Conopidae, usually known as the thick-headed flies, is a family of flies within the Brachycera suborder of Diptera. Flies of the family Conopidae are distributed worldwide except for the poles and many of the Pacific islands. About 800 species in 47 genera are described worldwide, approximately 70 of which are found in North America. The majority of conopids are black and yellow, or black and white, and often strikingly resemble wasps, bees, or flies of the family Syrphidae, themselves notable bee mimics. Conopids are most frequently found at flowers, feeding on nectar with their proboscis, which is often long.
The larvae of all conopids are internal parasites, most of aculeate (stinging) Hymenoptera. Adult females aggressively intercept and deposit eggs on their hosts in-flight, and the female's abdomen is modified to form what amounts to a "can opener" to pry open the segments of the host's abdomen as the egg is inserted. The subfamily Stylogastrinae, including the genus Stylogaster, is somewhat different, in that the egg itself is shaped somewhat like a harpoon, with a rigid barbed tip, and the egg is forcibly jabbed into the host. Some species of Stylogaster are obligate associates of army ants, using the ants' raiding columns to flush out their prey. More research is needed to determine the life histories of most Conopids.