Robber Fly – Laphria grossa

Robber Fly – Laphria grossa

color photo Robber Fly Laphria grossa with leaf beetle preyFamily Asilidae – Robber Flies
Live adult fly photographed at DuPage County Illinois. Size: 30mm.  Leaf beetle prey size: 10mm

color photo Robber Fly Laphria grossa with leaf beetle prey

This lucky gal has caught a clay-colored leaf beetle, and is busy sucking down its liquified insides through its sabre-like proboscis.  When she flew by me carrying this large beetle, she was making one very loud, low-pitched buzz.

It’s a marvellous sound, and these large robbers fly slow enough they are easily followed. Sometimes they’ll even sit still and pose, if you approach slowly and carefully you can get within a few inches. And that’s a thrill for me. I lose all track of time while stalking a big fly like this!

Male Bumble Bee
Male Bumble Bee
Robber Fly - Laphria thoracica
Female Laphria grossa

Some robber flies are convincing bumble bee mimics. This evolutionary adaptation allows them to reap the benefits of aposematic (warning) coloration without the high metabolic cost of constructing and maintaining a venom-delivery system.

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Tree Encyclopedia / North American Insects & Spiders

Online since 2002