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.