SOCIAL LIFE AMONG THE INSECTS1 By Professor WILLIAM MORTON WHEELER LECTURE III. PART 2. BEES SOLITARY AND SOCIAL The Meliponine, or stingless bees, are a very peculiar group of nearly 250 species, all confined to warm countries. Fully four fifths of the species occur only in the American tropics and only about one fifth in the Ethiopian, Indomalayan and Australian regions. All the Old World and the majority of the Neotropical forms belong to the genus Trigona; the remainder of the American species are placed in a separate genus, Melipona. The stingless bees are much less hairy and much smaller than the bumble-bees. Some of the species of Trigona measure less than 3 mm. in length and are therefore among the smallest of bees. The colonies vary greatly in population in different species. According to H. von Ihering, those of Melipona may comprise from 500 to 4,000, those of Trigona from 300 to 80,000 individuals. The name stingless as applied to these insects is not strictly accurate, because a vestigial sting is present. It is useless for defence, however, so that many of the species are quite harmless and are called "angelitos" by the Latin-Americans. But some forms are anything but little angels. When disturbed they swarm at the intruder, bury themselves in his hair, eye-brows and beard, if he has one, and buzz about with a peculiarly annoying, twisting movement. Others prefer to fly into the eyes, ears and nostrils, others have a penchant for crawling over the face and hands and feeding on the perspiration, or bite unpleasantly, and a few species spread a caustic secretion over the skin. On one occasion in Guatemala large patches of epidermis were thus burned off from my face by a small swarm of Trigona flaveola. There are three morphologically distinct castes. The queen differs from the worker in the smaller head, much more voluminous abdomen, more abundant pilosity, and in the form of the hind legs, the tibia of which are reduced in width and furnished with bristles also on their external surfaces, while the metatarsi are elongate, rounded and apically narrowed. The worker, therefore, really represents the typical female of the species morphologically, except that she is sterile, whereas the queen, except in her ovaries, exhibits a degeneration of the typical secondary characters of her sex. There is only one mother queen in a colony, but a number of young daughter queens are tolerated. New colonies are formed by swarming, that is, by single young queens leaving the colony from time to time, accompanied by detachments of workers, to found new nests. The body of the old queen is so obese and heavy with eggs and her wings are so weak that she can not leave the nest after it is once established. The nests of the Meliponinæ are extremely diverse in structure. They are usually in hollow tree-trunks or branches, less frequently in walls. Some of the species nest in the ground, and a few (T. kohli, fulviventris, crassipes, etc.,) actually build in the centers Cerumen spout, or nest entrance of a large colony of Trigona heideri Friese nesting in a hollow tree at Kartabo, British Guiana. About 1/3 natural size. Photograph by Mr. John Tee Van. Vol. XV.-21. 66 of termite nests. The nest is made of wax, which most of the species mix with earth, resin or other substances, so that it is chocolate brown or black and is called cerumen." The wax is secreted only between the dorsal segments of the abdomen, and is produced by the males as well as by the workers-the one case in which a male Hymenopteran seems to perform a useful social function. The workers not only collect nectar and pollen but they seem to have a greater propensity than other social bees for gathering propolis, resins and all kinds of gums and sticky plant-exudations. And unlike other bees they are also fond of visiting offal and the feces of animals. One species is said even to eat meat (T. argentata, according to Ducke). The entrance to the nest may be a simple hole, but more often it is a projecting cerumen spout or funnel, which differs considerably in different species (Fig. 46). In some East Indian Trigonas its lips are kept covered with sticky propolis to prevent the ingress of ants and other intruders (Fig. 47AB). In most of the South American species its orifice is guarded during the day by Cerumen entrances to nests of Meliponine bees. A. Of Trigona laeviceps of India in profile; B, same seen from the front (After C. S. P. Parish); C, nest entrance of Melipona quinquefasciata; D, nest entrance of Trigona limao After F. Silvestri. a special detachment of workers and is closed at night with a cerumen plate or screen. The interior of the nest presents a peculiar appearance. If it is in a hollow tree-trunk or branch the cavity is closed off at each end by a thick lump or plate of cerumen (the "batumen"). The nest proper (Figs. 48 and 49), constructed in the tubular space thus preempted, consists of two parts, one for the brood and one for the storage of various foods and building materials. The brood portion consists typically of a hollow spheroidal FIG. 48 Portion of nest of Melipona scutellaris, showing brood-comb (to the right) and the large honey pots and pollen pots (to the left). Subdiagrammatic drawing from Emile Blanchard. Nest of Melipona sp. in hollow log, showing brood-comb (to the left), pollen pots and honey pots (to the right). Photograph by Dr. E. F. Phillips. About one half natural size. envelope of irregular, interconnected cerumen laminæ, forming the walls of an elaborate system of anastomosing passage-ways and enclosing a large central space occupied by a series of combs of hexagonal cells. There is only one layer of cells in each comb and they all open upwards, not downwards as in the social wasps. In some species the combs are regular and disc- or ring-shaped structures, in others they are arranged in a spiral or more irregularly. Their cells are used exclusively for rearing the brood. In Melipona and some species of Trigona they are all of the same size, but in several South American species of the latter genus single larger cells are constructed, especially towards the periphery of the combs, for the rearing of queen larvæ. All this elaborate arrangement would seem to be a preparation for a very specialized system of caring for the young, but such is not the case. The workers, precisely as if they were solitary bees, put a quantity of pollen and honey into each cell, and after the queen has laid an egg in it, provide it with a waxen cover, so that the larva is reared exactly like that of a solitary bee. There is mass but not progressive provisioning and the adult bees do not come in contact with the growing larvæ. The queen-cells are treated in the same manner, the only differ |