BEETLE, an insect of the order Coleoptera. Beetles are distinguished from all other insects by the elytra or thickened fore wings, which are not actively used in flight, the hind wings being especially adapted for that purpose. The elytra cover and encase, thus protecting, the posterior segments of the thorax and the abdo men. The prothoracic segment is greatly en larged, often exarated in front, to receive the head. These characters are very persistent. There are few aberrant forms and the order is remarkably homogeneous and easily limited. The head is free from the thorax; it is scarcely nar rowed behind, and its position is usually hori zontal. The eyes are usually quite large, and there may be one or two ocelli — not more. The antennx are usually inserted just in front of the eyes, and rarely between them. They are either filiform where the joints are cylindri cal, as in the ground beetles (Carabidce), not enlarging toward the end, or serrate, as in the Elateride, where the joints are triangular and compressed, giving thereby a serrate outline to the inner edge; or clavate as in the Silphida, where the enlarged terminal joints give a rounded, club-shaped termination; or lamellate, when the terminal joints are prolonged inter nally, forming broad, leaf-like expansions, as in the Scarabceide, while the geniculate antenna is produced when the second and succeeding joints make an angle with the first. The mandibles are always well developed as biting and chewing organs, becoming abnormally en larged in the stag-beetles (Lucanus), while in certain Scarabwida they are small and mem branous. The maxillm prepare the food to be crushed by the mandibles. The greatly en larged prothorax is free and movable.
In the running species, as carabidce, the hind wings being useless are aborted, and very rarely in some tropical Lampyrida, and Scara bceidcr both pairs of wings are wanting in both sexes, though, as in the glow-worm and some of its allies, the females are apterous. The legs are well developed, as the beetles are among the most powerful running. insects, the hinder most pair of legs becoming oar-like in the swimming Dytiscsdce and some Hydrophilider, while in the Gyrinida both pairs of hind legs became broad and flat. The number of tarsal joints varies from the normal number five, to four and three joints, the terminal joint as usual being two-clawed. These claws are known to be wanting only in Phanceus, a scarabmid, and the aberrant family, Stylopsdee. According to the number of the tarsal joints the families of the Coleoptera have been grouped into the Pentamera (five-jointed), the Tetramera (four-jointed), the Trimera (three jointed), and the Heteromera, which are four jointed in the hind pair, while the first and second pairs are five-jointed. The abdomen,
usually partially concealed by the wings, is ses sile, its base broad; in form it is usually some what flattened.
A few genera are capable ‘g producing sounds by rubbing the limbs orl, elytra over finely wnnkled surfaces, which it Trox are situated on the side of the basal segiaents of the abdomen, and in Strategus on the‘tergum of the penultimate segment of the abdthnen, while such a surface is found in HigOus on the surface of the elytra.
The larvw when active and not iermanently enclosed (like the curculio) in the substances that form their food, are elongate!, flattened, wormlike, with a large head, wel-developed mouth-parts and three pairs of thoracic feet, either horny, or fleshy and retractile, while there is often a single terminal prop-leg on the terminal segment of the body and a lateral horny spine. The wood-boring larva of the Cerambycidcs are white, soft and more or less cylindrical, while those of the Curculionicia are footless or nearly so, and resemble those of the gall-flies, both the hymenopterous and the dipterous.
The pupa have free limbs, and are either enclosed in cocoons of earth, or, if wood-borers, in rude cocoons of fine chips and dust, united by threads, or a viscid matter supplied by the insect. None are known to be coarctate, though some Coccinelke transform within the old larva-skin, not rejecting it, as is usual in the group, while other pupa are enclosed in the cases in which the larva lived. In some Staphylinida the pupa shows a tendency to be come obtected, the limbs being soldered to the body, as if enclosed in a common sheath. Generally, however, the antenna are folded on each side of the clypeus, and the mandibles, maxilla and labial palpi appear as elongated papilla. The wing-pads being small are shaped like those of the adult Meloe, and are laid upon the posterior femora, thus exposing the meso and meta-thorax to view. The tarsal joints lie parallel on each side of the middle line of the body, the hinder pair not reaching to the tips of the abdomen, which ends in a pair of acute, prolonged, forked, incurved horny hooks, which must aid the pupa in working its way to the surface when about to transform into the beetle.