Robber flies are a diverse group of predatory flies that typically perch in an open area, swiveling their heads to look around, then flitting out to chase insect prey. Most have a long, tapered abdomen, a rather humpbacked appearance, and spiny legs, and typically rest with wings folded down the back. The face often appears bearded, and the mouthparts are a pointy knifelike proboscis for injecting saliva into prey. Between the two large compound eyes, the head is depressed, with three tiny eyes (ocelli) in that little valley. Many make a distinctive buzz or rattle in flight.
Larvae are grublike and live in or on soil, among decaying materials, or in rotting wood.
Similar species: Some robber flies are so long and slender they resemble damselflies. Many other robber flies have black and yellow striped patterns and make loud buzzing sounds as they fly; these are bee and wasp mimics. Some robber flies in the genus Laphria look almost exactly like bumble bees, complete with yellow fuzzy patches on their rather pudgy bodies. But true flies always have the same characteristics: only one pair of wings (bees and wasps have two pairs); the second pair of “wings” on true flies are reduced to tiny knobby structures called halteres (which function like gyroscopes, assisting flight). Also, flies usually have huge eyes and short antennae.