BEETLE, (AS. bitel, betel, literally 'biter,' from bitan. Engl. bite). An insect of the order Coleoptera. which seems to be wingless when at rest, but really possesses two pairs of wings. At rest one pair is folded beneath two horny cases that fit over the back and meet in the median dorsal line. These horny eases are the elytra or wing-covers, which are only the modified forewings; and they distinguish beetles from all other insects save the earwigs, which are easily separable upon other grounds.
The slight protection afforded by this armature seems to be very advantageous to beetles, for they form the largest order of existing insects. "In bodily form, ' says Dimmock, "the Coleoptera present every variation from long cylindrical to nearly globular, from hemispheres to extremely flattened disks, from straggling ant-like forms to compact seed-like ones." All, nevertheless, ex hibit a division of the body into three parts, which, however, are not the typical head, thorax, and abdomen, but a modification of these—bead, prothorax or fore body. and mesothorax and metathorax combined with the abdomen into a hind body.
The Head hears various appendages, and the mouth opens forward or downward. The mouth parts are strong. equably developed, and adapt ed both for gnawing and for seizing prey. The mandibles are large and strong, and in the males of some forms reach a great size. (See STAG BEETLE.) The Curculionidu, or snout beetles, have a long beak, but it is a prolonga tion of the head in front of the eyes, and not of any of the mouth parts.
The eyes are compound. and usually large and effective, except in a few cave-dwelling species. (See CAVE ANDIALs.) Ocelli are absent, as a rule, in the adult form. even where possessed by the larva'. The compound eyes vary greatly in form and appearance and number of facets, and sometimes are divided into upper and lower parts, so that the insect is really four-eyed; this is especially the ease in some water beetles, which may thus see what is going on both above and below the surface of the water as they swim. The antennae (most commonly eleven jointed ) are placed just in front of the eyes, and are organs not only of touch, but of smell and probably of hearing. They appear under a variety of forms, some of which are pretty eon stant throughout large groups, giving them such names as clavicorn, lamellieorn, serricorn, longi corn. etc. "The antennae are said to be clavate when thickened at the extremity, in the form of a club or knob; lamellate, when three or more of the terminal joints spread out in broad proc esses which lie flat upon one another; serrate, when the joints have on one side short angular processes like the teeth of a saw; pectinate, or comb-like, when the processes are fairly long and stand out nearly at right angles; or flabellate, if the processes are proportionately very long."
It is believed that the senses of smell and hear ing reside in the The former is evi dently well developed in most, if not all, beetles, while the latter seems certainly possessed by many. The tapping of such species as the `deathwatch' implies a listener of the same kind; and similar evidence is furnished by the fact that longieorns and some other beetles are often capable of producing sound by stridulat ing or rubbing together various external hard parts of the body, such as wings and legs, or surfaces and angles on the prothorax and meta thorax; they produce some tones that man is incapable of hearing. These organs are pos sessed chiefly by the males; and a resume of facts relating to it and to many other char acteristics distinguishing the sexes of beetles may be found in Chapter X. of Darwin's Descent of Man (London, 2d ed., 1374).
The Fore Body forms the second well-marked division of a beetle, and consists of the pro thorax, which in Coleoptera is not united solidly with the two other thoracic segments, but con nected movably with them. "Its tergite (prono tum) is a very prominent feature in all beetles, reaching back to the origin of the elytra." It is hollowed forward to receive the head. and in some groups it is modified in form or possesses horns and spines of extraordinary appearance. These, as a rule, are seen only in the males, however, and most prominently among the lamellieonis. This fore body wears the fore most pair of legs, with which the hinder pairs may or may not agree. Beetles use their legs more than their wings. They do fly, but less frequently and skillfully than they run, jump, climb, swim, and burrow. Most of them are extremely active, and hence have well-developed legs and feet. These are all much alike in the ground-runners and tree-climbers, but variety is found among those of more special haunts and habits. Thus, the jumpers have very long bind legs, with thickened femora: the diggers have thickened fore legs, with claws turned into exca vators: the aquatic beetles have all or a part of their legs disposed as oars, and made broad and flat and bordered with bristles. The parts of the legs vary considerably, and with such regu larity that the form of the coxa is used as one of the main standards in classifying families, while larger groups—Pentamera, Tetramera, etc.—are based on number and characteristics of joints in the tarsi. The tarsal joints are hairy beneath, and those of the anterior (and sometimes also the middle) pair of legs of many male beetles are modified to clasp more firmly the female during copulation." The most pe culiar of these modifications is seen among water beetles (Dysticidce). The legs of larvae are often reduced to mere rudiments, or are absent.