III.

Social Structure and Nesting Habits

Bees have diverse nesting and social habits. This diversity has provided scientists with a natural laboratory for the study of evolution and social behavior in insects (see Sociobiology).

A.

Solitary Bees

The primitive bees, like their relatives the wasps, are solitary. Each female makes her own burrow, in which she constructs earthen chambers to contain her young. She deposits pollen moistened with nectar or oil into individual cells until enough food has accumulated to provide for the young bee from egg hatching until the larva reaches full size. She then lays an egg on the pollen mass and seals the cell before going on to construct another cell.

B.

Social Bees

Some bees are communal. They are like solitary bees except that several females of the same generation use the same nest, each making her own cells for housing her eggs, larvae, and pupae. A few kinds of bees are semisocial—they live in small colonies of two to seven bees of the same generation, one of which is the queen, or principal egg layer; the others are worker bees. About 1000 species of bees live in small colonies consisting of a queen and a few daughter workers. In these colonies, the differences in appearance and behavior between workers and queens are scarcely distinguishable. Such species, called primitively eusocial, form temporary colonies that die out in autumn, and only the fertilized queens survive the winter. Bumblebees are familiar examples.

The eusocial, or truly social, bees live in large colonies consisting of females of two overlapping generations: mothers (queens) and daughters (workers). Males, called drones, play no part in the colony's organization and only mate with the queens. Larvae are fed progressively—that is, cells are opened as necessary or are left open so that workers can tend the larvae. Highly eusocial bees, a few hundred species, form permanent colonies in which the queen and worker castes are markedly different in structure, each specialized for its own activities and unable to survive without the other. Colonies of eusocial bees are complex, highly coordinated societies. Individual bees may have highly specialized functions within the colony. The tasks of defense, food collection and storage, reproduction, and many other activities are regulated by the colony's response to environmental conditions inside and outside the hive. Individuals communicate by means of chemical messages, touch, sound, and, in the case of honey bees, a symbolic dance language (to learn more about chemical communication, See Pheromone). The nests of many eusocial bees are very elaborate and may be constructed partially of wax secreted by the bees.

C.

Parasitic Bees

Parasitic, or cuckoo, bees are those that do not forage or make nests themselves but use the nests and food of other species of bees to provide for their parasitic young. Parasitic bees are of two types: cleptoparasitic bees and social parasites. Cleptoparasitic bees invade the nests of solitary bees, hide their eggs in the brood chambers before the hosts lay theirs, and close the chambers. The young of the parasitic bees then feed on the food that was stored in the chamber by the host female. The eggs or young larvae of the host bee are killed either by the parasitic female or by her larvae. Social parasites are bees that kill the resident queen, lay their own eggs in the host's cells, and then force the host's workers to raise the young parasitic bees. Females of parasitic bees lack such special features as pollen baskets or pollen brushes since they do not forage for food for their young.