Bees are adapted for feeding on nectar and pollen, the former primarily as an energy source, and the latter primarily for protein and other nutrients. Most pollen is used as food for larvae.
Bees have a long proboscis (a complex "tongue") that enables them to obtain the nectar from flowers. They have antennae almost universally made up of thirteen segments in males and twelve in females, as is typical for the superfamily. Bees all have two pairs of wings, the hind pair being the smaller of the two; in a very few species, one sex or caste has relatively short wings that make flight difficult or impossible, but none are wingless.
The smallest bee is the dwarf bee (Trigona minima), about 2.1 mm (5/64") long. The largest bee in the world is Megachile pluto, which can grow to a size of 39 mm (1.5"). Member of the family Halictidae, or sweat bees, are the most common type of bee in the Northern Hemisphere, though they are small and often mistaken for wasps or flies.
The best-known bee species is the Western honey bee, which, as its name suggests, produces honey, as do a few other types of bee. Human management of this species is known as beekeeping or apiculture.
Bees play an important role in pollinating flowering plants, and are the major type of pollinators in ecosystems that contain flowering plants. Bees may focus on gathering nectar or on gathering pollen, depending on their greater need at the time, especially in social species. Bees gathering nectar may accomplish pollination, but bees that are deliberately gathering pollen are more efficient pollinators.
It is estimated that one third of the human food supply depends on insect pollination, most of this accomplished by bees. Bees are extremely important as pollinators in agriculture, especially the domesticated Western honey bee, with contract pollination having overtaken the role of honey production for beekeepers in many countries.
Monoculture and pollinator decline (of many bee species) have increasingly caused honey bee keepers to become migratory so that bees can be concentrated in areas of pollination need at the appropriate season. Recently, many such migratory beekeepers have experienced substantial losses, prompting the announcement of investigation into the phenomenon, dubbed "Colony Collapse Disorder," amidst great concern over the nature and extent of the losses.
Many other species of bees such as mason bees are increasingly cultured and used to meet the agricultural pollination need. Bees also play a major, though not always understood, role in providing food for birds and wildlife. Many of these bees survive in refuge in wild areas away from agricultural spraying, only to be poisoned in massive spray programs for mosquitoes, gypsy moths, or other insect pests. Most bees are fuzzy and carry an electrostatic charge, thus aiding in the adherence of pollen. Female bees periodically stop foraging and groom themselves to pack the pollen into the scopa, which is on the legs in most bees, and on the ventral abdomen on others, and modified into specialized pollen baskets on the legs of honey bees and their relatives.
Visiting flowers can be a dangerous occupation. Many assassin bugs and crab spiders hide in flowers to capture unwary bees. Others are lost to birds in flight. Insecticides used on blooming plants can kill large numbers of bees, both by direct poisoning and by contamination of their food supply. A honey bee queen may lay 2000 eggs per day during spring buildup, but she also must lay 1000 to 1500 eggs per day during the foraging season, mostly to replace daily casualties - note, however, that most casualties are workers simply dying of old age rather than predation. Among solitary and primitively social bees, however, lifetime reproduction is among the lowest of all insects, as it is not uncommon for females of such species to produce fewer than 25 offspring.
Bees vary tremendously in size..Bees, like ants, are essentially a highly specialized form of wasp. The ancestors of bees were wasps in the family Crabronidae, and therefore predators of other insects. The switch from insect prey to pollen may have resulted from the consumption of prey insects that were flower visitors and were partially covered with pollen when they were fed to the wasp larvae. This same evolutionary scenario has also occurred within the vespoid wasps, where the group known as "pollen wasps" also evolved from predatory ancestors. Up until recently the oldest non-compression bee fossil had been Cretotrigona prisca in New Jersey amber and of Cretaceous age, a meliponine. A recently reported bee fossil, of the genus Melittosphex, is considered "an extinct lineage of pollen-collecting Apoidea sister to the modern bees", and dates from the early Cretaceous (~100 mya). Derived features of its morphology ("apomorphies") place it clearly within the bees, but it retains two unmodified ancestral traits ("plesiomorphies") of the legs (two mid-tibial spurs, and a slender hind basitarsus), indicative of its transitional status.
The earliest animal-pollinated flowers were pollinated by insects such as beetles, so the syndrome of insect pollination was well established before bees first appeared. The novelty is that bees are specialized as pollination agents, with behavioral and physical modifications that specifically enhance pollination, and are much more efficient at the task than beetles, flies, butterflies, pollen wasps, or any other pollinating insect.