SUBSOCIAL INSECTS Insects with incipiently social or subsocial behaviour belong to diverse groups and exhibit parental care for their offspring in various ways. In the common earwig (q.v.) the female deposits her eggs in a group in an excavation below the surface of the soil and rests over them until they hatch. The young remain for a few days with the parent who in this respect resembles a hen with her brood of chickens, and her solicitude for her offspring is main tained until they disperse. Among the Embioptera (see INSECTS) of warm countries Imms has observed similar behaviour with the Himalayan species Embia major which lives in dense silken tunnels beneath stones. The young, in this case, keep together in the parental abode and, where necessary, extend it by weaving tunnels for themselves. Among beetles, in the Scarabaeid Copris lunaris the male and female associate in pairs and excavate a chamber in the earth which they fill with ellipsoidal balls of dung in each of which an egg is laid. These are guarded while the larvae are feeding and growing within, and when the young beetles emerge the latter are escorted to the surface by both parents and the family then disperses. Other species of Copris and also other dung beetles like Geotrupes, Onthophagus and Minotaurus exhibit very similar parental care, higher or lower developed in the several cases. The ambrosia beetles of the family Scolytidae (see COLEOPTERAN construct galleries in the wood of trees. Both sexes work together but most of the work devolves upon the female who excavates circular pits along the tunnels lay ing an egg in each.
Omitting the Passalidae, which also exhibit marked social habits, mention must be made of certain beetles of the family Cucujidae recently found by Wheeler living along with their brood in the hollow leaf-stalks of young Tachigalia trees in British Guiana. The parent beetles live and feed along strands of specially nutritive tissue and while they are thus engaged, numbers of mealy-bugs (see SCALE INSECT) wander into the leaf stalk through the opening made by the beetles, settle in the grooves eaten out by the latter and feed on the nutritive tissue.
The beetles lay their eggs and their larvae devour the same food as the parents but, remarkable as it may seem, both the larvae and their parents have learned to stroke the mealy-bugs with their feelers thus stimulating them to exude honey-dew which they eagerly consume. The beetle larvae duly pupate in the leaf stalks and when the young beetles hatch out they remain with their parents, but soon commence egg-laying with the result that there is eventually a community of beetles, larvae, pupae and mealy-bugs of all ages living together. The subsocial beetles foreshadow the behaviour which obtains in the more highly or ganized social communities but, unlike the latter, they exhibit no structural or physiological differences between individuals which constitute separate castes.