Thursday, September 11, 2008

A Robber Fly

Today I'd like to introduce you to a Robber Fly, also known as an Assassin Fly or a Bee Killer. It belongs to the order Diptera (flies) and the Asilidae family, a huge family with 1,000 species in North America. This family is fierce, killing other insects, hence the violent common names. It's sort of like what a falcon is to other birds--out there watching and ready to dive in for the kill. The Robber Fly isn't fussy, it will eat just about any flying insect out there, including bees, wasps, dragonflies, grasshoppers, and other flies. Using its big eyes, it spots its prey, swoops down on it, and captures it mid-flight. It takes the prey to a perch and injects enzymes into the insect that immobilize it and start digesting it. Then the Robber Fly slurps up the liquid meal. Yum.

This is a male Robber Fly, probably in the genus Efferia, with 100 species in North America. Males have white bulbous claspers on the tip of the abdomen. Females have a swordlike ovipositor that extends from the abdomen and allows them to deposit eggs in dead flower heads, cracks in the soil, and other tiny spots.

The Robber Fly family can be distinguished by the "bearded" face, with lots of hair on it, and the concave top of the head between the eyes. That concave feature makes its large compound eyes seem really "buggy." The legs are strong and bristly, the better to hold onto its prey.

Do you see that sharp proboscis? Within it is a lancet, an even sharper pointy object. It allows the Robber Fly to stab its prey and inject fluids. It's reportedly sharp enough to pierce human skin, but fortunately Robber Flies haven't developed a taste for human flesh. Yet. (Insert cackling laugh here.)

Larvae overwinter in soil and emerge in the spring. It is thought that more species of Robber Flies still need to be described. Robber Flies are particularly common in sunny and arid areas and are most active during the warmer parts of the day, but I have to admit that I only noticed it for the first time this summer. It is so amazing how many different insects live so close to us and yet we know so little about them!

3 comments:

Anonymous said...

Good pics! I never even knew this type of fly existed. How do you know what people google to find your site? You ill friend in Indiana...ab

The Incredible Woody said...

That is one mean lookin' bug!!

Anonymous said...

I realize this comment is pretty late considering, but I actually found one of these guys on my front lawn in Amarillo, Texas. He wasn't happy when I tried to get a close-up, and made that point very clear! Thanks to your website I was able to determine what kind of bug this was, amazing creatures!

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