Contents
BEE,
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.
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.
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.
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.
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 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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.