These later stages, comprising the greater part of the larval history, are adapted for an inquiline or a parasitic life, where shelter is assured and food abundant, while the short-lived, active condition enables the newly-hatched insect to make its way to the spot favourable for its future development, clinging, for example, in the case of an oil-beetle's larva, to the hairs of a bee as she flies towards her nest.
The inquiline habit (" cuckoo-parasitism "), when one species makes use of the labour of another by invading the nest and laying her eggs there, is of frequent occurrence among Hymenoptera; and in some cases the larva of the intruder is not content with taking the store of food provided, but attacks and devours the larva of the host.
Other flies of this group have the inquiline habit, laying their eggs in the galls of other species, while others again pierce the cuticle of maggots or aphids, in whose bodies their larvae live as parasites.
Friese, the relations between the host and the inquiline are quite friendly, and the insects if they meet in the nestgalleries courteously get out of each other's way.
Sharp, in commenting on this strange behaviour, points out that the host can have no idea why the inquiline haunts her nest.
The colonies of Bombus illustrate the rise of the inquiline habit.