Coleoptera, a term used in zoological classification for the true beetles which form one of the best-marked and most natural of the orders into which the class Hexapoda (or Insecta) has been divided. For the relationship of the Coleoptera to other orders of insects see Hexapoda. The name (Gr. κολϵός, a sheath, and πτϵρά, wings) was first used by Aristotle, who noticed the firm protective sheaths, serving as coverings for the hind-wings which alone are used for flight, without recognizing their correspondence with the fore-wings of other insects.
These firm fore-wings, or elytra (fig. 1, A), are usually convex above, with straight hind margins (dorsa); when the elytra are closed, the two hind margins come together along the mid-dorsal line of the body, forming a suture. In many beetles the hind-wings are reduced to mere vestiges useless for flight, or are altogether absent, and in such cases the two elytra are often fused together at the suture; thus organs originally intended for flight have been transformed into an armour-like covering for the beetle’s hind-body. In correlation with their heavy build and the frequent loss of the power of flight, many beetles are terrestrial rather than aerial in habit, though a large proportion of the order can fly well.
Aristotle’s term was adopted by Linnaeus (1758), and has been universally used by zoologists. The identification of the elytra of beetles with the fore-wings of other insects has indeed been questioned (1880) by F. Meinert, who endeavoured to compare them with the tegulae of Hymenoptera, but the older view was securely established by the demonstration in pupal elytra by J. G. Needham (1898) and W. L. Tower (1903), of nervures similar to those of the hind-wing, and by the proof that the small membranous structures present beneath the elytra of certain beetles, believed by Meinert to represent the whole of the true fore-wings, are in reality only the alulae.
Structure.—Besides the conspicuous character of the elytra, beetles are distinguished by the adaptation of the jaws for biting, the mandibles (fig. 1, Bb) being powerful, and the first pair of maxillae (fig. 1, Bc) usually typical in form. The maxillae of the second pair (fig. 1, Bd) are very intimately fused together to form what is called the “lower lip” or labium, a firm transverse plate representing the fused basal portions of the maxillae, which may carry a small median “ligula,” representing apparently the fused inner maxillary lobes, a pair of paraglossae (outer maxillary lobes), and a pair of palps. The feelers of beetles differ greatly in the different families (cf. figs. 2b, 9b and 26b, c); the number of segments is usually eleven, but may vary from two to more than twenty.
The head is extended from behind forwards, so that the crown (epicranium) is large, while the face (clypeus) is small. The chin (gula) is a very characteristic sclerite in beetles, absent only in a few families, such as the weevils. There is usually a distinct labrum (fig. 1, Ba).
The prothorax is large and “free,” i.e. readily movable on the mesothorax, an arrangement usual among insects with the power of rapid running. The tergite of the prothorax (pronotum) is prominent in all beetles, reaching back to the bases of the elytra and forming a substantial shield for the front part of the body. The tergal regions of the mesothorax and of the metathorax are hidden under the pronotum and the elytra when the latter are closed, except that the mesothoracic scutellum is often visible—a small triangular or semicircular plate between the bases of the elytra (fig. 1, A). The ventral region of the thoracic skeleton is complex, each segment usually possessing a median sternum with paired episterna (in front) and epimera (behind). The articular surfaces of the haunches (coxae) of the fore-legs are often conical or globular, so that each limb works in a ball-and-socket joint, while the hind haunches are large, displacing the ventral sclerites of the first two abdominal segments (fig. 1, C). The legs themselves (fig. 1, A) are of the usual insectan type, but in many families one, two, or even three of the five foot-segments may be reduced or absent. In beetles of aquatic habit the intermediate and hind legs are modified as swimming-organs (fig. 2, a), while in many beetles that burrow into the earth or climb about on trees the fore-legs are broadened and strengthened for digging, or lengthened and modified for clinging to branches. The hard fore-wings (elytra) are strengthened with marginal ridges, usually inflected ventrally to form epipleura which fit accurately along the edges of the abdomen. The upper surface of the elytron is sharply folded inwards at intervals, so as to give rise to a regular series of external longitudinal furrows (striae) and to form a set of supports between the two chitinous layers forming the elytron. The upper surface often shows a number of impressed dots (punctures). Along the sutural border of the elytron, the chitinous lamella forms a tubular space within which are numerous glands. The glands occur in groups, and lead into common ducts which open in several series along the suture. Sometimes the glands are found beneath the disk of the elytron, opening by pores on the surface. The hind-wings, when developed, are characteristic in form, possessing a sub-costal nervure with which the reduced radial nervure usually becomes associated. There are several curved median and cubital nervures and a single anal, but few cross nervures or areolets. The wing, when not in use, is folded both lengthwise and transversely, and doubled up beneath the elytron; to permit the transverse folding, the longitudinal nervures are interrupted.
with feelers and palps; c, larva; d, pupa.
Ten segments can be recognized—according to the studies of K. W. Verhoeff (1804–1896)—in a beetle’s abdomen, but the tenth sternite is usually absent. On account of the great extension of the metathorax and the haunches of the large hind-legs, the first abdominal sternite is wanting, and the second is usually so much reduced that the foremost apparent ventral sclerite of the abdomen represents the third sternite. From this point backwards the successive abdominal segments, as far as the seventh or eighth, can be readily made out. The ninth and tenth segments are at most times retracted within the eighth. The female can protrude a long flexible tube in connexion with the eighth segment, carrying the sclerites of the ninth at its extremity, and these sclerites may carry short hairy processes—the stylets. This flexible tube is the functional ovipositor, the typical insectan ovipositor with its three pairs of processes (see Hexapoda) being undeveloped among the Coleoptera. In male beetles, however, the two pairs of genital processes (paramera) belonging to the ninth abdominal segment are always present, though sometimes reduced. Between them is situated, sometimes asymmetrically, the prominent intromittent organ.
In the structure of the digestive system, beetles resemble most other mandibulate insects, the food-canal consisting of gullet, crop, gizzard, mid-gut or stomach, intestine and rectum. The stomach is beset throughout its length with numerous small, finger-like caecal tubes. The excretory (malpighian) tubes are few in number, either four or six. Many beetles have, in connexion with the anus, glands which secrete a repellent acid fluid, serving as a defence for the insect when attacked. The “bombardier” ground beetles (fig. 5) have this habit. Oil-beetles (figs. 23 and 24) and ladybirds (fig. 32) defend themselves by ejecting drops of fluid from the knee-joints. The nervous system is remarkably concentrated in some beetles, the abdominal ganglia showing a tendency to become shifted forward and crowded together, and in certain chafers all the thoracic and abdominal ganglia are fused into a single nerve-centre situated in the thorax,—a degree of specialization only matched in the insectan class among the Hemiptera and some muscid flies.
Development.—The embryonic development (see Hexapoda) has been carefully studied in several genera of beetles. As regards growth after hatching, all beetles undergo a “complete” metamorphosis, the wing-rudiments developing beneath the cuticle throughout the larval stages, and a resting pupal stage intervening between the last larval instar and the imago. The coleopterous pupa (figs. 2d, 3c) is always “free,” the legs, wings and other appendages not being fixed to the body as in the pupa of a moth, and the likeness of pupa to perfect insect is very close.
|From Chittenden, Yearbook, 1894, U.S. Dept. of Agriculture.|
| Fig. 3.—Grain Weevils. a, Calandra granaria; b, larva; c, pupa;|
d, C. oryzae.
The most striking feature in the development of beetles is the great diversity noticeable in the outward form of the larva in different families. The larva of a ground-beetle or a carnivorous water-beetle (fig. 2 c) is an active elongate grub with well-armoured cuticle. The head—carrying feelers, mandibles and two pairs of maxillae—is succeeded by the three thoracic segments, each bearing a pair of strong five-segmented legs, whose feet, like those of the adult, carry two claws. Ten segments can be distinguished in the tapering abdomen, the ninth frequently bearing a pair of tail-feelers (cerci), and the tenth, attached ventrally to the ninth, having the anal opening at its extremity and performing the function of a posterior limb, supporting and temporarily fixing the tail end of the insect on the surface over which it crawls. Such a typically “campodeiform” grub, moving actively about in pursuit of prey, is the one extreme of larval structure to be noticed among the Coleoptera. The other is exemplified by the white, wrinkled, soft-skinned, legless grub of a weevil, which lives underground feeding on roots, or burrows in the tissues of plants (fig. 3 b). Between these two extremes we find various transitional forms: an active larva, as described above, but with four-segmented, single-clawed legs, as among the rove-beetles and their allies; the body well armoured, but slender and worm-like, with very short legs as in wireworms and mealworms (figs. 18, 21 b); the body shortened, with the abdomen swollen, but protected with tubercles and spines, and with longish legs adapted for an active life, as in the predaceous larvae of ladybirds; the body soft-skinned, swollen and caterpillar-like, with legs well developed, but leading a sluggish underground life, as in the grub of a chafer; the body soft-skinned and whitish, and the legs greatly reduced in size, as in the wood-feeding grub of a longhorn beetle. In the case of certain beetles whose larvae do not find themselves amid appropriate food from the moment of hatching, but have to migrate in search of it, an early larval stage, with legs, is followed by later sluggish stages in which legs have disappeared, furnishing examples of what is called hypermetamorphosis. For example, the grub of a pea or bean beetle (Bruchus) is hatched, from the egg laid by its mother on the carpel of a leguminous flower, with three pairs of legs and spiny processes on the prothorax. It bores through and enters the developing seed, where it undergoes a moult and becomes legless. Similarly the newly-hatched larva of an oil-beetle (Meloe) is an active little campodeiform insect, which, hatched from an egg laid among plants, waits to attach itself to a passing bee. Carried to the bee’s nest, it undergoes a moult, and becomes a fat-bodied grub, ready to lead a quiet life feeding on the bee’s rich food-stores.
Distribution and Habits.—The Coleoptera are almost world-wide in their distribution, being represented in the Arctic regions and on almost all oceanic islands. Most of the dominant families—such as the Carabidae (ground-beetles), Scarabaeidae (chafers), or Curculionidae (weevils) have a distribution as wide as the order. But while some large families, such as the Staphylinidae (rove-beetles) are especially abundant on the great northern continents, becoming scarcer in the tropics, others, the Cicindelidae (tiger-beetles), for example, are most strongly represented in the warmer regions of the earth, and become scarce as the collector journeys far to south or north. The distribution of many groups of beetles is restricted in correspondence with their habits; the Cerambycidae (longhorns), whose larvae are wood-borers, are absent from timberless regions, and most abundant in the great tropical forests. Some families are very restricted in their range. The Amphizoidae, for example, a small family of aquatic beetles, are known only from western North America and Eastern Tibet, while an allied family, the Pelobiidae, inhabit the British Isles, the Mediterranean region, Tibet and Australia. The beetles of the British islands afford some very interesting examples of restricted distribution among species. For example, large and conspicuous European beetles, such as the stag-beetle (fig. 1, Lucanus cervus) and the great water-beetle (Hydrophilus piceus, fig. 20), are confined to eastern and southern Britain, and are unknown in Ireland. On the other hand, there are Arctic species like the ground-beetle, Pelophila borealis, and south-western species like the boring weevil, Mesites Tardyi, common in Ireland, and represented in northern or western Britain, but unknown in eastern Britain or in Central Europe. Careful study of insular faunas, such as that of Madeira by T. V. Wollaston, and of the Sandwich Islands by D. Sharp, and the comparison of the species found with those of the nearest continental land, furnish the student of geographical distribution with many valuable and suggestive facts.
Notes on habit are given below in the accounts of the various families. In general it may be stated that beetles live and feed in almost all the diverse ways possible for insects. There are carnivores, herbivores and scavengers among them. Various species among those that are predaceous attack smaller insects, hunt in packs crustaceans larger than themselves, insert their narrow heads into snail-shells to pick out and devour the occupants, or pursue slugs and earthworms underground. The vegetable-feeders attack leaves, herbaceous or woody stems and roots; frequently different parts of a plant are attacked in the two active stages of the life-history; the cockchafers, for example, eating leaves, and their grubs gnawing roots. Some of the scavengers, like the burying beetles, inter the bodies of small vertebrates to supply food for themselves and their larvae, or, like the “sacred” beetle of Egypt, collect for the same purpose stores of dung. Many beetles of different families have become the “unbidden guests” of civilized man, and may be found in dwelling-houses, stores and ships’ cargoes, eating food-stuffs, paper, furniture, tobacco and drugs. Hence we find that beetles of some kind can hold their own anywhere on the earth’s surface. Some climb trees and feed on leaves, while others tunnel between bark and wood. Some fly through the air, others burrow in the earth, while several families have become fully adapted to life in fresh water. A large number of beetles inhabit the deep limestone caves of Europe and North America, while many genera and some whole families are at home nowhere but in ants’ nests. Most remarkable is the presence of a number of beetles along the seashore between tide-marks, where, sheltered in some secure nook, they undergo immersion twice daily, and have their active life confined to the few hours of the low ebb.
Stridulating Organs.—Many beetles make a hissing or chirping sound by rubbing a “scraper,” formed by a sharp edge or prominence on some part of their exoskeleton, over a “file” formed by a number of fine ridges situate on an adjacent region. These stridulating organs were mentioned by C. Darwin as probable examples of the action of sexual selection; they are, however, frequently present in both sexes, and in some families also in the larvae. An account of the principal types of stridulators that have been described has been published by C. J. Gahan (1900). The file may be on the head—either upper or lower surface—and the scraper formed by the front edge of the prothorax, as in various wood-boring beetles (Anobium and Scolytus). Or ridged areas on the sides of the prothorax may be scraped by “files” on the front thighs, as in some ground-beetles. Among the longhorn beetles, the prothorax scrapes over a median file on the mid-dorsal aspect of the mesothorax. In a large number of beetles of different families, stridulating areas occur on various segments of the abdomen, and are scraped by the elytra. It is remarkable that these organs are found in similar positions in genera belonging to widely divergent families, while two genera of the same family may have them in different positions. It follows, therefore, that they have been independently acquired in the course of the evolution of the Coleoptera.
Stridulating organs among beetle-larvae have been noted, especially in the wood-feeding grub of the stag-beetles (Lucanidae) and their allies the Passalidae, and in the dung-eating grubs of the dor-beetles (Geotrupes), which belong to the chafer family (Scarabaeidae). These organs are described by J. C. Schiödte and D. Sharp; in the stag-beetle larva a series of short tubercles on the hind-leg is drawn across the serrate edge of a plate on the haunch of the intermediate legs, while in the Passalid grub the modified tip of the hind-leg acts as a scraper, being so shortened that it is useless for locomotion, but highly specialized for producing sound. Whatever may be the true explanation of stridulating organs in adult beetles, sexual selection can have had nothing to do with the presence of these highly-developed larval structures. It has been suggested that the power of stridulation would be advantageous to wood-boring grubs, the sound warning each of the position of its neighbour, so that adjacent burrowers may not get in each other’s way. The root-feeding larvae of the cockchafer and allied members of the Scarabaeidae have a ridged area on the mandible, which is scraped by teeth on the maxillae, apparently forming a stridulating organ.
Luminous Organs.—The function of the stridulating organs just described is presumably to afford means of recognition by sound. Some beetles emit a bright light from a portion of their bodies, which leads to the recognition of mate or comrade by sight. In the wingless female glow-worm (Lampyris, fig. 15 f) the luminous region is at the hinder end, the organ emitting the light consisting, according to H. von Wielowiejski (1882), of cells similar to those of the fat-body, containing a substance that undergoes oxidation. The illumination is intermittent, and appears to be under the control of the insect’s nervous system. The well-known “fire-flies” of the tropics are large click-beetles (Elateridae), that emit light from paired spots on the prothorax and from the base of the ventral abdominal region. The luminous organs of these beetles consist of a specialized part of the fat-body, with an inner opaque and an outer transparent layer. Its structure has been described by C. Heinemann, and its physiology by R. Dubois (1886), who considers that the luminosity is due to the influence of an enzyme in the cells of the organ upon a special substance in the blood. The eggs and larvae of the fire-flies are luminous as well as the perfect beetles.
Fossil History.—The Coleoptera can be traced back farther in time than any other order of insects with complete transformations, if the structures that have been described from the Carboniferous rocks of Germany are really elytra. In the Triassic rocks of Switzerland remains of weevils (Curculionidae) occur, a family which is considered by many students the most specialized of the order. And when we know that the Chrysomelidae and Buprestidae also lived in Triassic, and the Carabidae, Elateridae, Cerambycidae and Scarabaeidae, in Liassic times, we cannot doubt that the great majority of our existing families had already been differentiated at the beginning of the Mesozoic epoch. Coming to the Tertiary we find the Oligocene beds of Aix, of east Prussia (amber) and of Colorado, and the Miocene of Bavaria, especially rich in remains of beetles, most of which can be referred to existing genera.
Classification.—The Coleoptera have been probably more assiduously studied by systematic naturalists than any other order of insects. The number of described species can now hardly be less than 100,000, but there is little agreement as to the main principles of a natural classification. About eighty-five families are generally recognized; the difficulty that confronts the zoologists is the arrangement of these families in “superfamilies” or “sub-orders.” Such obvious features as the number of segments in the foot and the shape of the feeler were used by the early entomologists for distinguishing the great groups of beetles. The arrangement dependent on the number of tarsal segments—the order being divided into tribes Pentamera, Tetramera, Heteromera and Trimera—was suggested by E. L. Geoffroy in 1762, adopted by P. A. Latreille, and used largely through the 19th century. W. S. Macleay’s classification (1825), which rested principally on the characters of the larvae, is almost forgotten nowadays, but it is certain that in any systematic arrangement which claims to be natural the early stages in the life-history must receive due attention. In recent years classifications in part agreeing with the older schemes but largely original, in accord with researches on the comparative anatomy of the insects, have been put forward. Among the more conservative of these may be mentioned that of D. Sharp (1899), who divides the order into six great series of families: Lamellicornia (including the chafers and stag-beetles and their allies with five-segmented feet and plate-like terminal segments to the feelers); Adephaga (carnivorous, terrestrial and aquatic beetles, all with five foot-segments); Polymorpha (including a heterogeneous assembly of families that cannot be fitted into any of the other groups); Heteromera (beetles with the fore and intermediate feet five-segmented, and the hind-feet four-segmented); Phytophaga (including the leaf-beetles, and longhorns, distinguished by the apparently four-segmented feet), and Rhynchophora (the weevils and their allies, with head prolonged into a snout, and feet with four segments). L. Ganglbauer (1892) divides the whole order into two sub-orders only, the Caraboidea (the Adephaga of Sharp and the older writers) and the Cantharidoidea (including all other beetles), since the larvae of Caraboidea have five-segmented, two-clawed legs, while those of all other beetles have legs with four segments and a single claw. A. Lameere (1900) has suggested three sub-orders, the Cantharidiformia (including the Phytophaga, the Heteromera, the Rhynchophora and most of the Polymorpha of Sharp’s classification), the Staphyliniformia (including the rove-beetles, carrion-beetles and a few allied families of Sharp’s Polymorpha), and the Carabidiformia (Adephaga). Lameere’s classification is founded on the number of abdominal sterna, the nervuration of the wings, the number of malpighian tubules (whether four or six) and other structural characters. Preferable to Lameere’s system, because founded on a wider range of adult characters and taking the larval stages into account, is that of H. J. Kolbe (1901), who recognizes three sub-orders: (i.) the Adephaga; (ii.) the Heterophaga, including the Staphylinoidea, the Actinorhabda (Lamellicornia), the Heterorhabda (most of Sharp’s Polymorpha), and the Anchistopoda (the Phytophaga, with the ladybirds and some allied families which Sharp places among the Polymorpha); (iii.) the Rhynchophora.
Students of the Coleoptera have failed to agree not only on a system of classification, but on the relative specialization of some of the groups which they all recognize as natural. Lameere, for example, considers some of his Cantharidiformia as the most primitive Coleoptera. J. L. Leconte and G. H. Horn placed the Rhynchophora (weevils) in a group distinct from all other beetles, on account of their supposed primitive nature. Kolbe, on the other hand, insists that the weevils are the most modified of all beetles, being highly specialized as regards their adult structure, and developing from legless maggots exceedingly different from the adult; he regards the Adephaga, with their active armoured larvae with two foot-claws, as the most primitive group of beetles, and there can be little doubt that the likeness between larvae and adult may safely be accepted as a primitive character among insects. In the Coleoptera we have to do with an ancient yet dominant order, in which there is hardly a family that does not show specialization in some point of structure or life-history. Hence it is impossible to form a satisfactory linear series.
In the classification adopted in this article, the attempt has been made to combine the best points in old and recent schemes, and to avoid the inconvenience of a large heterogeneous group including the vast majority of the families.
Adephaga.—This tribe includes beetles of carnivorous habit with five segments on every foot, simple thread-like feelers with none of the segments enlarged to form club or pectination, and the outer lobs (galea) of the first maxilla usually two-segmented and palpiform (fig. 4 b). The transverse fold of the hind-wing is towards the tip, about two-thirds of the wing-length from the base. At this fold the median nervure stops and is joined by a cross nervure to the radial, which can be distinguished throughout its length from the subcostal. There are four malpighian tubules. In the ovarian tubes of Adephaga small yolk-chambers alternate with the egg-chambers, while in all other beetles there is only a single large yolk-chamber at the narrow end of the tube. The larvae (fig. 2 c) are active, with well-chitinized cuticle, often with elongate tail-feelers (cerci), and with five-segmented legs, the foot-segment carrying two claws.
|Fig. 4.—Mormolyce phyllodes. Java. a, Labium; b, maxilla; c, labrum; d, mandible.|
The generalized arrangement of the wing-nervure and the nature of the larva, which is less unlike the adult than in other beetles, distinguish this tribe as primitive, although the perfect insects are, in the more dominant families, distinctly specialized. Two very small families of aquatic beetles seem to stand at the base of the series, the Amphizoidae, whose larvae are broad and well armoured with short cerci, and the Pelobiidae, which have elongate larvae, tapering to the tail end, where are long paired cerci and a median process, recalling the grub of a Mayfly.
|Fig. 5.—Pheropsophus Jurinei. W. Africa.||Fig. 6.—Carabus rutilans. Spain.|
The Dyticidae (fig. 2) are Adephaga highly specialized for life in the water, the hind-legs having the segments short, broad and fringed, so as to be well adapted for swimming, and the feet without claws. The metasternum is without the transverse linear impression that is found in most families of Adephaga. The beetles are ovoid in shape, with smooth contours, and the elytra fit over the edges of the abdomen so as to enclose a supply of air, available for use when the insect remains under water. The fore-legs of many male dyticids have the three proximal foot-segments broad and saucer-shaped, and covered with suckers, by means of which they secure a firm hold of their mates. Larval dyticids (fig. 2 b) possess slender, curved, hollow mandibles, which are perforated at the tip and at the base, being thus adapted for sucking the juices of victims. Large dyticid larvae often attack small fishes and tadpoles. They breathe by piercing the surface film with the tail, where a pair of spiracles are situated. The pupal stage is passed in an earthen cell, just beneath the surface of the ground. Nearly 2000 species of Dyticidae are known: they are universally distributed, but are most abundant in cool countries. The Haliplidae form a small aquatic family allied to the Dyticidae.
|Fig. 7.—Cicindela sylvatica
(Wood Tiger-Beetle). Europe.
|Fig. 8.—Manticora tuberculata.|
The Carabidae, or ground-beetles, comprising 13,000 species, form the largest and most typical family of the Adephaga (figs. 4, 5, 6), the legs of all three pairs being alike and adapted for rapid running. In many Carabidae the hind-wings are reduced or absent, and the elytra fused together along the suture. Many of our native species spend the day lurking beneath stones, and sally forth at night in pursuit of their prey, which consists of small insects, earthworms and snails. But a number of the more brightly coloured ground-beetles run actively in the sunshine. The carabid larva is an active well-armoured grub with the legs and cerci variable in length. Great differences in the general form of the body may be observed in the family. For example, the stout, heavy body of Carabus (fig. 6) contrasts markedly with the wonderful flattened abdomen and elytra of Mormolyce (fig. 4), a Malayan genus found beneath fallen trees, a situation for which its compressed shape is admirably adapted. Blind Carabidae form a large proportion of cave-dwelling beetles, and several species of great interest live between tide-marks along the seashore.
The Cicindelidae, or tiger-beetles (figs. 7, 8) are the most highly organized of all the Adephaga. The inner lobe (lacinia) of the first maxilla terminates in an articulated hook, while in the second maxillae (labium) both inner and outer lobes (“ligula” and “para-glossae”) are much reduced. The face (clypeus) is broad, extending on either side in front of the insertion of the feelers. The beetles are elegant insects with long, slender legs, running quickly, and flying in the sunshine. The pronotum and elytra are often adorned with bright colours or metallic lustre, and marked with stripes or spots. The beetles are fierce in nature and predaceous in habit, their sharp toothed mandibles being well adapted for the capture of small insect-victims. The larvae are more specialized than those of other Adephaga, the head and prothorax being very large and broad, the succeeding segments slender and incompletely chitinized. The fifth abdominal segment has a pair of strong dorsal hook-like processes, by means of which the larva supports itself in the burrow which it excavates in the earth, the great head blocking the entrance with the mandibles ready to seize on any unwary insect that may venture within reach.
Two or three families may be regarded as aberrant Adephaga. The Paussidae are a very remarkable family of small beetles, mostly tropical, found only in ants’ nests, or flying by night, and apparently migrating from one nest to another. The number of antennal segments varies from eleven to two. It is supposed that these beetles secrete a sweet substance on which the ants feed, but they have been seen to devour the ants’ eggs and grubs. The Gyrinidae, or whirligig beetles (fig. 9), are a curious aquatic family with the feelers (fig. 9, b) short and reduced as in most Paussidae. They are flattened oval in form, circling with gliding motion over the surface film of the water, and occasionally diving, when they carry down with them a bubble of air. The fore-legs are elongate and adapted for clasping, while the short and flattened intermediate and hind legs form very perfect oar-like propellers. The larva of Gyrinus (fig. 9, c) is slender with elongate legs, and the abdominal segments carry paired tracheal gills.
Staphylinoidea.—The members of this tribe may be easily recognized by their wing-nervuration. Close to a transverse fold near the base of the wing, the median nervure divides into branches which extend to the wing-margin; there is a second transverse fold near the tip of the wing, and cross nervures are altogether wanting. There are four malpighian tubes, and all five tarsal segments are usually recognizable. With very few exceptions, the larva in this group is active and campodeiform, with cerci and elongate legs as in the Adephaga, but the leg has only four segments and one claw.
|Fig. 10.—Silpha quadripunctata.
| Fig. 11.—Necrophorus vespillo|
(Sexton Beetle). Europe.
The Silphidae, or carrion beetles, form one of the best-known families of this group. They are rotund or elongate insects with conical front haunches, the elytra generally covering (fig. 10) the whole dorsal region of the abdomen, but sometimes leaving as many as four terga exposed (fig. 11). Some of these beetles are brightly coloured, while others are dull black. They are usually found in carrion, and the species of Necrophorus (fig. 11) and Necrophaga are valuable scavengers from their habit of burying small vertebrate carcases which may serve as food for their larvae. At this work a number of individuals are associated together. The larvae that live underground have spiny dorsal plates, while those of the Silpha (fig. 10) and other genera that go openly about in search of food resemble wood-lice. About 1000 species of Silphidae are known. Allied to the Silphidae are a number of small and obscure families, for which reference must be made to monographs of the order. Of special interest among these are the Histeridae, compact beetles (fig. 12) with very hard cuticle and somewhat abbreviated elytra, with over 2000 species, most of which live on decaying matter, and the curious little Pselaphidae, with three-segmented tarsi, elongate palpi, and shortened abdomen; the latter are usually found in ants’ nests, where they are tended by the ants, which take a sweet fluid secreted among little tufts of hair on the beetles’ bodies; these beetles, which are carried about by the ants, sometimes devour their larvae. The Trichopterygidae, with their delicate narrow fringed wings, are the smallest of all beetles, while the Platypsyllidae consist of only a single species of curious form found on the beaver.
(Mimic Beetle). Europe.
The Staphylinidae, or rove-beetles—a large family of nearly 10,000 species—may be known by their very short elytra, which cover only two of the abdominal segments, leaving the elongate hind-body with seven or eight exposed, firm terga (figs. 13, 14). These segments are very mobile, and as the rove-beetles run along they often curl the abdomen upwards and forwards like the tail of a scorpion. The Staphylinid larvae are typically campodeiform. Beetles and larvae are frequently carnivorous in habit, hunting for small insects under stones, or pursuing the soft-skinned grubs of beetles and flies that bore in woody stems or succulent roots. Many Staphylinidae are constant inmates of ants’ nests.
|Fig. 15.—Glow-worm. Lampyris noctiluca. a, Male;|
b, female; c, larva (ventral view). Europe.
Malacodermata.—In this tribe may be included a number of families distinguished by the softness of the cuticle, the presence of seven or eight abdominal sterna and of four malpighian tubes, and the firm, well-armoured larva (fig. 15, c) which is often predaceous in habit. The mesothoracic epimera bound the coxal cavities of the intermediate legs. The Lymexylonidae, a small family of this group, characterized by its slender, undifferentiated feelers and feet, is believed by Lameere to comprise the most primitive of all living beetles, and Sharp lays stress on the undeveloped structure of the tribe generally.
The Lampyridae are a large family, of which the glow-worm (Lampyris) and the “soldier beetles” (Telephorus) are familiar examples. The female “glow-worm” (fig. 15, b), emitting the well-known light (see above), is wingless and like a larva; the luminosity seems to be an attraction to the male, whose eyes are often exceptionally well developed. Some male members of the family have remarkably complex feelers. In many genera of Lampyridae the female can fly as well as the male; among these are the South European “fireflies.”
|Fig. 16.—Clerus apiarus
(Hive Beetle). Europe.
|Fig. 17.—Dermestes lardarius|
Trichodermata.—Several families of rather soft-skinned beetles, such as the Melyridae, Cleridae (fig. 16), Corynetidae, Dermestidae (fig. 17), and Dascillidae, are included in this tribe. They may be distinguished from the Malacodermata by the presence of only five or six abdominal sterna, while six malpighian tubes are present in some of the families. The beetles are hairy and their larvae well-armoured and often predaceous. Several species of Dermestidae are commonly found in houses, feeding on cheeses, dried meat, skins and other such substances. The “bacon beetle” (Dermestes lardarius), and its hard hairy larva, are well known. According to Sharp, all Dermestid larvae probably feed on dried animal matters; he mentions one species that can find sufficient food in the horsehair of furniture, and another that eats the dried insect-skins hanging in old cobwebs.
Sternoxia.—This is an important tribe of beetles, including families with four malpighian tubes and only five or six abdominal sterna, while in the thorax there is a backwardly directed process of the prosternum that fits into a mesosternal cavity. The larvae are elongate and worm-like, with short legs but often with hard strong cuticle.
|Fig. 18.—A, Wireworm; B, pupa of Click Beetle; C, adult Click|
Beetle (Agriotes lineatum).
The Elateridae or click beetles (fig. 18) have the prosternal process just mentioned, capable of movement in and out of the mesosternal cavity, the beetles being thus enabled to leap into the air, hence their popular name of “click-beetles” or “skip-jacks.” The prothorax is convex in front, and is usually drawn out behind into a prominent process on either side, while the elytra are elongate and tapering. Many of the tropical American Elateridae emit light from the spots on the prothorax and an area beneath the base of the abdomen; these are “fireflies” (see above). The larvae of Elateridae are elongate, worm-like grubs, with narrow bodies, very firm cuticle, short legs, and a distinct anal proleg. They are admirably adapted for moving through the soil, where some of them live on decaying organic matter, while others are predaceous. Several of the elaterid larvae, however, gnaw roots and are highly destructive to farm crops. These are the well-known “wire-worms” (q.v.).
|Fig. 19.—Catoxantha bicolor. Java.|
The Buprestidae are distinguished from the Elateridae by the immobility of the prosternal process in the mesosternal cavity and by the absence of the lateral processes at the hind corners of the prothorax. Many tropical Buprestidae are of large size (fig. 19), and exhibit magnificent metallic colours; their elytra are used as ornaments in human dress. The larvae are remarkable for their small head, very broad thorax, with reduced legs, and narrow elongate abdomen. They feed by burrowing in the roots and stems of plants.
Bostrychoidea.—This tribe is distinguished from the Malacoderma and allied groups by the mesothoracic epimera not bounding the coxal cavities of the intermediate legs. The downwardly directed head is covered by the pronotum, and the three terminal antennal segments form a distinct club. To this group belong the Bostrychidae and Ptinidae, well known (especially the latter family) for their ravages in old timber. The larvae are stout and soft-skinned, with short legs in correlation with their burrowing habit. The noises made by some Ptinidae (Anobium) tapping on the walls of their burrows with their mandibles give rise to the “death tick” that has for long alarmed the superstitious.
|Fig. 20.—Hydrophilus piceus|
(Black Water Beetle). Europe.
Clavicornia.—This is a somewhat heterogeneous group, most of whose members are characterized by clubbed feelers and simple, unbroadened tarsal segments—usually five on each foot—but in some families and genera the males have less than the normal number on the feet of one pair. There are either four or six malpighian tubes. A large number of families, distinguished from each other by more or less trivial characters, are included here, and there is considerable diversity in the form of the larvae. The best-known family is the Hydrophilidae, in which the feelers are short with less than eleven segments and the maxillary palpi very long. Some members of this family—the large black Hydrophilus piceus (fig. 20), for example—are specialized for an aquatic life, the body being convex and smooth as in the Dyticidae, and the intermediate and hind-legs fringed for swimming. When Hydrophilus dives it carries a supply of air between the elytra and the dorsal surface of the abdomen, while air is also entangled in the pubescence which extends beneath the abdomen on either side, being scooped in bubbles by the terminal segments of the feelers when the insect rises to the surface. Many of the Hydrophilidae construct, for the protection of their eggs, a cocoon formed of a silky material derived from glands opening at the tip of the abdomen. That of Hydrophilus is attached to a floating leaf, and is provided with a hollow, tapering process, which projects above the surface and presumably conveys air to the enclosed eggs. Other Hydrophilidae carry their egg-cocoons about with them beneath the abdomen. Many Hydrophilidae, unmodified for aquatic life, inhabit marshes. The larvae in this family are well-armoured, active and predaceous. Of the numerous other families of the Clavicornia may be mentioned the Cucujidae and Cryptophagidae, small beetles, examples of which may be found feeding on stored seeds or vegetable refuse, and the Mycetophagidae, which devour fungi. The Nitidulidae are a large family with 1600 species, among which members of the genus Meligethes are often found in numbers feeding on blossoms, while others live under the bark of trees and prey on the grubs of boring beetles.
|Fig. 21.—(a) Tenebrio molitor
(Flour Beetle). Europe.
(b) Larva, or mealworm.
|Fig. 22.—Blaps mortisaga|
(Churchyard Beetle). Europe.
Heteromera.—This tribe is distinguished by the presence of the normal five segments in the feet of the fore and intermediate legs, while only four segments are visible in the hind-foot. Considerable diversity is to be noticed in details of structure within this group, and for an enumeration of all the various families which have been proposed and their distinguishing characters the reader is referred to one of the monographs mentioned below. Some of the best-known members of the group belong to the Tenebrionidae, a large family containing over 10,000 species and distributed all over the world. The tenebrionid larva is elongate, with well-chitinized cuticle, short legs and two stumpy tail processes, the common mealworm (fig. 21) being a familiar example. Several species of this family are found habitually in stores of flour or grain. The beetles have feelers with eleven segments, whereof the terminal few are thickened so as to form a club. The true “black-beetles” or “churchyard beetles” (Blaps) (fig. 22) belong to this family; like members of several allied genera they are sooty in colour, and somewhat resemble ground beetles (Carabi) in general appearance.
|Fig. 23.—Meloe proscarabaeus
(Oil Beetle). Europe.
|Fig. 24.—Lytta vesicatoria|
(Blister Beetle). Europe.
The most interesting of the Heteromera, and perhaps of all the Coleoptera, are some beetles which pass through two or more larval forms in the course of the life-history (hypermetamorphosis). These belong to the families Rhipidophoridae and Meloidae. The latter are the oil beetles (fig. 23) or blister beetles (fig. 24), insects with rather soft cuticle, the elytra (often abbreviated) not fitting closely to the sides of the abdomen, the head constricted behind the eyes to form a neck, and the claws of the feet divided to the base. Several of the Meloidae (such as the “Spanish fly,” fig. 24) are of economic importance, as they contain a vesicant substance used for raising medicinal blisters on the human skin. The wonderful transformations of these insects were first investigated by G. Newport in 1851, and have recently been more fully studied by C. V. Riley (1878) and J. H. Fabre. The first larval stage is the “triungulin,” a tiny, active, armoured larva with long legs (each foot with three claws) and cercopods. In the European species of Sitaris and Meloe these little larvae have the instinct of clinging to any hairy object. All that do not happen to attach themselves to a bee of the genus Anthophora perish, but those that succeed in reaching the right host are carried to the nest, and as the bee lays an egg in the cell the triungulin slips off her body on to the egg, which floats on the surface of the honey. After eating the contents of the egg, the larva moults and becomes a fleshy grub with short legs and with paired spiracles close to the dorsal region, so that, as it floats in and devours the honey, it obtains a supply of air. After a resting (pseudo-pupal) stage and another larval stage, the pupa is developed. In the American Epicauta vittata the larva is parasitic on the eggs and egg-cases of a locust. The triungulin searches for the eggs, and, after a moult, becomes changed into a soft-skinned tapering larva. This is followed by a resting (pseudo-pupal) stage, and this by two successive larval stages like the grub of a chafer. The Rhipidophoridae are beetles with, short elytra, the feelers pectinate in the males and serrate in the females. The life-history of Metoecus has been studied by T. A. Chapman, who finds that the eggs are laid in old wood, and that the triungulin seeks to attach itself to a social wasp, who carries it to her nest. There it feeds first as an internal parasite of the wasp-grub, then bores its way out, moults and devours the wasp larva from outside. The wasps are said to leave the larval or pupal Metoecus unmolested, but they are hostile to the developed beetles, which hasten to leave the nest as soon as possible.
Strepsiptera.—Much difference of opinion has prevailed with regard to the curious, tiny, parasitic insects included in this division, some authorities considering that they should be referred to a distinct order, while others would group them in the family Meloidae just described. While from the nature of their life-history there is no doubt that they have a rather close relationship to the Meloidae, their structure is so remarkable that it seems advisable to regard them as at least a distinct tribe of Coleoptera.
They may be comprised in a single family, the Stylopidae. The males are very small, free-flying insects with the prothorax, mesothorax and elytra greatly reduced, the latter appearing as little, twisted strips, while the metathorax is relatively large, with its wings broad and capable of longitudinal folding. The feelers are branched and the jaws vestigial. The female is a segmented, worm-like creature, spending her whole life within the body of the bee, wasp or bug on which she is parasitic. One end of her body protrudes from between two of the abdominal segments of the host; it has been a subject of dispute whether this protruded end is the head or the tail, but there can be little doubt that it is the latter. While thus carried about by the host-insect, the female is fertilized by the free-flying male, and gives birth to a number of tiny triungulin larvae. The chief points in the life-history of Stylops and Xenos, which are parasitic on certain bees (Andrena) and wasps (Polistes), have been investigated by K. T. E. von Siebold (1843) and N. Nassonov (1892). The little triungulins escape on to the body of the bee or wasp; then those that are to survive must leave their host for a non-parasitized insect. Clinging to her hairs they are carried to the nest, where they bore into the body of a bee or wasp larva, and after a moult become soft-skinned legless maggots. The growth of the parasitic larva does not stop the development of the host-larva, and when the latter pupates and assumes the winged form, the stylopid, which has completed its transformation, is carried to the outer world. The presence of a Stylops causes derangement in the body of its host, and can be recognized by various external signs. Other genera of the family are parasitic on Hemiptera—bugs and frog-hoppers—but nothing is known as to the details of their life-history.
Lamellicornia.—This is a very well-marked tribe of beetles, characterized by the peculiar elongation and flattening of three or more of the terminal antennal segments, so that the feeler seems to end in a number of leaf-like plates, or small comb-teeth (fig. 26, b, c). The wings are well developed for flight, and there is a tendency in the group, especially among the males, towards an excessive development of the mandibles or the presence of enormous, horn-like processes on the head or pronotum. There are four malpighian tubes. The larvae are furnished with large heads, powerful mandibles and well-developed legs, but the body-segments are feebly chitinized, and the tail-end is swollen. They feed in wood or spend an underground life devouring roots or animal excrement.
The Lucanidae or stag beetles (figs. 1 and 25) have the terminal antennal segments pectinate, and so arranged that the comb-like part of the feeler cannot be curled up, while the elytra completely cover the abdomen. There are about 600 species in the family, the males being usually larger than the females, and remarkable for the size of their mandibles. In the same species, however, great variation occurs in the development of the mandibles, and the breadth of the head varies correspondingly, the smallest type of male being but little different in appearance from the female. The larvae of Lucanidae live within the wood of trees, and may take three or four years to attain their full growth. The Passalidae are a tropical family of beetles generally considered to be intermediate between stag-beetles and chafers, the enlarged segments of the feeler being capable of close approximation.
|Fig. 25.—Cladognathus cinnamomeus.
|Fig. 26.—Melolontha fullo (Cockchafer).|
S. Europe, b, Antenna of male;
c, antenna of female.
The Scarabaeidae or chafers are an enormous family of about 15,000 species. The plate-like segments of the feeler (fig. 26, b, c) can be brought close together so as to form a club-like termination; usually the hinder abdominal segments are not covered by the elytra. In this family there is often a marked divergence between the sexes; the terminal antennal segments are larger in the male than in the female, and the males may carry large spinous processes on the head or prothorax, or both. These structures were believed by C. Darwin to be explicable by sexual selection. The larvae have the three pairs of legs well developed, and the hinder abdominal segments swollen. Most of the Scarabaeidae are vegetable-feeders, but one section of the family—represented in temperate countries by the dor-beetles (Geotrupes) (fig. 28) and Aphodius, and in warmer regions by the “sacred” beetles of the Egyptians (Scarabaeus) (fig. 27), and allied genera—feed both in the adult and larval stages, on dung or decaying animal matter. The heavy grubs of Geotrupes, their swollen tail-ends black with the contained food-material, are often dug up in numbers in well-manured fields. The habits of Scarabaeus have been described in detail by J. H. Fabre. The female beetle in spring-time collects dung, which she forms into a ball by continuous rolling, sometimes assisted by a companion. This ball is buried in a suitable place, and serves the insect as a store of food. During summer the insects rest in their underground retreats, then in autumn they reappear to bury another supply of dung, which serves as food for the larvae. Fabre states that the mother-insect carefully arranges the food-supply so that the most nutritious and easily digested portion is nearest the egg, to form the first meal of the young larva. In some species of Copris it is stated that the female lays only two or three eggs at a time, watching the offspring grow to maturity, and then rearing another brood.
|Fig. 28.—Geotrupes Blackburnei.|
|Fig. 29.—Phaneus Imperator.
|Fig. 30.—Cetonia Baxii.|
Among the vegetable-feeding chafers we usually find that while the perfect insect devours leaves, the larva lives underground and feeds on roots. Such are the habits of the cockchafer (Melolontha vulgaris) and other species that often cause great injury to farm and garden crops (see Chafer). Many of these insects, such as the species of Phanaeus (fig. 29) and Cetonia (fig. 30), are adorned with metallic or other brilliant colours. The African “goliath-beetles” (fig. 31) and the American “elephant-beetles” (Dynastes) are the largest of all insects.
|Fig. 31.—Goliathus giganteus (Goliath Beetle).|
Anchistopoda.—The families of beetles included by Kolbe in this group are distinguished by the possession of six malpighian tubes, and a great reduction in one or two of the tarsal segments, so that there seem to be only four or three segments in each foot; hence the names Tetramera and Trimera formerly applied to them. The larvae have soft-skinned bodies sometimes protected by rows of spiny tubercles, the legs being fairly developed in some families and greatly reduced or absent in others. As might be expected, degeneration in larval structure is correlated with a concealed habit of life.
The Coccinellidae, or ladybirds (fig. 32), are a large family of beetles, well known by their rounded convex bodies, usually shining and hairless. They have eleven segments to the feeler, which is clubbed at the tip, and apparently three segments only in each foot. Ladybirds are often brightly marked with spots and dashes, their coloration being commonly regarded as an advertisement of inedibility. The larvae have a somewhat swollen abdomen, which is protected by bristle-bearing tubercles. Like the perfect insects, they are predaceous, feeding on plant-lice (Aphidae) and scale insects (Coccidae). Their rôle in nature is therefore beneficial to the cultivator. The Endomychidae (fig. 33), an allied family, are mostly fungus-eaters. In the Erotylidae and a few other small related families the feet are evidently four-segmented.
|Fig. 32.—Anatio ocellata
(Eyed Ladybird). Europe.
|Fig. 33.—Endomychus coccineus.|
|Fig. 34.—Sagra cyanea.
|Fig. 35.—Eumorphus ivguttatus.|
|Fig. 36.—Lophonocerus barbicornis. S. America.|
The Chrysomelidae, or leaf-beetles (figs. 34, 35), are a very large family, with “tetramerous” tarsi; there seem to be only four segments to the foot, but there are really five, the fourth being greatly reduced. The mandibles are strong, adapted for biting the vegetable substances on which these beetles feed, and the palps of the second maxillae have three segments. Most of the Chrysomelidae are metallic in colour and convex in form; in some the head is concealed beneath the prothorax, and the so-called “tortoise” beetles (Cassidinae) have the elytra raised into a prominent median ridge. The most active form of larva found in this family resembles in shape that of a ladybird, tapering towards the tail end, and having the trunk segments protected by small firm sclerites. Such larvae, and also many with soft cuticle and swollen abdomen—those of the notorious “Colorado beetle,” for example—feed openly on foliage. Others, with soft, white, cylindrical bodies, which recall the caterpillars of moths, burrow in the leaves or stems of plants. The larvae of the tortoise-beetles have the curious habit of forming an umbrella-like shield out of their own excrement, held in position by the upturned tail-process. The larvae of the beautiful, elongate, metallic Donaciae live in the roots and stems of aquatic plants, obtaining thence both food and air. The larva pierces the vessels of the plant with sharp processes at the hinder end of its body. In this way it is believed that the sub-aqueous cocoon in which the pupal stage is passed becomes filled with air.
The Cerambycidae, or longhorn beetles, are recognizable by their slender, elongate feelers, which are never clubbed and rarely serrate. The foot has apparently four segments, as in the Chrysomelidae. The beetles are usually elongate and elegant in form, often adorned with bright bands of colour, and some of the tropical species attain a very large size (figs. 36, 37). The feelers are usually longer in the male than in the female, exceeding in some cases by many times the length of the body. The larvae have soft, fleshy bodies, with the head and prothorax large and broad, and the legs very much reduced. They live and feed in the wood of trees. Consequently, beetles of this family are most abundant in forest regions, and reach their highest development in the dense virgin forests of tropical countries, South America being particularly rich in peculiar genera.
|Fig. 37.—Phryneta aurocincta. West Africa.|
The Bruchidae, or seed-beetles, agree with the two preceding families in tarsal structure; the head is largely hidden by the pronotum, and the elytra are short enough to leave the end of the abdomen exposed (fig. 38). The development of the pea and bean-beetles has been carefully studied by C. V. Riley, who finds that the young larva, hatched from the egg laid on the pod, has three pairs of legs, and that these are lost after the moult that occurs when the grub has bored its way into the seed. In Great Britain the beetle, after completing its development, winters in the seed, waiting to emerge and lay its eggs on the blossom in the ensuing spring.
|Fig. 38.—Bruchus piei
(Pea Beetle.) Europe.
Rhynchophora.—The Rhynchophora are a group of beetles easily recognized by the elongation of the head into a beak or snout, which carries the feelers at its sides and the jaws at its tip. The third tarsal segment is broad and bi-lobed, and the fourth is so small that the feet seem to be only four-segmented. There are six malpighian tubes. The ventral sclerite of the head-skeleton (gula), well developed in most families of beetles, is absent among the Rhynchophora, while the palps of the maxillae are much reduced. The larvae have soft, white bodies and, with very few exceptions, no legs.
chus ligustici. Europe.
|Fig. 42.—Lixus paraplecticus.|
Of the four families included in this group, the Anthribidae (fig. 39) have jointed, flexible palps, feelers—often of excessive length—with a short basal segment, and the three terminal segments forming a club, and, in some genera, larvae with legs. There are nearly 1000 known species, most of which live in tropical countries. The Brenthidae are a remarkable family almost confined to the tropics; they are elongate and narrow in form (fig. 40), with a straight, cylindrical snout which in some male beetles of the family is longer than the rest of the body.
|Fig. 43.—Scolytus ulmi. (Bark Beetle). Europe.|
The Curculionidae, or weevils (q.v.), comprising 23,000 species, are by far the largest family of the group. The maxillary palps are short and rigid, and there is no distinct labrum, while the feelers are usually of an “elbowed” form, the basal segment being very elongate (figs. 41, 42). They are vegetable feeders, both in the perfect and larval stages, and are often highly injurious. The female uses her snout as a boring instrument to prepare a suitable place for egg-laying. The larvae (fig. 3) of some weevils live in seeds; others devour roots, while the parent-beetles eat leaves; others, again, are found in wood or under bark. The Scolytidae, or bark-beetles, are a family of some 1500 species, closely allied to the Curculionidae, differing only in the feeble development of the snout. They have clubbed feelers, and their cylindrical bodies (fig. 43) are well adapted for their burrowing habits under the bark of trees. Usually the mother-beetle makes a fairly straight tunnel along which, at short intervals, she lays her eggs. The grubs, when hatched, start galleries nearly at right angles to this, and when fully grown form oval cells in which they pupate; from these the young beetles emerge by making circular holes directly outward through the bark.
Bibliography.—In addition to what may be found in numerous important works on the Hexapoda (q.v.) as a whole, such as J. O. Westwood’s Modern Classification of Insects, vol. i. (London, 1838); J. H. Fabre’s Souvenirs Entomologiques (Paris, 1879–1891); D. Sharp’s contribution to the Cambridge Natural History (vol. vi., London, 1899); and L. C. Miall’s Aquatic Insects (London, 1895), the special literature of the Coleoptera is enormous. Classical anatomical memoirs are those of L. Dufour (Ann. Sci. Nat. ii., iii., iv., vi., viii., xiv., 1824–1828); Ib. (ser. 2, Zool.) i., 1834; and H. E. Strauss-Dürkheim, Anatomie comparée des animaux articulées (Paris, 1828).
The wings of Coleoptera (including the elytra) are described and discussed by F. Meinert (Entom. Tijdsk. v., 1880); C. Hoffbauer (Zeit. f. wissen. Zool. liv., 1892); J. H. Comstock and J. G. Needham (Amer. Nat. xxxii., 1898); and W. L. Tower (Zool. Jahrb. Anat. xvii., 1903). The morphology of the abdomen, ovipositor and genital armature is dealt with by K. W. Verhoeff (Ent. Nachtr. xx., 1894, and Arch. f. Naturg. lxi., lxii., 1895–1896); and B. Wandolleck (Zool. Jahrb. Anat. xxii., 1905).
Luminous organs are described by H. von Wielowiejski (Zeits. f. wissen. Zool. xxxvii., 1882); C. Heinemann (Arch. f. mikr. Anat. xxvii., 1886); and R. Dubois (Bull. soc. zool. France, 1886); and stridulating organs by C. J. Gahan (Trans. Entom. Soc., 1900). See also C. Darwin’s Descent of Man and Selection in Relation to Sex (London, 1871).
Many larvae of Coleoptera are described and beautifully figured by J. C. Schiödte (Naturh. Tidsskr. i.-xiii., 1861–1872). Hypermetamorphosis in the Meloidae is described by G. Newport (Trans. Linn. Soc. xx., xxi., 1851–1853); C. V. Riley (Rep. U.S. Entom. Comm. i., 1878); J. H. Fabre (Ann. Sci. Nat. (4), ix., xix., 1848–1853); H. Beauregard (Les Insectes vésicants, Paris, 1890); and A. Chabaud (Ann. Soc. Ent. France, lx., 1891); in the Bruchidae by Riley (Insect Life, iv., v., 1892–1893); and in the Strepsiptera (Stylopidae) by K. T. E. von Siebold (Arch. f. Naturg. ix., 1843); N. Nassonov (Bull. Univ. Narsovie, 1892); and C. T. Brues (Zool. Jahrb. Anat. xiii., 1903).
For various schemes of classification of the Coleoptera see E. L. Geoffroy (Insectes qui se trouvent aux environs de Paris, Paris, 1762); A. G. Olivier (Coléoptères, Paris, 1789–1808); W. S. MacLeay (Annulosa Javanica, London, 1825); the general works of Westwood and Sharp, mentioned above; M. Gemminger and B. de Harold (Catalogus Coleopterorum, 12 vols., Munich, 1868–1872); T. Lacordaire and F. Chapuis (Genera des Coléoptères, 10 vols., Paris, 1854–1874); J. L. Leconte and G. H. Horn (Classification of Coleoptera of N. America, Washington, Smithsonian Inst., 1883); L. Ganglbauer (Die Käfer von Mitteleuropa, Vienna, 1892, &c.); A. Lameere (Ann. Soc. Ent. Belg. xliv., xlvii., 1900–1903); and H. J. Kolbe (Arch. f. Naturg. lxvii., 1901).
For the British species, W. W. Fowler (Coleoptera of the British Islands, 5 vols., London, 1887–1891) is the standard work; and W. F. Johnson and J. N. Halbert’s “Beetles of Ireland” (Proc. R. Irish Acad., 3, vi., 1902) is valuable faunistically. Among the large number of systematic writers on the order generally, or on special families, may be mentioned D. Sharp, T. V. Wollaston, H. W. Bates, G. C. Champion, E. Reitter, G. C. Crotch, H. S. Gorham, M. Jacoby, L. Fairmaire and C. O. Waterhouse. (G. H. C.)
- Instar is a convenient term suggested by D. Sharp to indicate a stage in the life-history of an insect between two successive castings of the cuticle.