Robber Fly - Holcocephala abdominalis
Family Asilidae - Robber Flies

Live adult robber flies photographed in the wild at DuPage County Illinois. Size =  8mm
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This is a small fly as robbers go. Very ethereal and difficult to follow, I have never been able to photograph with prey or witness any hunting.

There are over 7,000 species of robber flies world wide; nearly 1,000 in North America.  All robber flies have stout, spiny legs, a dense moustache of bristles on the face (mystax), and 3 simple eyes (ocelli) in a characteristic depression between their two large compound eyes. The mystax helps protect the head and face when the fly encounters prey bent on defense. 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. Many species have long, tapering abdomens, sometimes with a sword-like ovipositor. Others are fat-bodied bumble bee mimics; the effect is quite convincing.

References:
1.  Fritz Geller-Grimm, "Asilidae"
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Flies of North America - Order Diptera. Flies are prevalent in virtually all habitats, with over 16,000 species in North America. Flies can be distinguished from all other insects in that they only have one pair of normal wings. Most flies have compound eyes and mouthparts adapted for piercing, lapping or sucking fluids.
Flies Index | Flies Main | Tachinidae | Syrphidae | Bombyliidae | Asilidae
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