Many of the Tenebrionidae, notwithstanding their dark colours, are diurnal in habits, and some of them run with extreme velocity in places so bare and desert that the means of existence of the Insects is a mystery. Most of the Tenebrionidae, however, shun the light. The food is usually vegetable matter, and it is apparently preferred in a very dry state. Mr. Gahan has recently recorded that in Praogena the under surface of the head has the gular region striate for stridulating purposes. This is the only instance known of a voice-organ in this situation, and moreover is the only case in all the Tenebrionidae in which any sound-producing organ has been discovered. The larvae exhibit but little variety, they are elongate and cylindrical, with harder integument than is usual in Coleopterous larvae; they have six thoracic legs, and at the under side of the posterior extremity the anus serves as a very short pseudopod. The resemblance of these larvae to those of Elateridae is considerable; but though the body is terminated by one or two small processes, these never attain the complexity of the terminal segment of Elateridae. The common meal-worm—i.e. the larva of Tenebrio molitor—is a very characteristic example of the group. The pupae are remarkable on account of peculiar projections, of varied and irregular form, that exist on the sides of the abdominal segments. Britain is very poor in these Insects; our list of them scarcely attains the number of thirty species.
Fam. 63. Cistelidae.—Claws comb-like. The very obscure beetles forming this family are only separated from Tenebrionidae on account of their pectinate claws. About 500 species of Cistelidae are recorded; the early instars, so far as known, do not differ from those of Tenebrionidae; the larvae are believed to live on dead wood.
Fam. 64. Lagriidae.—Anterior coxal cavities closed, tips of the front coxae free, claws smooth, penultimate joint of the tarsi broader, pubescent beneath. This family has very little to distinguish it from Tenebrionidae, and the group Heterotarsini appears to connect the two. It is a small family of about 200 species, widely distributed, and represented in Britain by one species, Lagria hirta. The early instars are similar to those of the Tenebrionidae, except that the larva is less retiring in its habits and wanders about on foliage: it is of broader form than that of most of the Tenebrionidae. The pupa has long projections at the sides of the abdominal segments.
Fam. 65. Othniidae.—Only about ten species are known of this dubious family. They are small Insects with weak integument, and are said by Leconte and Horn to be distinguished from "degraded Tenebrionidae" by the more mobile abdominal segments, the hind-margins of which are semi-membranous. The antennae are of the clubbed shape, characteristic of "Clavicornia," but this also occurs in numerous undoubted Tenebrionidae. Species of Othnius have been found in Japan and Borneo, as well as in North America. Nothing is known as to their metamorphoses.
Fam. 66. Ægialitidae.—All the coxae very widely separated; no co-adaptation between the sides of the abdomen and the edges of the wing-cases; five ventral segments and tip of a sixth visible. Two minute and rare Insects from North-West America constitute this family. It is distinguished from Pythidae by the minute front coxae, widely separated, completely closed in, and deeply embedded in the prosternum.
Fam. 67. Monommidae.—This is a small family of less than 100 species, the members of which have the details of their external structure much modified, permitting the Insect to pack itself up in repose in a very perfect manner. They are of small size and oval form; and are absent from Europe and the Antipodes. Nothing appears to be known as to the metamorphosis.
Fam. 68. Nilionidae.—Broad, circular Heteromera, of moderate size, with the front coxae but little separated, and the anterior acetabula closed, though having the appearance of being open in consequence of the tips of the epimera being free. The inflexed portion of the wing-cases remarkably broad. A small family of less than fifty species, found on fungi, chiefly in South America. The metamorphoses are not known. It is of very doubtful validity.
Fam. 69. Melandryidae.—Head not constricted behind the eyes; anterior acetabula not closed; claws smooth. Prothorax broad behind. These are loosely-fitted-together Insects, of moderate or small size, frequenting dry wood or fungi. About 200 species are known, found chiefly in temperate regions. The few described larvae are rather varied in their details and cannot be generalised at present. The characters of the members of this family require fresh investigation.
Fam. 70. Pythidae.—Distinguished from Melandryidae by the prothorax being narrow behind. This is a small family of about 100 species, found in temperate regions in connection with timber. The species of Rhinosimus have the head prolonged in front of the antennae so as to form a beak. The larva of Pytho depressus is flat and has parallel sides; the body is terminated by two widely-separated sharp processes. It is found occasionally under the bark of firs in Scotland.
Fam. 71. Pyrochroidae.—Differs from Melandryidae by the head forming a very narrow neck behind, and by the penultimate tarsal joints being broad. They are feeble Insects, though active on the wing. They are destitute of any of the various remarkable structures found in Mordellidae. Only about forty species are known, and the family is confined to the north temperate region, being best represented in Japan. Pyrochroa rubens is common in some parts of England; the larva is found under the bark of tree-stumps; it is remarkably flat, and has the eighth abdominal segment unusually long, while the ninth terminates the body in the form of two long sharp processes.