Wherever evil buzzes through the air and into your Orange Crush, a winged avenger waits in the shadows... Holcocephala fusca by Thomas Shahan Related to ordinary houseflies, mosquitoes and other Diptera, more than 7,000 species of Asilidae can be found around the world, on every continent, in nearly every climate. Commonly called robber flies, hanging thieves or assassin flies, you might call these creatures the condors of the insect world, if condors routinely carried off and devoured everything from field mice to bison.