They are powerfully built, bristly flies with a short, stout proboscis enclosing the sharp, sucking hypopharynx.

[1][2] The name "robber flies" reflects their expert predatory habits; they feed mainly or exclusively on other insects and, as a rule, they wait in ambush and catch their prey in flight.

[3] The Asilidae, together with Bombyliidae and Therevidae, are the most representative families of the superfamily of Asiloidea and they form one of the most characteristic groups of the lower Brachycera.

In general, the family attacks a very wide range of prey, including other flies, beetles, butterflies and moths, various bees, ants, dragonflies and damselflies, ichneumon wasps, grasshoppers, and some spiders.

[5] When attacked, many Asilidae do not hesitate to defend themselves in turn using their probosces and may deliver intensely painful bites to humans if handled incautiously.

Some points of contrast between the families include that the labium in the Therevidae is not a piercing, predatory organ, but ends in two fleshy labella adapted to the sucking of liquid foods.

Again, the Therevidae commonly have fluffy setae above the mouthparts, unlike the stiff chaetae comprising the mystax of the Asilidae.

Female robber flies deposit whitish-colored eggs on low-lying plants and grasses, or in crevices within soil, bark, or wood.

After hatching, robber fly larvae generally seem to live in soil, rotting wood, leaf mold, and similar materials, some being predatory and others detrivorous.

The head is free and mobile and dichoptic in both sexes and has three ocelli arranged in a characteristic depression formed by the elevation of the compound eyes.

The mystax helps protect the head and face when the fly encounters prey bent on defense.

The strongly sclerotized proboscis is composed of the labium and maxillae which form a food canal, the labrum and a piercing organ, the hypopharynx.

The proboscis is either rounded in cross section or compressed laterally or dorsoventrally; it is usually stout and straight and is sometimes able to penetrate through the hard integument of Coleoptera.

The head is small, rugged, dark-pigmented and hypognathous, while the abdomen is composed of eight apparent urites, with the last two often fused and more or less reduced.

The larvae of most known asilids live in the soil or in the case of some taxonomic groups, in rotting organic material, usually wood and the bark of dead trees.

With regards to feeding behavior, most of the literature describes Asilidae larvae as entomophagous, but doubts remain about the real nature of the trophic regime and its mechanisms.

In general, predation in adults is concentrated in the hottest hours in open, sunny spaces, while at night, they take refuge in dense vegetation.

Puncture is followed by the injection of saliva, whose active components perform two functions: neurotoxins cause paralysis of the victim, while proteolytic enzymes lead to the breakup and liquefaction of internal tissues.

Some genera have been found to be monophagic, but more generally Asilidae are polyphagic, with behaviors that vary from narrow specialization[8] to broad prey choice.

Their biodiversity is lower in forested ecosystems, and where asilids do occur in such environments, they tend to concentrate in the glades and margins.

In those conditions, the interrupted canopy leaves space for various species of shrubs and herbaceous plants suited to asilid styles of predation.

However, the highest levels of biodiversity are in warm climates; tropical or subtropical and arid or semi-arid regions tend to have the greatest variety of species, followed by areas where rainfall is highly seasonal.

The 14 accepted subfamilies are:[12] The oldest known member of the family is Araripogon from the Early Cretaceous (Aptian) Crato Formation of Brazil.

Johan Christian Fabricius in five publications dated from 1775 to 1805, erected the genus Damalis and described 76 exotic and European species.

Other prominent authors dealing with the Asilidae during the 19th century included Pierre-Justin-Marie Macquart, Francis Walker, Camillo Rondani, and Jacques-Marie-Frangile Bigot.