ts of pollen collecting species, and lay their eggs in cells provisioned by the host bee. When the "cuckoo" bee larva hatches, it consumes the host larva's pollen ball, and often the host egg also. In particular, the Arctic species of Bumblebee, Bombus hyperboreus, is an aggressive brood parasite that invades and enslaves colonies of other bumblebees within the same subgenus, Alpinobombus. Unlike most socially parasitic bumblebees, which have lost the ability to collect pollen, B. hyperboreus retains functional pollen baskets and has been observed gathering pollen and nectar in the field. This retention of foraging ability may be an adaptation to the severe Arctic climate, in which the short breeding season and limited availability of host colonies favor flexibility and a degree of metabolic self-reliance. 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 gen