[1] They are generally large in size, including the largest known fly, Gauromydas heros (syn.

Mydidae are most diverse in southern Africa, but many species have also been described from North America, Chile, and Australia.

[2] Little is known about their biology, though Zikan reported the larvae of Gauromydas heros live in the subterranean detritus "pans" of Atta ants in southern Brazil, where they appear to be feeding on detritivorous Dynastinae (Coelosis spp.)

Others (e.g. Mydas maculiventris) are subterranean and feed on "white grubs" (Scarabaeidae: genus Phyllophaga) that attack the roots of grasses and could be potential biocontrol agents of white grubs in sod production areas.

[5][6] The oldest known member of the family is Cretomydas from the Early Cretaceous (Aptian) Crato Formation of Brazil.

The genus appears to have close affinites to the subfamily Diochlistinae, suggesting a Cretaceous diversification for the family.