Page:EB1911 - Volume 03.djvu/646

 feed for a time without conflict, but the Stelis, being the older, is the larger of the two. Finally the parasitic larva attacks the Osmia, and digging its mandibles into its victim’s head kills and eats it, taking from one to two days for the completion of the repast.

Social Bees.—The bees hitherto described are “solitary,” all the individuals being either males or unmodified females. The most highly developed of the long-tongued bees are “social” species, in which the females are differentiated into egg-laying queens and (usually) infertile “workers” (fig. 6). Verhoeff has discussed the rise of the “social” from the “solitary” condition, and points out that for the formation of an insect community three conditions are necessary—a nest large enough for a number of individuals, a close grouping of the cells, and an association between mother and daughters in the winged state. For the fulfilment of this last condition, the older insects of the new generation must emerge from the cells while the mother is still occupied with the younger eggs or larvae. One species of Halictus nearly reaches the desired stage; but the first young bees to appear in the perfect state are males, and when the females emerge the mother dies.

Among the social bees the mother and daughter-insects co-operate, and they differ from the “solitary” groups in the nature of their nest, the cells (fig. 25) of which are formed of wax secreted by special glands (fig. 5) in the bee’s abdomen, the wax being pressed out between the segmental sclerites in the form of plates (fig. 4), which are worked by the legs (fig. 7) and jaws into the requisite shape. In our well-known hive-bee (Apis) and humble-bees (Bombus) the wax glands are ventral in position, but in the “stingless” bees of the tropics (Trigona and Melipona) they are dorsal. A colony of humble-bees is started in spring by a female “queen” which has survived the winter. She starts her nest underground or in a surface depression, forming a number of waxen cells, roughly globular in shape and arranged irregularly. The young females (“workers”) that develop from the eggs laid in these early cells assist the queen by building fresh cells and gathering food for storage therein. The queen may be altogether relieved of the work of the nest as the season advances, so that she can devote all her energies to egg-laying, and the colony grows rapidly. The distinction between queen and worker is not always clear among humble-bees, the female insects varying in size and in the development of their ovaries. If any mishap befall the queen, the workers can sometimes keep the community from dying out. In autumn males are produced, as well as young queens. The community is broken up on the approach of winter, the males and workers perish, and the young queens after hibernation start fresh nests in the succeeding year.

(From Cheshire’s Bees and Bee-keeping.)

The appearance of the heavy-bodied hairy Bombi is well known. They are closely “mimicked” by bees of the genus Psithyrus, which often share their nests. These Psithyri have no pollen-carrying structures on the legs and their grubs are dependent for their food-supply on the labours of the Bombi, though, according to E. Hoffer’s observations, it seems that the female Psithyrus builds her own cells. The colonies of Bombus illustrate the rise of the inquiline habit. Many of the species are very variable and have been differentiated into races or varieties. F. W. L. Sladen states that a queen belonging to the virginalis form of Bombus terrestris often invades a nest belonging to the lucorum form, kills the rightful queen, and takes possession of the nest, getting the lucorum workers to rear her young. In the nests of Bombi are found various beetle larvae that live as inquilines or parasites, and also maggots of drone-flies (Volucella), which act as scavengers; the Volucella-fly is usually a “mimic” of the Bombus, whose nest she invades.

The “stingless” bees (Trigona) of the tropics have the parts of the sting reduced and useless for piercing. As though to compensate for the loss of this means of defence, the mandibles are very powerful, and some of the bees construct tubular entrances to the nest with a series of constrictions easy to hold against an enemy. The habits of the Brazilian species of these bees have been described in detail by H. von Jhering, who points out that their wax glands are dorsal in position, not ventral as in Bombus and Apis.

With Apis, the genus of the hive-bee, we come to the most highly-specialized members of the family—better known, perhaps than any other insects, on account of the long domestication of many of the species or races. In Apis the workers differ structurally from the queen, who neither builds cells, gathers food, nor tends brood, and is therefore without the special organs adapted