What is "robber fly"

Hornet \Hor"net\, n. [AS. hyrnet; akin to OHG. hornaz, hornuz, G. horniss; perh. akin to E. horn, and named from the sound it makes as if blowing the horn; but more prob. akin to D. horzel, Lith. szirszone, L. crabo.] (Zo["o]l.) A large, strong wasp. The European species ( Vespa crabro) is of a dark brown and yellow color. It is very pugnacious, and its sting is very severe. Its nest is constructed of a paperlike material, and the layers of comb are hung together by columns. The American white-faced hornet ( Vespa maculata) is larger and has similar habits.

Hornet fly (Zo["o]l.), any dipterous insect of the genus Asilus, and allied genera, of which there are numerous species. They are large and fierce flies which capture bees and other insects, often larger than themselves, and suck their blood. Called also hawk fly, robber fly.

To stir up a hornet's nest, to provoke the attack of a swarm of spiteful enemies or spirited critics. [Colloq.]

n. swift predatory fly having a strong body like a bee with the proboscis hardened for sucking juices of other insects captured on the wing [syn: bee killer]