 
 Berlese, A. 1909-13. Gli Insetti. Vol. i, 10 + 1004 pp., 1292 figs., 10 pis. Vol. 2, 
 
 240 pp. 233 figs. Milan. Contains exhaustive bibliographies.* 
 Sanderson, E. D., and Jackson, C. F. 1912. Elementary Entomology, 5 + 372 pp., 
 
 496 figs. Boston and New York. Ginn & Co. 
 Sanderson, E. D., and Peairs, L. M. 1917. School Entomology. 7 + 356 pp., 233 figs. 
 
 New York. John Wiley & Sons, Inc. 
 
432 ENTOMOLOGY 
 
 Lutz, F. E. 1918. Fieldbook of Insects. 9 + 5C9 pp., 101 pis. New York & London. 
 
 G. P. Putman's Sons.* 
 Comstock, J. H. 1920. An Introduction to Entomology. Second Ed. 18 + 220 pp., 
 
 220 figs. Ithaca, N. Y. Comstock Pub. Co.* 
 
 PHYLOGENY AND CLASSIFICATION 
 
 Kirby, W., and Spence, W. 1822-26 An Introduction to Entomologj-. 4 vols. 36 + 
 
 2413 pp., 30 pis. London. 
 Burmeister, H. 1832. Handbuch der Entomologie. 2 vols. 28 + 1746 pp., 16 taf. 
 
 Berlin. Translation of Band i : 1836. W. E. Shuckard. A Manual of Entomol- 
 ogy. 12 + 654 pp., 32 pis. London. Contains useful synopses of the older 
 
 systems of classification. 
 Westwood, J. O. 1839-40. An Introduction to the Modern Classification of Insects. 
 
 2 vols. 23 + 620 pp., 133 figs. London. 
 Packard, A. S. 1873. Our Common Insects. 255 pp., 268 figs. Boston. Estes & 
 
 Lauriat. 
 Lubbock, J. 1874. On the Origin and Metamorphoses of Insects. 16 + 108 pp., 63 figs., 
 
 6 pis. London. Macmillan & Co.* 
 Mayer, P. 1876. Ueber Ontogenie und Phylogenie der Insekten. Jenais. Zeits. 
 
 Naturw., bd. 10, pp. 125-221, taf. 6-6c. 
 Haase, E. 1881. Beitrag zur Phylogenie und Ontogenie der Chilopoden. Zeits. Ent. 
 
 Breslau, bd. 8, heft 2, pp. 93-115. 
 Packard, A. S. 1881. Scolopendrella and its Position in Nature. Amer. Nat., vol. 15, 
 
 pp. 698-704, fig. I. 
 Brauer, F. 1885. Systematisch-zoologische Studien. Sitzb. Akad. Wiss., Wien, bd. 91, 
 
 pp. 237-413.* 
 Grassi, B. 1885. I progenitori degli Insetti e dei Miriapodi. — Morfologia delle Scolo- 
 
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 ser. 5, vol. 19, p. 396. 
 Haase, E. 1889. Die Abdominalanhange der Insekten mit Beriicksichtigung der Myrio- 
 
 poden. Morph. Jahrb., bd. 15, pp. 33i-435> taf. 14, 15. 
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 Hopk. Univ., vol. 4, pp. 431-513, pis. 48-50. 
 Hyatt, A., and Arms, J. M. 1890. Insecta. 23 + 300 pp., 13 pis, 223 figs. Boston. 
 
 D. C. Heath & Co.* 
 Cholodkowsky, N. 1892. On the Morphology and Phylogeny of Insects. Ann. Mag. 
 
 Nat. Hist., ser. 6, vol. 10, pp. 429-451. 
 Grobben, C. 1893. A Contribution to the Knowledge of the Genealogy and Classification 
 
 of the Crustacea. Ann. Mag. Nat. Hist., ser. 6, vol. 11, pp. 440-473. Trans. 
 
 from Sitzb. Akad. Wiss. Wien, math.-nat. CI., bd. loi, heft 2, pp. 237-274, taf. i. 
 Hansen, H. J. 1893. A Contribution to the Morphology of the Limbs 
 
 and Mouth-parts of Crustaceans and Insects. Ann. Mag. Nat. Hist., ser. 6, 
 
 vol. 12, pp. 417-434. Trans, from Zool. Anz., jhg. 16, pp. 193-198, 201-212. 
 Pocock, R. I. 1893. On some Points in the Morphology of the Arachnida (s. s.) with 
 
 Notes on the Classification of the Group. Ann. Mag. Nat. Hist., ser. 6. vol. 11, 
 
 pp. 1-19, pis. I, 2. 
 Bernard, H. M. 1894. The Systematic Position of the Trilobites. Quart. Journ. Geol. 
 
 Soc. London, vol. 50, pp. 411-434, figs. 1-17. 
 Kenyon, F. C. 1895. The Morphology and Classification of the Pauropoda, with Notes on 
 
 the Morphology of the Diplopoda. Tufts Coll. Studies, no. 4, pp. 77-146, pis. 
 
 1-4.* 
 
LITERATURE 
 
 433 
 
 Schmidt, P. 1896. Beitrage zur Kenntnis der niederen Myriapoden. Zeits. wiss. Zool., 
 
 bd. 5Q, pp. 436-510, taf. 26, 27. 
 Wagner, J. 1895. Contributions to the Phylogeny of the Arachnida. Ann. Mag. Nat. 
 
 Hist., ser. 6, vol. 15, pp. 285-315. Trans, from Jenais. Zeits. Naturw., bd. 29, 
 
 pp. 123-156. 
 Sedgwick, A. 1895. Peripatus. Camb. Nat. Hist., vol. 5, pp. 1-26, figs. 1-14. 
 Sinclair, F. G. 1895. Myriapoda. Camb. Nat. Hist., vol. 5, pp. 27-80, figs. 15-46. 
 Sharp, D. 1895,1901. Insects. Camb. Nat. Hist., vols. 5, 6. 12 + 1130 pp., 618 figs. 
 
 London and New York. Macmillan & Co.* 
 Comstock, J. H. and A. B. 1895. A Manual for the Study of Insects. 7 + 70: pp., 797 
 
 figs., 6 pis. Ithaca, N. Y. Comstock Pub. Co. 
 Heymons, R. 1896. Zur Morphologic der Abdominalanhange bei den Insecten. Morph. 
 
 Jahrb., bd. 24, pp. 178-204, i taf. 
 Heymons, R. 1897. Mittheilungen iiber die Segmentierung und den Korperbau der 
 
 IMyriopoden. Sitzb. Akad. Wiss., Berhn, bd. 40, pp. 915-923, 2 figs. 
 Hansen, H. J., and Sorensen, W. 1897. The Order Palpigradi Thor. and its Relation- 
 ship to the Arachnida. Ent. Tidsk., arg. 18, pp. 223-240, pi. 4. 
 Packard, A. S. 1898. A Text-Book of Entomology. 17 -+- 729 pp., 654 figs. New York 
 
 and London. The Macmillan Co.* 
 Packard, A. S. 1899. Entomology for Beginners. Ed. 3. 16 + 367 pp., 273 figs. New 
 
 York. Henry Holt & Co.* 
 Von Zittel, K. A. 1900,1902. Te.xt-Book of Palaeontology. 2 vols. Trans. C.R.East- 
 man. London and New York. Macmillan & Co.* 
 Folsom, J. W. 1900. The Development of the Mouth Parts of Anurida maritima Guer. 
 
 Bull. Mus. Comp. Zool., vol. 36, pp. 87-157, pis. 1-8.* 
 Hansen, H. J. 1902. On the Genera and Species of the Order Pauropoda. Vidensk. 
 
 Medd. Naturh. Foren. Kjobenhavn (1901), pp. 323-424, pis. 1-6. 
 Carpenter, G. H. 1903. On the Relationships between the Classes of the Arthropoda. 
 
 Proc. R. Irish Acad., vol. 24, pp. 320-360, pi. 6.* 
 Enderlein, G. 1903. Ueber die Morphologic, Gruppierung und systematische SteUung 
 
 der Corrodentien. Zool. Anz., bd. 26, pp. 423-437, 4 figs. 
 Hansen, H. J, 1903. The Genera and Species of the Order Symphyla. Quart. Journ. 
 
 Micr. Sc, vol. 47 (n. s.), pp. i-ioi, pis. 1-7.- 
 Packard, A. S. 1903. Hints on the Classification of the Arthropoda; the Group, a Poly- 
 
 phyletic One. Proc. Amer. Phil. Soc, vol. 42, pp. 142-161. 
 Lankester, E. R. 1904. The Structure and Classification of the Arthropoda. Quart. 
 
 Journ. Micr. Sc, vol. 47 (n. s.), pp. 523-582, pi. 42. (From Encyc. Brit., ed. 10.) 
 Bomer, C. 1904. Zur Systematik der Hexapoden. Zool. Anz., bd. 27, pp. 511-533, 
 
 figs. 1-4.* 
 Bouvier, E. L. 1905, 1907. Monographic des Onychophores. Ann. Sc. nat. Zool., 
 
 ser. 9, t. 2, pp. 1-383, 140 figs., 13 pis.; t. 5, pp. 61-318, figs. 141-191.* 
 Carpenter, G. H. 1905. Notes on the Segmentation and Phylogeny of the Arthropoda, 
 
 with an Account of the Maxillae in Polyxenus lagurus. Quart. Journ. Micr. Sc, 
 
 vol. 49, pt. 3, pp. 469-491, pi. 28.* 
 Silvestri, F. 1907. Descrizione di un novo genere d'insetti apteygoti. *^11. Lab. Zool. 
 
 gen. agr., vol. i, pp. 296-311, 18 figs. 
 Handlirsch, A. 1908. Die Fossilen Insekten und die Phylogenie der Rezenten Formen. 
 
 49 + 1430 pp., 14 figs., 51 pis., etc. Leipzig. W. Engelmann.* 
 Sedgwick, A. 1908. The Distribution and Classification of the Onychophora. Quart. 
 
 Journ. Micr. Sc, vol. 52 (n. s.), pp. 379-406, figs. 1-13.* 
 Berlese, A. 1909. Monografia dei Myrientomata. Redia, vol. 6, pp. 1-182, 17 pis., 14 
 
 figs. 
 
434 ENTOMOLOGY 
 
 Pierce, W. D. 1909. A Monographic Revision of the Twisted Winged Insects comprising 
 the Order Strepsiptera Kirby. Bull. U. S. Nat. Mus. No. 66, pp. 12 + 232, figs. 
 1-3, pis. 1-15.* 
 
 Schepotieff, A. 1909. Studien iiber niedere Insecten. Zool. Jahrb., Abt. Syst. Geogr. 
 Biol., bd. 28, pp. 121-138, tab. 3-5. 
 
 Bomer, C. 1910. Die phylogenetische Bedeutung der Protura. Biol. Zentralbl. bd. 30, 
 pp. 633-641. 
 
 Prell, H. 1911-12. Beitrage zur Kenntniss der Protura. Zool. Anz., bd. 38, pp. 185-193; 
 bd. 39, pp. 357-365; bd. 40, 33-50- 
 
 Rimsky-Korsakow, M. 1911. Ueber die systematische Stellung der Protura Silvestri. 
 Zool. Anz., bd. 37, pp. 164-168, i fig. 
 
 Comstock, J. H. 1912. The Spider Book. 13 + 721 pp., 770 figs. New York. Double- 
 day, Page & Co.* 
 
 Handlirsch, A. 1913, 1920. Aus der Geschichte der Entomologie. Also chapters on 
 literature, technique, taxonomy, etc. In Schroder: Handbuch der Entomologie, 
 bd. 3, pp. 1-116, figs. 1-51.* 
 
 Silvestri, F. 1913. Descrizione di un nuovo ordine di insetti. Boll. Lab. Zool. gen. agr., 
 vol. 7, pp. 193-209, 13 figs. 
 
 Williams, C. B. 1913. A Summary of the Present Knowledge of the Protura. Ento- 
 mologist, vol. 46, pp. 225-232, figs. I, 2.* 
 
 Walker, E. M. 1914. . A New Species of Orthoptera, forming a New Genus and Family. 
 
 Can. Ent., vol. 46, pp. 93-99, pi. 6. 
 Banks, N. 1915. The Acarina or Mites. Rept. U. S. Dept. Agric, no. 108, 153 pp., 
 
 294 figs.* 
 Brues, C. T., and Melander, A. L. 1915. Key to the Families of North American Insects. 
 
 7 -f 140 pp., 18 pis. Boston, Mass. and Pullman, Wash. Pub. by the authors. 
 Crampton, G. C. 1915. The Thoracic Sclerites and the Systematic Position of Gryllo- 
 
 blatta campodeiformis Walker, a Remarkable Annectent " Orthopteroid " Insect. 
 
 Ent. News, vol. 26, pp. 337-350, pi. 13. 
 Crampton, G. C. 1916. The Orders and Relationships of Apterygotan Insects. Journ. 
 
 N. Y. Ent. Soc, vol. 24, pp. 267-301.* 
 Crampton, G. C. 1917. A Phylogenetic Study of the Terminal Abdominal Segments and 
 
 Appendages in Some Female Apterygotan and Lower Pterygotan Insects. Journ. 
 
 N. Y. Ent. Soc, vol. 25, pp. 225-237, pis. 16, 17.* 
 Crampton, G. C. 1917. A Phylogenetic Study of the Lateral Head, Neck and Prothoracic 
 
 Regions in Some Apterygota and Lower Pterygota. Ent. News, vol. 28, pp. 
 
 398-412, pi. 27.* 
 Caudell, A. N. 1918. Zorotypus hubbardi, a New Species of the Order Zoraptera from 
 
 the U. S. Can. Ent.,vol. 50, pp. 375-381. 
 Pierce, W. D. 1918. The Comparative Morphology of the Order Strepsiptera together 
 
 with Records and Descriptions of Insects. Proc. U. S. Nat. Mus., vol. 54, pp. 
 
 391-501, pis. 64-78,* 
 Brues, C. T. 1919. The Classification of Insects on the Characters of the" Larva and 
 
 Pupa. Biol. Bull., vol. 37, pp. 1-21.* 
 Crampton, G. C. 1919. Notes on the Phylogeny of the Orthoptera. Ent. News, vol. 
 
 30, pp. 42-48; 64-72. 
 Crampton, G. C. 1919. The Evolution of Arthropods and their Relatives, with especial 
 
 Reference to Insects. Amer. Nat., vol. 53, pp. 143-179.* 
 Crampton, G. C. 1919. Notes on the Ancestry of the Diptera, Hemiptera, and other 
 
 Insects related to the Neuroptera. Trans. Ent. Soc. London, pp. 93-118, 2 figs. 
 Walker, E. M. 1919. The Terminal Abdominal Structures of Orthopteroid Insects: a 
 
 Phylogenetic Study. Ann. Ent. Soc. Amer., vol. 12, pp. 267-326, pis. 20-28. 
 
LITERATURE 435 
 
 Caudell, A. N. 1920. Zoraptera not an Apterous Order. Proc. Ent. Soc. Washington, 
 
 vol. 22, pp. 84-97, pi. 6. 
 Crampton, G. C. 1920. Some Anatomical Details of the Remarkable Winged Zorapteron. 
 
 Zorotypus hubbardi Caudell, with Notes on its Relationships. Proc. Ent. Soc. 
 
 Washington, vol. 22, pp. 98-106, pi. 7. 
 Crampton, G. C. 1920. A Comparison of the External Anatomy of the Lower Lepidop- 
 
 tera and Trichoptera from the Standpoint of Phylogeny. Psyche, vol. 27, pp. 
 
 23-44, pi. 4.* 
 Crampton, G. C. 1920. Notes on the Lines of Descent of Lower Winged Insects. Psyche, 
 
 vol. 27, pp. 116-127, 6 figs. 
 Crampton, G. C. 1921. Preliminary Note on the interpretation of Insectan and Myrio- 
 
 podan structures through a comparison with the structures of Crustacea. Trans. 
 
 Ent. Soc. London, pp. 340-346. 
 Crampton, G. C. 1921. A Further Comparison of the Wings of Zoraptera, Psocids, and 
 
 Aphids, from the Standpoint of Phylogeny. Can. Ent., vol. 53, pp. 110-117, 
 
 pl. 3-* 
 Ewing, H. E. 1921. A Second Nearctic Species of Protura, Accrcntuliis barbcri, New 
 
 Species. Ent. News, vol. 32, pp. 239-241. 
 Ewing, H. E. 1921. New Genera and Species of Protura. Proc. Ent. Soc. Washington, 
 
 vol. 23, pp. 193-202, pl. 16. 
 Handlirsch, A. 1921. Philogenie oder Stammesgeschichte. In Schroder: Handbuch 
 
 der Entomologie, bd. 3, pp. 307-368, figs. 238-289. 
 Crampton, G. C. 1922. A Comparison of the First Maxillae of Apterygotan Insects and 
 
 Crusta,cea from the Standpoint of Phylogeny. Proc. Ent. Soc. Washington, vol. 
 
 24, pp. 65-82, figs. 1-6, pis. 8, 9.* 
 Walker, E. M. 1922. The Terminal Structures of Orthopteroid Insects: a Phylogenetic 
 
 Study. Ann. Ent. Soc. Amer., vol. 15, pp. 1-76, pis. i-ii. 
 
 GENERAL ANATOMY 
 
 De Reatmiur, R. A. F. 1734-42. Memoires pour servir a I'histoire des insectes. 7 vols. 
 
 Paris. 
 Lyonet, P. 1762. Traite anatomique de la Chenille, qui ronge le Bois de Saule. Ed. 2. 
 
 22 + 616 pp., 18 pis. La Haye. 
 Straus-Durckheim, H. 1828. Considerations generales sur I'anatomie comparee des 
 
 animaux articules, etc. 19 + 434 PP-, 10 pis. Paris. 
 Newport, G. 1839. Insecta. Todd's Cyclopaedia Anat. Phys., vol. 2, pp. 853-994, figs. 
 
 329-439- 
 Viallanes, H. 1882. Recherches sur I'histologie des insectes. Ann. Sc. nat. ZooL, ser. 6, 
 
 t. 14, pp. 1-348, pis. 1-18. 
 Miall, L. C, and Deimy, A. 1886. The Structure and Life-history of the Cockroach. 
 
 6 + 224 pp., 125 figs. London, Lovell Reeve & Co.; Leeds, R. Jackson. 
 Schaeffer, C. 1889. Beitrage zur Histologie der Insekten. Zool. Jahrb., Morph. Abth., 
 
 bd. 3, pp. 611-652, taf. 29, 30. 
 Lowne, B. T. 1890-92. The Anatomy, Physiology, Morphology and Development of the 
 
 Blow-fly (Calliphora erythrocephala) . A Study in the Comparative Anatomy and 
 
 Morphology of Insects. 8 -f 778 pp., 108 figs., 21 pis. London.* 
 Lang, A. 1891. Text-Book of Comparative Anatomy. Trans, by H. M. and M. Bernard. 
 
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 Comstock, J. H., and Kellogg, V. L. 1899. The Elements of Insect Anatomy. Rev. ed. 
 
 134 pp., II figs. Ithaca, N. Y. Comstock Publishing Co. 
 
436 ENTOMOLOGY 
 
 Hewitt, C. G. 1907-9. The Structure, Development, and Bionomics of the House-fly, 
 
 Musca domesticaLinn. Quart. Journ. Micr. Sc, vol. 51 (n. s.), pp. 395-448, pis. 
 
 22-26; vol. 52, pp. 495-545. pis. 30^33; vol. 54, PP- 347-414, pl- 22.* 
 Snodgrass, R. E. 1910. The Anatomy of the Honey Bee. Bull. U. S. Dept. Agr., 
 
 Bur. Ent., Tech. Ser. No. 18. 162 pp., 57 figs.* 
 Schroder, C. 1912-21. Handbuch der Entomologie. Bd. i, 3, Lief. 1-7, 928 pp., 716 
 
 figs. Jena. Gustav Fischer.* 
 Jordan, H. 1913. Vergleichende Physiologic wirbelloser Tiere. Bd. i, pp. 22 + 738, 
 
 277 figs. Jena. Gustav Fischer.* 
 
 HEAD AND APPENDAGES 
 
 Burgess, E. 1880. Contributions to the Anatomy of the Milk-weed Butterfly (Danais 
 
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 Ditnmock, G. 1881. The Anatomy of the Mouth Parts and of the Sucking Apparatus of 
 
 some Diptera. 50 pp., 4 pis. Boston. A. Williams & Co.* 
 Kraepelin, K. 1883. Zur Anatomic und Physiologic des Russels von Musca. Zeits. wiss. 
 
 Zool., bd. 39, pp. 683-719, taf. 40, 41. 
 Wedde, H, 1885. Beitrage zur Kenntniss des Rhynchotenriissels. Archiv Naturg. , jhg. 
 
 51, bd. I, pp. 1 13-143, taf. 6, 7. 
 Walter, A. 1885. Beitrage zur Morphologic der SchmetterUnge. Jenais. Zeits. 
 
 Naturw., bd. 18, pp. 751-807, taf. 23, 24. 
 Walter, A. 1885. Zur Morphologic der Schmettetlingsmundthcile. Jenais. Zeits. 
 
 Naturw., bd. 19, pp. 19-27. 
 Breithaupt, P. F. 1886. Uebcr die Anatomic und die Functioncn der Bienenzunge. 
 
 Archiv Naturg., Jhg. 52, bd. i, pp. 47-112, taf. 4, 5.* 
 Blanc, L. 1891. La tete du Bombyx mori a I'etat larvaire, anatomic et physiologic. 
 
 Trav. Lab. Etud. Soie, 1 889-1 890, 180 pp., 95 figs. Lyon. 
 Hansen, H. J. 1893. A Contribution to the Morphology of the Limbs and Mouth Parts 
 
 of Crustaceans and Insects. Ann. Mag. Nat. Hist., ser. 6, vol. 11, pp. 417-434. 
 
 Trans, from Zool. Anz., jhg. 16, pp. 193-198, 201-212. 
 Kellogg, V. L. 1895. The Mouth Parts of the Lepidoptera. Amer. Nat., vol. 29, pp. 
 
 546-556, pl. 25, figs. I, 2. 
 Folsom, J. W. 1899. The Anatomy and Physiology of the Mouth Parts of the Collem- 
 
 bolan, Orchcsclla cincta L. Bull. Mus. Comp. Zool., vol. 35, pp. 7-39, pls. i-4-* 
 Janet, C. 1899. Essai sur la constitution morphologiquc de la tete dc I'insecte. 74 pp., 
 
 7 pis. Paris. G. Carre et C. Naud. 
 Kellogg, V. L. 1899. The Mouth Parts of the Ncmatoccrous Diptera. Psyche, vol. 8, 
 
 pp. 303-306, 327-330, 346-348, 355-359, 363-365, figs. i-ii. 
 Folsom, J, W, 1900. The Development of the Mouth Parts of Anurida maritima Guer. 
 
 Bull. Mus. Comp. Zool., vol. 36, pp. 87-157, pis. 1-8.* 
 Comstock, J. H., and Kochi, C. 1902. The Skeleton of the Head of Insects. Amer. 
 
 Nat., vol. 36, pp. 13-15, figs. 1-29.* 
 Kellogg, V. L. 1902. The Development and Homologies of the Mouth Parts of Insects. 
 
 Amer. Nat., vol. 36, pp. 683-706, figs. 1-26. 
 Meek, W. J. 1903. On the Mouth Parts of the Hcmiptera. Kansas Univ. Sc. Bull., vol. 
 
 2 (12), pp. 257-277, pis. 7-11.* 
 Holmgren, N. 1904. Zur Morphologic des Insektenkopfes. Zeits. wiss. Zool., bd. 76, 
 
 pp. 439-477, taf. 27, 28.* 
 Kulagin, N. 1905. Der Kopfbau bei Culex und Anopheles. Zeits. wiss. Zool., bd. 83, 
 
 pp. 285-335, taf. 12-14.* 
 
LITERATURE 437 
 
 Demoll, R. 1908. Die Mundteile der solitiiren Apiden. Zeits. wiss. Zool., bd. 91, pp. 
 
 1-5 1, taf. I, 2, II figs. 
 Demoll, R. 1909. Die Mundteile der Vespen, etc. Zeits. wiss. Zool, bd. 92, pp. 187-209, 
 
 taf. II, 9 figs. 
 Wesche, W. 1909. The Mouth-parts of the Nemocera, etc. Journ. Roy. Micr. Soc, 
 
 pp. 1-16, pis. 1-4. 
 Tower, D. G. 1914. The Mechanism of the Mouth Parts of the Squash Bug, Anasa 
 
 tristis De Geer. Psyche, vol. 21, pp. 99-108, 2 pis.* 
 Peterson, A. 1915. Morphological Studies of the Head and Mouth Parts of the Thy- 
 
 sanoptera. Ann. Ent. Soc. Amer., vol. 8, pp. 20-59, 7 pls.* 
 Peterson, A. 1916. The Head-Capsule and Mouth-Parts of Diptera. 111. Biol. Monogr., 
 
 vol. 3, no. 2, 112 pp., 25 pis.* 
 Peacock, A. D. 1918. The Structure of the Mouth Parts and Mechanism of Feeding in 
 
 Pediculus humanus. Parasitology, vol. 11, pp. 98-117, 6 figs., i pi.* 
 Yuasa, H. 1920. The Anatomy of the Head and Mouth Parts of Orthoptera and Euplex- 
 
 optera. Journ. Morph., vol. 33, pp. 251-307, pis. 1-9.* 
 Crampton, G. C. 1921. The Sclerites of the Head, and the Mouth Parts of Certain. 
 
 Immature and Adult Insects. Ann. Ent. Soc. Amer., vol. 14, pp. 65-103, pis. 
 
 2-8.* 
 Crampton, G. C. 1921. The Origin and Homologies of the So-called "Superlinguae" or 
 
 " Paraglossae " (Paragnaths) of Insects and Related Arthropods. Psyche, vol. 
 
 28, pp. 84-92, pi. 5. 
 Crampton, G. C. 1922. The Derivation of Certain Types of Head Capsule in Insects 
 
 from Crustacean Protot>'pes, Proc. Ent. Soc. Washington, vol. 24, pp. 153-157, 
 
 pi. 15. 
 
 THORAX AND APPENDAGES; LOCOMOTION 
 
 Pettigrew, J. B. 1874. Animal Locomotion. 13 -f 264 pp., 130 figs. New Yoric 
 
 D. Appleton & Co. 
 Marey, E. J. 1874, 1879. Animal Mechanism. 16 + 283 pp., 117 figs. New York. 
 
 D. Appleton & Co. 
 Von Lendenfeld, R. 1881. Der Plug der Libellen. Ein Beitrag zur Anatomie und Phy- 
 
 siologie der Flugorgane der Insecten. Sitzb. Akad. Wiss. Wien, bd. 83, pp. 289- 
 
 376, taf. 1-7. 
 Dahl, F. 1884. Beitrage zur Kenntnis des Baues und der Funktionen der Insektenbeine. 
 
 Archiv Naturg., jhg. 50, bd. i, pp. 146-193, taf. 11-13. 
 Dewitz, H. 1884. Ueber die Fortbewegung der Thiere an senkrechten glatten Flachen 
 
 vermittelst eines Sekretes. Pfliiger's Archiv ges. Phys., bd. 3$, pp. 440-480, taf. 
 
 7-9- 
 Graber, V. 1884. Ueber die Mechanik des Insektenkorpers. I. Mechanik der Beine. 
 
 Biol. Centralbl., bd. 4, pp. 560-570. 
 Amans, P. 1885. Comparaisons des organes du vol dans le serie animale. Ann. Sc. nat. 
 
 Zool., ser. 6, t. 19, pp. 1-222, pis. 1-8. 
 Redtenbacher, J. 1886. Vergleichende Studien iiber das Fliigelgeader der Insecten. 
 
 Ann. naturh. Hofm. Wien, bd. i, pp. 153-232, taf. 9-20. 
 Amans, P. C. 1888. Comparaisons des organes de la locomotion aquatique. Ann. Sc. 
 
 nat. Zool., ser, 7, t. 6, pp. 1-164, pis. 1-6. 
 Ockler, A. 1890. Das Krallenglied am Insektenfuss. Archiv Naturg., jhg. 56, bd. i, 
 
 pp. 221-262, taf. 12, 13. 
 Demoor, J. 1891. Recherches sur la marche des Insectes et des Arachnides. Archiv. 
 
 Biol., t. 10, pp. 567-608, pis. 18-20. 
 
438 ENTOMOLOGY 
 
 Hoffbauer, C. 1892. Beitrage zur Kenntnis der Insektenfliigel. Zeits. wiss. Zool., bd. 
 
 54, pp. 579-630, taf. 26, 27, 3 figs.* 
 Sptiler, A. 1892. Zur Phylogenie und Ontogenie des Fliigelgeader der Schmetterlinge. 
 
 Zeits. wiss. Zool., bd. 53, pp. 597-646, taf. 25, 26. 
 Comstock, J, H. 1893. Evolution and Taxonomy. Wilder Quarter-Century Book, 
 
 pp. 37-114, pis. 1-3. Ithaca, N. Y. 
 Marey, E. J. 1895. Movement. 15 + 323 pp., 204 figs. New York. D. Appleton 
 
 & Co. 
 Comstock, J. H., and Needham, J. G. 1898-99. The Wings of Insects. Amer. Nat., vols. 
 
 32, ss, pp. 43-48, 81-89, 231-257, 335-340, 413-424, 561-565, 769-777, 903-9"» 
 
 117-126, 573-582, 845-860, figs. 1-90. Reprint, Ithaca, N. Y. Comstock 
 
 Pub. Co. 
 Verhoeff, K. W. 1902. Beitrage zur vergleichenden Morphologic des Thorax der Insekten 
 
 mit Beriicksichtigung der Chilopoden. Nova Acta Leop.-Carol. Akad, Naturf., 
 
 bd. 81 pp. 63-110, taf. 7-13. 
 Woodworth, C. W. 1906. The Wing Veins of Insects. Tech. Bull. Ent., U. of Cal. 
 
 A. E. S., vol. I, No. I, pp. 1-152, figs, i-ioi.* 
 Durken, B. 1907. Die Tracheenkiemenmuskulatur der Ephemeriden unter Beriicksichti- 
 gung der Morphologie des Insektenflugels. Zeits. wiss. Zool, bd. 87, pp. 435-SSo, 
 
 taf. 24-26, 30 figs.* 
 Snodgrass, R. E. 1908. A Comparative Study of the Thorax in Orthoptera, Euplex- 
 
 optera and Coleoptera. Proc. Ent. Soc. Wash., vol. 9, pp. 95-108, pis. 2-5. 
 Crampton, G. C. 1909. A Contribution to the Comparative Morphology of the Thoracic 
 
 Sclerites of Insects. Proc. Acad. Nat. Sc, Phila., vol. 61, pp. 3-54, figs. 1-21, pis. 
 
 1-4.* 
 Snodgrass, R. E. 1909. The Thorax of Insects and the Articulation of the Wings. Proc. 
 
 U. S. Nat. Mus., vol. 36, pp. 511-595, pis. 40-69, figs. 1-6.* 
 Snodgrass, R. E. 1910. The Thorax of the Hymenoptera. Proc. U. S. Nat. Mus., vol. 
 
 39, PP- 37-91, pis. 1-16.* 
 Stellwaag, F. 1910. Bau und Mechanik des Flugapparates der Biene. Zeits. wiss. Zool., 
 
 bd. 95, pp. 518-550, taf. 19, 20, figs. 1-6.* 
 Ritter, W. 1911. The Flying Apparatus of the Blow-fly. Smithson. Miscell. Coll., 
 
 vol. 56, No. 12, 76 pp., 7 figs., 19 pis.* 
 Pflugstaedt, H. 1S12. Die Halteren der Dipteren. Zeits. wiss. Zool., bd. 100, pp. 1-59, 
 
 taf. 1-4.* 
 Voss, F. 1904, 1912. Ueber den Thorax von Gryllus domesticus. Zeits. wiss. Zool, bd. 
 
 78, pp. 268-251, 23 figs., taf. 15, 16; bd. 100, pp. 589-834, 36 figs., taf. 19-28; bd. 
 
 loi, pp. 445-682, 16 figs., taf. 25-29.* 
 Crampton, G. C. 1916. The Phylogenetic Origin and the Nature of the Wings of Insects 
 
 according to the Paranotal Theory. Journ. N. Y. Ent. Soc, vol. 24, pp. 1-39, 
 
 pis. 1-2.* 
 Martin, J. F. 1916. The Thoracic and Cervical Sclerites of Insects. Ann. Ent. Soc. 
 
 Amer., vol. 9, pp. 35-83, pis. 1-4. 
 Comstock, J. H. 1918. The Wings of Insects. 18 -f 430 pp., 427 figs., 10 pis. Ithaca, 
 
 N. Y. Comstock Pub. Co.* 
 Mallock, H. R. A. 1919. Some Points in Insect Mechanics. Proc. Zool. Soc. London, 
 
 pp. 111-116. 
 Tillyard, R. J. 1919. The Panorpoid Complex. Part 3:— The Wing- Venation. Proc. 
 
 Linn. Soc. New South Wales, vol. 44, pt. 3, pp. 533-718, figs. 35-112, pis. 
 
 3I--35-* 
 Prochnow, O. 1921. Mechanik des Insektenfluges. In Schroder: Handbuch der Ento- 
 mologie, bd. i pp. 534-560, figs. 1-25. 
 
LITERATURE 
 
 ABDOMEN AND APPENDAGES 
 
 439 
 
 Dewitz, H. 1875. Ueber Bau und Entwickelung des Stachels und der Legescheide einiger 
 
 Hymenopteren und der grunen Heuschrecke. Zeits. wiss. Zool., bd. 25, pp. 174- 
 
 200, taf. 12, 13. 
 Adler, H. 1877. Lege-Apparat und Eierlegen der Gallwespen. Deuts. ent. Zeits., jhg. 
 
 21, pp. 305-332, taf. 2. 
 Dewitz, H. 1877. Ueber Bau und Entwickelung des Stachels der Ameisen. Zeits. wiss. 
 
 Zool., bd. 28, pp. 527-556, taf. 26. 
 Goossens, T. 1887. Les pattes des Chenilles. Ann. Soc. ent. France, s^r. 6, t. 7, pp. 
 
 385-404, pi. 7. 
 Graber, V. 1888. Ueber die Polypodie bei Insekten-Embryonen. ' Morph. Jahrb., bd. 13, 
 
 pp. 586-615, taf. 25, 26. 
 Haase, E. 1889. Ueber Abdominalanhange bei Hexapoden. Sitzb. Gesell. naturf. 
 
 Freunde, pp. 19-29. 
 Haase, E, 1889. Die Abdominalanhange der Insekten mit Beriicksichtigung der Myri- 
 
 opoden. Morph. Jahrb., bd. 15, pp. 331-435, taf. 14, 15. 
 Carlet, G. 1890. Memoire sur le venin et I'aiguillon de I'abeille. Ann. Sc. nat. Zool., ser. 
 
 7, t. 9, pp. 1-17, pl- I- 
 Packard, A. S. 1890. Notes on some points in the external structure and phylogeny of 
 
 Lepidopterous larvae. Proc. Bost. Soc. Nat. Hist., vol. 25, pp. 82-114, pis. 
 
 I, 2. 
 Wheeler, W. M. 1890. On the Appendages of the first abdominal Segment of embryo 
 
 Insects. Trans. Wis. Acad. Sc, vol. 8, pp. 87-140, pis. 1-3.* 
 Escherich, K. 1892. Die biologische Bedeutung der Genitalanhange der Insekten. Verb. 
 
 zool.-bot. Ges. Wien, bd. 42, pp. 225-240, taf. 4. 
 Graber. V. 1892. Ueber die morphologische Bedeutung der Abdominalanhange der 
 
 Insekten-Embryonen. Morph. Jahrb., bd. 17, pp. 467-482, 
 Escherich, K. 1894. Anatomische Studien iiber das mannliche Genital-system der Cole- 
 
 opteren. Zeits. wiss. Zool., bd. 57, pp. 620-641, taf. 26, 3 figs. 
 Verhoeff, C. 1894. Vergleichende Untersuchungen iiber die Abdominalsegmente der 
 
 weiblichen Hemiptera-Heteroptera und Homoptera. Verb. nat. Ver. Bonn, jhg. 
 
 50, pp. 307-374- 
 HeymoDS, R. 1895. Die Segmentirung des Insectenkorpers. Anh. Abh. Preuss. Akad. 
 
 "Wiss. Berlin, 39 pp., i taf. 
 Heymons, R. 1895. Die Embryonalentwickelung von Dermapteren und Orthopteren 
 
 unter besonderer Beriicksichtigung der Keimblatterbildung. 136 pp., 12 taf., ^^ 
 
 figs. Jena. 
 Pejrtoureau, S. A. 1895. Contribution a I'etude de la morphologie de I'armure genitale 
 
 des Insectes. 248 pp., 22 pis., 43 figs. Paris. 
 Verhoeff, C. 1895. Cerci und Styli der Tracheaten. Ent. Nachr., jhg. 21, pp. 166-168. 
 Heymons, R. 1896. Grundziige der Entwickelung und des Korperbaues von Odonaten 
 
 und Ephemeriden. Anh. Abh. Akad. Wiss. Berlin, pp. 66, 2 taf. 
 Heymons, R. 1896. Zur Morphologie des Abdominalanhange bei den Insekten. Morph. 
 
 Jahrb., bd. 24, pp. 178-204, taf. i. 
 Verhoeff, C. 1896. Zur Morphologie der Segmentanhange bei Insecten und Myriopoden. 
 
 Zool. Anz., bd. 19, pp. 378-383, 385-388. 
 Janet, C. 1897. Limites morphologiques des anneaux post-cephaliques et Musculature 
 
 des anneau\ post-thoraciques chez la Myrmica rubra. Note 16. 35 pp., 10 figs. 
 
 Lille. 
 Verhoeff, C. 1897. Bemerkungen iiber abdominale Korperanhange bei Insecten und 
 
 Myriopoden. Zool. Anz., bd. 20, pp. 293-300. 
 
440 ENTOMOLOGY 
 
 Janet, C. 1898. Aiguillon de la Myrmica rubra. Appareil de fermeture de la glande a 
 venin. Note i8. 27 pp., 3 pis. Paris. 
 
 Zander, E. 1903. Beitrage zur Morphologic der mannlichen Geschlechtsanhange der 
 Lepidopteren. Zeits. wiss. Zool., bd. 74, pp. 557-615, taf. 29, figs. 1-15.* 
 
 Verhoeff, K. W. 1917. Zur vergleichenden Morphologic des Abdomens der Colcoptcrcn, 
 etc. Zeits. wiss. Zool., bd. 117, pp. 130-204, 12 figs., 2 pis.* 
 
 Crampton, G. C. 1918. A Phylogcnctic Study of the Terminal Abdominal Structures 
 and Genitalia of Male Apterygota, Ephemcrids, Odonata, Plecoptcra, Neurop- 
 tera, Orthoptcra, and Their AUies. Bull. Brooklyn Ent. Soc, vol. 13, pp. 49-68, 
 pis. 2-7.* 
 
 Newell, A. G. 1918. The Comparative Morphology of the Genitalia of Insects. Ann. 
 Ent. Soc. Am'er., vol. 11, pp. 109-156, pis. 4-17.* 
 
 Crampton, G. C. 1920. A Comparison of the Genitalia of Male Hymenoptera, Mecop- 
 tera, Xeuroptera, Diptera, Trichoptera, Lepidoptera, Homoptera, and Strepsip- 
 tera, with Those of Lower Insects. Psyche, vol. 27, pp. 34-44, pis. 2-4.* 
 
 Crampton, G. C. 1920. Remarks on the Basic Plan of the Terminal Abdominal Struc- 
 tures of the Males of Winged Insects. Can. Ent., vol. 52, pp. 178-183, pi. 6. 
 
 Crampton, G. C. 1921. A Comparison of the Terminal Abdominal Structures of Insects 
 and Crustacea. Ent. News, vol. 32, pp. 257-264, pi. 5. 
 
 INTEGUMENT 
 
 Candeze, E. 1874. Les moyens d'attaque et de defense chez les Insectes. Bull. Acad. 
 
 roy. Belgique, ser. 2, t. 38, pp. 787-816. 
 Chun, C. 1876. Ueber den Bau, die Entwickelung und physiologische Bedeutung der 
 
 Rektaldriisen bei den Insekten. Abh. Senckenb. naturf. Gesell., bd. 10, pp. 27-55. 
 
 4 taf. Separate, 1875, 31 pp., 4 taf. Frankfurt a. M. 
 Scudder, S. H. 1877. Antigeny or Sexual Dimorphism in Butterflies. Proc. Amer. Acad. 
 
 Arts Sc, vol. 12, pp. 150-158. 
 Forel, A. 1878. Der Giftapparat und die Analdriisen der Ameisen. Zeits. wiss Zool., 
 
 bd. 30, supp., pp. 28-68, taf. 3, 4. 
 Schneider, R. 1878. Die Schuppen aus den verschiedenen Fliigel- und Korperteilen der 
 
 Lepidopteren. Zeits. gesammt. Naturw., bd. 51, pp. 1-59. 
 Scudder, S. H. 1881. Butterflies; Their Structure, Changes and Life-Histories, with 
 
 Special Reference to American Forms. 9+322 pp., 201 figs. New York. Henry 
 
 Holt & Co. 
 Klemensiewicz, S. 1882. Zur naheren Kenntniss der Hautdriisen bei den Raupen und 
 
 bei Malachius. Verb, zool.-bot. Gesell. Wien, bd. 32, pp. 459-474, 2 taf. 
 Dimmock, G. 1883. The Scales of Coleoptera. Psyche, vol. 4, pp. i-ii, 23-27, 43-47, 
 
 63-71, figs. i-ii. 
 Osten-Sacken, C. R. 1884. An Essay on Comparative Chaetotaxy, or the Arrangement 
 
 of Characteristic Bristles of Diptera. Trans. Ent. Soc. London, pp. 497-517. 
 Simmermacher, G. 1884. Untersuchungen iiber Haftapparate an Tarsalgliedern von 
 
 Insekten. Zeits. wiss. Zool., bd. 40, pp. 481-556, taf. 25-27, 2 figs. 
 Dahl, F. 1885. Die Fussdriisen der Insekten. Archiv mikr. Anat., bd. 25, pp. 236-263, 
 
 taf. 12, 13. — 
 
 Witlaczil, E. 1885. Die Anatomic der Psylliden. Zeits. wiss. Zool., bd. 42, pp. 569-638, 
 
 taf. 20-22. 
 Goossens, T. 1886. Des chenilles vesicantes. Ann. Soc. ent. France, ser. 6, t. 6, pp. 
 
 461-464.* 
 Minot, C. S. 1886. Zur Kenntniss der Insektenhaut. Archiv mikr. Anat., bd. 28, pp. 
 
 37-48, taf. 7. 
 
LITERATURE 44 1 
 
 Schaffer, C. 1889. Beitrage zur Histologic der Insekten. Zool. Jahrb., Abth. Anat. 
 
 Ont., bd. 3, pp. 611-652, taf. 29, 30. 
 Packard, A. S. 1890. Notes on some points in the external structure and phylogeny of 
 
 lepidopterous larvje. Proc. Bost. Soc. Nat. Hist., vol. 25, pp. 82-114, pis. i, 2. 
 Borgert, H. 1891. Die Hautdriisen der Tracheaten. 81 pp., taf. Jena. 
 Kellogg, V. L. 1894. The Taxonomic Value of the Scales of the Lepidoptera. Kansas 
 
 Univ. Quart., vol. 3, pp. 45-89, pis. 9, 10, figs. 1-17. 
 Lutz, K. G. 1895. Das Bluten der Coccinelliden. Zool. Anz., jhg. 18, pp. 244-255, i fig. 
 Packard, A. S. 1895-96. The Eversible Repugnatorial Scent Glands of Insects. Journ. 
 
 N. Y. Ent. Soc, vol. 3, pp. 1 10-127, pl- 5; vol. 4, pp. 26-32.* 
 Spiiler, A. 1895. Beitrag zur Kenntniss des feineren Baues und der Phylogenie der 
 
 Fliigelbedeckung der Schmetterlinge. Zool. Jahrb., Abth. .\nat. Ont., bd. 8, pp. 
 
 520-543, taf. 36. 
 Mayer, A. G. 1896. The Development of the Wing Scales and their Pigment in Butterflies 
 
 and Moths. Bull. Mus. Comp. Zool., vol. 29, pp. 209-236, pis. 1-7.* 
 Bordas, L. 1897. Description anatomique et etude histologique des glandes a venin des 
 
 Insectes hymenopteres. 53 pp., 2 pis. Paris. 
 Cuenot, L. 1897. Sur la saignee reflexe et les moyens de defense de quelques Insectes. 
 
 Arch. Zool. e.xp., ser. 3, t. 4, pp. 655-680, 4 figs. 
 Hilton, W. A. 1902. The Body Sense Hairs of Lepidopterous Larva;. Amer. Nat., vol. 
 
 36, pp. 561-578, figs. 1-23.* 
 Tower, W. L. 1902. Observations on the Structure of the Exuvial Glands and the For- 
 mation of the Exuvial Fluid in Insects. Zool. Anz., bd. 25, pp. 466-472, figs. 1-8. 
 Tower, W. L. 1903. The Development of the Colors and Color Patterns of Coleoptera, 
 
 with Observations upon the Development of Color in Other Orders of Insects. 
 
 Univ. Chicago, Decenn. Publ., vol. 10, 140 pp., 3 pis. 
 Plotnikow, W. 1904. Uber die Hautung und iiber einige Elemente der Haut bei den 
 
 Insekten. Zeits. wiss. Zool., bd. 76, pp. 333-366, taf. 21, 22, 2 figs. 
 Kapzov, S. 1911. Untersuchungen iiber den feineren Bau der Cuticula bei Insekten. 
 
 Zeits. wiss. Zool., bd. 98, pp. 297-337, taf. 14-16, 3 figs.* 
 Deegener, P. 1912. Haut und Hautorgane In Schroder: Handbuch der Entomologie, 
 
 bd. I, pp. 1-60, figs. 1-38.* 
 
 MUSCULAR SYSTEM 
 
 Lyonet, P. 1762. Traite anatomique de la Chenille qui ronge le Bois de Saule. Ed. 2. 
 
 22 4- 616 pp., 18 pis. La Haye. 
 Straus-Durckheim, H. 1828. Considerations generales sur I'anatomie comparee Hes 
 
 animaux articules, etc. 434 pp., 10 pis. Paris. 
 Newport. G. 1839. Insecta. Todd's Cyclopaedia Anat. Phys., vol. 2, pp. 853-994, fig<;. 
 
 329-439. 
 Lubbock, J. 1859. On the Arrangement of the Cutaneous Muscles of the Larva of Py- 
 
 g^era bucephala. Trans. Linn. Soc. Zool., vol. 22, pp. 163-191, 2 pis. 
 Plateau, F. 1865, 1866. Sur la force musculaire des insectes. Bull. Acad. roy. Belgique, 
 
 ser. 2, t. 20, pp. 732-757; t. 22, pp. 283-308. 
 Lubbock, J. 1877. On some Points in the Anatomy of Ants. Month. Micr. Journ., vol. 
 
 18, pp. 121-142, pis. 189-192. 
 Lubbock, J. 1879. On the Anatomy of Ants. Trans. Linn. Soc. Zool., ser. 2, vol. 2, pp. 
 
 141-154, 2 pis. 
 Von Lendenfeld, R. 1881. Der Flug der Libellen. Ein Beitrag zur .\natomie und Phy- 
 siologic der Flugorgane der Insecten. Sitzb. Akad. Wiss. Wien, bd. 83, pp. 289- 
 
 376, taf. 1-7. 
 
442 ENTOMOLOGY 
 
 Luks, C. 1882. Ueber die Brustmuskulatur der Insekten. Jenais. Zeits. Naturw., bd. 
 
 i6, pp. 529-552, taf. 22, 23. 
 Dahl, F. 1884. Beitrage zur Kenntnis des Baues und der Funktionen der Insektenbeine. 
 
 Archiv Naturg., jhg. 50, bd. i, pp. 146-193, taf. 11-13. 
 Van Gehuchten, A. 1886. Etude sur la structure intime de la cellule musculaire striee. 
 
 La Cellule, t. 2, pp. 289-453, pis. 1-6. 
 Miall, L. C, and Denny, A. 1886. The Structure and Life-history of the Cockroach. 
 
 London and Leeds.* (See pp. 71-84.) 
 Kolliker, A. 1888. Zur Kenntnis der quergestreiften Muskelfasern. Zeits. wiss. Zool., 
 
 bd. 47, pp. 689-710, taf. 44, 45. 
 Biitschli, O., und Schewiakoff, W. 1891. Ueber den feineren Bau der quergestreiften 
 
 Muskeln von Arthropoden. Biol. Centralb., bd. 11, pp. 33-39, figs. 1-7. 
 Rollet, A. 1891. Ueber die Streifen N. (Nebenscheiben), das Sarkoplasma und 
 
 Contraktion der quergestreiften Muskelfasern. Archiv mikr. x\nat., bd. 37, pp. 
 
 654-684, taf. 37. 
 Janet, C. 1895. Etudes sur les Fourmis, les Guepes et les Abeilles. Note 12. Structure 
 
 des Membranes articulaires des Tendons et des Muscles (Myrmica, Camponotus, 
 
 Vespa, Apis). 26 pp., 11 figs. Limoges. 
 Janet, C. 1895. Sur les Muscles des Fourmis, des Guepes et des Abeilles. Compt. rend. 
 
 Acad. Sc, t. 121, pp. 610-613, I fig. 
 Bauer, A. 1910. Die Muskulatur von Dytiscus marginalis. Zeits. wiss. Zool., bd. 95, 
 
 pp. 594-646, figs. 1-19.* 
 Deegener, P. 1913. Muskulatur und Endoskelett. In Schroder: Handbuch der 
 
 Entomologie, bd. i, pp. 438-465, figs. 320-335.* 
 Kielich, J. 1918. Beitrage zur Kenntnis der Insectenmuskeln. Zool. Jahrb., Abth. 
 
 Anat. Ont., bd. 40, pp. 515-536, pis. 25-26. 
 
 NERVOUS SYSTEM 
 
 Newport, G. 1832, 1834. On the Nervous System of the Sphinx Ligustri Linn, and on the 
 
 changes which it undergoes during a part of the Metamorphoses of the Insect. 
 
 Phil. Trans. Roy. Soc. London, vol. 122, pp. 383-398, 2 pis.* Part II Phil. 
 
 Trans. Roy. Soc. London, vol. 124, pp. 389-423, 5 pis. 
 Leydig, F. 1857. Lehrbuch der Histologie des Menschen und der Thiere. 12 -1- 551 pp., 
 
 figs. Frankfurt. 
 Flogel, J. H. L. 1878. Ueber den einheitlichen Bau des Gehirns in den verschiedenen 
 
 Insecten-Ordnungen. Zeits. wiss. Zool., bd. 30, Suppl., pp. 556-592, taf. 23, 24. 
 Newton, E. T. 1879. On the Brain of the Cockroach, Blatta orientalis. Quart. Journ. 
 
 Micr. Soc, n. s., vol. 19, pp. 340-356, pis. 15, 16. 
 Michels, H. 1880. Beschreibung des Nervensystems von Oryctes nasicornis imL^rven-, 
 
 Puppen- und Kaferzustande. Zeits. wiss. Zool., bd. 34, pp. 641-702, taf. 33-36. 
 Packard, A. S. 1880. The Brain of the Locust. Second Kept. U. S. Ent. Comm., pp. 
 
 223-242, pis. 9-15, fig. 9. Washington.* 
 Koestler, M. 1883. Ueber das Eingeweidenervensystem von Periplaneta orientalis. 
 
 Zeits. wiss. Zool., bd. 39, pp. 572-595, taf. 34. 
 Viallanes, H. 1884-87. Etudes histologiques et organologiques sur les centres nerveux et 
 
 les organes des sens des animaux articules. Mem. 1-5. Ann. Sc. nat. Zool., 
 
 ser. 6, t. 17-19; ser. 7, t. 2, 4; 22 pis. 
 Leydig, F. 1885. Zelle und Gewebe. Neue Beitrage zur Histologie des Tierkorpers, 
 
 219 pp., 6 taf. Bonn. 
 Binet, A. 1894. Contribution a I'etude du system nerveux sous-intestinal des insectes. 
 
 Journ. Anat. Phys., t. 30, pp. 449-580, pis. 12-15, 23 figs. 
 
LITERATURE 443 
 
 Pawlovi, M. I. 1895. On the Structure of the Blood- Vessels and Sympathetic Nervous 
 
 System of Insects, particularly Orthoptera. Works Lab. Zool. Cab. Imp. Univ. 
 
 Warsaw, pp. 96 + 22, tab. 1-6. In Russian. 
 Holmgren, E. 1896. Zur Kenntnis des Hauptnervensystems der Arthropoden. Anat. 
 
 Anz., bd. 12, pp. 449-457, 7 figs- 
 Kenyon, F. C. 1896. The Brain of the Bee. Journ. Comp. Neurol., vol. 6, pp. 133-210, 
 
 pis. 14-22. 
 Kenyon, F. C. 1896. The meaning and structure of the so-called "mushroom bodies" 
 
 of the hexapod brain. Amer. Nat., vol. 30, pp. 643-650, i fig. 
 Keynon, F. C. 1897. The optic lobes of the bee's brain in the light of recent neurological 
 
 methods. Amer. Nat., vol. 31, pp. 369-376, pi. 9- 
 Deegener, P. 1912. Nervensystem. In Schroder: Handbuch der Entomologie, bd. i, 
 
 pp. 76-139, figs- 39-78.* 
 Thompson, C. B. 1913. A Comparative Study of the Brains of Three Genera of Ants, 
 
 with Special Reference to the Mushroom Bodies. Journ. Comp. Zool., vol. 23, 
 
 PP- 515-572, 40 figs-* 
 
 SENSE ORGANS; SOUNDS 
 
 Miiller, J. 1826. Zur vergleichenden Physiologic des Gesichtsinnes der Menschen und 
 
 der Tiere. 462 pp., 8 taf. Leipzig. 
 Scudder, S. H. 1868. The Songs of the Grasshoppers. Amer. Nat., vol. 2, pp. 113-120.. 
 
 5 figs- 
 Scudder, S. H. 1868. Notes on the Stridulation of Grasshoppers. Proc. Bost. Soc. 
 
 Nat. Hist., vol. 11, pp. 306-313. 
 Graber, V. 1872. Bemerkungen iiber die Gehor- und Stimmorgane der Heuschreckeh und 
 
 Cicaden. Sitzb. Akad. Wiss. Wien, math.-naturw. CI., bd. 66, pp. 205-213, 2 figs. 
 Paasch, A. 1873. Von den Sinnesorganen der Insekten im AUgemeinen von Gehor- und 
 
 Geruchsorganen im Besondern. Archiv Naturg., jhg. 39, bd. i, pp. 248-275. 
 Forel, A. 1874. Les fourmis de la Suisse. Neue Denks. allg. Schweiz. Gesell. Naturw., 
 
 bd. 26, 480 pp., 2 taf. Separate, 1874, 4 + 457 pp., 2 taf. Geneve. 
 Mayer, A. M. 1874. Experiments on the supposed Auditory Apparatus of the Mosquito. 
 
 Amer. Nat., vol. 8, pp. 577-592, fig. 92. 
 Graber, V. 1876. Die tympanalen Sinnesapparate der Orthopteren. Denks. Akad. 
 
 Wiss. Wien, bd. 36, pp. 1-140, 10 taf. 
 Graber, V. 1876. Die abdominalen Tympanalorgane der Cicaden und Gryllodeen. 
 
 Denks. Akad. Wiss. Wien, bd. 36, pp. 273-296, 2 taf. 
 Mayer, P. 1877. Der Tonapparat der Cikaden. Zeits. wiss. Zool., bd. 28, pp. 79-92, 
 
 3 figs. 
 Lowne, B. T. 1878. On the Modifications of the Simple and Compound Eyes of Insects. 
 
 Phil. Trans. Roy. Soc. London, vol. 169, pp. 577-602, pis. 52-54. 
 Grenacher, H. 1879. Untersuchungen iiber das Sehorgan der Arthropoden, insbesondere 
 
 der Spinnen, Insekten und Crustaceen. 8 + 188 pp., 11 taf. Gottingen. 
 Hauser, G. 1880. Physiologische und histiologische Untersuchungen uber das Geruchs- 
 
 organ der Insekten. Zeits. wiss. Zool., bd. 34, pp. 367-403, taf. 17-19. 
 Graber, V. 1882. Die chordotonalen Sinnesorgane und das Gehor der Insecten. Archiv 
 
 mikr. Anat., bd. 20, pp. 506-640, taf. 30-35, 6 figs.; bd. 21, pp. 65-145, 4 figs.* 
 Lubbock, J. 1882. Ants, Bees and Wasps. 19 + 448 pp-, 5 pls-, 31 figs- London. 
 
 1884, 1901, New York. D. Appleton & Co. 
 Graber, V. 1883. Fundamentalversuche iiber die Helligkeits- und Farbenempfindlichkeit 
 
 augenloser und geblendeter Tiere. Sitzb. Akad. Wiss. Wien, bd. 87, pp. 201-236. 
 Graber, V. 1884. GrundUnien zur Erforschung des Helligkeits und Farbensinnes der 
 
 Tiere. 8-1-322 pp. Prag und Leipzig. 
 
444 ENTOMOLOGY 
 
 Lee, A. B. 1884. Bemerkungen iiber den feineren Bau der Chordotonal-Organe. Archiv 
 
 mikr. Anat., bd. 23, pp. 133-140, taf. 7b. 
 Lowne, B. T. 1884. On the Compound Vision and the Morphology of the Eye in Insects. 
 
 Trans. Linn. Soc. Zool., vol. 2, pp. 389-420, pis. 40-43. 
 Carriere, J. 1885. Die Sehorgane der Thiere, vergleichend anatomischdargestellt. 6 + 
 
 205 pp., I taf., 147 figs. Miinchen und Leipzig. R. Oldenbourg. 
 Hickson, S. J. 1885. The Eye and Optic Tract of Insects. Quart. Journ. Micr. Sc, vol. 
 
 25, pp. 215-251, pis. 15-17. 
 Plateau, F. 1885-88. Recherches experimentales sur la vision chez les Insectes. Bull. 
 
 Acad. roy. Belgique, ser, 3, t. 10, 14, 15, 16. Mem. Acad, roy. Belgique, t. 43, pp. 
 
 1-9 1. 
 Will, F. 1885. Das Geschmacksorganderlnsekten. Zeits. wiss. Zool., bd. 42., pp. 674- 
 
 707, taf. 27. 
 Forel, A. 1886-87. Experiences et remarques critiques sur les sensations des Insectes. 
 
 Rec. zool. Suisse, t. 4, pp. 1-50, 145-240, pi. i. 
 Mark, E. L. 1887. Simple Eyes in Arthropods. Bull. Mus. Comp. Zool., vol. 13, pp. 49- 
 
 105, pis. 1-5. 
 Patten, W. 1887, 1888. Studies on the Eyes of Arthropods. I. Development of the 
 
 Eyes of Vespa, with Observations on the Ocelli of some Insects. Journ. Morph., 
 
 vol. I, pp. 193-226, I pi. II. Eyes of Acilius. Journ. Morph., vol. 2^ pp. 97-190, 
 
 pis. 7-13. 
 Lubbock, J. 1888, 1902. On the Senses, Instincts and Intelligence of Animals, with 
 
 Special Reference to Insects. 29 + 292 pp., 118 figs. New York. D. Appleton 
 
 &Co. 
 Vom Rath, O. 1888. Ueber die Hautsinnesorgane der Insekten. Zeits. wiss. Zool., bd. 
 
 46, pp. 413-454, taf. 30, 31. 
 Ruland, F. 1888. Beitrage zur Kenntnis der antennalen Sinnesorgane der Insekten. 
 
 Zeits. wiss. Zool., bd. 46, pp. 602-628, taf. 37. 
 Lowne, B. T. 1889. On the Structure of the Retina of the Blowfly (Calliphora erythro- 
 
 cephala). Journ. Linn. Soc. Zool., vol. 20, pp. 406-417, pi. 27. 
 Packard, A. S. 1889. Notes on the Epipharynx, and the Epipharyngeal Organs of Taste 
 
 in Mandibulate Insects. Psyche, vol. 5, pp. 193-199, 222-228. 
 Pankrath, O. 1890. Das Auge der Raupen und Phryganidenlarven. Zeits. wiss. Zool., 
 
 bd. 49, PP- 690-708, taf. 34, 35. 
 Stefanowska, M. 1890. La disposition histologique du pigment dans les yeux des Arthro- 
 
 podes sous I'influence de la lumiere directe et de I'obscurite complete. Rec. zool. 
 
 Suisse, t. 5, pp. 151-200, pis. 8, 9. 
 Watase, S. 1890. On the Morphology of the Compound Eyes of Arthropods. Studies 
 
 Biol. Lab. Johns Hopk. Univ., vol. 4, pp. 287-334, pis. 29-35. 
 Weinland, E. 1890. Ueber die Schwinger (Halteren) der Dipteren. Zeits. wiss. Zool., 
 
 bd. 51, pp. 55-166, taf. 7-11. 
 Exner, S. 1891. Die Physiologic der fazettierten Augen von Krebsen und Insekten. 
 
 8 + 206 pp., 8 taf., 23 figs. Leipzig und Wien. 
 Von Adelung, N. 1892. Beitrage zur Kenntnis des tibialen Gehorapparates der Locusti- 
 
 den. Zeits. wiss. Zool., bd. 54, pp. 316-349, taf. 14, 15. 
 Nagel, W. 1892. Die niederen Sinne der Insekten. 68 pp., 19 figs. Tubingen. 
 Child, C. M. 1894. Ein bisher wenig beachtetes antennales Sinnesorgan der Insekten, 
 
 mit besonderer Beriicksichtigung der Culiciden und Chironomiden. Zeits. wiss. 
 
 Zool, bd. 58, pp. 475-528, taf. 30, 31. 
 Mallock, A. 1894. Insect Sight and the Defining Power of Composite Eyes. Proc. Roy. 
 
 Soc. London, vol. 55, pp. 85-90, figs. 1-3. 
 
LITERATURE 445 
 
 Vom Rath, O. 1896. Zur Kenntnis der Hautsinnesorgane und des scnsiblen Nerven- 
 
 systems der Arthropoden. Zeits. wiss. Zool., bd. 61, pp. 499-539, taf. 23, 24. 
 Redikorzew, W. 1900. Untersuchungen uber den Bau der Ocellen der Insekten. Zeits. 
 
 wiss. Zool., bd. 68, pp. 581-624, taf. 39, 40, figs. 1-7. 
 Reuter, E. 1896. Ueber die Palpen der Rhopaloceren, etc. Acta See. Sc. Fenn., t. 22, 
 
 pp. 16 4- 578, 6 tab. 
 Hesse, R. 1901. Untersuchungen uber die Organe der Lichtempfindung bei niederen 
 
 Thieren. VII. Von den Arthropoden- Augen. Zeits. wiss. Zool., bd. 70, pp. 347- 
 
 473, taf. 16-21, figs. I, 2. 
 Schenk, O. 1903. Die antennalen Hautsinnesorgane einiger Lepidoptcren und Hymen- 
 
 opteren mit besonderer Beriicksichtigung der sexuellen Unterschiede. Zool. 
 
 Jahrb., Abth. Anat. Ont., bd. 17, pp. 573-618, taf. 21, 22, 4 figs.* 
 Shull.A.F. 1907. TheStridulationof the Snowy Tree-cricket ((Ecanthusniveus). Can. 
 
 Ent., vol. 39, pp. 213-225, figs. 14, 15.* 
 Forel, A. 1908. The Senses of Insects. Trans, by M. Yearsley. 14 + 324 pp., 2 pis. 
 
 London. Methucn & Co.* 
 Dietrich, W. 1909. Die Facettenaugen der Dipteren. Zeits. wiss. Zool., bd. 92, pp. 
 
 465-539, taf. 22-25, 17 figs.* 
 Link, £. 1909. Ueber die Stirnaugen der Neuropteren und Lepidopteren. Zool. Jahrb., 
 
 Abt. Anat. Ont., bd. 27, pp. 213-242, taf. 15-17, 5 figs.* 
 Link, E. 1909. Ueber die Stirnaugen der hemimetabolen Insecten. Zool. Jahrb., Abt. 
 
 Anat. Ont , bd. 27, pp. 281-376, taf. 21-24, i4 figs.* 
 Lovell, J. H. 1910, 1912. The Color Sense of the Honey Bee. Amer. Nat., vol. 44, pp. 
 
 673-692; vol. 46, pp. 83-107. 
 Turner, C. H. 1910. Experiments on Color-vision of the Honey-bee. Biol. Bull., vol. 19, 
 
 pp. 257-279, 3 figs. 
 Allard, H. A. 1911. Studying the Stridulations of Orthoptera. Proc. Ent. Soc. Wash., 
 
 vol. 13, pp. 141-148. 
 Schon, A. 1911. Bau und Entwicklung des tibialen Chordotonalorgans bei der Honigbiene 
 
 und bei Ameisen. Zool. Jahrb., Abt. Anat. Ont., bd. 31, pp. 439-472, taf. 17-19, 
 
 9 figs.* 
 DemoU, R., and Scheuring, L. 1912. Die Bedeutung der Ocellen der Insecten. Zool. 
 
 Jahrb., Abt. Allg. Zool. Phys., bd. 31, pp. 519-628, 23 figs.* 
 Giinther, K. 1912. Die Sehorgane der Larve und Imago von Dytiscus marginalis. Zeits. 
 
 wiss. Zool., bd. 100, pp. 60-115, 36 figs.* 
 Hochreuther, P. 1912. Die Hautsinnesorgane von Dytiscus-margina'.is L., ihr Bau und 
 
 ihre Verbreitung am Korper. Zeits. wiss. Zool., bd. 103, pp. 1-114, 102 figs.* 
 Prochnow, O. 1912. Die Organe zur Lautausserung. In Schroder: Handbuch der 
 
 Entomologie., bd. i, pp. 61-75, figs. 1-12.* 
 Deegener, O. 1912-13. Sinnesorgane. In Schroder: Handbuch der Entomologie, bd. 
 
 I, pp. 140-233, figs- 79-152.* 
 Caesar, C. J. 1913. Die Stirnaugen der Ameisen. Zool. Jahrb., Abt. Anat. Ont., bd. 
 
 35, pp. 161-240, taf. 7-10, 29 figs.* 
 Jorschke, H. 1914, Die Facettenaugen der Orthopteren und Termiten. Zeits. wiss. 
 
 Zool., bd. Ill, pp. 153-280, figs. 1-57, pi. 4* 
 Mclndoo, N. E. 1914. The Olfactory Sense of the Honey Bee. Journ. Exp. Zool., vol. 
 
 16, pp. 265-346, 24 figs.* 
 Mclndoo, N. E. 1914. The Olfactory Sense of Hymenoptera. Proc. Acad. Nat. Sc, 
 
 pp. 294-341, 3 figs., pis. II, 12.* 
 Mclndoo, N. E. 1914. The Scent-producing Organ of the Honey Bee. Proc. Acad. 
 
 Nat. Sc, pp. 542-555, I fig., pis. 19, 20.* 
 
446 ENTOMOLOGY 
 
 Mclndoo, N. E. 1914. The Olfactory Sense of Insects. Smithson. Misc. Coll., vol. 63, 
 
 no. 9, pp. 1-63, figs. 1-6.* 
 Mclndoo, N. E. 1915. The Olfactory Sense of Coleoptera. Biol. Bull., vol. 28, pp. 
 
 407-460, 2 pis.* 
 Mclndoo, N. E. 1916. The Sense Organs on the Mouth Parts of the Honey Bee. Smith- 
 son. Misc. Coll., vol. 65, no. 14, 55 pp., 10 figs.* 
 Demoll, R. 1917. Die Sinnesorgane der Arthropoden, ihr Ban und ihre Funktion. 243 
 
 pp. Braunschweig. 
 Mclndoo, N. E. 1917. The Olfactory Organs of Lepidoptera. Journ. Morph., vol. 29, 
 
 PP- 33-54, 10 figs.* 
 Mclndoo, N. E. 1918. The Olfactory Organs of a Coleopterous Larva. Journ. Morph., 
 
 vol. 31, pp. 1 13-13 1, 33 figs-* 
 Mclndoo, N. E. 1918. The Olfactory Organs of Diptera. Journ. Comp. Neur., vol. 29, 
 
 pp. 457-484, 55 figs.* 
 Mclndoo, N. E. 1919. The Olfactory Sense of Lepidopterous Larvae. Ann. Ent. Soc. 
 
 Amer., vol. 12, pp. 65-84, figs. 1-53-* 
 Eltrihgham, H. 1919. . Butterfly Vision. Trans. Ent. Soc. London, pp. 1-49, pis. 1-5. 
 Ast, F. 1920. Ueber den feineren Bau der Facettenaugen bei Neuropteren. Zool. 
 
 Jahrb., Abth. Anat. Ont., bd. 41, pp. 411-458, taf. 26-33.* 
 Mclndoo, N. E. 1920. The Olfactory Sense of Orthoptera. Journ. Comp. Neur., vol. 
 
 31, pp. 405-427, 92 figs.* 
 
 DIGESTIVE SYSTEM 
 
 Fabre, J. L. 1862. Etude sur le r6le du tissu adipeux dans la secretion urinaire chez les 
 
 Insectes. Ann. Sc. nat. Zool., ser. 4, t. 19, pp. 351-382. 
 Plateau, F. 1874, Recherches sur les phenomenes de la digestion chez les Insectes. Mem. 
 
 Acad, ro}^ Belgique, t. 41, 124 pp., 3 pis. 
 De Bellesme, J. 1876. Physiologic comparee. Recherches experimentales sur la diges- 
 tion des insectes et en particulier de la blatte. 7 + 96 pp., 3 pis. Paris. 
 Helm, F. E. 1876. Ueber die Spinndriisen der Lepidopteren. Zeits. wiss. Zool., bd. 26, 
 
 pp. 434-469, taf. 27, 28. 
 Plateau, F. 1877. Note additionelle au Memoire sur les phenomenes de la digestion chez 
 
 les Insectes. Bull. Acad. roy. Belgique, ser. 2, t. 44, pp. 710-733. 
 Wilde, K. F. 1877. Untersuchungen iiber den Kaumagen der Orthopteren. Archiv 
 
 Naturg., jhg. 43, bd. i, pp. 135-172, 3 taf. 
 De Bellesme, J. 1878. Travaux originaux de Physiologie comparee. I. Insectes. 
 
 Digestion, Metamorphoses. 252 pp., 5 pis. Paris. 
 Schindler, E. 1878. Beitrage zur Kenntniss der Malpighi'schen Gefasse der Insecten 
 
 Zeits. wiss. Zool., bd. 30, pp. 587-660, taf. 38-40. 
 Frenzel, J. 1882. Ueber Bau und Thatigkeit des Verdauungskanals derLarve des Tene- 
 
 brio moUtor mit Beriicksichtigung anderer Arthropoden. Berl. ent Zeits., bd. 
 
 26, pp. 267-316, taf. 5.* 
 Leydig, F. 1883. Untersuchungen zur Anatomic und Histologic der Thiere. 174 pp., 
 
 8 taf. Bonn. 
 MetschnikoflF, E. 1883. Untersuchungen iiber die intrazeUulare Verdauung bei wirbel- 
 
 losen Tieren. Arb. .zool. Inst. Wien, bd. 5, pp. 141-168, 2 taf. 
 Schiemenz, P. 1883. Ueber das Herkommen des Futtersaftes und die Speicheldriisen 
 
 der Biene nebst cinen Anhangc iiber das Reichorgan. Zeits. wiss. Zool., bd. 38, 
 
 pp. 71-135, taf. 5-7. 
 Locy, W. A. 1884. Anatomy and Physiology of the family Nepidae. Amer. Nat., vol. 18, 
 
 pp. 250-255, 353-367, pis. 9-12. 
 
LITERATURE 447 
 
 Witlaczil, E. 1885. Zur ISlorphologie unci Anatomie der Cocciden. Zeits. wiss. Zool., 
 
 bd. 43, PP- 149-174, taf. 5. 
 Frenzel, J. 1886. Einigesiiber den Mitteldarm derlnsekten, so\\ae iiber Epithelregenera- 
 
 tion. Archiv mikr. Anat., bd. 26, pp. 229-306, taf. 7-9. 
 Kniippel, A. 1886. Ueber Speicheldriisen von Insecten. Archiv Naturg., jhg. 52, bd. i, 
 
 pp. 269-303, taf. 13, 14. 
 Cholodkovsky, N. 1887. Sur la morphologic de I'appareil urinaire des Lepidopteres. 
 
 Archiv. Biol., t. 6, pp. 497-514, pi. 17. 
 Faussek, V. 1887. Beitrage zur Histologic dcs Darmkanals dcr Insekten. Zcits. wiss. 
 
 Zool., bd, 45, pp. 694-712, taf. 36. 
 Blanc, L. 1889. Etude sur la secretion de la soie et sur la structure du brin ct de la have 
 
 dans Ic Bombyx mori. 56 pp., 4 pis. Lyon. 
 Kowalevsky, A. 1889. Ein Beitrag zur Kenntnis dcr Exkretionsorgane. Biol. Ccntralb., 
 
 bd. 9, pp. 33-47- 65-76, 127-128. 
 Van Gehuchten, A. 1890. Recherches histologiques sur I'appareil digestif de la larve de 
 
 la Ptychoptera contaminata, I Part. Etude du revetement epithelial et recher- 
 ches sur la secretion. La Cellule, t. 6, pp. 183-291, pis. 1-6. 
 Gilson, G. 1890, 1893. Recherches sur les cellules secretantcs. La soie et les appareils 
 
 sericigenes. I. Lepidopteres; II. Trichopteres, La Cellule, t. 6, pp. 115-182, pis. 
 
 1-3; t. 10, pp. 37-63, pl- 4- 
 Blanc, L. 1891. La tete du Bomby.x mori a I'etat larvaire, anatomie et physiologic. 
 
 Trav. Lab. Etud. Soie, 1889-1890, 180 pp., 95 figs. Lyon. 
 Wheeler, W. M. 1893. The primitive number of Malpighian vessels in Insects. Psyche, 
 
 vol. 6, pp. 457-460, 485-486, 497-498, 509-510, 539-541, 545-547, 561-564. 
 Bordas, L. 1895. Appareil glandulairc des Hymenopteres. (Glandcs salivaires, tube 
 
 digestif, tubes de Malpighi et glandcs venimeuses.) 362 pp., 11 pis. Paris. 
 Cuenot, L. 1895. Etudes physiologiques sur les Orthopteres. Arch. Biol., t. 14, pp. 
 
 293-341, pis. 12, 13. 
 Bordas, L. 1897. L'appareil digestif dcs Orthopteres. Ann. Sc. nat. Zool., ser. 8, t. 5, pp. 
 
 1-208, pis. 1-12. 
 Needham, J. C. 1897. The digestive epithehum of dragon fly nymphs. Zool. Bull., vol. 
 
 I, pp. 103-113, figs. i-io. 
 Folsom, J. W., and Welles, M. U. 1906. Epithelial Degeneration, Regeneration, and 
 
 Secretion in the Mid-intestine of CoUcmbola. Univ. 111. Bull., The Univ. Studies, 
 
 vol.2, no. 2, pp. 1-40, pis. 1-9. 
 Deegener, P. 1913. Der Darmtraktus und seine Anhange. In Schroder: Handbuch der 
 
 Entomologie, bd. i, pp. 234-315, figs. 153-211.* 
 
 CIRCULATORY SYSTEM 
 
 Graber, V. 1873. Ueber den propulsatorischen Apparat der Insekten. Archiv mikr. 
 
 Anat., bd. 9, pp. 129-196, 3 taf. 
 Graber, V. 1873. Ueber die Blutkorperchen der Insekten. Sitzb. Akad. Wiss. Wien, 
 
 math.-naturw. CI., bd. 64 (1871), pp. 9-44. 
 Graber, V. 1876. Ueber den pulsierendenBauchsinus dcr Insekten. Archiv mikr. Anat., 
 
 bd. 12, pp. 575-582, I taf. 
 Dogiel, J. 1877. Anatomie und Physiologic des Herzens der Larve von Corethra plumi- 
 
 cornis. Mem. Acad. St. Petersburg, ser. 7, t. 24, 37 pp., 2 pis. Separate, 
 
 Leipzig. Voss. 
 Vayssiere, A. 1882. Recherches sur I'organisation des larves des Ephemerines. Ann. Sc. 
 
 nat. Zool., ser. 6, t. 13, pp. 1-137, pis. i-ii. 
 
448 ENTOMOLOGY 
 
 Viallanes, H. 1882. Recherches sur I'histologie des Insectes, et sur les phenomenes histo- 
 logiques qui accompagnent le developpement post-embryonnaire de ces animaux. 
 Ann. Sc. nat. ZooL, ser, 6, t. 14, PP- X-34S, 4 pls. Bibl. Ecole, bd. 26, 348 pp., 
 18 pis. 
 
 Von Wielowiejski, H. R. 1886. Ueber das Blutgewebe der Insekten. Zeits. wiss. Zool., 
 
 bd. 43, PP- 512-536. J r^,- . 
 
 Dewitz, H. 1889. Eigenthatige Schwimmbewegung der Blutkorperchen der Glieder- 
 
 thiere. Zool. Anz., jhg. 12, pp. 457-464, i fig- 
 Kowalevsky, A. 1889. Ein Beitrag zur Kenntnis der Excretionsorgane. Biol. Centralb., 
 
 bd. 9, pp. 33-47, 65-76, 127-128. 
 Schaffer, C. 1889. Beitrage zur Histologie der Insekten. II. Ueber Blutbildungsherde 
 
 bei Insektenlarven. Zool. Jahrb., Abth. Anat. Ont., bd. 3, pp. 626-636, taf. 30. 
 Pawlowa, M. 1895. Ueber ampuUenartige Blutcirculationsorgane im Kopfe verschiedener 
 
 Orthopteren. Zool. Anz., jhg. 18, pp. 7-13, i fig. 
 Deegener, P. 1913. Zirkulationsorgane und Leibeshohle. In Schroder: Handbuch der 
 ' Entomologie, bd. i, pp. 383-437, figs- 275-319- 
 
 FAT BODY 
 
 Gadeau de Kerville, H. 1881, 1887. Les insectes phosphorescents. T. i, 55 pp., 4 pls-'. 
 
 t. 2, 135 pp. Rouen.* 
 Von Wielowiejski, H. R. 1882. Studien uber Lampyriden. Zeits. wiss. Zool., bd. 37; 
 
 pp. 354-428, taf. 23, 24. _ 
 
 Von Wielowiejski, H. 1883. Ueber den Fettkorper von Corethra plumicornis und seine 
 
 Entwicklung. Zool. Anz., jhg. 6, pp. 318-322. 
 Emery, C. 1884. Untersuchungen liber Luciola italica L. Zeits. wiss. Zool., bd. 40, PP- 
 
 338-355, taf. 19. 
 Dubois, R. 1886. Contribution a I'etude de la production de la lumiere par les etres 
 
 vivants.- Les Elaterides lumineux. Bull. Soc. zool. France, ann. ix, pp. 1-275, 
 
 pls. 1-9. 
 Heinemann C. 1886. Zur .\natomie und Physiologic der Leuchtorgane mexikanischer 
 
 Cucuj'o's. Archiv mikr. Anat., bd. 27, pp. 296-382. 
 Von Wielowiejski, H. R. 1886. Ueber das Blutgewebe der Insekten. Zeits. wiss. Zool., 
 
 bd. 43, PP- 512-536. , ^, ,-,j ^ J 
 
 Schaflfer, C. 1889. Beitrage zur Histologie der Insekten. III. Ueber Blutbildungsherde 
 
 bei Insektenlarven. Zool. Jahrb., Abth. Anat. Ont., bd. 3, pp. 626-636, taf. 30. 
 Von Wielowiejski, H. R. 1889. Beitrage zur Kenntnis der Leuchtorgane der Insecten. 
 
 Zool. Anz., jhg. 12, pp. 594-600. 
 Wheeler, W. M, 1892. Concerning the "blood tissue" of the Insecta. Psyche, vol. 6, 
 
 pp. 216-220, 233-236, 253-258, pi. 7. 
 Cuenot, L. 1895. Etudes physiologiques sur les Orthopteres. Arch. Biol., t. 14, pp. 
 
 293-341, pls. 12, i^. 
 Schmidt, P. 1895. On the Luminosity of Midges (Chironomidae). x\nn. Mag. Nat. Hist., 
 
 ser. 6, vol. 15, pp. 133-141- Trans, from Zool. Jahrb., Abth. Syst., etc., bd. 8, pp. 
 
 58-66, 1894. 
 Bruntz, L. 1904. Contribution a I'Etude de I'excretion chez les Arthropodes. Archiv. 
 
 Biol., t. 20, pp. 217-420, pls. 7-9. 
 Townsend, A. B. 1904. The Histology of the Light Organs of Photinus margineUus. 
 
 Amer. Nat., vol. 38, pp. 127-151, figs, i-ii.* 
 Lund, E. J. 1911. On the Structure, Physiology and Use of Photogenic Organs. Journ. 
 
 Exp. Zool., vol. II, PP- 415-461, pls- 1-3; figs- 1,2.* 
 
LITERATURE 449 
 
 McDermott, F. A. 1911. Some Further Observations on the Light Emission of American 
 
 Lampyrida". Can. Knt., vol. 43, pp. 399-406. 
 Coblentz, W. W. 1912. A Physical Study of the Firefly. Publ. No. 164, Carnegie Inst., 
 
 Wash., 47 pp., 14 figs., I pi.* 
 Glaser, R. W. 1912. A Contribution to Our Knowledge of the Function of the (Enocytes 
 
 of Insects. Biol. Bull., vol. 23, pp. 213-224.* 
 McDermott, F. A. 1912. Recent Advances in Our Knowledge of the Production of Light 
 
 in Living Organisms. Rept. Smithson. Inst. 191 1, pp. 345-362.* 
 
 RESPIRATORY SYSTEM 
 
 Dufour, L. 1852. Ktudes anatomiques et physiologiques et observations sur les larves des 
 
 Libellules. Ann. Sc. nat. Zool., ser. 3, t. 17, pp. 65-110, 3 pis. 
 Williams, T. 1853-57. On the Mechanism of Aquatic Respiration and on the Structure 
 
 of the Organs of Breathing in Invertebrate Animals. Trans. Ann. Mag. Nat. 
 
 Hist., ser. 2, vols. 12-19, 17 pis. 
 Rathke, H. 1861. Anatomisch-physiologische Untersuchungen uber den Athmungspro- 
 
 cess der Insecten. Schrift, phys.-oek. Gesell. Konigsberg, jhg. i, pp. 99-138, 
 
 taf. I. 
 Landois, H., und Thelen, W. 1867. Der Tracheenverschluss bei den Insekten. Zeits. 
 
 wiss. Zool., bd. 17, pp. 187-214, I taf. 
 Gerstacker, A. 1874. Ueber das Vorkommen von Tracheenkiemen bei ausgebildeten 
 
 Insecten. Zeits. wiss. Zool., bd. 24, pp. 204-252, i taf. 
 Packard, A. S. 1874. On the Distribution and Primitive Number of Spiracles in Insects. 
 
 Amer. Nat., vol. 8, pp. 531-534- 
 Palmen, J. A. 1877. Zur Morphologic des Tracheensystems. 10 + i49 PP-. 2 taf. 
 
 Helsingfors. 
 Sharp, D. 1877. Observations on the Respiratory Action of the Carnivorous Water 
 
 Beetles (Dytiscidae). Journ. Linn. Soc. Zool., vol. 13, pp. 161-183. 
 Poletajew, O. 1880. Quelques mots sur les organes respiratoires des larves des Odonates. 
 
 Hora; Soc. Ent. Ross., t. 15, pp. 436-452, 2 pis. 
 Krancher, O. 1881. Der Bau der Stigmen bei den Insekten. Zeits. wiss. Zool., bd. 35, 
 
 PP- 505-574, taf. 28, 29. 
 Vayssiere, A. 1882. Recherches sur I'organisation des larves des Ephemerines. Ann. Sc. 
 
 nat. Zool., ser. 6, t. 13, pp. 1-137, pls. i-n. 
 Macloskie, G. 1884. The Structure of the Tracheae of Insects. Amer. Nat., vol. 18, pp. 
 
 567-573, figs. 1-4. 
 Plateau, F. 1884. Recherches experimentales sur les mouvements respiratoires des 
 
 Insectes. Mem. Acad. roy. Belgique, t. 45, 219 pp., 7 pis., 56 figs. 
 Raschke, E. W. 1887. Die Larve von Culex nemorosus. Archiv Naturg., jhg. 53, bd. i, 
 
 pp. 133-163, taf. 5, 6. 
 Schmidt-Schwedt, E. 1887. Ueber Athmung der Larven und Puppen von Donacia 
 
 crassipes. Berlin, ent. Zeits., ,bd. 31, pp. 325-334, taf. 5b. 
 Haase, E. 1889. Die Abdominalanhange der Insekten mit Beriicksichtigung der Myri- 
 
 opoden. Morph. Jahrb., bd. 15, pp. 331-435, taf. 14, 15. 
 Cajal, S. R. 1890. Coloration par la methode de Golgi des terminaisons des trachees et 
 
 des nerfs dans les muscles des ailes des insectes. Zeits. wiss. Mikr., bd. 7, pp. 332- 
 
 342, taf. 2, figs. 1-3. 
 Von Wistinghausen, C. 1890. Ueber Tracheenendigungen in den Sericterien der Raupen . 
 
 Zeits. wiss. Zool., bd. 49, pp. 565-582, taf. 27.* 
 Stokes, A. C. 1893. The Structure of Insect Tracheae, with Special Reference to those of 
 
 Zaitha fluminea. Science, vol. 21, pp. 44-46, figs. 1-7. 
 29 
 
450 ENTOMOLOGY 
 
 Miall, L. C. 1895, 1903. The Natural History of Aquatic Insects, ii + 39S pp., 116 
 
 figs. London and New York. Macmillan & Co. 
 Sadones, J. 1895. L'appareil digestif et respiratoire larvaire des Odonates. La Cellule, 
 
 t. II, pp. 271-325, pis. 1-3. 
 Gilson, G., and Sadones, J. 1896. The Larval Gills of the Odonata. Journ. Linn. Soc. 
 
 Zool, vol. 25, pp. 413-418, figs. 1-3. 
 Holmgren, E. 1896. Ueber das respiratorische Epithel der Tracheen bei Raupen. 
 
 Festsk. Lilljeborg, Upsala, pp. 79-96, taf. 5, 6. 
 Manunen, H. 1912. Ueber die Morphologie der Heteropteren und Homopterenstigmen. 
 
 Zool. Jahrb., Abt. Anat. Ont., bd. 34, pp. 1 21-178, taf. 7-9, 22 figs.* 
 Deegener, P. 1913. Respirationsorgane. In Schroder: Handbuch der Entomologie, 
 
 bd. I, pp. 316-382, figs. 212-274.* 
 Vinal, S. C. 1919. The respiratory system of the Carolina locust (Dissosteira Carolina 
 
 Linne). Journ. N. Y. Ent. Soc, vol. 27, pp. 19-32, pis. 3-5. 
 
 REPRODUCTIVE SYSTEM 
 
 Huxley, T. H. 1858-59. On the Agamic Reproduction and Morphology of Aphis 
 
 Trans. Linn. Soc. Zool., vol. 22, pp. 193-236, 5 pis. 
 Wagner, N. 1865. Ueber die viviparen Gallmiickenlarven. Zeits. wiss. Zool., bd. 15, 
 
 ■ pp. 106-117. 
 Biitschli, O. 1871. Nahere Mittheilungen iiber die Entwicklung und den Bau der Samen- 
 
 faden der Insecten. Zeits. wiss. Zool., bd. 21, pp. 526-534, taf. 40, 41. 
 Will, L. 1883. Zur Bildung des Eies und des Blastoderms bei den viviparen Aphiden. 
 
 Arbeit, zool.-zoot. Inst. Univ. Wiirzburg, bd. 6, pp. 217-258, taf. 16. 
 Palmen, J. A. 1884. Ueber paarige Ausfiihrungsgange der Geschlechtsorgane bei Insecten. 
 
 Ein morphologische Untersuchung. 108 pp., 5 taf. Helsingfors. 
 Gilson, G. 1885. Etude comparee de la spermatogenese chez les Arthropodes. La 
 
 Cellule, t. I, pp. 7-188, pis. 1-8.* 
 Schneider, A. 1885. Die Entwicklung der Geschlechtsorgane der Insecten. Zool. 
 
 Beitr. von A. Schneider, bd. i, pp. 257-300, 4 taf. Breslau. 
 Spichardt, C. 1886. Beitrag zur Entwickelung der mannlichen Genitalien und ihrer 
 
 Ausfiihrgange bei Lepidopteren. Verb, naturh. Ver Bonn, jhg. 43, pp. 1-34, taf. i. 
 La Valette St. George. 1886, 1887. Spermatologische Beitrage. Arch. mikr. Anat., 
 
 bd. 27, pp. 1-12, taf. I, 2; bd. 28, pp. 1-13, taf. 1-4; bd. 30, pp. 426-434, taf. 25. 
 Von Wielowiejski, H. R. 1886. Zur Morphologie des Insectenovariums. Zool. Anz., 
 
 jhg. 9, pp. 132-139- 
 Korschelt, E. 1887. Ueber einige interessante Vorgange bei der Bildung der Insekteneier. 
 
 Zeits. wiss. Zool., bd. 45, pp. 327-397, taf. 18, 19. 
 Oudemans, J. T. 1888. Beitrage zur Kenntniss der Thysanura und Collembola. Bijdr. 
 
 Dierk., pp. 147-226, taf. 1-3. Amsterdam. 
 Leydig, F. 1889. Beitrage zur Kenntniss des thierischen Eies im unbefruchteten Zu- 
 
 stande. Zool. Jahrb., Abth. Anat. Ont., bd. 3, pp. 287-432, taf. 11-17. 
 Lowne, B. T. 1889. On the Structure and Development of the Ovaries and their Append- 
 ages in the Blowfly (Calliphora erythrocephala). Journ. Linn. Soc. Zool., vol. 20, 
 
 pp. 418-442, pi. 28.* 
 Ballowitz, E. 1890. Untersuchungen iiber die Struktur der Spermatozoen, zugleich ein 
 
 Beitrag zur Lehre vom feineren Bau der kontraktilen Elemente. Die Spermato- 
 zoen der Insekten. (I. Coleopteren.) Zeits. wiss. Zool., bd. 50, pp. 317-407, 
 
 taf. 12-15. 
 Henking, H. 1890-92. Untersuchungen iiber die ersten EntwicklungsvorgSnge in der 
 
 Eiern der Insekten. Zeits. wiss. Zool., bd. 49, pp. 503-564, taf. 24-26; bd. 51, pp 
 
 685-736, taf. 35-37; bd. 54, pp. 1-274, taf. 1-12, figs. 1-12. 
 
LITERATURE 45 1 
 
 Heymons, R. 1891. Die Entwicklung der weiblichen Geschlechtsorgane von Phyllo- 
 
 dromia (Blatta) germanica L. Zeits. wiss. Zool., bd. 53, pp. 434-536, taf. 18-20. 
 Ingenitzky, J. 1893. Zur Kenntnis der Begattungsorgane derLibelluliden. Zool. Anz., 
 
 jhg. 16, pp. 405-407, 2 figs. 
 Escherich, K. 1894. Anatomische Studien uber das mannliche Genital-system der Cole- 
 
 opteren. Zeits. wiss. Zool., bd. 57, pp. 620-641, taf. 26, figs. 1-3. 
 Toyama, K. 1894. On the Spermatogenesis of the Silk Worm. Bull. Coll. Agr. Univ. 
 
 Tokyo, vol. 2, pp. 125-157, pis. 3, 4. 
 Kluge, M.H. E. 1895. Das mannliche Geschlechtsorgan von Vespa germanica. Archiv. 
 
 Naturg., jhg. 61, bd. i, pp. 159-198, taf. 10. 
 Peytoureau, A. 1895. Contributions a I'etude de la morphologic de I'armure genitale des 
 
 Insectes. 248 pp., 22 pis., 43 figs. Paris. 
 Wilcox, E. V. 1895. Spermatogenesis of Caloptenus femur-rubrum and Cicada tibicen. 
 
 Bull. Mus. Comp. Zool., vol. 27, pp. 1-32, pis. 1-5.* 
 Wilcox, E. V. 1896. Futher Studies on the Spermatogenesis of Caloptenus femur-rubrum . 
 
 Bull. Mus. Comp. Zool., vol. 29, pp. 193-202, pis. 1-3. 
 Fenard, A. 1897. Recherches sur les organes complementaires internes de I'appareil 
 
 genital des Orthopteres. Bull. sc. France Belgique, t. 29, pp. 390-533, pls- 24-28. 
 Gross, J. 1903. Untersuchungeniiber die Histologic des Insectenovariums. Zool. Jahrb., 
 
 Abth. Anat. Ont., bd. 18, pp. 71-186, taf. 6-14.* 
 Griinberg, K. 1903. Unte|rsuchungen liber die Keim- und Nahrzellen in den Hoden und 
 
 Ovarien der Lepidoptera. Zeits. wiss. Zool., bd. 74, pp. 327-39S> taf. 16-18. 
 Holmgren, N. 1903. Ueber vivipare Insecten. Zool. Jahrb., bd. 19, pp. 431-468, 
 
 10 figs.* 
 Felt, E. P. 1911. Miastor americana Felt, an Account of Pedogenesis. Twenty-sixth 
 
 Rept. St. Ent. N.Y., pp. 82-104, figs. 7-9.* 
 Deegener, P. 1913, 1921. Geschlechtsorgane. In Schroder: Handbuch der Entomo- 
 
 logie, bd. I, pp. 466-533, figs. 336-390-* 
 Doncaster, L. 1914. The Determination of Sex. 12 -}- 172 pp., 22 pis. Cambridge., 
 
 Univ. Press. New York, G. P. Putnam's Sons.* 
 Doncaster, L. 1920. An Introduction to the Study of Cytology. 14 + 280 pp., figs. 
 
 1-3 1, pis. 1-24. Cambridge. Univ. Press. 
 
 EMBRYOLOGY 
 
 Leuckart, R. 1858. Die Fortpflanzung und Entwicklung der Pupiparen nach Beobach- 
 
 tungen an Melophagus ovinus. Abh. naturf. Geseil. HaUe, bd. 4, pp. 145-226, 3 
 
 taf. 
 Weismann, A. 1863. Die Entwicklung der Dipteren im Ei, nach Beob'achtungen an 
 
 Chironomus spec, Musca vomitoria und Pulex canis. Zeits. wiss. Zool., bd. 13, 
 
 pp. 107-220, 7 taf. Separate, 1864, 263 pp., 14 taf. 
 Metschnikoff, E. 1866. Embryologische Studien an Insecten. Zeits. wiss. Zool., bd. 16, 
 
 pp. 389-500, 10 taf. 
 Brandt, A. 1869. Beitrage zur Entwicklungsgeschichtc der Libelluliden und Hemipteren. 
 
 Mem. Acad. St. Petersbourg, ser. 7, t. 13, pp. 1-33, 3 pis. 
 Melnikow,N. 1869. Beitrage zur Embryonalentwicklung der Insekten. Archiv Naturg., 
 
 jhg. 35, bd. I, pp. 136-189, 4 taf. 
 Butschli, O. 1870. Zur Entwicklutagsgeschichte der Bienc. Zeits. wiss. Zool., bd. 20, 
 
 pp. 519-564, taf. 24-27. 
 Kowalevsky, A. 1871. Embryologische Studien an Wiirmern und Arthropoden. Mem. 
 
 Acad. St. Petersbourg, ser. 7, t. 16, pp. 1-70, 12 pis. 
 
452 ENTOMOLOGY 
 
 Hatschek, B. 1877. Beitrage zur Entwicklungsgeschichte der Lepidopteren. Jenais. 
 
 Zeits. Naturw., bd. ii, 38 pp., 3 taf., 2 figs. 
 Bobretzky, N. 1878. Ueber die Bildung des Blastoderms und der Keimblatter bei den' 
 
 Insecten. , Zeits. wiss. Zool., bd. 31, pp. 195-215, taf. 14. 
 Will, L. 1883. Zur Bildung des Eies und des Blastoderms bei den viviparen Aphiden. 
 
 Arbeit, zool.-zoot. Inst. Univ. Wiirzburg, bd. 6, pp. 217-258, taf. 16. 
 Ayers, H. 1884. On the Development of Qicanthus niveus and its Parasite Teleas. 
 
 Mem. Best. Soc. Nat. Hist., vol. 3, pp. 225-281, pis. 18-25, figs. 1-41.* 
 Patten, W. 1884. The Development of Phryganids, with a Preliminary Note on the 
 
 Development of Blatta germanica. Quart. Journ. Micr. Sc, vol. 24 (n.s.), pp. 
 
 549-602, pis. 36a, b, c. 
 Witlaczil, E. 1884. Entwicklungsgeschichte der Aphiden. Zeits. wiss. Zool., bd. 40, pp. 
 
 559-696, taf. 28-34.* 
 Korotneflf, A. 1886. Die Embryologie der Gryllotalpa. Zeits. wisB. Zool, bd. 41, pp. 
 
 570-604, taf. 29-31. 
 Blochmann, F. 1887. Ueber die Richtungskorper bei Insecteneiern. Morph. Jahrb., 
 
 bd. 12, pp. 544-574, taf. 26, 27. 
 Biitschli, O. 1888. Bemerkungen iiber die Entwicklungsgeschichte von Musca. Morph. 
 
 Jahrb., bd. 14, pp. 170-174, 3 figs. 
 Graber, V. 1888. Ueber die Polypodie bei Insekten-Embryonen. Morph. Jahrb., bd. 
 
 13, pp. 586-615, taf. 25, 26. 
 . Grabei, V. 1888. Ueber die primare Segmentirung des Keimstreifs der Insekten. 
 
 Morph.. Jahrb., bd. 14, pp. 345-368, taf. 14, 15, 4 figs. 
 Henking, H. 1888. Die ersten Entwicklungsvorgange im Fliegenei und freie Kernbildung. 
 
 Zeits. wiss. Zool., bd. 46, pp. 289-336, taf. 23-26, 3 figs. 
 "Will, L. 1888. Entwicklungsgeschichte der viviparen Aphiden. Zool. Jahrb., Abth. 
 
 Anat. Ont., bd. 3, pp. 201-286, taf. 6-10. 
 Cholodkovsky, N. 1889. Studien zur Entwicklungsgeschichte der Insekten. Zeits. 
 
 wiss. Zool., bd. 48, pp. 89-100. taf. 8. 
 Graber, V. 1889. Ueber den Bau und die phylogenetische Bedeutung der embryonalen 
 
 Bauchanhange der Insekten. Biol. Centralb., jhg. 9, pp. 355-363. 
 Heider, K. 1889. Die Embryonalentwicklung von Hydrophilus piceus L. I. Theil. 99 
 
 pp., 13 taf., 9 figs. Jena. 
 Wheeler, W. M. 1889. The Embryology of Blatta germanica and Doryphora decem- 
 
 lineata. Journ. Morph., vol. 3, pp. 291-386, pis. 15-21, figs. 1-16. 
 Carriere, J. 1890. Die Entwicklung der Mauerbiene (Chalicodoma muraria Fabr.) im 
 
 Ei. Archiv mikr. Anat., bd. 35, pp. 141-165, taf. 8, 8a. 
 Henking, H. 1890-92. Untersuchungen' iiber die ersten Entwicklungsvorgange in der 
 
 Eiern der Insekten. Zeits. wiss. Zool., bd. 49, pp. 503-564, taf. 24-26; bd. 51, pp. 
 
 685-736, taf. 35-37; bd. 54, pp. 1-274, taf. 1-12, figs. 1-12. 
 Wheeler, W. M. 1890. On the Appendages of the First Abdominal Segment of Embryo 
 
 Insects. Trans. Wis. Acad. Sc, vol. 8, pp. 87-140, pis. 1-3.* 
 Cholodkowsky, N. 1891. Die Embryonalentwicklung, von Phyllodromia (Blatta ger- 
 manica). Mem. Acad. St. Petersbourg, ser. 7, t. 38, 4 + 120 pp., 6 pis., 6 figs. 
 Graber, V. 1891. Ueber die embryonale Anlage des Blut- und Fettgewebes der Insekten; 
 
 Biol. Centralb., jhg. 11, pp. 212-224. 
 Wheeler, W. M. 1891. Neuroblasts in the Arthropod Embryo. Journ. Morph., vol. 4, 
 
 PP- 337-343, I fig- 
 Graber, V. 1892. Ueber die morphologische Bedeutung der ventralen Abdominalan- 
 
 hange der Insekten-Embryonen. Morph. Jahrb., bd. 17, pp. 467-482, figs. 1-6. 
 Korschelt, E., iind Heider, K. 1892. Lehrbuch der vergleichenden Entwicklungsge- 
 
 shichte der wirbellosen Thiere. Heft 2, pp. 761-890, figs. Jena.* Trans.: 1899. 
 
LITERATURE 453 
 
 M. Bernard and M. F. Woodward. Text-Book of the Embryology of Inverte- 
 brates. 12 + 441 pp., 198 figs. London, Swan Sonnenschein & Co., Ltd.; New 
 
 York, The Macmillan Co.* 
 Wheeler, W. M. 1893. A Contribution to Insect Embryology. Journ. Morph., vol. 8, 
 
 pp. 1-160, pis. 1-6, figs. 1-7. 
 Heymons, R. 1895. Die Embryonalentwickelung von Ucrmapteren und Orthopter^n 
 
 unter besonderer Beriicksichtigung der Keimblatterbildung. 8 -|- 136 pp, 12 taf., 
 
 33 figs. Jena. 
 He5rmons, R. 1896. Grundzuge der Entwickelung und des Korperbaues von Odonaten 
 
 und Ephemeriden. Anh. Abh. Akad. Wiss. Berlin, 66 pp., 2 taf. 
 Hesmions, R. 1897. Entwicklungsgeschichtliche Untersuchungen an Lepisma saccharina 
 
 L. Zeits. wiss. Zool., bd. 62, pp. 583-631, taf. 29, 30, 3 figs. 
 Kulagin, N. 1897. Beitriige zur Kenntnis der Entwicklungsgeschichte von Platygaster, 
 
 Zeits. wiss. Zool., bd. 63, pp. 195-235, taf. 10, 11. 
 Claypole, A. M. 1898. The Embryology and Oogenesis of Anurida maritima (Guer.), 
 
 Journ. Morph., vol. 14, pp. 219-300, pis. 20-25, 11 figs. 
 Uzel, H. 1898. Studien uber die Entwicklung der apterygoten Insecten. 6 + 58 pp 
 
 6 taf., 5 figs. Berlin. 
 Wilson, E. B. 1900. The Cell in Development and Inheritance. 21 + 483 pp., 194 figs 
 
 New York and London. The Macmillan Co. 
 Marchal, P. 1904. La Polyembryonie Specifique. Arch. Zool. exp. gen., ser. 4, t. 2, pp 
 
 257-335, pis. 9-I3-* 
 Heymons, R. 1912. Ueber den Genitalapparat und die Entwicklung von Hemimerus 
 
 talpoides Walk. Zool. Jahrb., Supplement 15, bd. 2, pp. 141-184, pis. 7-1 1, 3 figs 
 Korschelt, E. 1912. Zur Embryonalentwicklung des Dytiscus marginalis L. Zool 
 
 Jahrb., Supplement 15, bd.2, pp. 499-532, 24 figs.* 
 Blunck, H. 1914. Die Entwicklung des Dytiscus marginalis L. vom Ei bis zur 
 
 Imago. I Teil. Zeits. wiss. Zool., bd. iii, pp. 76-151, figs. 1-31.* 
 Nelson, J. A. 1915. The Embryology of the Honey Bee. 4 + 282 pp., 95 figs., 6 pis. 
 
 Princeton, N. J. Princeton Univ. Press.* 
 Strindberg, H. 1916. Zur Entwicklungsgeschichte und Anatomie der Mallophagen. 
 
 Zeits. wiss. Zool., bd. 115, pp. 382-459, figs. 1-38.* 
 Blunck, H. 1917. Die Entwicklung des Dytiscus marginalis L. vom Ei bis zum Imago. 
 
 2 Teil. Zeits. wiss. Zool., bd. 117, pp. 1-129, figs. 1-57.* 
 
 POSTEMBRYONIC DEVELOPMENT. METAMORPHOSIS 
 
 Weismann, A. 1864. Die nachembryonale Entwicklung der Musciden nach Beobach- 
 
 tungen an Musca vomitoria und Sarcophaga carnaria. Zeits. wiss. Zool., bd. 14, 
 
 pp. 187-336. 
 Weismann, A. 1866. Die Metamorphose von Corethra plumicornis. Zeits. wiss. Zool., 
 
 bd. 16, pp. 45-127, 5 taf. 
 Trouvelot, L. 1867. The American Silk Worm. Amer. Nat., vol. i, pp. 30-38, 85-94, 
 
 145-149, 4 figs., pis. 5, 6. 
 Brauer, F. 1869. Betrachtungen iiber die Verwandlung der Insekten im Sinne der Des- 
 
 cendenz-Theorie. Verh. zool.-bot. Gesell. Wien, bd. 19, pp. 299-318; bd. 28 
 
 (1878), 1879, pp. 151-166. 
 Ganin, M. 1869. Beitrage zur Kenntniss der Entwickelungsgeschichte bei den Insecten. 
 
 Zeits. wiss. Zool., bd. 19, pp. 381-451, 3 taf. 
 Chapman, T. A. 1870. On the Parasitisrn of Rhipiphorus paradoxus. Ann. Mag. Nat. 
 
 Hist., ser. 4, vol. 5, pp. 191-198. 
 Chapman, T. A. 1870. Some Facts towards a Life History of Rhipiphorus paradoxus. 
 
 Ann. Mag. Nat. Hist., ser. 4, vol. 6, pp. 314-326, pi. 16. 
 
454 ENTOMOLOGY 
 
 Lubbock, J. 1874, 1883. On the Origin and Metamorphoses of Insects. i6 + io8 pp., 
 
 6 pis., 63 figs. London. Macmillan & Co. 
 Ganin, M. 1876. [Materials for a Knowledge of the Postembryonal Development of 
 
 Insects. Warsaw.] (In Russian.) Abstracts: Amer. Nat., vol. 11, 1877, pp. 
 
 423-430; Zeits. wiss. Zool., bd. 28, 1877, pp. 386-389. 
 Riley, C. V. 1877. On the Larval Characters and Habits of the Blister-beetles belonging 
 
 to the Genera Macrobasis Lee. and Epicauta Fabr. ; with Remarks on other Species 
 
 of the Family Meloidas. Trans. St. Louis Acad. Sc, vol. 3, pp. 544-562, figs. 35- 
 
 39, Pl- 5- 
 Dewitz, H. 1878. Beitrage zur Kenntniss der postembryonalen Gliedmassenbildung bei 
 
 den Insecten. Zeits. wiss. Zool., bd. 30, suppl., pp. 78-105, taf. 5. 
 Packard, A. S. 1878. Metamorphoses [of Locusts]. First Rept. U. S. Ent. Comm., pp. 
 
 279-284, pis. 1-3, figs. 19, 20. 
 Metschnikoff, E. 1883. Untersuchungen iiber die intracellulare Verdauung bei wirbel- 
 
 losen Thieren. Arb. zool. Inst. Wien, bd. 5, pp. 141-168, taf. 13, 14. 
 Viallanes, H. 1883. Recherches sur I'histologie des Insectes et sur les phenomenes histo- 
 
 logiques qui accompagnent le developpement post-embryonnaire de ces animaux. 
 
 Ann. Sc. nat. Zool., ser. 6, t. 14, 348 pp., 18 pis. 
 Kowalevsky, A. 1885. Beitrage zur nachembryonalen Entwicklung der Musciden. 
 
 Zool. Anz., jhg. 8, pp. 98-103, 123-128, 153-157. 
 Schmidt, O. 1885. Metamorphose und Anatomie des mannlichen Aspidiotus nerii. 
 
 Archiv Naturg., jhg. 51, bd. i, pp. 169-200, taf. 9, 10. 
 Witlaczil, E. 1884. Zur Morphologie und Anatomie der Cocciden. Zeits. wiss. Zool., 
 
 bd. 43, PP- 149-174, taf. 5. 
 Kowalevsky, A. 1887. Beitrage zur Kenntniss der nachembryonalen Entwicklung der 
 
 Musciden. Zeits. wiss. Zool., bd. 45, pp. 542-594, taf. 26-30. 
 Van Rees, J. 1888. Beitrage zur Kenntnis der inneren Metamorphose von Musca vomi- 
 
 toria. Zool. Jahrb., Abth. Anat.,Ont., bd. 3, pp. 1-134, taf. i, 2, 14 figs. 
 Hyatt, A., and Anns, J. M. 1890. Insecta. 23 + 300 pp., 13 pis., 223 figs. Boston. 
 
 D. C. Heath & Co.* 
 Bugnion, E. 1891. Recherches sur le developpement post-embryonnaire, I'anatomie, et 
 
 les mcEurs de I'Encyrtus fuscicollis. Rec. zool. Suisse, t. 5, pp. 435-534, pis. 
 
 20-25. 
 Poulton, E. B. 1891. The External Morphology of the Lepidopterous Pupa: its Relation 
 
 to that of the other Stages and to the Origin and History of Metamorphosis. 
 
 Trans. Linn. Soc. Zool., ser. 2, vol. 5, pp. 245-263, pis. 26, 27. 
 Korschelt, E., iind Heider, K. 1892. Lehrbuch der vergleichenden Entwicklungsge- 
 
 schichte der wirbellosen Thiere. Heft 2, pp. 761-890, figs. Jena.* 
 Miall, L. C, and Hammond, A. R. 1892. The Development of the Head of Chironomus. 
 
 Trans. Linn. Soc. Zool., ser. 2, vol. 5, pp. 265-279, pis. 28-31. 
 Pratt, H. S. 1893. Beitrage zur Kenntnis der Pupiparen. Archiv Naturg., jhg. 59, bd. 
 
 I, pp. 151-200, taf. 6. 
 Gonin, J. 1894. Recherches sur la metamorphose des Lepidopteres. De la formation des 
 
 appendices imaginaux dans la cheniUe du Pieris brassicae. BuU. Soc. vaud. Sc. 
 
 nat., t. 30, pp. 1-52, 5 pis. 
 Miall, L. C. 1895. The Transformations of Insects. Nature, vol. 53, pp. 153-158. 
 Hyatt, A., and Anns, J. M. 1896. The Meaning of Metamorphosis. Nat. Sc, vol. 8, 
 
 pp. 395-403- 
 Kulagin, N. 1897 . Beitrage zur Kenntnis der Entwicklungsgeschichte von Platygaster. 
 
 Zeits. wiss. Zool., bd. 63, pp. 195-235, taf. 10, 11. 
 Packard, A. S. 1897. Notes on the Transformations of Higher Hymenoptera. Journ. 
 
 N. Y. Ent. Soc, vol. 4, pp. 155-166, figs. 1-5; vol. 5, pp. 77-87, 109-120, figs. 6-13. 
 
LITERATURE 455 
 
 Pratt, H. S. 1897. Tmaginal Discs in Insects. Psyche, vol. 8, pp. 15-30, ii figs. 
 Packard, A, S. 1898. A Text-Book of Entomology. 17 + 729 pp., 654 figs. New York 
 
 and London. The Macmillan Co.* 
 Boas, J. E. V. 1899. Einige Bemerkungen iiber die Metamorphose der Insecten. Zool. 
 
 Jahrb., Abth. Syst., bd. 12, pp. 385-402, taf. 20, figs. 1-3. 
 Lameere, A. 1899. La raison d'etre des metamorphoses chez les Insectes. Ann. Soc. 
 
 ent. Belg., t. 43, pp. 619-636. 
 Perez, C. 1899. Sur la metamorphose des insectes. Bull. Soc. ent. France, pp. 398-402. 
 Wahl, B. 1901. Ueber die Entwicklung der hypodermalen Imaginalscheiben im Thorax 
 und Abdomen der Larve von Eristalis Latr. Zeits. wiss. Zool., bd. 70, pp. 171-191, 
 
 taf. 9, figs. 1-4. . 
 Perez, C. 1902. Contribution a I'etude des metamorphoses. Bull. sc. France. Belg., t. 
 
 37, pp. 195-427, pis. 10-12, 32 figs. 
 Deegener, P. 1904, Die Entwicklung des Darmcanals der Insecten wahrend der Meta- 
 morphose. Zool. Jahrb., Abth. Anat. Ont., bd. 20, pp. 499-676, taf. 33-43-* 
 Powell, P. B. 1904-05. The Development of Wings of Certain Beetles, and some Studies 
 
 of the Origin of the Wings of Insects. Journ. N. Y. Ent. Soc, vol. 12, pp. 237-243, 
 
 pis. 11-17; vol. 13, pp. 5-22.* 
 Perez, C. 1910. Recherches histologiques sur la metamorphose des Muscides. Arch. 
 
 Zool. exp. gen., ser. 5, t. 4, pp. 1-270, pis. 1-16, 162 figs. 
 Carpenter, G. H. 1921. Insect Transformation. 10 + 282 pp., 1 24 figs., 4 pis. London. 
 
 Methuen & Co. 
 
 AQUATIC INSECTS 
 
 Dufotir, L. 1849. Des divers modes de respiration aquatique dans les insectes. Compt * 
 
 rend. Acad. Sc, t. 29, pp. 763-770. Ann. Mag. Nat. Hist., ser. 2, vol. 6, i85o,pp- 
 
 112-118. 
 Dufour, L. 1852. Etudes anatomiques et physiologiques et observations sur les larves 
 
 des Libellules. Ann. Sc. nat. Zool., ser. 3, t. 17, pp. 65-110, 3 pis. 
 Hagen, H. A. 1853. Leon D ufour uber die Larven der Libellen mit Beriicksichtigung der 
 
 friiheren Arbeiten. (Ueber Respiration der Insecten.) Stett. ent. Zeit., bd. 14, 
 
 pp. 98-106, 237-238, 260-270, 311-325, 334-346. 
 Williams, T. 1853-57. On the Mechanism of Aquatic Respiration and on the Structure 
 
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456 ENTOMOLOGY 
 
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LITERATURE 457 
 
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 Poulton, E. B. 1892. Further experiments upon the colour-relation between certain 
 
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 Ent. Soc. London, pp. 293-487, pis. 14, 15. 
 
458 ENTOMOLOGY 
 
 Urech, F. 1892. Bebachtungen uber die zeitlicbe Succession der Auf tretens der Farben- 
 
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LITERATURE 459 
 
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460 ENTOMOLOGY 
 
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LITERATURE 4OI 
 
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 Moulton, J. C. 1909. On Some of the Principal Mimetic (Miillerian) Combinations of 
 
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 Gerould, J. H. 1916. Mimicry in Butterflies. Amer. Nat., vol. 50, pp. 184-192. 
 Yoimg, R. T. 1916. Some Experiments on Protective Coloration. Journ. Exp. Zool., 
 
 vol. 20, pp. 457-507, 8 figs., 3 pis.* 
 Carpenter, G. D. 1921. Experiments on the Relative Edibility of Insects, with Special 
 
 Reference to Their Coloration. Trans. Ent. Soc. London, pp. 1-105. 
 
 INSECTS IN RELATION TO PLANTS 
 
 Darwin, C. 1877. The Effects of^Cross and Self Fertilisation in the Vegetable Kingdom. 
 8 + 482 pp. New York. D. Appleton & Co. 
 
462 ENTOMOLOGY 
 
 Lubbock, J. 1882. On British Wild Flowers considered in Relation to Insects. Ed. 4. 
 
 16 + 186 pp., 130 figs. London. Macmillan & Co. 
 Muller, H, 1883. The Fertilisation of Flowers. 12+669 pp., 186 figs. London. Mac- 
 millan & Co. 
 Darwin, C. 1884. The Various Contrivances by which Orchids are fertilised by Insects. 
 
 Ed. 2. 16 + 300 pp., 38 figs. New York. D. Appleton & Co. 
 Darwin, C. 1884. Insectivorous Plants. 10 + 462 pp., 30 figs. New York. D. 
 
 Appleton & Co. 
 Forbes, S. A. 1886. Studies on the Contagious Diseases of Insects. Bull. 111. St. Lab. 
 
 Nat. Hist., vol. 2, pp. 257-321, i pi. 
 Thaxter, R. 1888. The Entomophthoreae of the United States. Mem. Bost. Soc. Nat. 
 
 Hist., vol. 4, pp. 133-201, pis. 14-21. 
 Robertson, C. 1889-99. Flowers and Insects. I-XIX. Bot. Gaz., vols. 14-22, 25, 28. 
 Seitz,A. 1890,1893,1894. Allgemeine Biologie der Schmetterlinge. Zool. Jahrb., Abth. 
 
 Syst., etc., bd. 5, pp. 281-343; bd. 7, pp. 131-186, 823-851.* 
 Eckstein, K. 1891. Pflanzengallen und Gallentiere. 88 pp., 4 taf. Leipzig. R. Freese. 
 Robertson, C. 1891-96. Flowers and Insects. Trans. Acad. Sc, St. Louis, vols. 5-7. 
 Cooke, M. C. 1892. Vegetable Wasps and Plant Worms. 5 + 364 pp., 4 pis., 51 figs. 
 
 London. 
 Riley, C. V. 1892. Some Interrelations of Plants and Insects. Proc. Biol. Soc. Wash., 
 
 vol. 7, pp. 81-104, figs. 1-15. 
 Riley, C. V. 1892. The Yucca Moth and Yucca Pollination. Third Ann. Rept. Mo. 
 
 Bot. Garden, pp. 99-158, pis. 34-43- 
 Moller, A. 1893. Die Pilzgarten einiger siidamericanischer Ameisen. • Bot. Mitt, aus den 
 
 Tropen, heft 6. 7 + 127 pp., 7 taf., 4 figs. Jena. G.Fischer. 
 Trelease, W. 1893. Further Studies of Yuccas and their Pollination. Fourth Ann. 
 
 Rept. Mo. Bot. Garden, pp. 181-226, pis. 1-23. 
 Adler, H., and Straton, C. R. 1894. Alternating Generations. A Biological Study of 
 
 Oak Galls and Gall Flies. 40 + 198 pp., 3 pis. Oxford. Clarendon Press.* 
 Webster, F. M. 1894. Vegetal Parasitism among Insects. Journ. Columbus Hort. Soc, 
 
 pp. 1-19, pis. 3-5, figs. I, 2. 
 Heim, F. L. 1898. The Biologic Relations between Plants and Ants. Ann. Rept. Smiths. 
 
 Inst. 1896, pp. 411-455, pis. 17-22. Trans, from Compt. rend. 24me Sess. Ass. 
 
 fr. I'av. Sc. 189s, pp. 31-75- 
 Schimper, A. F. W. 1898. Pflanzen-Geographie auf physiologischer Grundlage. 18 + 
 
 876 pp., 502 figs., 5 plates, 4 maps. Jena. G. Fischer. (See pp. 147-170.)* 
 
 Trans: 1903. W. R. Fischer. Plant-Geography upon a Physiological Basis. 
 
 30 + 839 pp., 502 figs., 4 maps. Oxford, Clarendon Press. (See pp. 126-156.)* 
 Needham, J. G. 1900. The Fruiting of the Blue Flag (Iris versicolor L.) . Amer. Nat., 
 
 vol. 34, pp- 361-386, pi. I, figs. 1-4. 
 Gibson, W.H. 1901. Blossom Hosts and Insect Guests. 19 + 197 pp., figs. New York. 
 
 Newson & Co. 
 Connold, E. T. 1902. British Vegetable Galls. 12 + 312 pp., 130 pis., 10 figs. New 
 
 York. E. P. Dutton & Co. 
 CookjM.T. 1902-04. Galls and Insects Producmg Them. Pts. MX. Ohio Nat., vols. 
 
 2-4, pis. Same, Bull. Ohio St. Univ., ser. 6, no. 15; ser. 7, no. 20; ser 8, no. 13. 
 Needham, J. G. 1903. Button-Bush Insects. Psyche, vol. 10, pp. 22-31. 
 Cowan, T. W. 1904. The Honey Bee: its Natural History, Anatomy and Physiology. 
 
 Ed. 2. 12 + 220 pp., 73 figs. London. Houlston & Sons.* 
 Rossig, H. 1904. Von welchen Organen der Gallwespenlarven geht der Reiz zur Bildung 
 
 der Pflanzengalle aus? Zool. Jahrb., Abth. Syst., etc., bd. 20, pp. 19-90, taf. 
 i-6.* 
 
LITERATURE 463 
 
 Chadwick, G. H. 1908. Catalogue of the "Phytoptid ' Galls of North America. In 
 
 Bull. N. Y. State Mus., no. 124, pp. 1 18-155.* 
 Casteel, D. B. 1912. The Manipulation of the Wa.x Scales of the Honey Bee. Circ. 161, 
 
 U. S. Dept. Agr., Bur. Ent. 13 pp., 7 figs. 
 Casteel, D. B. 1912. The Behavior of the Honey Bee in Pollen Collecting. Bull. 121, 
 
 U. S. Dept. Agr., Bur. Ent. 36 pp., 9 figs.* 
 Cosens,A. 1912. A Contribution to the Morphology and Biology of Insect Galls. Trans. 
 
 Canadian Inst., vol. 9, pp. 297-387, 13 pis., 9 figs. 
 Thompson, S. M. 1915. An Illustrated Catalogue of American Insect Galls. 116 pp., 
 
 21 pis. Ed. by E. P. Felt. R. I. Hospital Trust Co. Nassau, Rensselaer Co., 
 
 N. Y. 
 Felt, E. P. 1917. Key to American Insect Galls. Bull. N. Y. State Mus., no. 200. 
 
 310 pp., 250 figs., 16 pis.* 
 Rand, F. V., and Pierce, W. D. 1920. A coordination of our knowledge of insect trans- 
 mission in plant and animal diseases. Phytopathology, vol. 10, pp. 189-231.* 
 
 INSECTS IN RELATION TO OTHER ANIMALS 
 
 Aughey, S. 1878. Notes on the Nature of the Food of the Birds of Nebraska. First 
 
 Rept. U. S. Ent. Comm., Appendix 2, pp. 13-62. 
 Forbes, S. A. 1878. The Food of Illinois Fishes. Bull. 111. St. Lab. Nat. Hist., vol. i, no. 
 
 2, pp. 71-89. 
 Forbes, S. A. 1880. The Food of Birds. Trans. 111. St. Hort. Soc, vol. 13 (1879), pp. 
 
 120-172. 
 Forbes, S. A. 1880. On Some Interactions of Organisms. Bull. 111. St. Lab. Nat. Hist., 
 
 vol. I, no. 3, pp. 3-17. 
 Forbes, S. A. 1880. The Food of Fishes. Bull. 111. St. Lab. Nat. Hist., vol. i, no. 3, pp. 
 
 18-65. 
 Forbes, S. A. 1880. On the Food of Young Fishes. Bull. 111. St. Lab. Nat. Hist., vol. i, 
 
 no. 3, pp. 66-79. 
 Forbes, S. A. 1880. The Food of Birds. Bull. 111. St. Lab. Nat. Hist., vol. i, no. 3, pp. 
 
 80-148. 
 Forbes, S. A. 1883. The Regulative Action of Birds upon Insect Oscillations. Bull. 
 
 111. St. Lab. Nat. Hist., vol. i, no. 6, pp. 3-32. 
 Forbes, S. A. 1883. The Food of the Smaller Fresh- Water Fishes. Bull. 111. St. Lab. 
 
 Nat. Hist., vol. i, no. 6, pp. 65-94. 
 Forbes, S. A. 1883. The First Food of the Common White-Fish. Bull. 111. St. Lab. Nat. 
 
 Hist., vol. I, no. 6, pp. 95-109. 
 Dimmock, G. 1886. Belostomidae and some other Fish-destroying Bugs. Ann. Rept. 
 
 Fish Game Comm. Mass., pp. 67-74, i fig.* 
 Forbes, S. A. 1888. Studies on the Food of Fresh- Water Fishes. Bull. 111. St. Lab. Nat. 
 
 Hist, vol. 2 pp. 433-473- 
 Forbes, S. A. 1888. On the Food Relations of Fresh- Water Fishes: a Summary and 
 
 Discussion. Bull. 111. St. Lab. Nat. Hist., vol. 2, pp. 475-538. 
 Wilcox, E.V. 1892. The Food of the Robin. Bull. Ohio Agr. Exp. Sta., no. 43, pp. 115- 
 
 131- 
 Beal, F. E. L. 1897. Some Common Birds in their Relations to Agriculture. Farmer's 
 
 Bull. U. S. Dept. Agric, no. 54, pp. 1-40, figs. 1-22. 
 Kirkland, A. H. 1897. The Habits, Food and Economic Value of the American Toad. 
 
 Bull. Hatch Exp. Sta. Mass. Agr. Coll., no. 46, pp. 3-30, pi. 2. 
 Judd, S. D. 1899. The EflBciency of Some Protective Adaptations in Securing Insects 
 
 from Bir ds. Amer. Nat., vol. 33, pp. 461-484. 
 
464 ENTOMOLOGY 
 
 Palmer, T. S. 19C0. A Review of Economic Ornithology. Yearbook U. S. Dept. Agric. 
 
 1899, pp. 259-292. 
 Judd, S, D. 1901. The Food of Nestling Birds. Yearbook U. S. Dept. Agric. 1900, pp. 
 
 411-436, pis. 49-53, figs. 48-56. 
 Forbes, S. A. 1903. Studies of the Food of Birds, Insects and Fishes. Second Ed. Bull. 
 
 111. St. Lab. Nat. Hist., vol. i, no. 3. 
 Weed, C. M., and Dearborn, N. 1903. Birds in their Relations to Man. 8 + 380 pp., 
 
 figs. Philadelphia and London. J. B. Lippincott Co.* 
 Washburn, F. L. 1918. Injurious Insects and Useful Birds. 18 + 453 pp., 414 figs., 
 
 4 pis. Philadelphia and London. J. B. Lippincott Co. 
 Undefhill, B. M. 1920. Parasites and Parasitosis of the Domestic Animals. 19 + 379 
 
 pp., 172 figs., 8 pis. New York. The Macmillan Co. 
 
 INSECTS IN RELATION TO DISEASES 
 
 Kanthack, A. A., Durham, H. E., and Blandford, W. F. H. 1898. On Nagana, or Tsetse 
 
 fly disease. Proc. Roy. Soc. Lond., vol. 64, pp. 100-118. 
 Finlay, C. J. 1899. Mosquitoes considered as Transmitters of Yellow Fever and Malaria. 
 
 Psyche, vol. 8 pp. 379-384. 
 Nuttall, G. H. F. 1899. On the role of Insects, Arachnids and Myriapods, as carriers in 
 
 the spread of Bacterial and Parasitic Diseases of Man and Animals. A Critical 
 
 and Historical Study. Johns Hopk. Hosp. Rept., vol. 8, no. i, 154 pp., 3 pis. 
 Ross, R. 1899. Life-History of the Parasites of Malaria. Nature, vol. 60, pp. 322-324. 
 Chiisly, C. 1900. Mosquitoes and Malaria: a summary of knowledge on the subject up 
 
 to date; with an account of the natural history of mosquitoes. 9 + 80 pp., 5 pis. 
 
 London. 
 Howard, L. O. 1900. Notes on the Mosquitoes of the United States: giving some account 
 
 of their structure and biology, with remarks on remedies. Bull. U. S. Dept. Agric, 
 
 Div. Ent., no. 25 (n. s.), 70 pp., 22 figs. 
 Howard, L. O. 1900. A contribution to the study of the insect fauna of human excrement 
 
 (with especial reference to the spread of typhoid fever by flies) . Proc. Wash. Acad. 
 
 Sc, vol. 2, pp. 541-604, pis. 30, 31, figs. 17-38. 
 Ross, R. 1900. Malaria and Mosquitoes. Nature, vol. 61, pp. 522-527. 
 Ross. R., and Fielding-Otild, R. 1900. Diagrams illustrating the Life-history of the 
 
 Parasites of Malaria. Quart. Journ. Micr. Sc, vol. 43 (n. s.), pp. 571-579, pis. 30, 
 
 31- 
 Grassi, B. 1901. Die Malaria-Studien eines Zoologen. 8 + 250 pp., 8 taf. Jena. G. 
 
 Fischer. 
 Howard, L. O. 1901. ^Mosquitoes; how they live; how they carry disease; how they are 
 
 classified; how they may be destroj^ed. 15 -f- 241 pp., 50 figs., i pi. New York. 
 
 McClure, Phillips & Co. 
 Sternberg, G. M. 1901. The Transmission of Yellow Fever by Mosquitoes. Pop. Sc. 
 
 Mon., vol. 59, pp. 225-241. 
 ■Howard, L. O. 1902. Insects as Carriers and Spreaders of Disease. Year-book U. S. 
 
 Dept. Agric. 1901, pp. 177-192, figs. 5-20. 
 Braxm, M. 1903. Die thierischen Parasiten des Menschen. Rev. Ed. 12-1-360 pp., 
 
 272 figs. Wiirzburg. 
 Sternberg, G. M. 1903. Infection and Immunity; with special Reference to the Preven- 
 tion of Infectious Diseases. 5 + 293 pp., 12 figs. New York and London. G. P. 
 
 Putman's Sons. 
 Blanchard, R. 1905. Les ]\Ioustiques, histoire naturelle et medicale. 673 pp., 316 figs. 
 
 Paris. De Rudeval. 
 
LITERATURE 465 
 
 Austen, E. E. 1903. A Monograph of the Tsetse FHes. 9 + 319 pp., 9 pis. London. 
 
 British Museum. 
 Braun, M. 1906. The Animal Parasites of Man. Trans. Sambon and Theobald. 19 + 
 
 453 PP-> 294 figs. New York. Wm. Wood & Co. 
 Bruce, D. 1907. Trypanosomiasis.- In Osier's Modern Medicine, vol. i, pp. 460-487, 
 
 tigs. 31-34, pi. 4. Philadelphia and New York. Lea Bros. & Co. 
 Calvert, W. J. 1907. Plague. In Osier's Modern Medicine, vol. 2, pp. 760-780. 
 
 Philadelphia and New York. Lea Bros. & Co. 
 Carroll, J. 1907. Yellow Fever. In Osier's Modern Medicine, vol. 2, pp. 736-759. 
 
 Philadelphia and New York. Lea Bros. & Co. 
 Craig, C. F. 1907. The Malarial Fevers. In Osier's Modern Medicine, vol. i, pp. 392- 
 
 448, figs. 26-30, pis. 1-3. Philadelphia and New York. Lea Bros. & Co. 
 Griinberg, K. 1907. Die blutsaugenden Dipteren. 6 + 188 pp. Jena. G. Fischer. 
 Jackson, T.W. 1907. Tropical Medicine. 8 + 536 pp., 106 figs. Philadelphia. P. 
 
 Blakiston's Son & Co. 
 Laveran, A., and Mesnil, F. 1907. Trypanosomes and Trypanosomiases. Trans. D. 
 
 Nabarro. 19 + 538 pp., 81 figs., i pi. London. Bailliere, Tindall & Co.* 
 Mitchell, E. G. 1907. Mosquito Life. 22 + 281 pp., 54 figs. New York and London. 
 
 G. P. Putnam's Sons. 
 Stephens, J. W. W., and Christophers, S. R. 1908. The Practical Study of Malaria and 
 
 Other Blood Parasites. Ed. 3. 18 + 414 pp., 128 figs. London. Williams and 
 
 Norgate. 
 Boyce, R. W. 1909. Mosquito or Man? The Conquest of the Tropical World. 16 + 
 
 267 pp., 44 figs. London. John Murray. 
 Calkins, G. N. 1909. Protozoology. 9 + 349 PP-, 125 figs., 4 pis. New York and 
 
 Phila. Lea & Febiger.* 
 Thimm, C. A. 1909. Bibliography of Trypanosomiasis. 22S pp. London. ^^Sleeping 
 
 Sickness Bureau. 
 Braun, M., and Liihe, M. 1910. A Handbook of Practical Parasitology. Tr. L. Forster. 
 
 8 + 208 pp., 100 figs. London. John Bale, Sons & Danielsson. 
 Doane, R. W. 1910. Insects and Disease. 14 +227 pp., 112 figs., i pi. New York. 
 
 Henry Holt & Co.* 
 Austen, E.E. 1911. A Handbook of the Tsetse-flies (Genus Glossina). 10 + no pp., 24 
 
 figs., 10 pis. London. British Museum. 
 Doane, R. W. 1911, 1912. An Annotated List of the Literature on Insects and Disease. 
 
 Journ. Econ. Ent., vol. 4, pp. 386-398; vol. 5, pp. 268-285. 
 Howard, L. O. 1911. The House Fly; Disease Carrier. 19 + 312 pp., 40 figs., r pi. 
 
 New York. F. A. Stokes Co.* 
 Manson, P. 1911. Tropical Diseases. Ed. 6. 22 + 968 pp., 254 figs., 15 pis. 
 
 London and New York. Cassell & Co. 
 Reed, W., Carroll, J., Gorgas, W. C, and others. 1911. Yellow Fever; a Compilation of 
 
 Various Publications. Doc. No. 822, U. S. Senate, 6ist Congress. 250 pp., 7 figs., 
 
 5 pis. Washington. Govt. Printing Office. 
 Brues, C. T. 1913. The Relation of the Stable Fly (Stomoxys calcitrans) to the Trans- 
 mission of Infantile Paralysis. Journ. Econ. Ent., vol., 6, pp. 101-109. 
 Herms, W. B. 1915. Medical and Veterinary Entomology. 12 + 393 PP-. 228 figs. 
 
 New York. The Macmillan Co. 
 Riley, W. A., and Johannsen, O. A. 1915. Handbook of Medical Entomology. 9 + 348 
 
 pp., 174 figs. Ithaca, N. Y. Comstock Pub. Co.* 
 Chandler, A. C. 1918. Animal Parasites and Human Disease. 13 + 570 pp., 254 figs. 
 
 New York. John Wiley & Sons, Inc.* 
 
466 ENTOMOLOGY 
 
 Pierce, W. D. 1921. Sanitary Entomology, Entomology of Disease, Hygiene and Sanita- 
 tion. 26 + 518 pp., 88 figs. Boston. R. G. Badger.* 
 
 INTERRELATIONS OF INSECTS 
 
 Van Beneden, P. J. 1876, Animal Parasites and Messmates. 28 + 274 pp., 83 figs. 
 
 New York. D. Appleton & Co. 
 McCook, H. C. 1877. Mound-making Ants of the Alleghenies, their Architecture and 
 
 Habits. Trans. Amer. Ent. Soc, vol. 6, pp. 253-296, figs. 1-13. 
 Fabre, J. H. 1879-1905. Souvenirs entomologiques. Etudes sur I'instinct et les moeurs 
 
 des insectes. 9 Series. Paris. C. Delagrave. Trans, of Ser. I: 1901. Fatre, 
 
 J. H. Insect Life. 12 + 320 pp., 16 pis. London and New York. The Mac- 
 
 millan Co 
 Forbes, S. A. 1880. Notes on Insectivorous Coleoptera. Bull. 111. St. Lab. Nat. Hist., 
 
 vol. I, no. 3, pp. 153-169. Second Ed., 1903. 
 McCook, H. C. 1880. The Natural History of the Agricultural Ant of Te.xas. 310 pp., 
 
 24 pis. Philadelphia. J. B. Lippincott & Co. 
 Webster, F. M. 1880. Notes upon the Food of Predaceous Beetles. Bull. 111. St. Lab. 
 
 Nat. Hist., vol. i, no. 3, pp. 149-152. Second Ed., 1903. 
 McCook, H. C. 1881. Note on a new Northern Cutting Ant, Atta septentrionalis. Proc. 
 
 Acad. Nat. Sc. Phila. 1880, pp. 359-363, i fig. 
 McCook, H. C. 1881. The Shining Slavemaker. Notes on the Architecture and Habits 
 
 of the American Slave-making Ant, Polyergus lucidus. Proc. Acad. Nat. Sc. 
 
 Phila. 1880, pp. 376-384, pi. 19. 
 Lubbock, J. 1882, 1902, 1904. Ants, Bees and Wasps. 19 + 448 pp., 31 figs., 5 pis. 
 
 New York. D. Appleton & Co. 
 McCook, H. C. 1882. The Honey Ants of the Garden of the Gods, and the Occident Ants 
 
 of the American Plains. 188 pp., 13 pis. Philadelphia. J. B. Lippincott & Co. 
 Forbes, S. A. 1883. The Food Relations of the Carabidae and Coccinellidae. Bull. 111. 
 
 St. Lab. Nat. Hist., vol. i, no. 6, pp. 33-64. 
 Cheshire, F. R. 1886. Bees and Bee-keeping. 2 vols. Vol. i, 7 + 336 pp., 8 pis., 71 
 
 figs; vol. 2, 652 pp., 127 figs., I pi. London. L. Upcott Gill. 
 Seitz, A. 1890, 1893, 1894. Allgemeine Biologie der Schmetterlinge. Zool. Jahrb., Abth. 
 
 Syst., etc., bd. 5, pp. 281-343; bd. 7, pp. 131-186, 823-851.* 
 Verhoeff, C. 1892. Beitrage zur Biologie der Hymenoptera. Zool. Jahrb., Abth. Syst., 
 
 etc., bd. 6, pp. 680-754, taf. 30, 31. 
 Wasmann, E. 1894. Kritisches Verzeichnis der myrmekophUen und termitophilen 
 
 Arthropoden. 231 pp. Berlin. F. L. Dames. 
 Grassi, B., and Sandias, A. 1896-97. The Constitution and Development of the Society 
 
 of Termites, etc. Trans, by W. F. H. Blandford. Quart. Journ. Micr. Sc, vol. 
 
 39, pp. 245-322, pis. 16-20; vol. 40, pp. 1-75. 
 Janet, C. 1896. Les Fourmis. Bull. Soc. zool. France, vol. 21, pp. 60-93. Sep., 37 pp. 
 
 Paris. 
 Howard, L. O. 1897. A Study in Insect Parasitism. Bull. U. S. Dept. Agric, Div. Ent., 
 
 tech. ser. no. 5, pp. 1-57, figs. 1-24. 
 Peckham, G. W., and E. G. 1898. On the Instincts and Habits of the Solitary Wasps. 
 
 Bull Wis. Geol. Nat. Hist. Surv., no. 2, sc. ser. no. i, 4 + 245 pp., 14 pis. 
 Wasmann, E. 1898, Die Gaste der Ameisen und Termiten. Illustr. Zeits. Ent., bd. 3, 
 
 I taf. 
 Benton, F. 1899. The Honey Bee: A Manual of Instruction in Apiculture. Bull. U. S. 
 
 Dept. Agric, Div. Ent., no. 1 (n. s.), pp, 1-118, pis. i-n, figs. 1-76.* 
 Fielde, A. M. 1901. A Study of an Ant. Proc. Acad. Nat. Sc. Phila., vol. 53, pp. 425- 
 
 449- 
 
LITERATURE 467 
 
 Fielde, A. M. 1901. Further Study of an Ant. Proc. Acad. Nat. Sc. Phila., vol. 53, pp. 
 
 521-544- 
 Wheeler, W. M. 1901. The Compound and Mixed Nests of American Ants. Amer. Nat. , 
 
 vol. 35, pp. 4.31, 513, 701, 791, figs. 1-20. 
 Enteman, M. M. 1902. Some Observations on the Behavior of the Social Wasps. Pop. 
 
 Sc. Men., vol. 61, pp. 339-351- 
 Fielde, A.M. 1902. Notes on an Ant. Proc. Acad. Nat. Sc. Phila., vol. 54, pp. 599-625. 
 Dickel, F. 1903. Die Ursachen der geschlechtlichen DifTerenzirung im Bienenstaat. 
 
 Archiv. ges. Phys., bd. 95, pp. 66-106, fig. i. 
 Fielde, A. M. 1903, Supplementary Notes on an Ant. Proc. Acad. Nat. Sc. Phila., vol. 
 
 55. PP- 491-495- 
 Heath, H. 1903. The Habits of California Termites. Biol. Bull., vol. 4, pp. 47-63, figs. 
 
 1-3- 
 Janet, C. 1903. Observations sur les guepes. 85 pp., 30 figs. Paris. C. Naud. 
 Melander, A. L., and Brues, C. T. 1903. Guests and Parasites of the Burrowing Bee 
 
 Halictus. Biol. Bull., vol. 5, pp. 1-27, figs. 1-7. 
 Fielde, A. M. 1904. Power of Recognition among Ants. Biol. Bull, vol. 7, pp. 227-250, 
 
 4 figs- 
 Fielde, A. M., and Parker, G. H. 1904. The Reactions of Ants to Material Vibrations. 
 
 Proc. Acad. Nat. Sc. Phila., vol. 56, pp. 642-650.* 
 Wheeler, W. M. 1904. A New Type of Social Parasitism among Ants. Bull. Amer. 
 
 Mus. Nat. Hist., vol. 20, pp. 347-375. 
 Emery, C. 1904. Zur Kenntniss des Polymorphismus der Ameisen. Zool. Jahrb., Sup- 
 plement, bd. 7, pp. 587-610, 6 figs. 
 Forel, A. 1904. Ueber Polymorphismus und Variation bei den Ameisen. Zool. Jahrb., 
 
 Supplement, bd. 7, pp. 571-586. 
 Peckham, G. W., and E. G. 1906. Wasps, Social and Solitary. 15 + 311 pp. Boston 
 
 and New York. Houghton, Mifflin & Co. 
 Holmgren, N. 1906. Studien liber sudamerikanische Termiten. Zool. Jahrb., Abt. 
 
 Anat. Ont., bd. 23, pp. 521-676, 81 figs.* 
 Wheeler, W. M. 1906. The Habits of the Tent-building Ant (Cremastogaster lineolata 
 
 Say). Bull. Amer. Mus. Nat. Hist., vol. 22, pp. 1-18, pis. 1-6. 
 Wheeler, W. M. 1906. On the Founding of Colonies by Queen Ants, etc. Bull. Amer. 
 
 Mus. Nat. Hist., vol. 22, pp. 33-105, pis. 8-14. 
 Wheeler, W. M. 1907. The Polymorphism of Ants, with an Account of Some Singular 
 
 Abnormalities due to Parasitism. Bull Amer. Mus. Nat. Hist., vol. 23, pp. 1-93, 
 
 pis. 1-6. 
 Wheeler, W. M. 1907. The Fungus-growing Ants of North America. Bull. Amer. Mus. 
 
 Nat. Hist., vol. 23, pp. 669-807, pis. 49-53, 31 figs.* 
 Pricer, J. L. 1908. The Life History of the Carpenter Ant. Biol. Bull, vol. 14, pp. 177- 
 
 218, figs. 1-7.* 
 Donisthorpe, J. K. 1910. Some Experiments with Ants' Nests. Trans. Ent. Soc. 
 
 London, pp. 142-150. 
 Wheeler, W. M. 1910. Ants; their Structure, Development and Behavior. 25 + 663 
 
 pp., 286 figs., I pi. New York. Columbia Univ. Press.* 
 Crawley, W. C. 1912. Parthenogenesis in Worker Ants, with Special Reference to Two 
 
 Colonies of Lasius niger Linn. Trans. Ent. Soc. London, 191 1, pp. 657-663.* 
 Sladen, F. W. L. 1912. The Humble-Bee, its Life-History and How to Domesticate it. 
 
 13 -1- 283 pp., 34 figs., 6 pis. London. Macmillan & Co. 
 Fuller, C. 1915. Observations on Some South African Teimites. Ann. Natal Mus., 
 
 vol. 3, pp. 329-504, 16 figs., pis. 25-35. 
 
468 ENTOMOLOGY 
 
 Thompson, C. B. 1917. Origin of the Castes of the Common Termite, Leucotermes 
 
 flavipes Kol. Journ. Morph., vol. 30, pp. 83-153, 8 pis.* 
 Wheeler, W. M. 1918. A study of some ant larvae, with a consideration of the origin and 
 
 meaning of the social habit among insects. Proc. Amer. Phil. Soc, vol. 57, pp. 
 
 293-343, 12 figs. 
 Thompson, C. B. 1919. The Development of the Castes of Nine Genera and Thirteen 
 
 Species of Termites. Biol. Bull., vol. 36, pp. 379-398. 
 Thompson, C. B., and Snyder, T. E. 1919. The Question of the Phylogenetic Origin of 
 
 the Termite Castes. Biol. Bull., vol. 36, pp. 1 15-132. 
 Wheeler, W. M. 1919. The parasitic Aculeata, a study in evolution. Proc. Amer. Phil. 
 
 Soc, vol. 58, pp. 1-40. 
 Banks, N., and Snyder, T. E. 1920. .\ Revision of the Nearctic Termites, with Notes on 
 
 Biology and Geographic Distribution. Bull. U. S. Nat. Mus., no. 108, 8 + 228 
 
 pp., 70 figs., 35 pis.* 
 Wheeler, W. M. 1921. A Study of Some Social Beetles in British Guiana and of Their 
 
 Relations to the Ant-plant Tachigalia. Zoologica, vol. 3, pp. 35-126, 5 pis.* 
 
 INSECT BEHAVIOR 
 
 Pouchet, G. 1872. De I'influence de la lumiere sur les larves de dipteres privees d' organes 
 
 e.xterieurs de la vision. Rev. Mag. Zool, ser. 2, t. 23, pp. 110-117, etc., pis. 12-16. 
 Fabre, J. H. 1879-1905. Souvenirs entomologiques. Etudes sur I'instinct et les moeurs 
 
 des insectes. 9 Series. Paris. C. Delagrave. Trans, of Ser. I: 1901. Fabre, 
 
 J. H. Insect Life. 12 +320 pp., 16 pis. London and New York. The Mac- 
 
 millan Co. 
 Lubbock, J. 1882, 1884. Ants, Bees and Wasps. 19 + 448 pp., 31 figs., 5 pis. New 
 
 York. D. Appleton & Co. 
 Graber, V. 1884. Grundlinien zur Erforschung des Helligkeits- und Farbensinnes der 
 
 Tiere. 8 + 322 pp. Prag und Leipzig. 
 Romanes, G. J. 1884. Animal Intelligence. 14 + 520 pp. New York. D. Appleton 
 
 & Co. 
 Lubbock, J. 1888. On the Senses, Instincts and Intelligence of Animals, with Special 
 
 Reference to Insects. 29 + 292 pp., 118 figs. New York. D. Appleton & Co. 
 Plateau, F. 1889. Recherches e.xperimentales sur la Vision chez les Arthropodes. Mem. 
 
 cour. Acad. roj-. Belgique, t. 43, pp. 1-91. 
 Eimer, G. H. T. 1890. Organic Evolution as the Result of the Inheritance of Acquired 
 
 Characters according to the Laws of Organic Growth. 28 + 435 pp. Trans, by 
 
 J. T. Cunningham. London and New York. Macmillan & Co. 
 Loeb, J. 1890. Der Heliotropismus der Thiere und seine Uebereinstimmung mit dem 
 
 Heliotropismus der Pflanzen. 118 pp. Wiirzburg. 
 Seitz, A. 1890. Allgemeine Biologie der Schmetterlinge. Zool. Jahrb., Abth. Syst., bd. 
 
 5, pp. 281-343. 
 Exner, S. 1891. Die Physiologie der facettirten Augen von Krebsen und Insecten. 8 + 
 
 206 pp., 8 taf., 23 figs. Leipzig und Wien. 
 Loeb, J. 1891. Ueber Geotropismus bei Thieren. Arch. ges. Phys., bd. 49, pp. 175-189, 
 
 figs. 
 Morgan, C. Lloyd. 1891. Animal Life and Intelligence. 13 + 512 pp., 40 figs. Boston. 
 
 Ginn & Co. 
 James, W. 1893. The Principles of Psychology. 2 vols. 18 + 1393 pp., 94 figs. New 
 
 ' York. Henry Holt & Co. 
 Loeb, J. 1893. Ueber kunstliche Umwandlung positiv heliotropischer Thiere in negativ 
 
 heliotropische und umgekehrt. Arch. ges. Phys., bd. 54, pp. 81-107. 
 
LITERATURE 469 
 
 Baldwin, J. M. 1896. Heredity and Instinct. Science, vol. 3 (n. s.), pp. 438-441, 558- 
 
 561. 
 Morgan, C. Lloyd, 1896. Habit and Instinct. 351 pp. London and New York. E. 
 
 Arnold. 
 Davenport, C. B. 1897, 1899. E.xperimental Morphology. 2 Pts. 32 + 508 pp, 140 
 
 figs. New York and London. The Macmillan Co. 
 Loeb, J. 1897. Zur Theorie der physiologischen Licht- und Schwerkraftwirkungen. 
 
 Arch. ges. Phys., bd. 64, pp. 439-466. 
 Bethe, A. 1898. Durfen wir den Ameisen und Bienen psychische Qualitaten zuschreiben? 
 
 Archiv ges. Phys., bd. 70. pp. 15-110, taf. i, 2, 5 figs. 
 Peckham, G. W., and E. G. 1898. On the Instincts and Habits of the Solitary Wasps. 
 
 Bull. Wis. Geol. Nat. Hist. Surv., no. 2, so. ser. no. i. 4 + 245 pp., 14 pis. 
 Verwom, M. 1899. General Physiology. An Outline of the Science of Life. Trans. 
 
 by F. S. Lee. 16 + 615 PP-> 285 figs. London and New York. Macmillan & Co. 
 Wasmann, E. 1899. Die psychischen Fahigkeiten der Ameisen. Zoologica, heft 26. 
 
 6 + 132 pp., 3 taf. Stuttgart. E. Nagele. 
 Wheeler, W. M. 1899. Anemotropism and Other Tropisms in Insects. Arch. Entw. Org., 
 
 bd. 8, pp. 373-381. 
 Whitman, C. O. 1899. Animal Behavior. Biol Lect., Marine Biol. Lab., Woods Hole, 
 
 Mass., 1898, pp. 285-338. Boston. Ginn & Co. 
 Loeb, J. 1900. Comparative Physiology of the Brain and Comparative Psychology. 309 
 
 pp., 39 figs. New York, G. P. Putnam's Sons. London, J. Murray.* 
 Morgan, C. Lloyd. 1900. Animal Behaviour. 8 + 344 pp., 26 figs. London. E. 
 
 Arnold. 
 Radl, E. 1901. Ueber den Phototropismus einiger Arthropoden. Biol. Centralb., bd. 
 
 21, pp. 75-86. 
 Radl, E. 1901. Untersuchungen iiber die Lichtreactionen der Arthropoden. Arch. ges. 
 
 Phys., bd. 87, pp. 418-466. 
 Enteman, M. M. 1902. Some Observations on the Behavior of the Social Wasps. Pop. 
 
 Sc. Mon., vol. 61, pp. 339-351- 
 Weismann, A. 1902. Vortrage iiber Descendenztheorie. 2 vols. 12 + 456 pp., 95 figs.; 
 
 6 + 462 pp., 3 pis., 36 figs. Jena. G. Fischer. See pp. 159-181. 
 Kathariner, L. 1903. Versuche iiber die Art der Orientierung bei der Honigbiene. Biol. 
 
 Centralb., bd. 23, pp. 646-660, i fig. 
 Morgan, T. H. 1903. Evolution and Adaptation. 13 + 470 pp., 5 figs. New York and 
 
 London. The Macmillan Co. 
 Parker, G. H. 1903. The Phototropism of the Mourning-cloak Butterfly, Vanessa antiopa 
 
 Linn. Mark Anniv. Vol., pp. 453-469, pi. ^s-* 
 Fielde, A. M., and Parker, G. H. 1904. The Relations of Ants to Material Vibrations. 
 
 Proc. Acad. Nat. Sc. Phila., vol. 56, pp. 642-650.* 
 Forel, A. 1904. The Psychical Faculties of Ants and some other Insects. Ann. Rept. 
 
 Smiths. Inst. 1903, pp. 587-599. Trans, from Proc. Fifth Intern. Zool. Congr. 
 
 Berlin, 1901, pp. 141-169. 
 Jennings, H. S. 1904. Contributions to the Study of the Behavior of Lower Organisms. 
 
 256 pp., 81 figs. Carnegie Inst. Washington.* 
 Carpenter, F. W. 1905. The Reactions of the Pomace Fly (Drosophila ampelophila 
 
 Loew) to Light, Gravity and Mechanical Stimulation. Amer. Nat., vol. 39, pp. 
 
 157-171.* 
 Hartman, C. 1906. Observations on the Habits of some Solitary Wasps of Texas. Bull. 
 
 • Univ. Texas, no. 65, sc. ser. no. 7, pp. 1-73, 4 pis. 
 Holmes, S. J. 1905. The Reactions of Ranatra to Light. Journ. Comp. Neur. Psych., 
 
 vol. 15, pp. 305-349, figs. 1-6. 
 
470 ENTOMOLOGY 
 
 Loeb, J. 1905. Studies in General Physiology. 2 vols. 24 + 782 pp., 162 figs. Univ. 
 
 Chicago Decenn. Publ., ser. 2, vol. 15, pts. i, 2. 
 Wasmann, E. 1905. Comparative Studies in the Psychology of Ants and of Higher Ani- 
 mals. 10 + 200 pp. St. Louis and Freiburg, B. Herder; London and Edinburgh, 
 
 Sands & Co.* 
 Holmes, S. J. 1906. Death-feigning in Ranatra. Journ. Comp. Neur. Psych., vol. 16, 
 
 pp. 200-216. 
 Barrows, W. M. 1907. The Reactions of the Pomace Fly, Drosophila ampelophila Loew, 
 
 to Odorous Substances. Journ. Exp. Zool., vol. 4, pp. 515-537, figs. 1-5. 
 Buckingham, E. N. 1911. Division of Labor Among Ants. Proc. Amer. Acad. Arts. 
 
 Sc, vol. 46, pp. 425-507, I pi.* 
 Herms, W. B. 1911. The Photic Reactions of Sarcophagid Flies, etc. Journ. Exp. Zool., 
 
 vol. 10, pp. 167-226, figs. 1-25.* 
 Mast, S. O. 1911. Light and the Behavior of Organisms. 11 -f- 410 pp., 35 figs. New 
 
 York. John Wiley & Sons.* 
 Severin, H. H. P. and H. C. 1911. An Experimental Study on the Death-Feigning of 
 
 Belostoma (Zaitha Aucct.) flumineum Say and Nepa apiculata Uhler. Be- 
 havior Monogr., vol. i, no. 3, 44 pp., i pi.* 
 Gee, W. P., and Lathrop, F, H. 1912. Death Feigning in Conotrachelus nenuphar Herbst. 
 
 Ann. Ent. Soc. Amer., vol. 5, pp. 391-399, i fig.* 
 Patten, B. M. 1914. A Quantitative Determination of the Orienting Reaction of the 
 
 Blowfly Larva (Calliphora erythrocephala Meigen). Journ. E.xp. Zool., vol. 17, 
 
 pp. 213-280, figs. 1-24.* 
 Dolley, W. L., Jr. 1916. Reactions to light in Vanessa antiopa, with special reference to 
 
 circus movements. Journ. Exp. Zool., vol. 20, pp. 357-420, figs. 1-21.* 
 Loeb, J., and Wasteneys, H. 1916. The Relative Efficiency of Various Parts of the Spec- 
 trum for the Heliotropic Reactions of Animals and Plants. Journ. Exp. Zool., 
 
 vol. 20, pp. 217-236, 6 figs. 
 Cole, W. H. 1917. The Reactions of Drosophila ampelophila Loew to Gravity, Centrifu- 
 
 gation, and Air Currents. Journ. Anim. Behav., vol. 7, pp. 71-80.* 
 Mclndoo, N. E. 1917. Recognition Among Insects. Smiths. Misc. Coll., vol. 68, no. 
 
 2, 78 pp.* 
 Bouvier, E. L. 1918. La Vie psychique des Insectes. 300 pp., 16 figs. Paris. Ernest 
 
 Flammarion.* 
 Lodge, O. C. 1918. An Examination of the Sense-reactions of Flies. Bull. Ent. Res., 
 
 vol. 9, pp. 141-151, 4 pis. 
 Loeb, J. 1918. Forced Movements, Tropisms,. and Animal Conduct. 209 pp., 42 figs. 
 
 Philadelphia. J. B. Lippincott Co.* 
 Rau, P. and N. 1918. Wasp Studies Afield. 372 pp., 68 figs. Princeton, N. J. 
 
 Princeton. Univ. Press. 
 Howes, P. G. 1919. Insect Behavior. 176 pp., many pis. Boston. R. G. Badger. 
 Riley, C. F. C. 1921. Responses of the Large Water-Strider, Gerris remigis Say, to 
 
 Contact and Light. Ann. Ent. Soc. Amer., vol. 14, pp. 231-289, figs. 1-12.* 
 
 GEOGRAPHICAL DISTRIBUTION 
 
 Darwin, C. 1859,1869. On the Origin of Species by means of Natural Selection. Pp- 
 II +440. New York. D. Appleton & Co. See pp. 302-357. 
 
 LeConte, J. L. 1859. The Coleoptera of Kansas and Eastern New Mexico. Smithson. 
 Contrib., vol. 11, 6 -|- 58 pp., 2 pis., map. 
 
 Bates, H. W. 1864. The Naturalist on the River Amazons. 12 -|- 466 pp., figs. London. 
 J. Murray. 
 
LITERATURE 47I 
 
 Wallace, A. R. 1865. On the Phenomena of Variation and Geographical Distribution as 
 
 illustrated by the Papilionidae of the Malayan Region. Trans. Linn. Soc. Zool., 
 
 vol. 25, pp. 1-71, pis. 1-8. 
 "Wallace, A. R. 1869. The Malay Achipelago. 12 + 638 pp., 51 figs., 10 maps. New 
 
 York. Harper & Bros. 
 Murray, A, 1873. On the Geographical Relations of the Chief Coleopterous Faunae. 
 
 Journ. Linn. Soc. Zool, vol. 11, pp. 1-89. 
 Belt, T. 1874, 1888. The Naturalist in Nicaragua. 32 + 403 PP-j figs. London. J. 
 
 MuTTa.y; E. Bumpus. 
 Wallace, A. R. 1876. The Geographical Distribution of Animals. 2 vols. Vol. i, 21 + 
 
 503 pp., 13 pis., 5 maps; vol. 2, 8 + 607 pp., 7 pis., 2 maps. New York. Harper 
 
 & Bros. 
 Semper, K. 1881. Animal Life as affected by the Natural Conditions of Existence. 1 6 + 
 
 472 pp., 106 figs., 2 maps. New York. D. Appleton & Co. 
 Wallace, A. R. 1881. Island Life, or the Phenomena and Causes of Insular Faunas and 
 
 Floras, etc. 16 + 522 pp., 26 maps and figs. New York. Harper & Bros. 
 Gill, T. 1884. The Principles of Zoogeography. Proc. Biol. Soc. Wash., vol. 2, pp. 1-39. 
 Forbes, H. O. 1886. A Naturalist's Wanderings in the Eastern Archipelago. 19 + S36 
 
 pp., figs., pis., maps. New York. Harper & Bros. 
 Schwarz, E. A. 1888. The Insect Fauna of Semitropical Florida, with Special Regard to 
 
 the Coleoptera. Ent. Amer., vol. 4, pp. 165-175. 
 Merriam, C. H. 1890. Results of a Biological Survey of the San Francisco Mountain 
 
 Region and Desert of the Little Colorado, Arizona. U. S. Dept. Agric, Div. 
 
 Ornith. Mamm., N. A. Fauna, no. 3. 6 + 136 pp., 13 pis., 5 maps, 2 figs. 
 Schwarz, E. A. 1890. On the Coleoptera common to North America and other Countries. 
 
 Proc. Ent. Soc. Wash., vol. i, pp. 182-194. 
 Seitz,A. 1890,1893,1894. AUgemeine Biologic der Schmetterlinge. Zool. Jahrb., Abth. 
 
 Syst, etc., bd. 5, pp. 281-343; bd. 7, pp. 131-186, 823-851.* 
 Trouessart, E. L. 1890. La Geographie Zoologique. 11 +338 pp., 63 figs., 2 maps. 
 
 Paris. 
 Wallace, A, R. 1890. A Narrative of Travels on the Amazon and Rio Negro, etc. Ed. 3. 
 
 14 + 363 pp., 16 pis. London, New York and Melbourne. Ward, Lock & Co. 
 Bates, H. W. 1892. The Naturalist on the River Amazons. Reprint. 89 + 395 pp., 
 
 figs. London. J. Murray. 
 Distant, W. L. 1892. A Naturalist in the Transvaal. 16 + 277 pp., pis. figs. London. 
 
 R. H. Porter. 
 Hudson, W.H. 1892. The Naturalist in La Plata. 8 + 388 pp., figs. London. Chap- 
 man & Hall. 
 Webster, F. M. 1892. Modern Geographical Distribution of Insects in Indiana. Proc. 
 
 Ind. Acad, Sc, pp. 81-88, map. 
 Merriam, C. H. 1893. The Geographic Distribution of Life in North American, with 
 
 special Reference to the Mammalia. Smithson. Rept. 1891, pp. 365-415. From 
 
 Proc. Biol. Soc. Wash., vol. 7, pp. 1-64. 
 Elwes, H. J. 1894. The Geographical Distribution of Butterflies. Trans. Ent. Soc. 
 
 London, Proc, pp. 52-84. 
 Hamilton, J. 1894. Catalogue of the Coleoptera common to North America, Northern 
 
 Asia and Europe, with Distribution and Bibliography. Trans. Amer. Ent. Soc, 
 
 vol. 21, pp. 345-416 + 19. 
 Merriam, C. H. 1894. Laws of Temperature Control of the Geographic Distribution of 
 
 Terrestrial Animals and Plants. Nat. Geogr. Mag., vol. 6, pp. 229-238, 3 maps. 
 Scudder, S. H. 1894. The Effect of Glaciation and of the Glacial Period on the Present 
 
 Fauna of North America. Amer. Journ. Sc, sen 3, vol. 48, pp. 179-187. 
 
472 ENTOMOLOGY 
 
 Webster, F. M. 1894. Some Insect Immigrants in Ohio. Bull. Ohio Agr. Exp. Sta., 
 
 ser. 2, vol. 6, no. 51 (1893), pp. 118-129, figs. 17, 18. 
 Whymper, E. 1894. Travels amongst the Great Andes of the Equator. 24 + 456 pp., 
 
 20 pis., 4 maps, 118 figs. New York. C. Scribner's Sons. 1891. Suppl. Ap- 
 pendix. 22 + 147 pp., figs. London. J. Murray. 
 Beddard, F. E. 1895. A Text-book of Zoogeography. 8-1-246 pp., 5 maps. Cambridge, 
 
 England. University Press. 
 Howard, L. O. 1895. Notes on the Geographical Distribution within the United States 
 
 of certain Insects injuring Cultivated Crops. Proc. Ent. Soc. Wash., vol. 3, pp. 
 
 219-226. 
 Webster, F. M. 1895. Notes on the Distribution of some Injurious Insects. Proc. Ent. 
 
 Soc. Wash., vol. 3, pp. 284-290. 
 Webster, F. M. 1896. The Probable Origin and Diffusion of Blissus leucopterus and 
 
 Murgantia histrionica. Journ. Cine. Soc. Nat. Hist., vol. 18, pp. 141-155, fig. i, 
 
 pl- 5. 
 Carpenter, G. H. 1897. The Geographical Distribution of Dragon-flies. Proc. Roy. 
 
 Dublin Soc, vol. 8, pp. 439-468, pl. 17. 
 Heilprm, A. 1897. The Geographical and Geological Distribution of Animals. 12-1-435 
 
 pp., map. New York. D. Appleton & Co. 
 Sairille-Kent, W. 1897. The Naturalist in Australia. 15 + 302 pp., 50 pis., 104 figs. 
 
 London. Chapman & Hall. 
 Webster, F. M. 1897. Biological Effects of Civilization on the Insect Fauna of Ohio. 
 
 Fifth Ann. Rept. Ohio St. Acad. Sc, pp. 32-46, 2 figs. 
 Merriam, C. H. 1898. Life Zones and Crop Zones of the United States. Bull. U. S. 
 
 Dept. Agric, Div. Biol. Surv., no. 10, pp. 1-79, map. 
 Webster, F. M. 1898. The Chinch Bug. Bull. U. S. Dept. Agric, Div. Ent., no. 15 
 
 (n. s.), 82 pp., 19 figs. (See pp. 66-82.) 
 Semon, R. 1899. In the Australian Bush and on the Coast of the Coral Sea, etc. 15 -f- 
 
 552 pp., 4 maps, 86 figs. London and New York. Macmillan & Co. 
 Tower, W. L. 1900. On the Origin and Distribution of Leptinotarsa decem-lineata Say, 
 
 and the Part that some of the Climatic Factors have played in its Dissemination. 
 
 Proc. Amer. Ass. Adv. Sc, vol. 49, pp. 225-227. 
 Adams, C. C. 1902. Postglacial Origin and Migrations of the Life of tlie Northeastern 
 
 United States. Journ. Geogr., vol. i, pp. 303-310, 352-357; rnap. 
 Adams, C. C. 1902. Southeastern United States as a Center of Geographical Distribution 
 
 of Flora and Fauna. Biol. Bull, vol. 3, pp. 115-131.* 
 Tutt, J. W. 1902. The Migration and Dispersal of Insects. 132 pp. London. E. Stock. 
 Webster, F. M. 1902. The Trend of Insect Diffusion in North America. Thirty-second 
 
 Ann. Rept. Ent. Soc. Ontario (1901), pp. 63-67, maps 1-3. 
 Webster, F. M. 1902. Winds and Storms as Agents in the Diffusion of Insects. Amer. 
 
 Nat., vol. 36, pp. 795-801. 
 Webster, F. M. 1903. The Diffusion of Insects in North America. Psyche, vol. 10, pp. 
 
 47-58, pl. 2. 
 Jacobi, A. 1904. Tiergeographie. 152 pp., 2 maps. Leipzig. 
 Morse, A. P. 1904. Researches on North American Acridiidae. Publ. No. 18, Carnegie 
 
 Inst. Wash. 55 pp., 8 pis., 13 figs. 
 Adams, C. C. 1909. The Coleoptera of Isle Royale, Lake Superior, and their Relation to 
 
 the North American Centers of Dispersal. In Adams' Ecol. Survey. Rept. Univ. 
 
 Mich. Mus., pp. 157-191. 
 Shelford, V. E. 1911. Physiological Animal Geography. Journ. Morph., vol. 22, pp. 
 
 551-618, 19 figs. 
 Shamion, H. J. 1915. Do Insects Migrate Like Birds? Harper's Mag., Sept., pp. 
 
 609-618, 7 figs. 
 
LITERATURE 473 
 
 GEOLOGICAL DISTRIBUTION 
 
 Herr, O. 1847-53. Die Insectenfauna der Tertiargebilde von ffiningen und von Radoboj 
 in Croatien. 3 Th. 644 pp., 40 taf. Leipzig. From Neue Denks. schweiz. 
 Gesell. Naturw., bd. 8, 11, 13. 
 Scudder, S. H. 1880. The Devonian Insects of New Brunswick. Ajin. Mem. Bost. See. 
 
 Nat. Hist., 41 pp., I pi. 
 Scudder, S. H. 1882. A Bibliography, of Fossil Insects. Bibl. Contrib. Libr. Harv. Univ. , 
 
 no. 13. 47 pp. Cambridge, Mass.* 
 Scudder, S. H. 1885. The Earliest Winged Insects of America: a Re-e.xamination of the 
 Devonian Insects of New Brunswick, etc. 8 pp., i pi., 2 figs. Cambridge, Mass. 
 Scudder, S. H. 1885. Systematische Uebersicht der fossilen Myriopoden, Arachnoideen 
 und Insekten. In K. A. Zittel: Handbuch der Palaeontologie, abth. i, bd. 2, pp. 
 721-831, figs. 894-1109. Trans. 190c: C. R. Eastman. Text-Book of Palaeon- 
 tology, vol. I, pp. 682-691, figs. ir4i-i476. London and New York. Macmillan 
 & Co.* 
 Scudder, S. H. 1886. The Cockroach of the Past. In L. C. Miall and A. Denny: The 
 Structure and Life-History of the Cockroach, pp. 205-220, figs. 1 19-1 25. London 
 and Leeds.* 
 Scudder, S. H. 1886. Systematic Review of our Present Knowledge of Fossil Insects. 
 
 Bull. U. S. Geol. Surv., no. 31, 128 pp. Washington. 
 Scudder, S. H. 1889. The Fossil Butterflies of Florissant. Eighth Ann. Rept. Dir. U. S. 
 
 Geol. Surv., pp. 433-474, pi. 53. Washington. 
 Scudder, S. H. 1890. The Work of a Decade upon Fossil Insects. Psyche, vol. 5, pp. 
 
 287-295. 
 Scudder, S. H. 1890, A Classed and Annotated Bibliography of Fossil Insects. Bull. 
 
 U. S. Geol. Surv., no. 69, loi pp. Washington.* 
 Scudder, S. H. 1890. The Tertiary Insects of North America. U. S. Geol. Surv. Terr., 
 
 vol. 13, 734 pp., 28 pis., I map, 3 figs. Washington. 
 Scudder, S. H. 1891. Index to the Known Fossil Insects of the World, including Myria- 
 
 pods and Arachnids. Bull. U. S. Geol. Surv., no. 71, 744 PP- Washington.* 
 Scudder, S. H. 1892. Some Insects of Special Interest from Florissant, Colorado, and 
 other Points in the Territories of Colorado and Utah. Bull. U. S. Geol. Surv., no. 
 93, 35 PP-, 3 pls- Washington. 
 Scudder, S. H. 1893. Insect Fauna of the Rhode Island Coal Field. Bull. U. S. Geol. 
 
 Surv., no. loi, 27 pp., 2 pis. Washington. 
 Scudder, S. H. 1893. The American Tertiary Aphidse, with a List of the Known Species 
 and Tables for their Determination. Thirteenth Ann. Rept. U. S. Geol. Surv., pt. 
 2, pp. 341-372, pis. 102-106. Washington. 
 Scudder, S. H. 1893. Tertiary Rhynchophorous Coleoptera of the United States. Mon- 
 
 ogr. U. S. Geol. Surv., vol. 21, 11 -f 206 pp., 12 pis. Washington. 
 Brongniart, C. 1894. Recherches pour servir a I'histoire des insectes fossiles des temps 
 
 primaires, etc. 2 vols. 537 pp., 37 pis. St. Etienne. 
 Scudder, S. H. 1894. Tertiary Tipulidse, with Special Reference to those of Florissant, 
 
 Colorado. Proc. Amer. Phil. Soc, vol. 32, 83 pp., 9 pis. 
 Scudder, S. H. 1896. Revision of the American Fossil Cockroaches, with Descriptions of 
 
 New Forms. Bull. U. S. Geol. Surv., no. 124, 176 pp., 12 pis. Washington. 
 Goss, H. 1900. The Geological Antiquity of Insects. Ed. 2. 4 + 52 PP. London. 
 
 Gurney & Jackson.* 
 Scudder, S. H. 1900. Adephagous and Clavicorn Coleoptera from the Tertiary Deposits 
 at Florissant, Colorado, etc. Monogr. U. S. Geol. Surv., vol. 40, 148 pp-, n pls. 
 Washington. 
 
474 ENTOMOLOGY 
 
 Scudder, S. H. 1900. Canadian Fossil Insects. 4. Additions to the Coleopterous Fauna 
 
 of the Interglacial Clays of the Toronto District, etc. Contrib. Can. Pal., Geol. 
 
 Surv. Can., vol. 2, pp. 67-92, pis. 6-15. Ottawa. 
 Handlirsch, A. 1908. Die Fossilen Insekten und die Phylogenie der Rezenten Formen. 
 
 Ein Handbuch fur Palaontologen und zoologen. 49 + 1430 pp., 14 fig?., 51 pis., 
 
 etc. Leipzig. W. Engelman.* 
 Handlirsch, A. 1920,1921. Palaeontologie. In Schroder: Handbuch der Entomologie, 
 
 bd. 3, pp. 117-306, figs. 52-237.* 
 
 INSECT ECOLOGY 
 
 Davenport, C. B. 1897, 1899. Experimental Morphology. 2 Pts. 29 + 508 pp., 140 
 
 figs. New York and London. The Macmillan Co.* 
 Chittenden, F. H. 1900. Insects and the Weather: Observations During the Season of 
 
 1899. Bull. U. S. Dept. Agric, Div. Ent., no. 22 (n. s.), pp. 51-64. 
 Morgan, T. H. 1903. Evolution and Adaptation. 13 + 470 pp., 7 figs. New York. 
 
 The Macmillan Co. 
 Morse, A. P. 1904. Researches on North American Acridiidae. 55 pp., 13 figs., 8 pis. 
 
 Carnegie Inst. Washington. 
 Clements, F. E. 1905. Research Methods in Ecology. 17 + 334 pp., 85 figs. Lincoln, 
 
 Neb. University Pub. Co.* 
 Hart, C. A., and Gleason, H. A. 1907. On the Biology of the Sand Areas of Illinois. 
 
 BuU. 111. State Lab. Nat. Hist., vol. 7, pp. 137-272, pis. 8-23.* 
 Herms, W. B, 1907. An Ecological and Experimental Study of Sarcophagidae with 
 
 Relation to Lake Beach Debris. Journ. Exp. 2k)ol., vol. 4, pp. 45-83, 7 figs.* 
 Morgan, T. H. 1907. Experimental Morphology. 12 + 454 pp., 25 figs. New York. 
 
 The Macmillan Co. 
 Morse, A. P. 1907. Further Researches on North American Acridiidse. 54 pp., 9 pis.. 
 
 Carnegie Inst. Washington. 
 Shelford, V. E. 1907. Preliminary Note on the Distribution of the Tiger Beetles (Cicin- 
 
 dela)and its Relation to Plant Successsion. Biol. Bull., vol. 14, pp. 9-14. 
 Sanderson, E. D. 1908. The Relation of Temperature to the Hibernation of Insects. 
 
 Journ. Econ. Ent., vol. i, pp. 56-65, 2 figs. 
 Sanderson, E. D. 1908. The Influence of Minimum Temperatures in Limiting the 
 
 Northern Distribution of Insects. Journ. Econ. Ent., vol. i, pp. 245-262, 7 maps. 
 Warming, E. 1909. Oecology of Plants. An Introduction to the Study of Plant- 
 Communities. II +422 pp. Oxford. Clarendon Press.* 
 Bachmetjew, P. 1910. Experimentelle entomologische Studien. 10 + 944 + 108 pp.. 
 
 31 figs. Leipzig. W. Engelmann. 
 Sanderson, E, D. 1910. The Relation of Temperature to the Growth of Insects. Journ . 
 
 Econ. Ent., vol. 3, pp. 1 13-140, figs. 6-26.* 
 Doten, S. B. 1911. Concerning the Relation of Food to Reproductive Activity and 
 
 Longevity in Certain Hymenopterous Parasites. Techn. Bull. Agr. Exp. Sta. 
 
 Univ. Nevada, no. 78, 30 pp., 10 pis. 
 Shelford, V. E. 1911. Ecological Succession. III. A Reconnaissance of its Causes in 
 
 Ponds with Particular Reference to Fish. Biol. Bull., vol. 22, pp. 1-38.* 
 Watson, J. R. 1911. A Contribution to the Study of the Ecological Distribution of the 
 
 Animal Life of North Central New Mexico, with Especial Attention to the Insects. 
 
 Rept. No. I, Natural Resources Survey, Conservation and Natural Resources 
 
 Commission, New Mexico, pp. 67-117. Santa Fe, N. M. New Mexican Print- 
 ing Co. 
 Riley, C. F. C. 1912. Observations on the Ecology of Dragon-fly Nymphs: Reactions to 
 
 Light and Contact. Ann. Ent. Soc. Amer., vol. 5, pp. 273-292.* 
 
LITERATURE 475 
 
 Shelford, V. E. 1912. Ecological Succession. IV. Vegetation and the Control of Land 
 
 Animal Communities. Biol. Bull., vol. 23, pp. 59-99, figs. 1-6.* 
 Shelford, V. E. 1912. Ecological Succession. V. Aspects of Physiological Classifica- 
 tion. Biol. Bull., vol. 23, pp. 331-370.* 
 Adams, C. C. 1913. Guide to the Study of Animal Ecology. 12 + 183 pp., 7 figs. New 
 
 York. The Macmillan Co.* 
 Cameron, A. E. 1913. General Survey of the Insect Fauna of the Soil within a Limited 
 
 Area near Manchester. Journ. Econ. Biol., vol. 8, pp. 159-204, 2 pis.* ' 
 Headlee, T. J. 1913. Some Facts Regarding the Influence of Temperature and Moisture 
 
 Changes on the Rate of Insect Metabolism. Science, n. s., vol. 36, p. 310. 
 Shelford, V. E. 1913. Animal Communities in Temperate America. A Study in Animal 
 
 Ecology. 13+362 pp., 306 figs., 9 diagrams, 2 maps. Chicago. Univ. 
 
 Chicago Press.* 
 Shelford, V. E. 1913. The Reactions of Certain Animals to Gradients of Evaporating 
 
 Power of Air. A Study in Experimental Ecology. Biol. Bull.,vol. 25, pp. 79-120.* 
 Vestal, A. G. 1913. Local Distribution of Grasshoppers in Relation to Plant Associations. 
 
 Biol. Bull., vol. 25, pp. 141-180, I fig.* 
 Vestal, A. G. 1913. An Associational Study of Illinois Sand Prairie. Bull. 111. State Lab. 
 
 Nat. Hist., vol. 10, pp. 1-96, pis. 1-5.* 
 Baxmiberger, J. P. 1914. Studies in the Longevity of Insects. Ann. Ent. Soc. Amer., 
 
 vol. 7, pp. 323-353-* 
 Headlee, T. J. 1914. Some Data on the Effect of Temperature and Moisture on the Rate 
 
 of Insect Metabolism. Journ. Econ. Ent., vol. 7, pp. 413-417. 
 Krogh, A. 1914. On the influence of the temperature on the rate of embryonic develop- 
 ment. Zeits. allgem. Phys., bd. 16, pp. 163-177, figs. 1-8. 
 Krogh, A. 1914. On the rate of development and CO2 production of chrysalides of 
 
 Tenebrio molitor at different temperatures. Zeits. allgem. Phys., bd. i6, pp. 
 
 178-190, figs. 1-3. 
 Parks, T. H. 1914. Effect of Temperature upon the Oviposition of the Alfalfa Weevil 
 
 (Phytonomus posticus Gyllenhal). Journ. Econ. Ent., vol. 7, pp. 417-421, 3 figs. 
 Peairs,L. M. 1914. The Relation of Temperature to Insect Development. Journ. Econ. 
 
 Ent., vol. 7, pp. 174-179, figs. 10-15. 
 Shelford, V. E. 1914. The Importance of the Measure of Evaporation in Economic 
 
 Studies of Insects. Journ. Econ. Ent., vol. 7, pp. 229-233. 
 Shelford, V. E. 1914. An Experimental Study of the Behavior Agreement among the 
 
 Animals of an Animal Community. Biol. Bull., vol. 26, pp. 294-315, figs. 1-41.* 
 Vestal A. G. 1914. Internal Relations of Terrestrial Associations. Amer. Nat., vol. 
 
 48, pp. 413-445- 
 Weiss, H. B. 1914. Thermal Conductivity of Cocoons. Psyche, vol. 21, pp. 45-5°- 
 Bishopp, F. C, Dove, W. E., and Parman, D. C. 1915. Notes on Certain Points of Eco- 
 nomic Importance in the Biology of the House Fly. Journ. Econ. Ent., vol. 
 
 8, pp. 54-71- 
 Bueno, J. R. de la T. 1916. Aquatic Hemiptera. A Study in the Relation of Structure 
 
 to Environment. Ann. Ent. Soc. Amer., vol. 9, pp. 353-365. 
 Rau, P. and N. 1916. The Sleep of Insects; an Ecological Study. Ann. Ent. Soc. 
 
 Amer., vol. 9, pp. 227-274.* 
 Baumberger, J. P. 1917. Hibernation: a Periodical Phenomenon. Ann. Ent. Soc. 
 
 Amer., vol. 10, pp. 179-186.* 
 Elwyn, A. 1917. Effect of Humidity on Pupal Duration and on Pupal Mortality of 
 
 Drosophila ampelophila Loew. Bull. Amer. Mus. Nat. Hist, vol. 37, pp. 347^353- 
 Headlee, T. J. 1917. Some Facts Relative to the Influence of Atmospheric Humidity on 
 
 Insect Metabolism. Journ. Econ. Ent., vol. 10, pp. 31-38. 
 
476 ENTOMOLOGY 
 
 Loeb, J., and Northrop, J. H. 1917. On the Influence of Food and Temperature upon the 
 
 Duration of Life. Journ. Biol. Chem., vol. 32, pp. 103-121. 
 Tillyat'd, R. J. 1917. The Biology of Dragonflies. 12 + 396 pp., 188 figs. Cambridge. 
 
 University Press. 
 Ely, C. R. 1918. Recent Entomological Chemistry and Some Notes concerning the 
 
 Food of Insects. Proc. Ent. Soc. Washington, vol. 20, pp. "12-18. 
 Headlee, T. J. 1918. Climate and Insect Investigations. Rept. Dept. Ent., N. J. Agr. 
 
 E.xp. Sta., 191 7, pp. 442-445- 
 Shelford, V. E. 1918. Physiological Problems in the Life-Histories of Animals with 
 
 Particular Reference to their Seasonal Appearance. Amer. Nat., vol. 52, pp. 129- 
 
 154.* 
 Baumberger, J. P. 1919. A nutritional study of insects with special reference to micro- 
 organisms and their substrata. Journ. Exp. Zool., vol. 28, pp. 1-81, 18 figs.* 
 Riley, C. F. C. 1919. Some Habitat Responses of the Large Water-Strider, Gerris 
 
 remigis Say. Amer. Nat. vol. 53, pp. 394-414; 483-505. 
 Brues, C. T. 1920, The Selection of Food-Plants by Insects, with Special Reference to 
 
 Lepidopterous Larvae. Amer. Nat, vol. 54, pp. 313-332. 
 Dozier, H. L. 1920. An Ecological Study of Hammock and Piney Woods Insects in 
 
 Florida. Ann. Ent. Soc. Amer., vol. 13, pp. 325-380, 22 figs.* 
 Pannan, D. C. 1920. Observations on the Effect of Storm Phenomena on Insect Activity. 
 
 Journ. Econ. Ent., vol. 13, pp. 339-343- 
 Peterson, A. 1920. Some Studies on the Influence of Environmental Factors on the 
 
 Hatching of the Eggs of Aphis avenae Fabricius and Aphis pomi DeGeer. Ann. 
 
 Ent. Soc. Amer., vol. 13, pp. 391-400, pi. 31.* 
 Riley, C. F. C. 1919. Some Habitat Responses of the Large Water-Strider, Gerris 
 
 remigis Say. Amer. Nat., vol. 52, pp. 394-631, figs. 1-6.* 
 Riley, C. F. C. 1920. Migratory Responses of Water-Striders during Severe Droughts. 
 
 Bull. Brooklyn Ent. Soc, vol. 15, pp. i-io. 
 Claassen, P. W. 1921. Typha Insects: Their Ecological Relationships. Cornell Univ. 
 
 Agr. Exp. Sta., Memoir 47, pp. 459-529, pis. 39-48.* 
 Craighead, F. C. 1921. Hopkins Host-Selection Principle as Related to Certain Ceram- 
 
 bjxid Beetles. Journ. Agr. Res., vol. 22, pp. 189-220. 
 Headlee, T. J. 1921. The Response of the Bean Weevil to Different Percentages of 
 
 Atmospheric Moisture. Journ. Econ. Ent, vol. 14, pp. 264-268, fig. 5. 
 Livingston, B. E., and Shreve, F. 1921. The Distribution of Vegetation in the United 
 
 States, as Related to Climatic Conditions. Carnegie Inst. Washington, Pub. 
 
 No. 284, 16 + 590 pp.^ 74 figs., 73 pis.* 
 Ping, C. 1921. The Biology of Ephydra subopaca Loew. Cornell Univ. Agr. Exp. Sta., 
 
 Memoir 49, pp. 557-616, pis. 54-S7-* 
 Riley, C. F. C. 1921. Distribution of the Large Water-Strider, Gerris remigis Say, 
 
 throughout a River System. Ecology, vol. 2, pp. 32-36, figs. 1-3. 
 
 INSECTS IN RELATION TO MAN 
 
 Harris, T. W. 1862. A Treatise on Some of the Insects Injurious to Vegetation. Third 
 
 Ed. II -f 640 pp., 278 figs., 8 pis. Boston. 
 Lintner, J. A. 1882. Importance of Entomological Study, etc. First Ann. Rept. Inj. 
 
 Ins., pp. 1-80, figs. 1-12. 
 Saunders, W. 1883. Insects Injurious to Fruits. 436 pp., 440 figs. Philadelphia. J. B. 
 
 Lippincott & Co. 
 Packard, A. S. 1889. Guide to the Study of Insects. Ed. 9. 12 + 715 pp., 668 figs., 
 
 15 pis. New York. Henry Holt & Co. 
 
LITERATURE 477 
 
 Howard, L. O. 1894. A Brief Account of the Rise and Present Condition of Official Eco- 
 nomic Entomology. Insect Life, vol. 7, pp. 55-107. 
 Sempers, F. W. 1894. Injurious Insects and the Use of Insecticides. 10 + 216 pp., i pi., 
 
 184 fijis. Philadelphia. W. A. Burpee & Co. 
 Smith, J. B. 1896. Economic Entomology for the Farmer and Fruit-Grower, etc. Pp 
 
 12 + 1 1-48 1, 483 figs. Philadelphia. J. B. Lippincott Co. 
 Howard, L. O. 1899. The Economic Status of Insects as a Class. Science, vol. 9 (n. s.) 
 
 pp. 233-247. 
 Theobald, F. V. 1899. A Text-Book of Agricultural Zoology. 17 + 511 pp., 225 figs 
 
 Edinburgh and London. Wm. Blackwood & Sons. 
 Howard, L. O. 1900. Progress in Economic Entomology in the United States. Yearbook 
 
 U. S. Dept. Agric, 1899, pp. 135-156, pi. 3- 
 Sanderson, E. D. 3902. Insects Injurious to Staple Crops. 10 + 295 pp., 163 figs 
 
 New York. John Wiley & Sons. 
 Lodeman, E. G. 1903. The Spraying of Plants. 17 + 399 pp., 92 figs. New York 
 
 The Macmillan Co.* 
 Chittenden, F. H. 1907. Insects Injurious to Vegetables. 14 -f 262 pp., 163 figs, 
 
 New York. Orange Judd Co.* 
 Johnson, W. G. 1908. Fumigation Methods. 16 + 313 pp., 83 figs. New York 
 
 Orange Judd Co. 
 Smith, J. B. 1909. Our Insect Friends and Enemies. 314 pp., 121 figs. Philadelphia. 
 
 J. B. Lippincott Co. 
 O'Kane, W. C. 1912. Injurious Insects; How to Recognize and Control Them. 11 + 
 
 414 pp., 606 figs. New York. Macmillan Co. 
 Sanderson, E. D. 1912. Insect Pests of Farm, Garden and Orchard. 12 + 684 pp., 513 
 
 figs. New York. John Wiley & Sons. 
 Bourcart, E. 1913. Insecticides, Fungicides and Weed Killers. Trans, by D. Grant. 
 
 35 + 431 pp. London. Scott, Greenwood & Son. New York. D. Van Nost- 
 
 rand Co. 
 Herrick, G. W. 1914. Insects Injurious to the Household and Annoying to Man. 17 + 
 
 470 pp., 152 figs., 8 pis. New York. - The Macmillan Co.* 
 Imms, A. D. 1914. The Scope and Aims of Applied Entomology. Parasitology, vol. 7, 
 
 pp. 69-87.* 
 Slingerland, M. V., and Crosby, C. R. 1914. Manual of Fruit Insects. 16 + 503 pp., 
 
 396 figs. New York. The Macmillan Co.* 
 Hewitt, C. G. 1916. A Review of Applied Entomology in the British Empire. Ann. Ent. 
 
 Soc. Amer., vol. 9, pp. 1-34. 
 Osbom, H. 1916. Agricultural Entomology. Pp. 4 + 17-347, 252 figs. Philadelphia 
 
 and New York. Lea & Febiger. 
 Crosby, C. R., and Leonard, M. D. 1918. Manual of Vegetable-Garden Insects. 15 + 
 
 391 pp., 232 figs. New York. The Macmillan Co.* 
 Lochhead, W. 1919. Classbook of Economic Entomology. 14 -|- 436 pp., 257 figs. 
 
 _ Philadelphia. P. Blakiston's Son & Co.* 
 Femald, H. T. 1921. Applied Entomology. 14 + 386 pp., 388 figs. New York. 
 
 McGraw-Hill Book Co., Inc. 
 Sanderson, E. D., and Peairs, L. M. 1921. Insect Pests of Farm, Garden and Orchard. 
 
 Ed. 2. 6 + 707 pp., 604 figs. New York. John Wiley & Sons, Inc. 
 Most of the literature on the economic entomology of the United States is contained in 
 the following works: Reports U. S. Ent. Commission; Repts. Govt. Entomologists; Bulletins 
 U. S. Dept. Agric, Bur. Ent.; Bull. U. S. Dept. Agric; Journ. Agric. Research, U. S. 
 Dept. Agric; Insect Life; Reports and Bulletins by the several State Entomologists; 
 Bulletins of the various Experiment Stations; Journal of Economic Entomology. 
 
INDEX 
 
 An asterisk * denotes an illustration. 
 
 Abbott, 461 
 
 Abdomen, 60; appendages of, *6i, *i32, 
 
 *i33; extremity, 62; modifications, 61; 
 
 segments, 60 
 Acacia, *2so 
 
 Accessory glands, *i24, 125 
 Acclimatization, 360 
 Acerentomon, *6 
 A chortiles,'^* 10 
 Acone, 98 
 
 Acridiidae (see Locustida). 
 Aculeata, 19 
 Adams, 339, 472, 475 
 Adaptations, of larvae, 145; of legs, 48, *5o; 
 
 of mandibles, *36; protective, 245 
 Adaptive coloration, 194; classification, 210; 
 
 evolution, 211 
 Adelung, von, 444 
 Adier, 439, 462 
 Adventitia, no 
 Adventitious resemblance, 197 
 Aedes, 255, 269 
 ^geria, sexual coloration, 184 
 -Estivation, 366 
 Ageronia, 92 
 
 Aggressive resemblance, 210 
 Agrionidae, caudal gills, *ii9 
 Air, movement, 368; of soil, 350; of water, 
 
 383 
 Air-sacs, 117 
 Alary muscles, *io9 
 .\lbinism, 179 
 Aldrich, 384, 414, 426 
 Alexander, 460 
 
 Alimentary tract (see Digestive system) . 
 Allard, 445 
 
 Alluring coloration, 210 
 Alternation of generations, 216 
 Amans, 437, 455 
 Amber insects, 341, 345 
 Ametabola, 140 
 Ammophila, *3i7 
 Amnion, *i3i, 135 
 Amphidasis, 178 
 
 Amphigony, 358 
 
 Amphipyra, 304 
 
 Ampullaceum, *85 
 
 Anajapyx, *6, 21 
 
 Anal glands, 73, *io3 
 
 Anasa, *i38 
 
 Anderson, 269 
 
 Androconia, *7i, 72 
 
 Anemotropism, 305 
 
 Aner gates, 294 
 
 AngrcBcuni, 221 
 
 Anisota, *i52 
 
 Anisotropic, 78 
 
 Annelids, in relation to arthropods, 5, *8 
 
 Anomma, 293 
 
 Anopheles, 250, 251 
 
 Anophthalmus, 100 
 
 Anosia berenice, 337; plexippus, antenna of, 
 *32; dispersal, 325; eclosion, 152; 
 so-called mandibles, 40; mimicry, *20i, 
 207; pupa, *i47; pupation, 147; scale, 
 *7o; wing, *55 
 
 Anteclypeus, 29 
 
 Antecoxal piece, *47 
 
 Antennae, forms of, *32; functions, ^:^; sex- 
 ual differences, *3S 
 
 Antennal comb, *2 28, 229; neuromere, *43; 
 segment, 44; sensilla, 84, *85 
 
 Anthononius grandis, activity, 353; aestiva- 
 tion, 366; coloration, 378; develop- 
 ment, SS5, 359, 360; fecundity, 376; 
 food, 376; hibernation, 361; longevity, 
 377; rainfall on, 366; spread in U. S., 
 418; winds on, 368 
 
 Anthrax, 269 
 
 Anthrenus, *6g 
 
 Antigeny, 34, *i84 
 
 Ant-plants, *23o 
 
 Ants, castes of, 289; color sense, 100; facets, 
 31; general account, 289; habits, 291; 
 harvesting ants, 297, 400; honey ants, 
 *294; hunting ants, 293; larvae, 290; 
 leaf-cutting, *295; nests, 290; photo- 
 tropism, 310; slavemaking, 293 
 
48o 
 
 INDEX 
 
 Anurida, development of mouth parts, 
 *i32; germ band, *i32; habits, 170; 
 pigment, 177 
 
 Anus, *66, 105 
 
 Aorta, *io9 
 
 Apanteles, *2 73 
 
 Apatetic colors, 210 
 
 A pat lira, scales, 172; colors, 175 
 
 Aphididas, development, 359; galls of, * 2 14; 
 reproduction, 358 
 
 Aphidius, 273 
 
 Apis mellifera, antennal sensilla, *85; ce- 
 phalic glands, 107; comb, 282, *283; 
 control of sex, 286; determination of 
 caste, 286; foot, *5i; general account, 
 281; hair, *227; larvae, *284;legs, *228; 
 mandible, *36; mimicry, *202; modi- 
 fications in relation to flowers, *228; 
 mouth parts, *42; ocellus, *96; oviposi- 
 tor, *64; pupa, *284; reproductive sys- 
 tem, *i26; tongue, *86; wax, *74, 282 
 
 Apneustic, 117, 169 
 
 Apodemes, *48 
 
 Apodous larvae, 44, 5 1 
 
 Apophyses, *48 
 
 A poms, 319 
 
 Appendages, development of, *i3i 
 
 Apple, insects of, 212, 410 
 
 Aptera, 7 
 
 Apterygota, 9 
 
 Aquatic insects, adaptations of, 165; condi- 
 tions of existence, 382; food, 165,* 386; 
 locomotion, 166; origin, 171; respira- 
 tion, 168; systematic position, 165 
 
 Arachnida, *2 
 
 Arctic realm, 331 
 
 Arista, *32 
 
 Aristida, 297 
 
 Arixeniidae, 10 
 
 Arms, J. M., 21, 431, 432, 454 
 
 Army worm, 339 
 
 Arthropoda, characters of, *i; classes, 2; 
 interrelationships, 4; naturalness of 
 phylum, 7; phylogeny, *8 
 
 Asclepias, 221, *222, *223 
 
 Asecodes, 274 
 Ashmead, 327 
 Aspidiotus perniciosits, spread of, 418; 
 
 \vinter-killing of, 363 
 Assembling, 90 
 Associations, 393, 394 
 Ast, 446 
 
 Atelnra, *300 
 
 Atemeles, *299 
 
 Atmosphere, 351; composition of, 367; 
 
 movement, 368^ temperature, 352 
 Atta, 293, *295 
 Attactis, 27 
 
 Auditory hairs, 94; organs, 94, *9S 
 Aughey, on insectivorous birds, 243, 463 
 Auricle, *228, 229 
 Austen, 465 
 Australian realm, 332 
 Austral region, 332 
 Autecology, 348 
 AiUomeris, 73 
 Ayers, 61, 452 
 
 Bachmetjew, 364 
 
 Back, E. A., 429 
 
 Backswimmers (see Notonecta). 
 
 Baldwin, 469 
 
 Ball, E. D., 426 
 
 Ballowitz, 450 
 
 Banks, 430, 434 
 
 Barber, 384, 456 
 
 Barriers, 324 
 
 Barrows, 303, 470 
 
 Basement membrane, *67, 69, *io5 
 
 Basiconicum, 84, *85 
 
 Basidium, *2i8 
 
 Basilarchia, mimicry, *2oi, 207; protective 
 
 resemblance, 196 
 Bates, on mimicry, 202, 459, 470, 471 
 Batesian mimicry, 203 
 Bateson, 458 
 Bauer, 442- 
 
 Baumberger, 354, 361, 373, 374, 475, 476 
 Beal, 240, 463 
 Bean weevil (see Bruchus). 
 Beddard, 457, 460, 472 
 Bees, color sense of, 100; hairs, *68 
 Beetles, sounds of, 91 
 Behavior of insects, 302 
 Bellesme, de, 446 
 Belostoma, digestive system of, ^105; pre- 
 
 daceous, 166, 233 
 Belt, on leaf-cutting ants, 295, 471 
 Bembidion, 303, 349 
 Benacus, *i5; caecum, 105; mouth parts, 
 
 *39; predaceous, 166 
 Beneden, van, 466 
 Beneficial insects, 41 1 
 Benton, oh honey bee, 286, 466 
 
INDEX 
 
 481 
 
 Berlese, 160, 431, 433 
 
 Bernard, 432 
 
 Bertkau, 126 
 
 Bethe, 292, 469 
 
 Bethune, 429 
 
 Betten, 456 
 
 Binet, 442 
 
 Biotic conditions, 379, 387 
 
 Birches, insects of, 212 
 
 Bird, H., 349 
 
 Birds, insectivorous, 239; regulating insect 
 
 oscillations, 243 
 Bishopp, 352, 365, 475 
 Bittacomorpha, *i20, 169 
 Biltactis, *i6, *49 
 Bitter rot, 219 
 Black-flies, 233 
 Blackiston, 460 
 Blanc, 436, 447 
 Blanchard, 464 
 Blandford, 464 
 Blastoderm, *i3o 
 Blastophaga, 428 
 Blatchley, 426 
 
 Blalla, muscles of, *77; respiration, *i2i 
 Blattidje, 10 
 Blind insects, 2,3 
 Blissus leiicopterusy distribution of, 339; 
 
 drought on, 366; incubation, 359; 
 
 losses through, 410; rainfall on, 367 
 Blochmann, 452 
 Blood, corpuscles, *iio; course of, no, 
 
 *iii; function, in; gills, 119 
 Bluebird, food of, 241 
 Blunck, 453 
 Boas, 455 
 Bobretzky, 452 
 Boll weevil (see Anlhonomus). 
 Boll worm (see Chloridea). 
 Bolton, 430 
 Bombiis, antenna of, *32; general account, 
 
 287; larva, *i42; mimicry, *2io; respi- 
 ration, *i2i; taste cup, *88 
 Bombyx mori, Malpighian tubes of, *io8; 
 
 mid intestine, *io5; cenocytes, *n4; 
 
 silk glands, *76 
 Bordas, 441, 447 
 Boreal region, 332 
 Borgert, 441 
 Borner, 433, 434 
 Bot flies, 234 
 Bourcart, 477 
 31 
 
 Bouvier, 433, 470 
 
 Boyce, 465 
 
 Brachiniis, 73 
 
 Brachj'pterism, 397 
 
 Braconidas, 273 
 
 Brain, 80, *82; functions of, 82 
 
 Branchial respiration, 169 
 
 Brandt, 451 
 
 Brauer, on classification, 7; types of larvae, 
 
 142)432, 453 
 Br aula. 272 
 Braun, 464, 465 
 Breed, on phagocytosis, 160 
 Breithaupt, 436 
 Bridges, 461 
 Britton, 425 
 Brongniart, on Carboniferous insects, 341, 
 
 344,.473 
 Brown-tail moth (see Euproctis). 
 Bruce, 263, 264, 465 
 Bruchophagiis, *I39 
 Bruchus, metabolism, 364, 370 
 Brues, 269, 359, 366, 372, 374, 434, 465, 467, 
 
 476 
 Bruner, 426 
 
 Brunner von Wattenwyl, 458 
 Bruntz, 448 
 Buckingham, 470 
 Bugnion, 162, 454 
 Bumblebees, general account, 287 
 Bureau of Entomology, 428 
 Burge, lis 
 Burger, 370 
 
 Burgess, A. F., 368, 429 
 Burgess, E., 436 
 Burmeister, 431, 432 
 Bursa copulatrix, 125 
 Busck, 139 
 Biithus, *2 
 Butler, 459 
 
 Biitschli, 442, 450, 451, 452 
 Butterflies, eclosion of, 152, *i53; fossil, 
 
 *346 
 
 Cabbage butterfly (see Pier is rapa). 
 
 Caeca, gastric, *io2, *io3, 104 
 
 Cacilius, *io6 
 
 Cascum, *io4, *io5 
 
 Caesar, 445 
 
 Cajal, 449 
 
 Calkings, 465 
 
 CaUiphora, compound eyes of, *97, *98 
 
482 
 
 INDEX 
 
 Callosamia, antennae, 2>y': assembling, 90; 
 
 cocoon, 356; sexual coloration, *i85 
 Caloptenus, olfactory organ of, *88; tym- 
 panal organ, *95 
 Calopteryx, development of, *i34; sexual 
 
 coloration, 185 
 Calvert, 465 
 Cameron, 475 
 
 Campodea, 6, *g, 21, 60, *i42 
 Candeze, 440 
 
 Canker worms, as food of birds, 243 
 Cannon, 307 
 Canthon, *5o 
 Capitate, *32 
 Carabids, anal glands of, 73, *io3; food of, 
 
 233; predaceous, 271 
 Carabidoid larva, *i57 
 Carahus, alimentary tract of, *io3 
 Carboniferous insects, 341, 342 
 Cardiac valve, *ioi, 102, *io4 
 Cardo, *37 
 Carle t, 439 
 
 Carpenter, F. W., 469 
 Carpenter, G. H., 5, 7, 43I) 433, 455, 45^, 
 
 461, 472 
 Carpocapsa pomonclla, development, 356, 
 360; hibernation, 361; incubation, 358; 
 temperature on, 356; winter-killing of, 
 362 
 Carriere, 444, 452 
 Carrion insects, 236 
 Carroll, 253, 255, 465 
 Cams, 430 
 Casteel, 229, 463 
 Catbird, foot of, 240 
 Caterpillar, 137; pupation of, 147, *i49 
 Catocala, protective resemblance, *i9s; 
 
 scent tufts, 49 
 Caiogenus, antenna of, *32 
 Caudal gills, 170 
 Caudell, 434, 435 
 Cecidomyiidie (see Itonidida). 
 Cecropia adettopus, 230, *23i, *232 
 Cecropia moth (see Samia). 
 Centipede, *5 
 Centrolecithal, *i30 
 Cerambyx, facets of, 31; ovipositor, *63 
 Ceralina, 277 
 Ceratomegilla, 336 
 Cerceris, 319 
 Cerci, *g, 62, *6s, *6s 
 Cercopoda, 62 
 
 Ceroplaslcs, 75 
 
 Cerura, 74 
 
 Cervical sclerites. 29 
 
 Chadwick, 463 
 
 Chajticum, 84, *85 
 
 Chalcididae, 27, 273 
 
 Chandler, 465 
 
 Chapman, 453 
 
 Chelostoma, *68 
 
 Chemotropism, 302 
 
 Cheshire, 42, 64, 229, 283 
 
 Child, 444 
 
 Chilopoda, 3, *5 
 
 Chinch bug (see Blissiis). 
 
 Chionaspis, 141 
 
 Chironomus, nervous system, *82; pupal 
 
 eggs, 128 
 Chitin, 66 
 
 Chittenden, 429, 474, 477 
 Chloridea obsoleta, development, 359; rain- 
 fall on, 366 
 Chlorophyll, as a pigment, 175 
 Cholera, 268 
 
 Cholodkovsky, 432, 447, 452 
 Chordotonal organs, *95 
 Chorion, *i29, 141 
 Christophers, 465 
 Christy, 464 
 Chro mosomes, 1 2 9 
 Chrysalis, 137 
 Chrysobothris, integument of, *67 
 
 Chrysomelidae, silk glands of, 77 
 Chrysopa, *i6; cocoon of, *i48; laying eggs, 
 *i4o; mandibles, *36; predaceous, 270; 
 silk glands, 77 
 
 Chun, 440 
 
 Cicada, metamorphosis of, *i39; molts, 145; 
 sound, 91 
 
 Cicindela, leg of, *5o; mandible, *s6; pre- 
 daceous, 271; variation in coloration, 
 183, 189, *I92 
 
 Cicindelidae, ecological succession of, 407; 
 eggs, 350, 351 
 
 Cimbex, repellent glands, 73 
 
 Circular muscles, *io5, 106 
 
 Circulation, *iii 
 
 Circulatory system, 109 
 
 Cirphis unipuncta, 339 
 
 Claassen, 476 
 
 Claspers, *65, *66 
 
 Claus, 432 
 
 Clavate, *32 
 
INDEX 
 
 483 
 
 Claypole, 453 
 
 Clements, 474 
 
 Climatal coloration, 179 
 
 Clisodon, 225 
 
 Cloaca, 62 
 
 Clover, insects of, 212, 410; pollination of, 
 225 
 
 Clypeus, 28, *4o 
 
 Clylra, embryology of, *i30, *i3i, *i3S, 
 *i36 
 
 Cnemidotus, 118 
 
 Coarctate pupa, 147 
 
 Coblentz, 116, 449 
 
 Coccinella, distribution of, 336 
 
 Coccinellidc-E, predaceous, 271; silkglands, 77 
 
 Cochineal, 413 
 
 Cockerell, 347, 426 
 
 Cockroach, cephalic ganglia of, *82; fossil, 
 *343j 345; mouth parts, *35; muscles, 
 *53> *77; respiration, *i2i; salivafy 
 gland, *io7; spermatozoon, *i25 
 
 Cocoon, *i48, *isi 
 
 Codling moth (see Carpocapsa). 
 
 Cceloconicum, 84, *85 
 
 Ccelom sacs, "135 
 
 Coleoptera, 16, *i5, 24 
 
 Colias, albinism of, 180; color sense, 100; 
 sexual coloration, *i84 
 
 Collembola, alimentary tract of, *ioi; de- 
 fined, 9; furcula, 62; primitive condi- 
 tion, 21; ventral tube, 62 
 
 Colletes, hairs of, *68 
 
 Colon, *io2, 105 
 
 Colopha, gall of, *2i4 
 
 Coloradia, 414 
 
 Color, effects of food on, 176; sources of, 172 
 
 Colorado potato beetle (see Leptinotarsa). 
 
 Coloration, adaptive, 194, 210; climatal, 
 179; development of, 187; effects of 
 moisture and temperature on, 178; 
 seasonal, 180; sexual, 184; variation in, 
 188; warning, 199 
 
 Color patterns, development of, 187; ori- 
 gin, 186 
 
 Colors, combination, 175; pigmental, 174; 
 structural, 172 
 
 Color sense, 100 
 
 Commissures, 80, *82 
 
 Communities, 393; classification of, 389, 
 393; distribution of, 389; examples of, 
 394; grasshopper, 394; stream, 397; in 
 New Mexico, 399 
 
 Complete metamorphosis, 137 
 
 Compound eyes, *25; origin, 100; physiol- 
 ogy) 98; structure, *97, *98 
 
 Comstock, A. B., 128, 290 
 
 Comstock, J. H., 56, 424, 427, 431, 432, 433, 
 434, 435, 436, 438, 455, 45^ 
 
 Comte, 267 
 
 Cone cells, 97, *98 
 
 Conidia, *2i8 
 
 Conidiophores, *2i8 
 
 Connold, 462 
 
 Conradi, 426 
 
 Conseil, 267 
 
 Consocies, 393 
 
 Cook, A. J., 426 
 
 Cook, M. T., 462 
 
 Cooke, 462 
 
 Cooley, 426 
 
 Cooties (see Pediculus). 
 
 Cope, on segmentation, 27 
 
 Copidosoma, 273, 412 
 
 Copris, spermatozoon of, *i25 
 
 Coprophaga, 373 
 
 Coquillett, 424 
 
 Corbiculum, *228 
 
 Cordley, 426 
 
 Cordyceps, *2i7 
 
 Corethra, chordotonal organs of, *95; imag- 
 inal buds, *i6i 
 
 Corn borer (see Pyrausta). 
 
 Corn ear worm (see Chloridea). 
 
 Corn insects, 212, 410 
 
 Cornea, *97, *98 
 
 Corrodentia, *i2 
 
 Corydaloides, 344 
 
 Cosens, 215, 463 
 
 Costa, *54 
 
 Coste, 457 
 
 Cotton boll weevil (see Anthonomus) . 
 
 Cotton boll worm (see Chloridea). 
 
 Cotton worm, 410 
 
 Cowan, 462 
 
 Coxa, 48 
 
 Craig, 465 
 
 Craighead, 476 
 
 Crampton, 21, 23, 25, 434, 435, 437, 438,. 440 
 
 Crawley, 467 
 
 Cremaster, 147 
 
 Cremastogaster, 291 
 
 Cricket, stridulation of, 93 
 
 Crioceris, 338 
 
 Crop, *i02, *io3 
 
484 
 
 Crosby, 424, 477 
 
 Crustacea, 2 
 
 Cryptorhynchus, 338 
 
 Crystalline cone, 97, *98 
 
 Ctenocephalus, *20 
 
 Cubitus, *54 
 
 Cucurbit wilt, 219 
 
 Cuenot, 441, 447, 448 
 
 Ciilex, antennae of, *34; characteristics, 251; 
 filariasis transmitted by, 265; hiberna- 
 tion, 310; larva, *i68; mouth parts, 
 *4i; respiration, 169; tropisms, 310 
 
 Cutaneous respiration, 169 
 
 Cuticula, 66, *67, *68 
 
 Cuticular colors, 1 74 
 
 Cyaniris pseudargiolus, coloration of, 178; 
 geographical varieties, 328; melanism, 
 180; polymorphism, *i8i; sexual color- 
 ation, 184 
 
 Cybister, leg of, *i67; locomotion, 167, 168 
 
 Cychrits, 91 
 
 Cyllene, metamorphosis of, *i37 
 
 Cynipidse, abdomen of, 61; galls, *2i3, 
 *2i4; parthenogenesis, 127, 216 
 
 Cyrtophyllus, stridulation of, 93 
 
 Dahl, 437, 440, 442 
 
 Darkness, as affecting pigmentation, 177 
 
 Darts, *64 
 
 Darwin, 317, 412, 461, 462, 470 
 
 Dasyneura, egg of, *i39, 140; ovipositor, *63 
 
 Davenport, 308, 352, 353, 360, 364, 469, 474 
 
 Davis, J. J., 426 
 
 Davis, K. C, 456 
 
 Dean, 425 
 
 Dearborn, on insectivorous birds, 242, 243, 
 
 245, 464 
 Deegener, 441, 442, 443, 445, 447, 448, 450, 
 
 45i> 455 
 Demoll, 437, 445, 446 
 Demoor, 437 
 
 Denny, 66, 78, 431, 435, 442 
 Dermaptera, 10 
 Dermestidae, 236 
 Deutocerebrum, 80, 135 
 Deutoplasm, *i29 
 Development, 129 
 Development, threshold of, 355 
 Developmental zero, 355 
 Devonian insects, 340, 341 
 Dewar, 461 
 Dewitz, 437, 439, 448, 454 
 
 Diabrotica, distribution of, 337 
 
 Diacrisia, cocoon of, 148 
 
 Diapheromera, 195, 359 
 
 Diastole, in 
 
 Dibrachys, 274 
 
 Dichoptic, *32 
 
 Dickel, 467 
 
 Dictyoneiira, 344 
 
 Dietrich, 445 
 
 Digestive system, loi; of beetle, *ioy, 
 Belosloma, *io5; Collembola, *ioi; 
 grasshopper, *io2; histology, *io5; 
 106; moth, *io4; Myrmeleon, *io3 
 
 Digoneutic, 182 
 
 Dimmock, on assembling, 91; on mouth 
 parts of mosquito, *4i; 436, 440, 457, 
 463 
 
 Dimorphism, 180 
 
 Dinar da, *2gg 
 
 Dineutus, antenna of, *32; eyes, *30 
 
 Diplopoda, *3 
 
 Diptera, 19, *2o; eyes of, *3i; halteres, loi; 
 mouth parts, *4i; origin, 25; sounds, 
 91; spiracles, 60 
 
 Direct metamorphosis, 138 
 
 Directing tube, 76 
 
 Diseases, their transmission by insects, 218, 
 248 
 
 Dispersal, 322; centers of, 339; means of, 
 323; in North America, 335 
 
 Dissosteira, protective resemblance of, 196; 
 stridulation, 92 
 
 Distant, 471 
 
 Distribution, former highways of, 325; geo- 
 graphical, 322; geological, 340; tem- 
 perature on, 362 
 
 Diving beetles (see DytiscidcB). 
 
 Dixey, 208, 457, 458, 460 
 
 Doane, 465 
 
 Dogiel, 447 
 
 Dolbear, on stridulation, 93 
 
 Dolichopodidae, 49 
 
 Dolley, 470 
 
 Donacia, 79, 165, 169 
 
 Doncaster, 451 
 
 Donisthorpe, 467 
 
 Dorfmeister, 457 
 
 Dorsal vessel, *io9, *iio 
 
 Doten, 376, 426, 474 
 
 Dove, 352, 365, 475 
 
 Dozier, 476 
 
 Drift, insect, 1 70 
 
INDEX 
 
 485 
 
 Drone, *282 
 Drosera, 216 
 Drosophila, chemotropism of, 303; egg, 
 
 ♦139; food, 373, 376; humidity on, 365; 
 
 melanism, 180; phototropism, 310, 311 
 Drought, 366 
 Dubois, 448 
 
 Ductus ejaculatorius, *i24 
 Dufour, 449, 455 
 Durham, 464 
 Diirken, 438 
 Dyar, on molts, 145 
 Dynastes hercules, 27; tityiis, distribution of, 
 
 337 
 Dysentery, 268 
 Dytiscidae, 166, 167 
 Dytiscus, caecum of, 105; leg of, *5o; pre- 
 
 daceous, 233; respiration, 169 
 Dzierzon's theory, 286 
 
 Ecdysis, 140, 144 
 
 Ecilon, *295; eyes of, 31; habits, 233, 290,293 
 
 Eckstein, 462 
 
 Eclosion, 152 
 
 Ecology, 348 
 
 Economic entomologist, 420 
 
 Ectoderm, 130, *i3i 
 
 Edwards, on /. ajax, 182; on P. tharos, 182 
 
 Effective temperatures, 355 
 
 Egg-guide, *67 
 
 Egg-nucleus, *i29 
 
 Eggs, form of, *i39; number, 141; size, 140 
 
 Eimer, 468 
 
 Ejaculatory duct, *i24 
 
 Elaplirus, stridulation of, 91 
 
 Electricity, 368 
 
 Eleodinae, 372 
 
 Ellema, protective resemblance of, 196 
 
 Elm, insects of, 212 
 
 Elm leaf beetle (see GaleruccUa). 
 
 Eltringham, 446, 461 
 
 Elwes, 471 
 
 Elwyn, 365, 475 
 
 Ely, 476 
 
 Elytra, 53 
 
 Enihia, 12 
 
 Embioptera, ix 
 
 Embryology, 129 
 
 Emery, 448, 467 
 
 Emcsa, 322 
 
 Empis, nervous system of, *82 
 
 Empodium, 48 
 
 Emptisa, *2i8 
 
 Enderlein, 433 
 
 Endoskeleton, 46, *48 
 
 Engelmann, 430 
 
 Enteman, 289, 321, 459, 467, 469 
 
 Entoderm, 130, 135, *i36 
 
 Entomophagous, 373 
 
 Entomophthoracea;, 217, *2i8 
 
 Environment, 387, 389 
 
 Ephemerida, *i3, 14; abdominal segments 
 of, 60; eyes, 31; origin, 23 
 
 Ephydra, 383, 414 
 
 £/)/f aw/a, hypermetamorphosis of, 156, *i57 
 
 Epicranium, 28 
 
 Epigamic colors, 211 
 
 Epimeron, *45, *47 
 
 Epipharynx, 35 
 
 Episternum, *45, *47 
 
 Epitheca, dorsal vessel of, *iio 
 
 Equilibrium, 382 
 
 Erebus agrippina, 27; odora, 323, 337 
 
 Ergatoid, 290 
 
 Eriocepliala, mouth parts of, 40 
 
 Eristalis, mimicry by, *202; respiration, 169 
 
 Eruciform larvae, 24, *i43, 160 
 
 Erynnis manitoba, distribution of, *332 
 
 Escherich, 439, 451 
 
 Essig, 425 
 
 Ethiopian realm, 331 
 
 Etiolin, 193 
 
 Etoblattina, 343 
 
 Eucone, 98 
 
 Eitdamus proteus, distribution of, *332 
 
 Eiigercon, *344 
 
 Euphoria, mouth parts of, 36, *2 2 7 
 
 Euplexoptera (see Dermaptera). 
 
 Euplcea, colors of, 175 
 
 Euproctis chrysorrhoea, phototropism of, 
 309; spread, 417; winter-killing of, 362 
 
 European corn borer (see Pyrausta). 
 
 Euschistus, antenna of, *32 
 
 Eutermes, 281 
 
 Eiithrips, *i4 
 
 Evaporation, 369; adaptations to, 372; on 
 eclosion, 372; gradients, 371; on hatch- 
 ing, 371; on life cycle, 371; on metabo- 
 lism, 369; reactions to, 370 
 
 Everes, androconium of, *7i 
 
 Ewing, 4, 359, 435 
 
 Excrements, 105 
 
 Exner, on compound eyes, 98, 444, 468 
 
 Expiration, 123 
 
486 
 
 INDEX 
 
 Exuviae, 144 
 
 Eyes, compound, *30, *97; kinds of, *3o; 
 
 sexual differences in, *3i; simple, *30, 
 
 *3i 
 
 Fabre, J. H., 316, 466, 468 
 
 Fabre, J. L., 446 
 
 Facets, *30 
 
 Fat-body, distribution of, 112, *ii3; func- 
 tions, 112; structure, 112, *ii3, *ii4 
 
 Fat-cells, 112, *ii3 
 
 Faunae of islands, 326 
 
 Faunal realms, 328, *329 
 
 Faussek, 447 
 
 Felt, E. P., 423, 451, 463 
 
 Female genitalia, 62, *6s 
 
 Femur, *47, 48, *49 
 
 Fenard, 451 
 
 Fenestrate membrane, 97, *98 
 
 Feniseca, 271 
 
 Fernald, C. H., 213, 423, 425, 426 
 
 Fernald, H. T., 426, 432, 477 
 
 Fertilization, 129 
 
 Fidonia, antennal sensilla, *85 
 
 Fielde, 290, 292, 307, 466, 467, 469 
 
 Fielding-Ould, 464 
 
 Filariasis, 265 
 
 Filiform, *32 
 
 Filippi's glands, *76 
 
 Finlay, 253, 464 
 
 Finn, on mimicry, 206; on warning colora- 
 tion, 199; 460, 461 
 
 Fire blight, 218 
 
 Fire-flies, 115, 116 
 
 Fischer, 45 8 
 
 Fishes, insectivorous, 237 
 
 Fitch, 423 
 
 Flagellum, *32 
 
 Fleas, *2o, 234 
 
 Fletcher, 429 
 
 Flight, mechanics of, 57 
 
 Flint, W. P., 425 
 
 Flogel, 442 
 
 Fluted scale, 428 
 
 Follicles, 124, *i27 
 
 Folsom, 433, 436, 447 
 
 Food, its effects on color, 176, 378; on fecun- 
 dity, 376; on growth, 375; habits, 373; 
 on hibernation, 378; on longevity, 377; 
 on oviposition, 376; plants, 373; rela- 
 tions, 378; on reproduction, 376; selec- 
 tion, 374; on sex-determination, 376 
 
 Food reservoir, 102, *io4 
 
 Forbes, H. O., 471 
 
 Forbes, S. A., on corn root louse, 298; on 
 economic entomologist, 420; food of 
 Carabidae, 271; insectivorous birds, 
 239; insectivorous fishes, 237; insect 
 oscillations, 243; 424, 462, 463,. 464, 466 
 
 Forbush, 213, 423 
 
 Fore intestine, *ioi, *io2 
 
 Forel, on ants, 291; on taste, 85; 440, 443, 
 444, 445, 467, 469 
 
 Forficulidae, 10 
 
 Formations, 393, 394 
 
 Formative cells, 69, *7i 
 
 Formica, exsectoides, mounds of, 2gi;fusca, 
 289, 293, 294; pratcnsis, eyes of, 33; 
 sangiiinea, 294 
 
 Fossil insects, localities for, 340 
 
 Fossilization, 340 
 
 Free pupa, 146 
 
 French, G. H., 424 
 
 Frenulum, 54 
 
 Frenzel, 446, 447 
 
 Friese, 459 
 
 Front, *28, *29 
 
 Frontal ganglion, 81, *82 
 
 FuUer, 467 
 
 Fundament, 131 
 
 Fungi of insects, *2i 7, *2 1 8 
 
 Furcae, 46, *48 
 
 Furcula, 62 
 
 Futaki, 266 
 
 Gadeau de Kerville, 448 
 
 Gad flies, 233 
 
 Galapagos Islands, Orthoptera of, 326 
 
 Galea, *35, 37, *38 
 
 Galerita, anal glands of, 73; antenna, *32; 
 
 sternites, *47 
 Galerucella luleola, 419 
 Galls, *2i3, *2i4 
 Ganglia, cephalic, *43, 80, *82; functions of, 
 
 82 
 Ganglion, structure of, 81, *83; suboesopha- 
 
 geal, *8i, *82; supraoesophageal, 80, 
 
 *82 
 
 Ganglion cells, 81, *83 
 Ganin, on Platygaster, *is8, 454 
 Garman, 426, 456 
 Gastric cffica, *io2, *io3, *I04 
 Gastro pacha, larval coloration, 177; stinging 
 hair, *72 
 
INDEX 
 
 487 
 
 Gastraphilus, 235 
 
 Gastrulation, *i3o 
 
 Gee, 470 
 
 Gehuchten, van, on digestion, 104; 442, 447 
 
 Gens, *29 
 
 Geniculate, *32 
 
 Genitalia, 62; of female, 62; grasshopper, 
 
 *67; male, 64; moth, *66 
 Geographical, distribution, t,22; varieties, 
 
 328 
 Geological distribution, 340 
 Geometridse, legs of larva% 5 r 
 Geotropism, 306 
 Gerephemera, 342 
 Germ band, *i3o; types of, 133 
 Germ cells, 129 
 Germinal vesicle, 129 
 Gerould, 180, 459, 461 
 Gerris, *i66; locomotion of, 168; thigmo- 
 
 tropism, 304 
 Gerstacker, 449 
 Gibson, A., 429 
 Gibson, W. H., 462 
 Gill, T., 471 
 Gillette, 426 
 Gills, *ii8, *ii9, 169 
 Gilson, 447, 450, 456 
 Gipsy moth (see Porthetria). 
 Girault, on numbers of eggs, 141 
 Gizzard, 102, *io3 
 
 Glaciation, its efifects on distribution, 325 
 Glands. 72: accessory, *i24, *i26; alluring, 
 
 74; repellent, 73; salivary, *io6, *io7; 
 
 silk, 75, *76, wax, 74 
 Glandular hairs, *72, *73 
 Glaser, 114, 449 
 Gleason, 474 
 Glenn, 356 
 Glossa, *35, 7,t, *^2 
 Glossina, 262, *263 
 Glover, 427 
 Golgi, on malaria, 248 
 Goliathus, endoskeleton of, *48 
 Gonapophyses, *63, *64 
 Gongylus, 210 
 Gonin, 454 
 Goossens, 439, 440 
 Gorgas, 256, 465 
 Gortner, 174, 459 
 Goss, 473 
 Gossard, 425, 426 
 Gould, 457 
 
 Graber, on chordotonal organ, *95; hal teres, 
 loi; hearing, 94; 431, 437, 439, 443, 
 447, 452, 468 
 
 Graham, 269 
 
 Grasshopper, adaptations, 397; alimentary 
 tract, *io2; communities, 394; geni- 
 talia, *67; hearing, *94 
 
 Grassi, on Termes, 279; 432, 464, 466 
 
 Green bug (see T 0x0 pier a). 
 
 Gregory, 376 
 
 Gregson, 176 
 
 Grenacher, on compound eye, 98, 100, 443 
 
 Grobben, 432 
 
 Gross, 451 
 
 Grossbeck, 384, 456 
 
 Growth, 144 
 
 Grub, 137 
 
 Griinberg, 451, 465 
 
 Gryllidse, 10 
 
 Grylloblattidae, 10 
 
 Gryllotalpa, leg of, *5o; maternal care, 76 
 
 Gryllus, sense hairs, *9o; stridulation, 92 
 
 Gula, 29, 37 
 
 Giinther, 445 
 
 Guy6not, 376 
 
 Gynandromorphism, 127, *i28 
 
 Gyrinidae, eyes of, *30 
 
 Gyrinus, locomotion of, 168; respiration, 
 169; tracheal gills, *ii8 
 
 Haase, 432, 439, 449, 460 
 
 Hsemolymph, no 
 
 Hagen, 279, 430, 455, 457 
 
 Hairs, development of, *68, 69; functions, 
 
 69; histology, *6g; modifications, *68; 
 
 pollen-gathering, *6o, *227; protective, 
 
 245; tenent, *72 
 Halisidota, distribution of, 336 
 Halobaies, 170 
 Halteres, 53, loi 
 
 Hamilton, on holarctic beetles, 331, 471 
 Hammar, 358, 360 
 Hammond, A. R., 454 
 Hammond, J. H., Jr., 312 
 Hamuli, 54 
 
 Handlirsch, 8, 347, 433, 434, 435, 474 
 Hansen, 432, 433, 436 
 Harmolita, 273 
 Harned, 426 
 Harpactophagous, 373 
 Har pains, labium of, *38; maxilla, *38 
 Harris, 423, 476 
 
INDEX 
 
 Hart, 456, 474 
 
 Hartman, 469 
 
 Harvey, 425 
 
 Hatching, 141 
 
 Hatschek, 452 
 
 Hauser, on smell, 87, 443 
 
 Haushaltef, 268 
 
 Haviland, on termites, 281 
 
 Hawaii, beetles of, 326; Hymenoptera, 327 
 
 Hayward, on stridulation, 93 
 
 Head, 28; segmentation of, *43 
 
 Headlee, 356, 359, 364, 367, 370, 372, 425, 
 
 475-376 
 Hearing, 94 
 
 Heart, *io9, *iio, *iii 
 Heath, on Termopsis, 278, 467 
 Heer, on fossil insects, 341, 473 
 Heider, 452, 454 
 Heilprin, 472 
 Heim^ 462 
 Heinemann, 448 
 Heliconiidae, mimicry, 202 
 HcUophila (see Cirphis). 
 Heliotropism, 306; machine to illustrate, 
 
 311 
 Helm, 446 
 Hemelytra, 53 
 
 Hemerocampa, parasites of, 274 
 Hemimeridae, 10 
 
 Hemimerus, *ii; hypopharynx of, *38 
 Hemiptera, 16; mouth parts, *39; odors, 73; 
 
 origin, 23 
 Henking, 450, 452 
 Henneguy, 431 
 Hennings, 370 
 Henshaw, 430 
 
 Heptagenia, hypopharynx of, *;,& 
 Hermaphroditism, 125 
 Herms, 425, 465, 470, 474 
 Herrick, 424, 426, 477 
 Hesse, 445 
 
 Hessian fly (see Mayetiola). 
 Hctarius, 300 
 Heterocera, 18 
 Heterogeny, 127 
 Heterogony, 358 
 Heterometabola, 138 
 Heterophaga, 19 
 
 Heteroptera, *i6; spiracles of, 60 
 Hewitt, 375, 429, 436, 477 
 Hexagenia, *i^, 14; male genitalia, *65; 
 
 tracheal gills, *ii8 
 
 Hexapoda, defined, 4 
 
 Heymons, 139, 433, 439, 451, 453 
 
 Hibernation, 361 
 
 Hicks, on olfactory pits, 88 
 
 Hickson, 444 
 
 Higgins, 456 
 
 Hildebrand, 384 
 
 Hilton, 441 
 
 Hind intestine, *io2, *io4 
 
 Hinds, 354, 355, 359, 360, 361, 366, 367, 377, 
 
 378, 426 
 Histogenesis, 160 
 Histolysis, 160 
 Hochreuther, 445 
 Hodgkiss, 424 
 Hoffbauer, 438 
 Holarctic realm, 331 
 Holcaspis, galls of, *2i3, *2i4 
 Holmes, 69, 470 
 Holmgren, 436, 443, 450, 451, 467 
 Holometabola, 137 
 Holopneustic, 117, 168 
 Holoptic, *32 
 Homoptera, 16 
 Honey, 285, 413 
 Honey ants, *294 
 Honey bee (see Apis mellifera). 
 Hopkins, A. D., 426, 429 
 Hopkins, F. G., on pigments, 175, 458 
 Hoplia, sexual coloration of, 185 
 Horn, on Cicindela, 189 
 Houghton, 426 
 House fl}^ (see Miisca). 
 Houser, 425 
 Howard, 274, 338, 423, 428, 429, 431, 464, 
 
 465, 466, 472, 477 
 Howes, 470 
 
 Hubbard, on parasitism. 274 
 Huber, on wax, 282 
 Hudson, 471 
 Humboldt ia, 232 
 Hunter, S. J., 356, 426, 431 
 Hunter, W. D., 354, 355, 359, 360, 361, 366, 
 
 367, 368, 375, 376, 378, 428, 429 
 Huxlej^, 450 
 Hyaloplasm, 78 
 
 Hyatt and Arms, 21, 160, 431, 432, 454 
 Hybernia, 176 
 Hydno phylum, *232 
 Hydrophilus, *i5, *i66; antennae, 33; leg, 
 
 ■•167; locomotion, 166; male genitalia, 
 
 *65; respiration, 169 
 
489 
 
 Hydrotropism, 303 
 
 Hydrous, tergites of, *46 
 
 Hylastinus, 338 
 
 Hylobius, glandular hairs of, *72 
 
 Hymenoptera, defined, 18; cephalic glands, 
 107; eyes of sexes, *32; internal meta- 
 morphosis, 162; mouth parts, *42; 
 ocelli, 31; origin, 25; sounds, 91; wing, 
 *56 
 
 Hypatus, 364 
 
 Hypera, 338 
 
 Hypermetamorphosis, 156 
 
 Hyperparasitism, 274 
 
 Hyphze, 217 
 
 Hyphantria, 246 
 
 Ilypoderma, lar\'a of, *i42; lincala, habits 
 of, 235; losses through, 411 
 
 Hj-podermal colors, 174 
 
 HjTJodermis, *67, *68 
 
 Hypognathous, 11 
 
 Hypopharynx, *ss, 37, *38, *4i 
 
 I eery a, 428 
 
 Ichneumonid^, *2 72 
 
 Ileum, *io5 
 
 Imaginal buds, *i6r, *i62 
 
 Imago, 137 
 
 Imms, 477 
 
 Incomplete metamorphosis, 138 
 
 Incubation, 358 
 
 Indirect metamorphosis, 137 
 
 Ingenitzky, 451 
 
 Injurious insects, 410; introduction of, 416 
 
 Ino, antennal sensilla of, *85 
 
 Inquilines, 215, 281 
 
 Insecta, defined, 4 
 
 Insectivorous birds, 239; fishes, 237; plants, 
 216; vertebrates, 236 
 
 Inspiration, 123 
 
 Instar, 140 
 
 Instinct, 313; apparent rationality of, 314; 
 basis of, 313; flexibility, 316; inflexi- 
 bility, 315; modifications, 315; origin, 
 317; stimuli, 314; and tropisms, 318 
 
 Integument, 65 
 
 Intelligence, 318 
 
 Interactions of organisms, 379 
 
 Intercalary, appendages, *i32; neuromere, 
 *43; segment, 44 
 
 Interglacial beetles, 346 
 
 Interrelations, of insects, 270; of orders, 20 
 
 Intima, *76, 106, *i2i 
 
 Iphiclides ajax, polymorphism of, 181 
 Iridescence, 172 
 Iris pigment, *96, *97 
 Iris versicolor, *2 20, *2 2i 
 Irritants, 246 
 Isaria, 217 
 
 Isia, cocoon of, 148; hairs, 69, 146; hiberna- 
 tion, 361; molts, 145 
 Island fauna?, 326 
 Isolation, 328 
 Isoptera, 11 
 
 Isosoma (see HarmoUta). 
 Isotropic, 78 
 
 Ithomiinae, mimicry, 202, 203 
 Itonididse, galls of, 214; paedogenesis, 128 
 
 Jackson, C. F., 431 
 
 Jackson, T. W., 465 
 
 Jacobi, 461, 472 
 
 James, W., 468 
 
 Janet, on Atelura, *3oo; on muscles, *78; 
 436, 4395 440, 442, 466, 467 
 
 Japan, 415 
 
 Japanese beetle (see PopiUia). 
 
 Japyx, 9, 22; spiracles of, 60 
 
 Jennings, 469 
 
 Johannsen, 456, 465 
 
 Johnson, R. H., 459 
 
 Johnson, W. G., 426, 477 
 
 Jordan, 436 
 
 Jorschke, 445 
 
 Judd, on food of bluebird, 242; mimicry, 
 208; protective adaptations, 245; pro- 
 tective resemblance, 198; warning col- 
 oration, 199; 460, 463, 464 
 
 Jugum, 54 
 
 Jurassic insects, 341, 345 
 
 Kala-azar, 269 
 
 Kallima, protective resemblance of, *i94 
 
 Kanthack, 464 
 
 Kapzov, 441 
 
 Kathariner, 469 
 
 Katydid, stridulation of, 93 
 
 Kellogg, on Mallophaga, 233; mouth parts, 
 
 40; phototropism, 310; pilifers, */\o; 
 
 scales, 70, 172; swarming, 286; 431, 
 
 43S> 436, 458 
 Kenyon, 432, 443 
 Kidney tubes, *io8 
 Kielich, 442 
 Kilborne, 269 
 
490 
 
 INDEX 
 
 Kingsley, on Arthropoda, 7 
 
 Kirby, 431, 432 
 
 Kirkland, 463 
 
 Klemensiewicz, 440 
 
 Kluge, 451 
 
 Knuppel, 447 
 
 Koch, 250 
 
 Kochi, 436 
 
 Koestler, 442 
 
 Kolbe, 431 
 
 Kolliker, 442 
 
 Korotneff, 452 
 
 Korschelt, 450, 452, 453, 454 
 
 Kowalevsky, 447, 448, 451, 454 
 
 Kraepelin, 436 
 
 Krancher, 449 
 
 Krause's membrane, *78 
 
 Krogh, on temperature- velocity, 357; pupal 
 
 development, 359 
 Krukenberg, 67 
 Kulagih, 41, 436, 453, 454 
 
 Labellum, *4i, *42 
 
 Labial, neuromere, *43, 81, 135; segment, 44 
 
 Labium, 29, *-s5 37, *38, *39*4i 
 
 Labrum, *29, *35, *39 
 
 Lac, 75, 413 
 
 Lachnosterna, antenna of, *32; cocoon, 148; 
 
 larva, *i42 
 Lacinia, *35, 37, *38 
 Lagoa, legs of, 51; stinging hairs, *73 
 Lamarck, on instinct, 317 
 Lameere, 455 
 Lamellate, *32 
 Landois, 449 
 Lang, 435 
 
 Langley, on luminosity, 115 
 Lankester, 433 
 Larvae, 137; adaptations of, 145; legs, 50; 
 
 nutrition, 145; parasitic, 275; types of, 
 
 *I42 
 
 Lasiiis, age of, 289; nest, 291; parthenogene- 
 sis, 128 
 Lathrop, 470 
 
 Laveran, on malaria, 248, 465 
 Laverania, 248, *249 
 Leachia, eyes of, *3o 
 Leaping, 52 
 LeBaron, 424 
 LeConte, 470 
 Lee, on halteres, loi; 444 
 Legs, adaptations of, 48, *5o; larval, 50; 
 
 Legs, mechanics, *52; muscles, *S5', seg- 
 ments, *49 
 
 Lendenfeld, von, 437, 441 
 
 Leng, 456 
 
 Lens, *96 
 
 Leonard, 477 
 
 Leopard moth (see Zeiizera). 
 
 Lepidocyrtus, scales of, 70 
 
 Lepidoptera, defined, 18; internal metamor- 
 phosis, *i62; molts, 145; mouth parts, 
 *4o; origin, 25; reproductive organs, 
 *i24, *i 26; silk glands, * 76; spiracles, 60 
 
 Lepidotic acid, 176 
 
 Lepisma, *g, 21, *i42; spiracles of, 60 
 
 Leptinotarsa decemlineata, aestivation, 366; 
 color pattern, 175, 186, *i9i; distribu- 
 tion, 336, 338; dorsal wall, *i35; ento- 
 derm, *i36; folding of wing, *57; 
 hibernation, 365; spread, 338; varia- 
 tion in coloration, *i9i 
 
 Leptocoris, 339 
 
 Leptosphceria, 219 
 
 Leptospira, 255 
 
 Lerema, ocellus of,- 31 
 
 Leuckart, 451 
 
 Leucocytes, *iio, 114, 160 
 
 Leydig, 442, 446, 450 
 
 Libellula, *i4, *i42 
 
 Lice, biting, *i2, 223; sucking, *i5, 234 
 
 Life zones, 332, *sss 
 
 Light, 351; on activity, 352; growth, 352; 
 pigmients, 177 
 
 Ligula, *38 ' 
 
 Limacodes, scale of, *6g 
 
 Una, color changes of, 190; distribution, 
 336; germ band, *i3i; glands, 74 
 
 Linden, von, 458, 459 
 
 Lingua, ^38 
 
 Link, 445 
 
 Linnaeus, on orders of insects, 7 
 
 Lintner, 423, 476 
 
 Lithomantis, *2,AZ 
 
 Livingston, 369, 389, 391, 476 
 
 Lloyd, 456 
 
 Locality studies, 319 
 
 Lochhead, 477 
 
 Locustidae, 10; molts of, 144 
 
 Locy, 446 
 
 Lodeman, 477 
 
 Lodge, 470 
 
 Loeb, 302, 304, 305, 306, 308, 309, 311, 373, 
 468, 469, 470, 476 
 
491 
 
 Lomechusa, *2<)g 
 
 Longitudinal muscles, *io5, io6 
 
 Lord, 268 
 
 Lorum, *42 
 
 Losses through insects, 410 
 
 Lovell, 445 
 
 Low, on malaria, 250 
 
 Lowe, 424 
 
 Lowne, 435, 443, 444, 450 
 
 Lubbock, on ants, 289, 290, 292, 294, 297, 
 298, 307; larval characters, 146; mus- 
 cles, 78; vision, 99; 432, 441, 443, 444, 
 454, 462 
 
 Lucanus, cocoon of, 148; dorsal vessel, *io9; 
 spiracles, *i2o 
 
 Lucilia, *3o6 
 
 Lugger, 425 
 
 Liihe, 465 
 
 Luks, 442 
 
 Luminosity, 114 
 
 Lund, 448 
 
 Lutz, 383, 385, 432, 456 
 
 Lycana, facets of, 31 
 
 Lycaenid larvae, alluring gland of, 74 
 
 Lyais, mimicked, 206, 207 
 
 Lyon, 304 
 
 Lyonet, on muscles, 78; 435, 441 
 
 MacGillivray, 456 
 
 Machilis, 9, 21; abdominal appendages, *6i; 
 nervous system, *8i; scales, *69; 
 spiracles, 60 
 
 Macloskie, 449, 455 
 
 Macrosiphum pisi, interactions of, 380 
 
 Madeira Islands, beetles of, 326 
 
 Maggot, 137 
 
 Malacopoda (see Onychophora). 
 
 Malacosoma, eggs, 141 
 
 Malaria, 248, ^249 
 
 Male genitalia, 64, *65, *66 
 
 Mallock, A., 444 
 
 Mallock, H. R. A., 438 
 
 Mallophaga, *i2, 233 
 
 Malpighian tubes, *io8 
 
 Mammen, 450 
 
 Mandibles, *35; adaptations of, *2>^; Culex, 
 *4i; Lepidoptera, *4o 
 
 Mandibular, neuromere, *43, 81, 135; seg- 
 ment, 44 
 
 Mandibulate mouth parts, *35; orders, 34 
 
 Mandus, 461 
 
 Mann, 141 
 
 Manomcra, *iq^ 
 
 Manson, on filariasis, 265; malaria, 250; 465 
 
 Mantida;, 10, 270 
 
 Mantis pa, 24; metamorphosis of, *i43 
 
 Maples, insects of, 212 
 
 Marchal, 136, 453 
 
 Marey, on wing vibration, 58; 437, 438 
 
 Ma'T gar opus, 269 
 
 Marine insects, 170 
 
 Mark, E. L., 444 
 
 Marlatt, 428, 429 
 
 Marshall, on adaptive coloration, 206, 207, 
 460, 461 
 
 Martin, 438 
 
 Mast, 470 
 
 Maternal provision, 276 
 
 Maturation, 129 
 
 Maxillae, 37, *38 
 
 Maxillary, neuromere, *43, 81, 135; seg- 
 ment, 44 
 
 Maxillulae, 36 
 
 Mayer, A. G., on color pattern, 188; Papilio, 
 179; scales, 71 ; 441, 458, 460 
 
 Mayer, A. M., on Culex, 94, 443 
 
 Mayer, P., 432, 443 
 
 Mayetiola destructor, distribution, 368; 
 evaporation on, 371; longevity, 377; 
 losses through, 410; moisture on, 365 
 
 May fly, male genitalia of, *65; wings, *56 
 
 McAtee, 461 
 
 McColloch, 359, 367, 368 
 
 McCook, on ants, 291, 294, 295, 296, 297, 
 466 
 
 McDermott, 449 
 
 McEwen, 311 
 
 Mclndoo, 90, 445, 446, 470 
 
 Mealworm (see Tenebrio). 
 
 Meconium, 152 
 
 Mecoptera, defined, 17; origin, 24 
 
 Media, *54, 55 
 
 Median segment, 44, 61 
 
 Meek, 436 
 
 Megackile, hairs of, *68 
 
 Megalodacnc, antenna of, *32 
 
 Meganeura, 344 
 
 Megarhyssa,* 272 
 
 Megilla (see Ceratomegilla). 
 
 Melander, 426, 467 
 
 Melanism, 180 
 
 Melanoplus, alimentary tract of, *io2; 
 facets, *3o; genitalia, *6y; mandible, 
 *36; respiration, 122; skull, *29 
 
492 
 
 INDEX 
 
 Melanotus, larva of, *i42 
 
 Meldola, 460 
 
 Melissodes, 225 
 
 Melnikow, 451 
 
 Melo'e, antenna of, 2,3', hypermetamorphosis, 
 156 
 
 Melolontha, male reproductive system, 
 *i24; olfactory pits, 88 
 
 Mendelism, 209 
 
 Menopon, *i2 
 
 Mentum, *35, 37 
 
 Merriam, on life zones, 332, 471, 472 
 
 Merrifield, 457, 458 
 
 Merrill, 425 
 
 Mesenchyme, *i36 
 
 Mesenteron, *io2, *io3, *io4, 136 
 
 Mesnil, 465 
 
 Mesoderm, 130, *i36 
 
 Meso-entoderm, *i3i 
 
 Mesothorax, 44 
 
 Metabola, 140 
 
 Metallic colors, 173 
 
 Metamorphosis, defined, 137; external, 137; 
 internal, 160; significance, 159; sys- 
 tematic value, 24 
 
 Metatarsus, *2 28 
 
 Metathorax, 44 
 
 MetschnikoflF, 446, 451, 454 
 
 Miall, on chitin, 66; muscles, 78, 431, 435, 
 442, 450, 454, 456 
 
 Miaslor, paedogenesis of, *i28 
 
 Michels, 442 
 
 Michelson, 173, 174 
 
 Microcentrum, stridulation of, 92, *93 
 
 Microphaga, 373 
 
 Micropteryx, mouth parts of, 40 
 
 Micropyle, 129, 141 
 
 Mid intestine, *io2, *io3, *io4 
 
 Milkweed, pollination of, 221, *2 22 
 
 Mimicry, 201; evolution of, 208 
 
 Minot, 440 
 
 Miocene insects, 341, 345 
 Mitchell, 465 
 
 Moisture, 364; its effects on activity, 365; 
 aestivation, 366; coloration, 178; eclo- 
 sion, 365; hibernation, 365; metabo- 
 lism, 364; mortality, 365; oviposition, 
 
 36s 
 Molanna, *i7 
 Moles, insectivorous, 236 
 Moller, on leaf-cutting ants, 295, 462 
 Mollock, on vision, 99 
 
 Molting, 144, 359 
 Molts, number of, 144 
 Moniliform, *3,2 
 Mononychus, 226 
 Monophagous, 373 
 Mordella, facets of, 31 
 Mores, 393 
 
 Morgan, C. Lloyd, 207, 468, 469 
 Morgan, H. A., 426 
 Morgan, T. H., 377, 469, 474 
 Morpho, scales of, 70, 172 
 Morrill, 354 
 
 Morse, A. P., 396, 397, 472, 474 
 Mosaic diseases, 319 ~ 
 
 Mosquito, antennae of, *34; hearing, 94; 
 hibernation, 311; locomotion of larvae, 
 167; in relation to malaria, 248, 250; 
 mouth parts, *4i; respiration, 169; 
 tropisms, 311 
 Moulton, 461 
 
 Mouth parts, dipterous, *4i; hemipterous, 
 
 *39; hymenopterous, *42; lepidopter- 
 
 ous, *4o; mandibulate, *35; orthopter- 
 
 ous, *35; suctorial, 38 
 
 Muir, 23 
 
 Miiller, F., on mimicry, 204; wings, 53; 
 
 460 
 Muller. H., 462 
 
 Miiller, J., mosaic theory of, 98, 443 
 Miillerian mimicry, 203, 204 
 Murray, 471 
 
 Miisca, egg of, *i39; facets, 31; fungus of, 
 
 *2i8; molts, 145; oviposition, 365; 
 
 ovum, *i29; in relation to t>'phoid 
 
 fever, 257, 258, 259 
 
 Muscidae, cardiac valve of, *io4; imaginal 
 
 buds, *i6i 
 Muscles, circular and longitudinal, ro6; of 
 cockroach, *53, *77; of leg, *sy, num- 
 ber, 77; structure, *78; of mng. *so 
 Muscle-tension theory, 311 
 Muscular, power, 79; system, 77 
 MiUilla, stridulation of, 92 
 Muttkowski, 456 
 Mycetophaga, 374 
 Myrientomata, 6, *7 
 Myriopoda, 5 
 Myrmecocystus, 295 
 Myrmecodia, 232 
 
 Myrmecopkana, mimicry, by, *205 
 Myrmecophilism, 297 . ' 
 Myrmedonia, 300 
 
493 
 
 Myrmeleon, digestive system of, *io3; pre- 
 
 daceous, 270; silk glands, 77 
 Myrmica, *2gg 
 Mystacides, androconia of, 72 
 
 Nagana, 263 
 
 Nagel, 444 
 
 Nearctic realm, 331 
 
 Necrophagous, 373 
 
 Necrophorus, 236, 276 
 
 Needham, 54, 104, 424, 438, 447, 456, 
 462 
 
 Nelson, 453 
 
 Nemobius, leg of, *5o 
 
 Neotropical realm, 331 
 
 Nepa, respiration of, 169 
 
 Nephrocyte, 1 10 
 
 Nerves, of head, 81, *82; structure, *8i 
 
 Nervous system, 80; development of, 133, 
 *i3S 
 
 Nervures, 54 
 
 Neuration, *54, *55, *56 
 
 Neuroblasts, *i35 
 
 Neuromeres, 44, 134; of head, *43, So 
 
 Neuroptera, defined, 17; metamorphosis of, 
 24, *i43 
 
 Newbigin, 458, 460 
 
 Newcomer, 362 
 
 Newell, A. G., 440 
 
 Newell, W., 426 
 
 New Mexico, insect communities in, 399 
 
 Newport, on metamorphosis, 162; muscles, 
 78; 435, 441, 442 
 
 Newton, 442 
 
 NicoUe, 267 
 
 Noguchi, 255, 256 
 
 Northrop, 373, 476 
 
 Notolophiis, olfactory organs of, 89 
 
 Notoneda, *i66; locomotion of, *i66; res- 
 piration, 169 
 
 Notum, 45 
 
 Novius, 275, 412, 428 
 
 Nucleolus, 129 
 
 Number of insects, 27 
 
 Nuttall, 464 
 
 Nymph, 139 
 
 Oaks, insects of, 212, 410 
 Oberea, eyes of, 30 
 Obtect pupa, *i47 
 Occipital foramen, 29, *30 
 
 Occiput, 29 
 
 Ocelli, *3i; structure of, 95; vision bv, 
 96 
 
 Ockler, 437 
 
 Ocular, neuromere, *43; segment, 44 
 
 Odonata, abdominal segments of, 60; copu- 
 lation of, 65; defined, 14; ocelli, 31; 
 origin, 23; spiracles, 60 
 
 Odors, 73; efficiency of, 246 
 
 Odynertcs, 225 
 
 (Ecanlkus, abdominal appendages of, 61, 
 *i33; embryo, *i33; stridulation, 93 
 
 (Ecophylla, 291 
 
 (Edipoda, dorsal vessel of, *iio 
 
 (Eneis, distribution of, 325 
 
 (Enocytes, *ii4 
 
 (Esophageal commissures, *82 
 
 Esophagus, *io2, *io3, *io4 
 
 (Estridae, 234 
 
 O'Kane, 426, 477 
 
 Olfactory organs, 87, *88, *89 
 
 Oligocene insects, 341 
 
 Oligophagous, 373 
 
 Oligotoma, *ii 
 
 Ommatidium, *97, *98 
 
 Onthophagus, mandible of, *t,6 
 
 Onychophora, 2. *3 
 
 Ophthalmia, 269 
 
 Ore hell mum, stridulation of, 92 
 
 Orders of insects, 7, *25 
 
 Oriental realm, 332 
 
 Origin of arthropods, *8; of insects, 6 
 
 Oroya fever, 269 
 
 Orthoptera, abdominal segments of, 60; 
 defined, 9; ecological succession, 408; 
 origin, 22; stridulation, 92, *93 
 
 Osborn, 426, 477 
 
 Osburn, 384, 386, 387, 456 
 
 Osmeterium, *74 
 
 Osmia, 225 
 
 Osmoderma, cocoon of, 148 
 
 Osten-Sacken, 440 
 
 Ostium, *i09, *iio 
 
 Oudemans, 450 
 
 Oustalet, 455 
 
 Ovaries, 123, *i26 
 
 Ovariole, 125 
 
 Oviducts, 125, *i26 
 
 Ovipositor, 62, *63, *67 
 
 Ovogenesis, 129 
 
 Ovum, of Musca, *i29; Vanessa, *i2 7 
 
 Ox-warble, *i42, 235 
 
494 
 
 Paasch, 443 
 
 Packard, on Anophthalmus, 100; Arthro- 
 poda, 7; classification, 7; Mantispa, 
 143; olfactory pits, 88; relationships of 
 orders, 22; segmentation, 27; types of 
 larvae, 142; wings, 53; 423, 427, 431, 
 432, 433, 439, 442, 444, 449, 454, 455, 
 461, 476 
 
 Pasdogenesis, 128 
 
 Palaearctic realm, 331 
 
 Palaoblatlina, *34i 
 
 Palaeodictyoptera, 347 
 
 Palmen, 449, 450 
 
 Palmer, 464 
 
 Palpifer, *35, 37, *38 
 
 Palpiger, *35, 37, *38 
 
 Palpus, *2,S, 37, *38, *40 
 
 Pankrath, 444 
 
 Panorpidae, 18; legs of, 51 
 
 Pantophagous, 373 
 
 Papilio, colors of, 179; egg, *i39; facets, 31; 
 head of pupa, *i47; melanism, 180; 
 mimicry, 202, 205; osmeterium, *74; 
 protective resemblance, 196; cenea, 
 mimicry by, 202, 205 
 
 Paraglossa, *s5, 37, *38 
 
 Paragnaths, 37 
 
 Paralysis, infantile, 269 
 
 Paraponyx, *ii9, 170 
 
 Paraptera, 46 
 
 Parasita, defined. 16 
 
 Parasitic insects, 233, 271, 275; in relation 
 to birds, 245 
 
 Parasitism, 235, 271; economic importance 
 of, 274 
 
 Parcohlatta, mouth parts of, *35 
 
 Parker, on phototropism, 309, 469 
 
 Parks, 354, 475 
 
 Parman, 352, 363, 365, 475, 476 
 
 Parrott, 424 
 
 Parthenogenesis, 127, 216, 286, 290, 358 
 
 Passalus, cocoon of, 148; stridulation, 91 
 
 Patagia, 45 
 
 Patch, E. M., 425 
 
 Patten, B. M., 470 
 
 Patten, W., 444, 452 
 
 Pawlovi, 443 
 
 Pawlowa, 448 
 
 Payne, 311 
 
 Peacock, 437 
 
 Peairs, 426, 431, 475, 477 
 
 Pea louse (see Macrosiphum). 
 
 Peck, W. D., 423 
 
 Peckham, on behavior, 316, 318, 319, 466, 
 467, 469 
 
 Pecten, *228 
 
 Pectinate, *32 
 
 Peciinophora gossypiella, 419 
 
 Pedicel, *32 
 
 Pediculidae, 234 
 
 Pediculus, *i5, 234, 267, 268 
 
 Pelocoris, leg of, *5o 
 
 Penis, 64, *65, 124 
 
 Pepsis, 277 
 
 Perez, 455 
 
 Pericardial, ceUs, no; chamber, *io9, *i23 
 
 Peripatus, characters of, 2, *3, 5; systematic 
 position, 5 
 
 Periplaneta, olfactory pits of, 88 
 
 Peripodal, cavity, 161; membrane, 161; sac, 
 161 
 
 Peritrophic membrane, 106 
 
 Perla, olfactory pits of, 88 
 
 Perlidae, *i3, 14; nymph, *i42; tracheal 
 gUls, *ii8 
 
 Permian insects, 344 
 
 Peterson, 371, 437, 476 
 
 Petiolata, 19 
 
 Pettigrew, 437 
 
 Pettit, 426 
 
 Petunia, *2 25 
 
 Peytoureau, 439, 451 
 
 Pflugstaedt, 438 
 
 Phagocytes, 114, 160 
 
 PhancBus, legs of, 49, *5o 
 
 Pharynx, 102 
 
 Phasmidas, 10, *i95 
 
 Philiptschenko, 44 
 
 PhiUips, E. F., 429 
 
 Phillips, W. J., 368 
 
 Phlebotomus fever, 269 
 
 Phormia, antenna of, *32; eyes, *3i; meta- 
 morphosis, *i38; phototropism, 310 
 
 Phosphorescence, 114 
 
 Pholinus, luminosity of, *ii5 
 
 Photogeny, 114 
 
 Photopathy, 307 
 
 Photophil, 307 
 
 Photophob, 307 
 
 Phototaxis, 307 
 
 Phototropism, 306 
 
 Photurts, 116 
 
 Phragmas, 46, *48 
 
 Phthirius, 234 
 
INDEX 
 
 495 
 
 Phyciodes, coloration of, 178, *i82 
 
 Phylloxera, 350, 410, 416 
 
 Phylogeny, 5, *8, *2$ 
 
 Phytonomus, spread of, 338 
 
 Phytophaga, *i9 
 
 Phytophagous, 373 
 
 Pictet, on coloration, 176, 179 
 
 Piepers, 460 
 
 Pierce, 24, 157, 354, 360, 368, 375, 376, 378, 
 434, 463, 466 
 
 Pieris, color sense of, 100; dispersion, 322; 
 .fat-cells, *ii3; imaginal buds, *i62; 
 olfactory organs, *9o; scale, *6g; napi: 
 temperature experiments on, 182; pro- 
 todice: sexual coloration of, *i84; 
 rapa: androconium of, *7i; developing 
 wing, *i63; distribution, 338; eggs, 
 *i4o; food plants, 213; hair, *68; larval 
 tissues, *ii3; pupal coloration, 177; 
 wing vibration, 59; xanthodice, distri- 
 bution of, 322 
 
 Pigmental colors, 174 
 
 Pigments, of eyes, *96, *97, *98, *99; nature 
 of, 175; of Pieridc-e, 175 
 
 Pilifers, *4o 
 
 Pimpla, 274 
 
 Pine, insects of, 212 
 
 Ping, 476 
 
 Pinguicula, 216 
 
 Pink boll worm {set PecHnophora). 
 
 Placodeum, *85 
 
 Plague, 260 
 
 Planta, *2 28 
 
 Plant lice (see AphididcB). 
 
 Plants, diseases of, 218; insectivorous, 216; 
 insects in relation to, 212 
 
 Plasma, no 
 
 Plasmodium, 248 
 
 Plateau, on color sense, 100; muscular 
 power, 79; respiration, 123; 441, 444, 
 446, 449, 468 
 
 Platephemera, *342 
 
 Platheniis, abdominal appendages of, *66; 
 antenna, *32 
 
 Plalygaster, hypermetamorphosis of, 146, 
 *IS8 
 
 Platypsyllus, 234 
 
 Platyptera, defined, 10; origin of, 22, *2$ 
 
 Plecoptera, defined, 14, *i3; nymph, *i42; 
 origin, 22, *25 
 
 Pleistocene insects, 341 
 
 Pleurites, *45, *47 
 
 Pleuron, 45 
 
 Plotnikow, 441 
 
 Pocock, 432 
 
 Podical plate, *()^ 
 
 Podisus, egg of, *i39; predaceous, *27o 
 
 Pcecilocapsus, color changes of, 190 
 
 Pogonomytmex, 297 
 
 Polar bodies, *i29 
 
 Poletajew, 449, 455 
 
 Poliomyelitis, 269 
 
 Polistes, behavior of, 316, 321; habits, 288; 
 wing vibration, *58 
 
 Poliles, on Iris, *226 
 
 Pollenizers, insect, 225 
 
 Pollination, 219, 225; of Iris, *22o; milk- 
 weed, 221, *222; orchids, 221; Yucca, 
 
 222, *224 
 
 Pollinia, *22 2 
 
 Polyhia, 287 
 
 Polyembryony, 136 
 
 Polyergus, 294 
 
 Polygoneutic, 182 
 
 Polygonia, dimorphism of, 180; egg, *i39 
 
 Polymorphism, 289 
 
 Polynema, 158 
 
 Polyphagous, 373 
 
 Polyphemus (see Telea). 
 
 Polyphylla, assembling of, 90 
 
 Polyrhachis, 291 
 
 Pomace flies (see Drosophila). 
 
 Pompilus, behavior of, 316, 319 
 
 Popillia japonica, 418 
 
 Porthetria dispar, damage by, 416; distribu- 
 tion by winds, 368; gynandromor- 
 phism, *i28; tracheoles, *i2i 
 
 Postclypeus, 29 
 
 Postgense, 29 
 
 Postscutellum, *45, *46 
 
 Potato beetle (see Leptinolarsa). 
 
 Pouchet, 468 
 
 Poulton, on adaptive coloration, 206, 207, 
 209; on colors of larvas and pupae, 177; 
 454, 457, 458, 459, 460, 461 
 
 Powell, 139, 455 
 
 Pratt, 454, 455 
 
 Precipitation, 366 
 
 Predaceous insects, 233, *27o; in relation 
 to birds, 245 
 
 PreU, 434 
 
 Premandibular, appendages, *i32; segment, 
 *43, 44 
 
 Pressure, 363 
 
496 
 
 INDEX 
 
 Pricerj 467 
 Primitive insects, 20 
 
 streak, 130 
 Primordial insect, 21 
 Priomis, assembling of, 91; eggs, 141 
 Proboscis, *40 
 
 Procephalic lobes, *i32, *i33 
 Prochnow, 438, 445 
 Proctodaeum, *io2, 104, 131 
 Proctotrypidae, 27, 274 
 Prodoxus, 224 
 Prodryas, *346 
 Prognathous, 11 
 Promethea (see Callosamia). 
 Pronotum, *46 
 Pronuba, *223, *224 
 Propodeum, 44 
 Propolis, 283 
 Prolapteron, 6 
 Protective, adaptations, 245; mimicry, 
 
 *20i, 206; resemblance, *i94, 198 
 Prothorax, 44 
 Protocerebrum, 80, 135 
 Protoparce, head of moth, *4o; larva, *si; 
 
 moth, *225; parasitized larva, *273 
 Protura, 6, *7 
 
 Proventriculus, *io2, *io3, *io4 
 
 Pseudocercus, *6i, 62, *65 
 
 Pseudocone, *98 
 Pseudomyrma, 230 
 
 Psocidae, *i2 
 
 Pteromalus, oviposition of, 376 
 
 Pteronarcys, *i3; tracheal gills of, 119 
 
 Pterygota, 9 
 
 Ptilodadyla, antenna of, *32 
 
 Pulvillus, 48, *5i 
 
 Punktsubstanz, 81 
 
 Punnett, 209, 461 
 
 Pupfe, 137,-146; emergence of, 152; protec- 
 tion, 148; respiration, 147 
 
 Pupal stage, significance of, 159, 162 
 
 Puparium, 147, 372 
 
 Pupation of a caterpillar, 147, *i49 
 
 Putnam, on habits of Bombus, 287 
 
 Pyloric valve, 104 
 
 Pyrausta nubilalis, spread of, 418 
 
 Pyrophila, thigmotropism of, 304 
 
 Pyrophorus, luminosity of, 115 
 
 Pyrrharctia (see Isia). 
 
 Quaintance, 359, 366, 372, 428 
 Quaternary insects, 346 
 
 Quayle, 425 
 Quedkis, 300 
 Queen, honey bee, *282; termite, *278 
 
 Radius, *54 
 Rddl, 469 
 Rainfall, 366 
 
 Ranatra, 166; phototropism of, 311; respira- 
 tion, 169 
 Rand, 463 
 Raschke, 449 
 
 Rath, vom, on sense hairs, *9o; 444, 445 
 Rathke, 449 
 
 Rationality, apparent, 314; lack of, 321 
 Rau, 352, 470 
 Realms, faunal, 328, *329 
 Reaumur, de, 435 
 Receptaculum seminis, 125, *i26 
 Recognition markings, 211 
 Rectal respiration, 119, 170 
 Rectum, 105 
 Recurrent nerve, 81, *83 
 Redikorzew, on ocelli, *96, 445 
 Redtenbacher, 437 
 Reed, on yellow fever, 253, 465 
 Rees, van, 454 
 Reichenbach, on ants, 128 
 Relapsing fever, 267 
 
 Relationships, of arthropods, 4, *7; oi 
 orders, 20, *25 
 
 Repellent glands, 73 
 
 Replacements, 190 
 
 Reproduction, of plant lice, 358 
 
 Reproductive system, 123 
 
 Respiration, 122, 147, 155 
 
 Respiratory system, 116, *ii7 
 
 Reticitlitermes, 279, 281 
 
 Retina, *g6 
 
 Retinula, *g(), *g% 
 
 Renter, 445 
 
 Rhabdom, *g(), 97, *98 
 
 Rheotropism, 304 
 
 Rhipiphorus, 156 
 
 Rhopalocera, 18 
 
 Rhyphus, *5S 
 
 Ricketts, 267, 269 
 
 Riley, C. F. C, 304, 470, 474, 476 
 
 Riley, C. V., on hypermetamorphosis, 156; 
 losses through insects, 410; pollination 
 of Yucca, 222; pupation, 147; 377, 4io> 
 412, 425, 427, 454, 462 
 Riley, W. A., 139, 465 
 
497 
 
 Rimsky-Korsakow, 6, 434 
 
 Ritter, 438 
 
 Robertson, 462 
 
 Robin, food of, 240 
 
 Rocky Mountain locust, dispersion of, 322; 
 
 as food of birds, 243 
 Rocky Mountain spotted fever, 269 
 Rolfs, 426 
 Rollet, 442 
 
 Romanes, on instinct, 317, 468 
 Rosenau, 269 
 Ross, on malaria, 250, 464 
 Rossig, 462 
 Rostrum, 39 
 Roziles, *296 
 Ruggles, 425 
 Ruland, 444 
 
 Sadones, 450, 455, 456 
 
 Saliva, of Dytiscus, 107; mosquito, 107 
 
 Salivary glands, *io6, *io7 
 
 Sambon, on malaria, 250 
 
 Samia cccropia, antennas of, *2,y, cocoon, 
 *i5i; egg, 141; food plants, 213; geni- 
 talia, *66; head of larva, *74; Malpigh- 
 ian tubes, *io8; ocelli, *3i; odor, 74, 
 scales, *7i 
 
 Sanderson, 356, 359, 360, 362, 365, 366, 370, 
 426, 431, 474, 477 
 
 Sandias, 466 
 
 San Jose scale insect (see Aspidiotus perni- 
 ciosiis) . 
 
 Saprophagous, 373 
 
 Sarcolemma, *78 
 
 Sarcophaga, nervous system of, *82 
 
 Sarcophagous, 373 
 
 Satiirma, hairs of, *68 
 
 Saunders, 429, 476 
 
 Saville-Kent, 472 
 
 Scales, arrangement of, *7o; development, 
 70, *7i; form, *6g, *7i; occurrence of, 
 69; uses, 70 
 
 Scape, *32 
 
 Scarabaeidoid larva, 157 
 
 Scavenger insects, 236 
 
 Schaffer, on scales, 70; 435, 441, 448 
 
 Schenk, on sensilla, 84, *85, 89, 445 
 
 Schepotiefif, 6, 434 
 
 Scheuring, 445 
 
 Schewiakoff, 442 
 
 Schiemenz, 446 
 
 Schimper, 462 
 32 
 
 Schindler, 446 
 
 Schistocerca, distribution of, 323, 339; of 
 Galapagos Islands, 326; isolation, 328 
 
 Sckizoneura, wax of, 75 
 
 Schizura, protective resemblance of, *io6 
 
 Schmidt, O., 454 
 
 Schmidt, P., 433, 448 
 
 Schmidt-Schwedt, 449 
 
 Schneider, A., 450 
 
 Schneider, R., 440 
 
 Schoene, 424 
 
 Schon, 445 
 
 Schroder, 436 
 
 Schwarz, on distribution, 336, 337; myrme- 
 cophilism, 300, 471 
 
 Schwedt, 455 
 
 Sclerite, 28 
 
 Scolopendra, *5, 401 
 
 Scolopendrella, *6, 21 
 
 Scorpion, *2, 401 
 
 Scudder, on albinism, 180; coloration, 187; 
 fossil insects, 341, 345, 346, 347; glaci- 
 ation, 326; mimicry, 203; Orthoptera 
 of Galapagos Islands, 326, 328; spread 
 of P. rapa, 338; stridulation, 92; 443, 
 457, 471, 473> 474 
 
 Scutellum, *45 
 
 Scutum, *45 
 
 Seasonal coloration, 180 
 
 Sedgwick, 433 
 
 Segmentation, of arthropods, 27; germ 
 band, *i3i, 132; head, *43 
 
 Segments of abdomen, 60 
 
 Seitz, 457, 462, 466, 468, 471 
 
 Sematic colors, 210 
 
 Seminal ducts, 124; receptacle, 125, *i26; 
 vesicle, *i24 
 
 Semon, 472 
 
 Semper, C, on scales, 70 
 
 Semper, K., 471 
 
 Sempers, 477 
 
 Sense organs, 83 
 
 Sensilla, 84, *8s 
 
 Serosa, *i3i, *i34 
 
 Sessili ventres, *i9 
 
 Setaceous, *32 
 
 Setae, modifications of, 69 
 
 Seventeen-year locust, 145 
 
 Severin, 359, 371, 470 
 
 Sex-determination, 376 
 
 Sexual coloration, 184 
 
 Shannon, 472 
 
498 
 
 INDEX 
 
 Sharp, on AUa, 293; Hawaiian beetles, 326; 
 metamorphosis, 159; 415, 431, 433, 449, 
 
 455 
 
 Sheath, *64 
 
 Shelford, R., 460 
 
 Shelf ord, V. E., on chemical conditions, 383; 
 communities, 393, 397; environments, 
 388, 389; evaporation, 368, 369, 370, 
 371; physical conditions, 384; succes- 
 sion, 404, 406, 407, 408; tension lines, 
 399; tiger beetles, 174, 175, 183, 189, 
 350; 459, 472, 474, 475, 576 
 
 Sherman, F., Jr., 426 
 
 Sherman, J. D., Jr., 386, 456 
 
 Shreve, 389, 391, 476 
 
 ShuU, 94, 445 
 
 Silk, 76 
 
 Silk glands, 75, *y6 
 
 Silkworm (see Bombyx mori). 
 
 Silpha, distribution of, 336 
 
 Silurian insects, 341 
 
 Silvestri, on Anajapyx, *6; 433, 434 
 
 Simmermacher, 440 
 
 Simpson, 358 
 
 Simulium, 233; respiration, 170 
 
 Sinclair, 433 
 
 Siphonaptera, *2o; origin of, *25, 26 
 
 Sirex, ovipositor of, *64 
 
 Sirrine, 424 
 
 Sitaris, 156 
 
 Size of insects, 27 
 
 Skin, 66 
 
 SkuU, 28, *29 
 
 Skunk, insectivorous, 236 
 
 Sladen, 287, 467 
 
 Sleep of insects, 352 
 
 Sleight, 385, 456 
 
 Slingerland, 411, 424, 477 
 
 Smell, 87; end-organs of, *88, *89 
 
 Sminthurus, *io 
 
 Smith, E. F., 219 
 
 Smith, J. B., 425, 477 
 
 Smith, R. C, 426 
 
 Smith, T., 269 
 
 Snodgrass, 24, 326, 328, 436, 438 
 
 Snow flea, *io 
 
 Snyder, 468 
 
 Societies, 389 
 
 Soil, 348; nutriment in, 351; structure of, 
 348; temperature, 350 
 
 Soldier, ants, 289; termites, *277 
 
 Somatic cells, 129 
 
 Sorensen, 433 
 
 Sounds, 91 
 
 Spence, 431, 432 
 
 Spermatheca, 125, *i26 
 
 Spermatogenesis, 129 
 
 Spermatophores, 124 
 
 Spermatozoa, 124, *i25 
 
 Sperm-nucleus, 129 
 
 Speyer, on hermaphroditism, 126 
 
 Sphecina, 277 
 
 Sphecius, 277 
 
 Sphex, *223; behavior of, 316, 318, *3i9 
 
 Sphingidae, as poUenizers, 221, *2 25 
 
 Sphinx, alimentary tract of, *io4; dispersal, 
 323; pulsations of heart, 112; trans- 
 formation, *i63 
 
 Spichardt, 450 
 
 Spillman, 268 
 
 Spines, 69 
 
 Spinneret, *74, 75 
 
 Spiracles, closure of, *i2o; number, 60, 119 
 
 Sbiroholiis, *3 
 
 Si^irochata, 267 
 
 Spongioplasm, 78 
 
 Sporotrichum, 218, 367 
 
 Spuler, on scales, 70; 438, 441, 458 
 
 Spur, *49 
 
 Squama, 54 
 
 Squash bug, metamorphosis of, *i38 
 
 Stadium, 140 
 
 Stagmomantis , leg of, *5o 
 
 Standfuss, temperature experiments of, 183, 
 458 
 
 Stedman, 426 
 
 Stefanowska, on pigment, 99; 444 
 
 Stegomyia, 255 
 
 Stellwaag, 438 
 
 Stenanima, 292 
 
 Stenobothrus, blood corpuscles of, *iio; 
 stridulation of, 92 
 
 Stenodictya, *343, 344 
 
 Stephens, 465 
 
 Stereotropism, 303 
 
 Sternberg, 250, 251, 464 
 
 Sternum, *47 
 
 Stigmata (,see Spiracles). 
 
 Sting of honey bee, *64 
 
 Stinging hairs, *73 
 
 Stings, efficiency of, 246 
 
 Stipes, *35, 37, *38 
 
 Stokes, 449 
 
 Stomach, *io4 
 
499 
 
 Stomachic ganglion, 8i, *8s 
 
 Stomatogastric nerve, 8i, *83 
 
 Stomodaeum, *io2, 131 
 
 Strata, 393 
 
 Slratiomys, 360 
 
 Straton, 462 
 
 Straus-Diirckheim, on muscles, 78; 435, 441 
 
 Strength, muscular, 79 
 
 Strepsiptera, 17, 137, 157 
 
 Stridulation, 92, *93 
 
 Strindberg, 453 
 
 Strong, R. P., 266 
 
 Strottgylonotus, 294 
 
 Structural colors, 172 
 
 Styloconicum, 84, *85 
 
 Stylops, hypermetamorphosis of, 157 
 
 Subcosta, *54 
 
 Subgalea, *38 
 
 Submentum, *35, *38 
 
 Suboesophageal ganglion, *8i, *82 
 
 Succession, 404; causes of, 404; ecological, 
 406; of forest communities, 406; geolog- 
 ical, 404; of Orthoptera, 408; seasonal, 
 405; of tiger beetles, 407 
 
 Suctorial mouth parts, 38 
 
 Suffusion, 178 
 
 Summers, 426 
 
 Superlingua;, 36, *38, *i32, 133 
 
 Superlingual, neuromere, *43, 81, 135; seg- 
 ment, 44 
 
 Supracesophageal ganglion, 80, *82 
 
 Suranal plate, 62, *67 
 
 Surface film, 168 
 
 Suspensor, 125 
 
 Suspensory muscles, *iio 
 
 Swarming, 286 
 
 Swenk, 426 
 
 Symbiosis, 299 
 
 Symons, 426 
 
 Sympathetic system, *8i, *83 
 
 Symphyla, 3, *6 
 
 Synchronism, of fireflies, 116 
 
 SjTiecology, 348 
 
 Syrphidae, silk glands of, 77 
 
 Systole, III 
 
 Tabanidae, 233 • 
 
 Tabanus, nervous system, *82; olfactory 
 
 organ, *89 
 Tachardia, 75 
 Tactile hairs, 69, 84, *8s 
 Tanidia, *i2 2 
 
 Tarantula, 401 
 
 Tarsus, *48 
 
 Taschenberg, 430 
 
 Taste, 84; end-organs of, *86, *87, *88 
 
 Taxis, 302 
 
 Tegmina, 53 
 
 Tegulae, 46 
 
 Telea polyphemus, cocoon of, 148; eclosion, 
 152; larval growth, 144; silk glands, 75; 
 spinning, 151 
 
 Teleas, 158 
 
 Telson, 60 
 
 Temperature, 352; acclimatization to, 360; 
 on activity, 353; on coloration, 182; on 
 distribution, 362; on hibernation, 361; 
 on incubation, 358; limits, 352; on 
 reproduction, 358; of soil, 350 
 
 Temperature-constant, 355 
 
 Tenebrio molitor, development, 359, 360; 
 incubation, 359; metabolism, 370 
 
 Tenent hairs, *72 
 
 Tension lines, 399 
 
 Tenthredinidae, larval legs of, 51 
 
 Tenthredopsis, larva of, *i42 
 
 Tentorium, 29, *3o 
 
 Terebrantia, *i9 
 
 Tergites, *45, *46 
 
 Tergum, 45 
 
 Termites, American species of, 279; archi- 
 tecture, *28o; classes of, *277; "com- 
 pass," *28o,- food of, 279; mandibles, 
 *36; origin of castes, 279; queen, *278; 
 ravages, 281 
 
 Termitidae, 11 
 
 Termitophilism, 281 
 
 Tertnitoxinia, 126, 127 
 
 Termopsis, 278 
 
 Tertiary insects, 341, 345 
 
 Testes, *i24 
 
 Tetralonia, 225 
 
 Tettigoniidae, 10; ovipositor, *6y, spermato- 
 zoon, *I25 
 
 Texas fever, 269 
 
 Thalessa (see Megarhyssa) . 
 
 Thanaos, androconia of, 72; claspers, 65 
 
 Thayer, 461 
 
 Thaxter, on Empusa, 217, *2i8; 462 
 
 Thelen, 449 
 
 Theobald, 477 
 
 Thermotropism, 312 
 
 Thigmotropism, 303 
 
 Thimm, 465 , 
 
500 
 
 INDEX 
 
 Thomas, 424, 427 
 
 Thompson, C. B., 443, 468 
 
 Thompson, S. M., 463 
 
 Thorax, differentiation of, 44; parts of, *45; 
 sclerites of, *45, *46, *47 
 
 Thread-press, *76 
 
 Thyridopteryx, eggs of, 141 
 
 Thysanoptera, *i4, 15; origin of, 22,, *2$ 
 
 Thysanura, 8, *9; abdominal segments, 60; 
 primitive, 20 
 
 Thysanuriform, 24, *i42, *i43, 160 
 
 Tibia, 48, *49 
 
 Tiger beetles (see CicindelidcB) . 
 
 Tillyard, 438, 476 
 
 Tipula, *2o 
 
 Titanophasma, 27 
 
 Toad, insectivorous, 236 
 
 Tongue, 37 
 
 Torre-Bueno, 475 
 
 Touch, 84 
 
 Tower, D. G., 437 
 
 Tower, W. L., on color patterns, 186; 
 cuticular colors, 175; distribution of 
 Lcptinoiarsa, 336; folding of wing, 56, 
 *57; hibernation, 365; integument, 
 *67; origin of wings, 53; structural 
 colors, 173; 441, 459, 472 
 
 Townsend, A. B., 448 
 
 Townsend, C. H. T., 426 
 
 Toxoptera graminum, development of, 356, 
 364; distribution of, 368 
 
 Toyama, 451 
 
 Tracheae, development of, 135, *i36; dis- 
 tribution, *ii7, *ii8; structure, *i2i 
 
 Tracheal gills, *ii8, 169 
 
 Tracheation, types of, 117 
 
 Tracheoles, *i2i, 122 
 
 Trelease, 462 
 
 Tremex, *i9 
 
 Trench fever, 268 
 
 Triassic insects, 345 
 
 Trie kins, 225 
 
 Trichodeum, 84, *85 
 
 Trichogen, *68, 69, *7i 
 
 Trichogranima, 274 
 
 Trichoptera, 18, *i7; origin of, *25; silk 
 glands, 77 
 
 Trichopterygidae, size of, 27; 273 
 
 Trimen, on dispersal, 323; on P. ccnca, 202, 
 205; 459, 460 
 
 Trimerotropis, protective resemblance of, 
 196, *i97 
 
 Trimorphism, 180 
 
 Triphleps, egg ofj *i39 
 
 Tritocerebrum, 80, 135 
 
 Triungulin, 156, *i57 
 
 Trochanter, 48, *49, 50 
 
 Trochantin, 48 
 
 Trogoderma, 2,11 
 
 Tropcca luna, cocoon of, 148 
 
 Trophallaxis, 301 
 
 Tropical region, 335 
 
 Tropidacris, 27; respiratory muscles of, *i23 
 
 Tropisms, 302 
 
 Trouessart, 471 
 
 Trouvelot, on cocoon-spinning, 151; eclo- 
 
 sion, 152; larval growth, 144; 453 
 Trypanosomes, 261, *262, *264 
 Trypanosomiases, 261, 263, 264 
 Tryphana, 116 
 Tsetse fly, 262, *263 
 Tuberculosis, 269 
 Turner, loi, 445 
 Tutt, 472 
 
 Typhoid fever, 257 
 Typhus, 266 
 
 Uhler, on distribution, 337 
 
 Uichanco, 358 
 
 Underbill, 464 
 
 Urech, 457, 458 
 
 Uric acid, 108; as a pigment, 175 
 
 Urosternite, 60 
 
 Urotergite, 60 
 
 Useful insects, 411 
 
 Utricularia, 217 
 
 Uzel, 453 
 
 Vagina, 125, *i26 
 
 Valette St. George, la, 450 
 
 Vanessa, development of scales of, *7i ; head 
 of butterfly, *4o; antiopa: 246; photo- 
 tropism, 309; atalanla: color change, 
 190; cardui: dispersion, 322, 326; geo- 
 graphical variation, 328; polychloros: 
 coloration, 179; melanism, 180; urticce: 
 coloration, 176; melanism, 180; tem- 
 perature experiments, 183 
 
 Variation in coloration, 188, *i9i, *I92 
 
 Variations, 190 
 
 Vas deferens, *i24 
 
 Vayssiere, 447, 449, 455 
 
 Vedalia (see Novius). 
 
 Vegetation map of U. S., *39i 
 
INDEX 
 
 Veins, *54 
 
 Velum, *228 
 
 Venation, *54 
 
 Ventral sinus, no, *i23 
 
 Ventral tube, 62 
 
 Ventriculus, *io4 
 
 Verhoeff, 438, 439, 440, 466 
 
 Vernon, 459 
 
 Vertex, 28 
 
 Vervvorn, on phototropism, 308; 469 
 
 Vespa, nests of, *288; olfactory organ, *89; 
 
 sensillum, *85; taste cups, *87; tongue, 
 
 *86 
 Vespidas, 287 
 Vestal, 394, 475 
 Viallanes, 435, 442, 448, 454 
 Vinal, 450 
 Vision, 95 
 
 Vitelline membrane, *i29 
 Vitreous body, 95, *96 
 Voliicclla, mimicry by, *2io; predaceous, 271 
 Voss, F., 438 
 Voss, H. v., 459 
 
 Wagner, F. v., 459 
 
 Wagner, J., 433 
 
 Wagner, N., 450 
 
 Wahl, 455 
 
 Walker, E. M., 434, 435 
 
 Walker, J. J., 456 
 
 Walking, 51 
 
 Walking-stick, *i95 
 
 Wallace, on mimicry, 203; 459, 460, 471 
 
 Walsh, on losses through insects, 410; 424 
 
 Walter, on mouth parts, 40; 436 
 
 Walton, 428 
 
 Warming, 474 
 
 Warning coloration, 199 
 
 Washburn, 425, 464 
 
 Wasmann, on myrmecophilism, 297; 466, 
 469, 470 
 
 Wasps, 287 
 
 Wasteneys, 470 
 
 Watase, 444 
 
 Water, 382; circulation of, 384; contents 
 of, 383; depth, 386; pressure, 385; of 
 soil, 350; temperature of, 385; vegeta- 
 tion of, 386 
 
 Watson, 474 
 
 Wax, 413 
 
 Wax, glands, 74; pincers, *2 28,^229 
 
 Webb, 429 
 
 Webster, F. M., on dispersal, 323, 335, 338, 
 
 368; losses through insects, 410; 425, 
 
 460, 462, 466, 471, 472 
 Webster, R. L., 426 
 Wedde, 436 
 Weed, C. M., on birds in relation to insects, 
 
 242, 243, 245; 426, 464 
 Weinland, 444 
 Weismann, on imaginal buds, 161; instinct, 
 
 317; temperature experiments, 182; 
 
 451, 453, 457, 458, 459, 460, 469 
 Weiss, 156, 311, 475 
 Welch, 456 
 Welles, 447 
 Wesche, 437 
 
 West wood, on Brachinus, 73; 431, 432 
 Wheeler, on ants, 289, 297, 320; Malpighian 
 
 tubes, 108; protective coloration, 178; 
 
 trophallaxis, 301; tropisms, 302, 303, 
 
 305, 306, 311; 439, 447, 448, 452, 453, 
 
 467, 468, 469 
 White, F. B., 455 
 Whitman, 469 
 
 Whymper, on distribution, 322; 472 
 Wickham, 347 
 Wielowiejski, von, 448, 450 
 Wilcox, 451, 463 
 Wilde, 446 
 Wilder, 267 
 
 Will, F., on taste, 85; 444 
 Will, L., 450, 452 
 Williams, C. B., 434 
 Williams, T., 449, 455 
 Wilson, 453 
 Wilt, cucurbit, 219 
 Wind, distribution by, 323, 368 
 Wings, 53; folding of, 56, *57; modifications 
 
 of, 53; muscles of, *59; venation, *54; 
 
 vibration, 57, *58, 91 
 Wistinghausen, von, 449 
 Witlaczil, 440, 447, 452, 454 
 W^odsedalek, 377 
 Wollaston, on beetles of Madeira Islands, 
 
 326 
 Woodward, 453 ' 
 
 Woodworth, 425, 438 
 Worker, ant, 289; bee, *282, 286; termite, 
 277, *278; wasp, 288 
 
 Xanthophyll, as a pigment, 176, 193 
 Xenoneura, *342 
 Xiphidium, stridulation of, 92 
 
502 
 
 INDEX 
 
 Yapp, 369 Z ait ha, 171 
 
 Yaws, 269 Zander, 440 
 
 Yellow fever, 252 Zeuzera pyrina, 419 
 
 Yolk, *i29, *i3o Zittel, von, 433 
 
 Yothers, 361, 377 Zones, life, *2,3z 
 
 Young, R. T., 461 Zoraptera, 12, 22 
 
 Yuasa, 437 Zorotypus, 12, 22 
 
 Yucca, pollination of, 222, *2 24 Zugmayer, 461 
 
a: 
 
 I