A Robber Fly is shown eating a bee at Pine Grove Furnace.
A Robber Fly is shown eating a bee at Pine Grove Furnace. (COURTESY OF PAUL WOLF)

The Asilidae are the robber fly family, also called assassin flies. They are powerfully built, bristly flies with short, sharp, stout sucking mouthparts. The name "robber flies" reflects their notoriously aggressive predatory habits; they feed mainly on other insects and they largely wait in ambush and catch their prey in flight.

Length is ½ to 1 ½ inches. The mystax and occular fringe bristles are clearly seen. The body plan is similar to the mosquito, but the proboscis is short and the legs, built for catching prey in flight, are spined and powerful. The two wings are folded along the abdomen.

All robber flies have stout, spiny legs and 3 simple eyes (ocelli) in a characteristic depression between their two large compound eyes.


The mystax probably affords some protection for the head and face when the flies deal with struggling prey; various Asilidae prey on formidable species including bees, grasshoppers, dragonflies and even other Asilidae. Some Asilidae do however specialize in smaller prey, and this is reflected in their more graceful build.

In general the family attacks a very wide range of prey, including other flies, beetles, butterflies and moths, various bees, ants, dragon and damselflies, wasps, grasshoppers, and some spiders. They do so apparently irrespective of any repugnant chemicals the prey may have at its disposal.



The Robber Fly seen here was photographed at Pine Grove Furnace near the Swamp Trail. I saw him capture the bee he is eating but was unable to get that shot. However, I did get this shot of him eating the bee. Camera used was Canon 50D with 70-300mm lens, at 300mm, F-16, 2,000th second, ISO 3200, no flash.

Paul Wolf is an amateur photographer residing in Hanover.