common name for any of the insects that constitute the superfamily Apoidea of the order Hymenoptera, which also includes wasps and ants. About 20,000 species exist, varying from minute forms only 2 mm (0.08 in) long to large insects that are 4 cm (1.6 in) long.

Characteristics

Like wasps, most female bees have functioning stings. Unlike wasps, however, they are dependent on pollen as a protein source and on nectar (or sometimes oils) from flowers as an energy source. Adult females collect pollen primarily to feed their larvae, although the adults also feed on pollen as well as nectar. The pollen they inevitably lose in going from flower to flower is important to the plant because some of it lands on the pistils of other flowers of the same species, achieving cross-pollination. Bees are, in fact, the most important pollinating insects.

Social structure AND NESTING HABITS

The great majority of bee species are solitary, each female making its own nest and storing provisions for its larvae. Some bees are communal. They are like solitary bees, except that several females of the same generation use the same nest, each making its own cells for housing its 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, and the others workers. Probably 1000 or more species of bees live in small colonies consisting of a queen and a few daughter workers, with the castes scarcely distinguishable. Such species, called primitively eusocial, form temporary colonies that normally break up in autumn, with only the fertilized queens surviving the winter. Bumblebees are familiar examples. The eusocial (“truly social”) bees live in large colonies consisting of females of two generations: mothers (queens) and daughters (workers); males play no part in the colony’s organization, but are important for egg fertilization.

Solitary Bees.

The primitive bees, like the wasps from which they arose, are solitary. Each female makes its own burrow and cells, and each cell is provisioned with a mass of pollen moistened with nectar or oil. When enough food is accumulated in a cell to provide for the young bee from egg hatching until the larva reaches full size, the female lays an egg in the cell, which it then seals before going on to construct another cell.

Social Bees.

Communal bees make similar nests and cells, except that the nest itself (usually a burrow in the soil) is occupied by several bees. Semisocial and most primitively eusocial bees also make nests and cells like those of their solitary relatives, except that construction and cell provisioning are often joint projects. 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. In the colonies of bumblebees and the highly eusocial bees, the cells are made at least in part of wax secreted by the bees. In bumblebees and true honeybees, the feeding of larvae is progressive; that is, cells are opened as necessary or are left wide open so that workers can tend the larvae. Bumblebees and highly eusocial bees are also the only groups of bees that store honey and pollen for adult as well as larval consumption.

Parasitic Bees.

Parasitic bees are those that do not make nests or forage themselves, but rather 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, open the brood chambers or enter open brood chambers, hide their eggs 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 egg or young larva of the host bee is either killed by the parasitic female or by her larvae. Social parasites are bees that kill the resident queen and force the workers to raise the young parasitic bees. Females of both cleptoparasitic bees and social parasites lack such special features as pollen baskets or pollen brushes since they do not forage for food for their young.

CLASSIFICATION

Bees are divided into a number of families, largely on the basis of mouthparts and other characteristics that are difficult to see without dissection. Although most do not have a distinctive appearance to set them apart, families are the basic subdivisions of the Apoidea; the major ones are described below.

Colletidae.

The family Colletidae differs from all other families in that the glossa (tongue) is broad and blunt or two-lobed. In this they resemble wasps and hence have been regarded as the most primitive bees. The broad tongue, however, may be an adaptation for painting the interior surfaces of their brood cells with a secretion that hardens into a cellophane-like membrane characteristic of Colletid nests. All Colletids are solitary.

Halictidae.

Members of the enormous, worldwide family Halictidae are often called “sweat bees,” because some of them are attracted to perspiration. Their nests are burrows in the ground or, rarely, in rotten logs. Cells are excavated at the ends and sides of tunnels in the soil and are lined with a thin, waxlike layer. Many Halictids are solitary, but some are communal and others parasitic. A few South American species are semisocial, and hundreds of species are primitively eusocial. The latter range from species living in colonies of only two to four individuals—a queen and one to three workers—to species living in colonies of several hundred. The castes often appear identical. Because of their great abundance, Halictids are extremely important in the pollination of vegetation and crops. At least one species, the alkali bee (Nomia melanderi) of the western U.S., is commercially important because it is a major pollinator of alfalfa. Many alfalfa-seed growers prepare special beds made of moist soil in which aggregations of the solitary nests of Nomia can develop.

Andrenidae.

This large family of short-tongued bees makes nests in the soil that consist of burrows with a number of branches, each ending in one or more cells. In most species the cells are lined with a layer of secreted waterproof plastic-like material. Andrenids are solitary or communal, and they pollinate many trees, shrubs, and herbs. They are increasingly important in the pollination of commercial crops.

Megachilidae.

One of the principal characteristics of this large, worldwide family is the pollen-carrying brush, or scopa, on the underside of the abdomen of females (except for parasitic forms). Some species make burrows in the ground or in pithy stems. Most, however, appropriate holes made in dead logs by beetles, or in the ground by various burrowing insects. Other species construct cells in exposed situations. The Megachilids are solitary, with the exception of a few communal species, but unlike most solitary bees, they do not line their cells with a secreted material. Instead, they bring outside material such as leaves, pebbles, down, or resin for construction of the cell lining or of the entire cell. Megachilids are important pollinators of many plants. The alfalfa leaf-cutter bee (Megachile rotundata) is even more important than the alkali bee in alfalfa pollination, and a significant industry has developed around it.

Anthophoridae.

This large and diverse worldwide family of long-tongued bees contains three subfamilies. The first, the Nomadinae, consists of parasitic bees. The second subfamily, Anthophorinae, contains a large number of hairy, robust bees that are usually solitary but sometimes parasitic or communal. Most Nomadinae construct burrows leading to cells that are thinly lined with a waxy secretion. Nearly all the species of the third subfamily, Xylocopinae, nest in wood or stems, excavating their own burrows or taking advantage of burrows made by previous generations. Included in the subfamily are the carpenter bees, which cut holes into solid wood and sometimes damage human structures. The remaining Xylocopinae are small, slender bees that nest in pithy stems. Most Xylocopinae are basically solitary, although long-lived, so that several adults are often found in a nest; some Old World species of the Xylocopinae, however, form small eusocial colonies.

Apidae.

This family differs from all other bees in that the pollen brush, which is restricted to the hind leg, is reduced to a row of long hairs surrounding a smooth space on the tibia. Thus, these are the only bees in which the pollen-carrying arrangement can be described as a pollen basket, or corbicula. The family is divided into four major groups.

Orchid Bees.

The first group is the Euglossini, or orchid bees, found only in the American Tropics. The species consist of middle-size to large, often brilliantly metallic, extremely long-tongued bees that are essential to orchid pollination. These bees are solitary or live in colonies but, as far as is known, none is truly social. Two genera are parasites.

Bumblebees.

This group, the Bombini, contains only the familiar hairy bumblebees, Bombus, and the related Psithyrus, social parasites of Bombus. With their large size and furry covering, bumblebees range farther north than any other bees, because they are able to control their body temperature better than most insects. The nests containing their primitively eusocial colonies are made in cavities such as old mouse nests. Each large, overwintered queen forms its own nest in the spring and rears a group of workers, much smaller than itself, who then take over foraging activities while the queen lays eggs. Bumblebees are important in the pollination of natural vegetation. Some have commercial importance, especially in seed production of red clover. In New Zealand, this forage crop produced no seed until bumblebees from England were introduced.

Stingless honeybees.

The third group, the tropical, eusocial, stingless honeybees (Meliponinae), ranges in size from the smallest of all bees to species larger than honeybees. Although their stings are reduced and do not function, many species are by no means defenseless. Attack consists of biting and of crawling into the eyes, ears, nose, and hair of animals that disturb them. Nests are constructed of cerumen, a mixture of resin and wax, with mud sometimes added. The brood cells, unlike those of true honeybees, open upward and are arranged in horizontal combs or in clusters. Stingless-bee colonies vary from a few hundred up to the largest colonies of all bees, with more than 100,000 individuals. Each colony contains a queen that becomes swollen with eggs and unable to fly. Young queens, rather than old queens as in true honeybees, leave to establish new colonies. No parasitic stingless bees exist; a few species, however, live by robbing.

True honeybees.

The fourth and last group of Apidae is the Apinae. It contains only the genus Apis, the true honeybee, with about five eusocial species. Once restricted to Europe, Asia, and Africa, the common honeybee has since been introduced into all parts of the world. Originally it was the European races that were carried to other continents. Such races are not well adapted to the Tropics and in 1957 an African race was introduced into Brazil to improve the honey production in tropical regions. Its escape and hybridization with the bees of European origin already there resulted in the Africanized “killer” bees—so named for their aggressive tendencies—that have spread over South America and have now reached the U.S.-Mexican border.        C.D.M., CHARLES D. MICHENER, Ph.D.

For details of the social organization, complex communication, and economic importance of the common honeybee, see HONEYBEE,.

For further information on this topic, see the Bibliography, sections 466. Entomology, 600. Honeybee.