Page:Encyclopædia Britannica, Ninth Edition, v. 6.djvu/151

C L E P T E K A 127 the sides of the abdouieu. The elytra are always present except in the females of a few species, as the Glow-worm, and are generally large enough to cover the upper surface of the abdomen and to concsal the under wings when at rest. In Brachelytrous Beetles, however, they are exceedingly short, and the wings in these are only shielded by being folded more than once beneath them. The elytra when at rest meet on the middle of the back, their internal margins forming a straight longitudinal line or suture highly characteristic of the Coleoptera ; but even this character is not universal, as in the Oil Beetles (Meloe) and a few others the one elytron partly folds over the other. The posterior wings are large, veined, and membranaceous and form the true organs of night, but they are much more frequently absent than the elytra, and where this occurs, as in manyCarabideous Beetles, the latter are more or less soldered together. During flight the elytra are either extended horizontally or merely raised without being separated, as in the Rose-Chafers (Cetonia) ; and as might be expected from their general stoutness of body and comparative deficiency of wings, the flight of beetles is heavy and seldom long sustained. Their weakness in this respect is further shown in the apparent inability of many species suddenly to alter their course so as to avoid collision with any object that may unexpectedly come in their way, a defect popularly but erroneously attributed, in. the phrase " as blind as a beetle," to weakness of sight rather than of wing. In certain water beetles (Dytiscidce) a pair of alula?, or winglets, are developed at the inner angle of the elytra. The colouring of the chitinous integument of beetles is often exceedingly brilliant, and the elytra and other parts of many species are largely used in the manufacture of personal ornaments. This colouring can in many instances be shown to bear a close resemblance to that of surrounding nature ; thus burrowing beetles, and those which dwell in subterranean .caves, are generally black or brown ; Weevils, found on the ground, are earth-coloured ; while arboreal species of this and other groups are of various shades of green. Bates found a species of beetle, on a particular tree in South America, which so resembled the bark on which it spent its existence as to be, when motionless, no longer visible. This assimilation in colour to surrounding nature is probably useful in assisting them to elude their enemies ; and when the markings are such as to render the beetle conspicuous it is of ten provided with, and no doubt protected by, an offensive odour or nauseous juices ; thus the naturalist already mentioned found on a sandy beach two species of Tiger Beetles, the one of a pallid hue like the sand it ran upon, the other of a brilliant and conspicuous copper colour, but having " a strong, offensive, putrid, and musky odour," from which the other was entirely free. Fireflies, a group of Coleopterous insects, are also exceed ingly conspicuous, but are similarly protected. The phenomena of mimicry, or the imitation of one animal by another for protective purposes, have been, observed in several instances among beetles. Mr Belt, in his interesting work, The Naturalist in Nicaragua, states that he captured what he supposed was a hairy caterpillar, but on closer inspection he found it to be a Longicorn Beetle, the antennae being concealed among the hair. Hairy caterpillars are almost universally rejected by insect- eating animals, and thus probably this beetle shared in the immunity from attack accorded to its model. A species of beetle found in South America closely resembles a bee found in the same locality, its body being covered with hair and its legs similarly tufted ; another, with yellow banded abdomen, sufficiently resembled a wasp as to make its captor both cautious and timid in handling it at first. Oue of the Chrysomdidce (Crioceris mer Jiff era) is said to disguise itself by covering its upper surface with its own dung ; while many species to be afterwards noticed, when in danger, simulate death. Brilliant colouring in beetles is not as in some orders of animals a characteristic mainly of the male sex, both sexes being usually simihr in this respect, while in those cases in which they differ, the female is generally the more gaudy insect. The chief external difference, however, between the sexes in many beetles is to be found in the presence of horns on the head and thorax of the males. These vary exceedingly in their development even in individuals of the same species, while in their form they resemble the horns of the rhinoceros, and the antlers of the stag ; and as among mammals the reindeer is exceptional in the possession of antlers by both sexes, so among beetles there is at least one species, Phanaeus landfer, in which both male and female are similarly equipped. The male beetle has not been observed to use its horns either for purposes of offence or defence, some of the most pugnacious species being entirely destitute of them ; and in Darwin s opinion these appendages have been acquired merely as ornaments. The abdomen of Coleopterous insects is sessile, that is, attached to the thorax by its largest transverse diameter. On the under side it is always of a firm horny consistence, while the upper surface is generally soft, being protected by the elytra and wings ; when these, however, are absent or abbreviated, it is as hard above as below. It bears the organs of generation as well as the respiratory openings, or stigmata, which form the apertures of the tracheae by means of which air is disseminated through all parts of the insect system. -Beetles belonging to several distinct families possess stridulating organs, and these are generally found in both sexes. The apparatus by which the sound, loud enough to be heard in many cases at some yards distance, is produced, consists of a couple of delicate rasps placed on the upper surface of the abdomen, on the elytra, or on the prothorax, and a scraper formed by the margins of the elytra, the edges of the abdominal segments, or the mesothorax, the rapid motion of the latter over the rasps producing the sound. In many cases, according to Darwin, the males only stridulate, the females being destitute of those organs, and in such cases the sound is employed as a call to the female ; with most beetles, however, the stridulation proceeds from both sexes and serves as a mutual call. Beetles are entirely destitute of stinging organs, but a few are furnished with a retractile tube, or ovipositor, at the extremity of the abdomen, by means of which they deposit their eggs in the cracks of wood and other suitable localities. The eggs of beetles are deposited in a great variety of situations, and in the case of a certain group of Staphylinidce found in the nests of white ants in South America, it was recently discovered by Schb dte that the eggs are not deposited at all, but remain in the abdomen until they are hatched. These ovo- viviparous beetles are only one-tenth of an inch in length, and have the abdominal region enormously distended and turned over so as to rest on the back. Dung beetles deposit their eggs in the midst of the manure on which the future larva; feed ; the Sacred Beetle of Egypt rolling each of hers about until a globular pellet is formed, when the whole is buried in the ground ; while the Sexton Beetle finds an appropriate nidus for her eggs in the dead bodies of animals. One species of Cleridai selects the nest of the solitary bee, another (Plate VII. fig. 31) that of the hive bee, while several species of Rose Beetles choose the nest of the ant for this purpose. The water beetles belonging to the genus Hydrophilu* deposit their eggs in a single mass, which they surround with a oocoon, formed of a silky substance secreted by

certain glands in the abdomen, and then either fix this to