Promachus is a genus of robber flies. It is part of the subfamily Asilinae. The Asilidae are a family of robber flies, also called killer flies. They are strong, hairy flies with short, sturdy proboscis that cover the sharp sucking hypopharynx. The name "robber fly" reflects their notorious predatory habits; they feed mainly or exclusively on other insects and, as a rule, they wait in ambush and catch their prey in flight.