A wee killer

Should you be a small winged critter, you'll not want to get on the radar screen connected to these eyes. Especially if it's hungry.

While sitting placidly on the porch of a friend's house in Ross County today, sipping some java and watching the landscape, I noticed some TINY fly-like insects perching on the tips of old, snapped off scapes of Hosta plants. Little did I realize that they were savage merchants of death, albeit on a minute scale.

The dime backdrop provides some scale, but as it is being held a few inches away to avoid spooking the bug, our subject looks larger than it really is. And it still looks small. And tiny it be. These flies were small enough that with my naked eye I couldn't really be sure what they were. After seeing one of them make a sally out from its perch and grab something even smaller, I figured it was predaceous.

Macro photography comes in very handy when trying to study elfin subjects, but this one taxed the limits of my gear. I probably took 90 photos, and only six or so were keepers. But they're plenty good enough to figure out its identity.

This is an incredibly tiny robber fly, Holcocephala fusca, no known common name. They're every bit the fearless brutes of their larger, more conspicuous brethren, I am here to attest. The above photo shows typical hunting posture. They'll sit patiently until something catchable wings by, then make a rapid darting flight and seize the victim in midair.

Once the prey has been captured, it is brought back to the perch. This Holcocephala has nabbed a tiny - I mean really tiny - flower fly, or perhaps something in the Hymenoptera, I'm not sure. The robber fly is only about 7 millimeters long, so its victim must only tape out at 3 mm or so. I later saw one grab what appeared to be a little wasp, but it was nearly as large as the robber fly.

After the prey is immobilized, the fly inserts its proboscis and begins the process of pumping in chemicals that liquefy the innards of its meal. Once everything inside has melted to a nice sauce-like consistency, the robber fly sucks it back out like a child slurping up a milkshake through a drinking straw.

This process takes a while. The meal pictured above took the fly the better part of half an hour to consume. Yes, I spent a good chunk of my life today observing Lilliputian robber fly behavior. What of it?

Promachus hinei, the Red-footed Cannibal Fly. This is the other extreme in the world of robber flies. This one is eating one of those giant fuzzy bumblebees. It might take one thousand Holcocephala fusca's to make one of these.

Every time I learn about something like the subject of this blog entry, I wonder how many other fascinating critters lurk under my nose, tiny but fascinating, too small to readily grab our attention.