In two of the families - the Mutillidae and Thynnidae - the females are wingless and the larvae live as parasites in the larvae of other insects; the female Mutilla enters humble-bees' nests and lays her eggs in the bee-grubs.
Most of the genera are " solitary " in habit, the female sex being undifferentiated; but among the humble-bees and hive-bees we find, as in social wasps and ants, the occurrence of workers, and the consequent elaboration of a wonderful insect-society.
Other flies of the genus Volucella, larger and heavier in build than Eristalis, resemble humble-bees in colour and form, and it was formerly supposed that the purpose of this similarity was to enable the flies to enter with impunity the nests of the humble-bees and to lay their eggs amongst those of the latter insects.
Among the humble-bees (Bombus) the workers help the queen, who takes her share in the duties of the nest; the distinction between queen and workers is therefore less absolute than in the hive-bees (Apis), whose queen, relieved of all nursing and building cares by the workers, devotes her whole energies b FIG.
The tongue is bifid at the tip in a few genera; usually it is pointed and varies greatly in length, being comparatively short in Andrena, long in the humble-bees(Bombus), and longest in Euglossa, a tropical American genus of solitary bees.