The Mydidae (alternative spelling Mydaidae), or Mydas flies, are a small (fewer than 400 species), cosmopolitan family of rather large flies - including, in fact, the largest known fly, Gauromydas heros (syn.Mydas heros). Many of the species, in addition to their large size, are mimics of stinging Hymenopterans, especially wasps. They are most diverse and abundant in arid regions of the world, but can be found in other habitats. They are infrequently encountered as the adult life span appears quite short, and little is known about their biology, though larvae of some species appear to be subterranean predators of ants.
For terms see Morphology of Diptera. Mydids are medium to very large flies (9mm.-60 mm. bodylength). The abdomen is long and cylindrical in section. It is slightly tapered apically in the male, and usually widest at segment 4 in the female.The second segment of the antenna forms a club. Mydids are sparsely pilose, and lack bristles except on the legs. The hindleg is much longer and stronger than either the middle leg or the foreleg and the hind femur is usually swollen, and bears ventral spines. The hind tibia has an apical spur or bristles. The wings are long, narrow to wide. Most of the veins end in the upper margin before apex.
Bequaert, M. 1963. Contribution a la connaissance morphologique et a la classification des Mydaidae (Diptera). Bull. Inst. Roy. Sciences Natur. Belg. 37:1-18.
Oosterbroek, P. 1998. 41. Mydidae. In P. Oosterbroek: The families of Diptera of the Malay Archipelago. Brill: Boston. p. 95.
Sack P. (1934) 23. Mydaidae. In: Lindner E. (Ed) Die Fliegen der palaearktischen Region. Band 4(5), 1–29. Schweizerbart‘sche Verlagsbuchhandlung, Stuttgart, 1–29.Keys to Palaearctic species but now needs revision (in German).