Bees are winged insects that form a monophyletic clade Anthophila within the superfamily Apoidea of the order Hymenoptera, with over 20,000 known species in seven recognized families.[1][2][3] Some species – including honey bees, bumblebees, and stingless bees – are social insects living in highly hierarchical colonies, while over 90% of bee species – including mason bees, carpenter bees, leafcutter bees, and sweat bees – are solitary. Members of the most well-known bee genus, Apis (i.e. honey bees), are known to construct hexagonally celled waxy nests called hives.

Unlike the closely related wasps and ants, who are carnivorous/omnivorous, bees are herbivores that specifically feed on nectar (nectarivory) and pollen (palynivory), the former primarily as a carbohydrate source for metabolic energy, and the latter primarily for protein and other nutrients for their larvae. They are found on every continent except Antarctica, and in every habitat on the planet that contains insect-pollinated flowering plants. The most common bees in the Northern Hemisphere are the Halictidae, or sweat bees, but they are small and often mistaken for wasps or flies. Bees range in size from tiny stingless bee species, whose workers are less than 2 millimeters (0.08 in) long,[4] to the leafcutter bee Megachile pluto, the largest species of bee, whose females can attain a length of 39 millimeters (1.54 in). Vertebrate predators of bees include primates and birds such as bee-eaters; insect predators include beewolves and dragonflies.

Bees are best known for their ecological roles as pollinators and, in the case of the best-known species, the western honey bee, for producing honey, a regurgitated and dehydrated viscous mixture of partially digested monosaccharides kept as food storage of the bee colony. Pollination management via bees is important both ecologically and agriculturally, and the decline in wild bee populations has increased the demand and value of domesticated pollination by commercially managed hives of honey bees. Human beekeeping or apiculture (meliponiculture for stingless bees) has been practiced as a discipline of animal husbandry for millennia, since at least the times of Ancient Egypt and Ancient Greece. Bees have appeared in mythology and folklore, through all phases of art and literature from ancient times to the present day, although primarily focused in the Northern Hemisphere where beekeeping is far more common. In Mesoamerica, the Maya have practiced large-scale intensive meliponiculture since pre-Columbian times.

Evolution
The immediate ancestors of bees were stinging wasps in the family Ammoplanidae, which were predators of other insects.[5] The switch from insect prey to pollen may have resulted from the consumption of prey insects which were flower visitors and were partially covered with pollen when they were fed to the wasp larvae. This same evolutionary scenario may have occurred within the vespoid wasps, where the pollen wasps evolved from predatory ancestors.[6]

Based on phylogenetic analysis, bees are thought to have originated during the Early Cretaceous (about 124 million years ago) on the supercontinent of West Gondwana, just prior to its breakup into South America and Africa. The supercontinent is thought to have been a largely xeric environment at this time; modern bee diversity hotspots are also in xeric and seasonal temperate environments, suggesting strong niche conservatism among bees ever since their origins.[7]

Genomic analysis indicates that despite only appearing much later in the fossil record, all modern bee families had already diverged from one another by the end of the Cretaceous. The Melittidae, Apidae, and Megachilidae had already evolved on the supercontinent prior to its fragmentation. Further divergences were facilitated by West Gondwana's breakup around 100 million years ago, leading to a deep Africa-South America split within both the Apidae and Megachilidae, the isolation of the Melittidae in Africa, and the origins of the Colletidae, Andrenidae and Halictidae in South America. The rapid radiation of the South American bee families is thought to have followed the concurrent radiation of flowering plants within the same region. Later in the Cretaceous (80 million years ago), colletid bees colonized Australia from South America (with an offshoot lineage evolving into the Stenotritidae), and by the end of the Cretaceous, South American bees had also colonized North America.[7] The North American fossil taxon Cretotrigona belongs to a group that is no longer found in North America, suggesting that many bee lineages went extinct during the Cretaceous–Paleogene extinction event (the "K-Pg extinction").[7]

Following the K-Pg extinction, surviving bee lineages continued to spread into the Northern Hemisphere, colonizing Europe from Africa by the Paleocene, and then spreading east to Asia. This was facilitated by the warming climate around the same time, allowing bees to move to higher latitudes following the spread of tropical and subtropical habitats. By the Eocene (~45 mya) there was already considerable diversity among eusocial bee lineages.[8][a] A second extinction event among bees is thought to have occurred due to rapid climatic cooling around the Eocene-Oligocene boundary, leading to the extinction of some bee lineages such as the tribe Melikertini. During the Paleogene and Neogene periods, bee lineages expanded worldwide. This came about as continental drift and changing climates created new barriers and habitats, isolating populations and driving the evolution of many new tribes.[7]

Fossils
The oldest non-compression bee fossil is Cretotrigona prisca, a corbiculate bee of Late Cretaceous age (~70 mya) found in New Jersey amber.[6] A fossil from the early Cretaceous (~100 mya), Melittosphex burmensis, was initially considered "an extinct lineage of pollen-collecting Apoidea sister to the modern bees",[11] but subsequent research has rejected the claim that Melittosphex is a bee, or even a member of the superfamily Apoidea to which bees belong, instead treating the lineage as incertae sedis within the Aculeata.[12]

The Allodapini (within the Apidae) appeared around 53 Mya.[13] The Colletidae appear as fossils only from the late Oligocene (~25 Mya) to early Miocene.[14] The Melittidae are known from Palaeomacropis eocenicus in the Early Eocene.[15] The Megachilidae are known from trace fossils (characteristic leaf cuttings) from the Middle Eocene.[16] The Andrenidae are known from the Eocene-Oligocene boundary, around 34 Mya, of the Florissant shale.[17] The Halictidae first appear in the Early Eocene[18] with species[19][20] found in amber. The Stenotritidae are known from fossil brood cells of Pleistocene age.[21]