Robber flies comprise the family Asilidae, which are also known as assassin flies. There are about 7,000 species and they are found on every continent except Antarctica.
They are named for their extremely aggressive and indiscriminate predation. This is the 19th-century sense of a robber, as a bandit who waylays innocent travellers, rather than the modern synonym for a thief. Robber flies don’t steal anything, however they will attack almost any insect, including bees and wasps, and even some spiders.
They are accomplished acrobatic flyers and often catch their prey on the wing. To help with this they have very large eyes that are raised high on the head, like pop-up headlights. Once a victim is caught, they inject it with a paralysing neurotoxin that contains enzymes to digest the internal organs, which the fly sucks up with its proboscis.
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