Most bees are polylectic (generalist) meaning they collect pollen from a range of flowering plants, but some are oligoleges (specialists), in that they only gather pollen from one or a few species or genera of closely related plants.
Specialist pollinators also include bee species which gather floral oils instead of pollen, and male orchid bees, which gather aromatic compounds from orchids (one of the few cases where male bees are effective pollinators).
Bees are able to sense the presence of desirable flowers through ultraviolet patterning on flowers, floral odors,and even electromagnetic fields. Once landed, a bee then uses nectar quality and pollen taste to determine whether to continue visiting similar flowers.
In rare cases, a plant species may only be effectively pollinated by a single bee species, and some plants are endangered at least in part because their pollinator is also threatened.
But, there is a pronounced tendency for oligolectic bees to be associated with common, widespread plants visited by multiple pollinator species. For example, the creosote bush in the arid parts of the United States southwest is associated with some 40 oligoleges.
As mimics and models
Many bees are aposematically coloured, typically orange and black, warning of their ability to defend themselves with a powerful sting. As such they are models for Batesian mimicry by non-stinging insects such as bee-flies, robber flies and hoverflies, all of which gain a measure of protection by superficially looking and behaving like bees.
Bees are themselves Müllerian mimics of other aposematic insects with the same colour scheme, including wasps, lycid and other beetles, and many butterflies and moths (Lepidoptera) which are themselves distasteful, often through acquiring bitter and poisonous chemicals from their plant food.
All the Müllerian mimics, including bees, benefit from the reduced risk of predation that results from their easily recognised warning coloration.
Bees are also mimicked by plants such as the bee orchid which imitates both the appearance and the scent of a female bee; male bees attempt to mate (pseudocopulation) with the furry lip of the flower, thus pollinating it.
As brood parasites
In Southern Africa, hives of African honeybees (A. mellifera scutellata) are being destroyed by parasitic workers of the Cape honeybee, A. m. capensis. These lay diploid eggs (“thelytoky”), escaping normal worker policing, leading to the colony’s destruction; the parasites can then move to other hives.
The cuckoo bees in the Bombus subgenus Psithyrus are closely related to, and resemble, their hosts in looks and size. This common pattern gave rise to the ecological principle “Emery’s rule”.
Others parasitize bees in different families, like Townsendiella, a nomadine apid, two species of which are cleptoparasites of the dasypodaid genus Hesperapis, while the other species in the same genus attacks halictid bees.
Four bee families (Andrenidae, Colletidae, Halictidae, and Apidae) contain some species that are crepuscular. Most are tropical or subtropical, but some live in arid regions at higher latitudes. These bees have greatly enlarged ocelli, which are extremely sensitive to light and dark, though incapable of forming images.
Some have refracting superposition compound eyes: these combine the output of many elements of their compound eyes to provide enough light for each retinal photoreceptor. Their ability to fly by night enables them to avoid many predators, and to exploit flowers that produce nectar only or also at night.
Predators, parasites and pathogens
Vertebrate predators of bees include bee-eaters, shrikes and flycatchers, which make short sallies to catch insects in flight. Swifts and swallows fly almost continually, catching insects as they go. The honey buzzard attacks bees’ nests and eats the larvae. The greater honeyguide interacts with humans by guiding them to the nests of wild bees. The humans break open the nests and take the honey and the bird feeds on the larvae and the wax. Among mammals, predators such as the badger dig up bumblebee nests and eat both the larvae and any stored food.
Specialist ambush predators of visitors to flowers include crab spiders, which wait on flowering plants for pollinating insects; predatory bugs, and praying mantises, some of which (the flower mantises of the tropics) wait motionless, aggressive mimics camouflaged as flowers. Beewolves are large wasps that habitually attack bees; the ethologist Niko Tinbergen estimated that a single colony of the beewolf Philanthus triangulum might kill several thousand honeybees in a day: all the prey he observed were honeybees. Other predatory insects that sometimes catch bees include robber flies and dragonflies. Honey bees are affected by parasites including acarine and Varroa mites. However, some bees are believed to have a mutualistic relationship with mites.