All robber flies have stout, spiny legs, a dense moustache of bristles on the face, and 3 simple eyes. The antennae are short, 3-segmented, sometimes with a bristle-like structure called an arista. The short, strong proboscis is used to stab and inject victims with saliva containing neurotoxic and proteolytic enzymes which paralyze and digest the insides; the fly then sucks the liquefied meal much like we vacuum up an ice cream soda through a straw. Adult robber flies attack other flies, beetles, butterflies and moths, various bees, dragon and damselflies, ichneumon wasps, grasshoppers, and some spiders. Courtship behavior consists of the male glomming onto the female as if she were prey.
Adult robber flies perch on stems of low plants or other objects and attack prey in the air. Adults lay eggs into soil or plants. The larvae are often found in decaying organic matter, such as dung heaps and rotting logs, but are also found in ordinary soil.