A bumblebee, also written bumble bee, is a member of the bee genus Bombus, in the family Apidae. The brood parasitic or cuckoo bumblebees have sometimes been classified as a subgenus or genus, Psithyrus, but are now usually treated as members of Bombus. This genus is the only extant group in the tribe Bombini, though a few extinct related genera are known from fossils.