Tag Archives: Robber Fly

PHOTOS OF THE WEEK: Flying Insects Gregarious and Nefarious!

During the Lost Lake birding walk recently, we came across two insects  that caught us by surprise. No doubt we’ve all known humans that we call “social butterflies.” Well, the birders saw instead a gathering of “social” dragonflies! And we spotted a furry and ferocious predator from the strange “robber fly” family.

Many of us commented that we usually think of dragonflies as loners, cruising up and down a marsh or patrolling a field alone. Occasionally we see mating pairs darting over the surface of a pond in tandem. But we were all quite intrigued by a group of unidentified, very similar dragonflies just hanging out together on a log. (The photo below is by fellow birder, Mike Kent. Thanks, Mike!)

Chalk-fronted Corporal dragonflies gathered on a log at Lost Lake Nature Park

After some research by Ewa Mutzenmore, another fellow birder, we learned that these are Chalk-fronted Corporals (Ladona julia) which Wikipedia tells us “are gregarious for dragonflies, and are commonly seen perching in groups.” In fact the “bug lady” at the University of Wisconsin Madison’s website says that in her area “On cool, spring days, hundreds of CfCs may congregate on/over warm road surfaces.” We evidently are well within their complete west-to east range across southern Canada and the northern United States. Where have they been all my life?

The male’s thorax features two showy white bars (presumably like a corporal’s stripes) on the upper part of their thoraxes and a waxy white coating (“pruinosity”) that develops on their thorax and at the base of their abdomen as they mature. The females are similar, but their corporal’s stripes and pruinosity are duller brownish gray. So by my count, Mike’s photo contains three males and four females. The juveniles are pinkish brown with a black stripe down the abdomen, according to the “bug lady’s” photos. Pruinosity, she tells us,  is a sign of breeding readiness, so maybe this gathering is resting a bit before summer’s Big Event!

Like many dragonflies, Chalk-fronted Corporals readily approach humans (or tolerate groups of them like we birders!), even plucking mosquitoes and other biting insects out of the air around us as we walk. Well, they are welcome to the ones feeding on me these warm spring days!

We also spotted what we think is a Robber Fly (family Asilidae). How’s this insect for some drama, eh? (Photo by birding group member , Ewa Mutzenmore. Thank you, Ewa!)

The predatory Robber Fly has an appearance and behavior that fits its name!

These fierce predators can snatch a wide range of insects from mid-air using their pincer feet and then pierce them with their proboscis. The end result is that the prey – which can include other robber flies – is paralyzed, liquefied within and then consumed. (I know…Yuck!) These are tough customers for other insects – though not for us, unless we handle them and why would we? They are not put off by insects that release noxious chemicals and will even attack yellow jackets and other wasps who are pretty fierce fighters themselves! From its black and yellow appearance, I’m guessing this may be one of the robber family whose coloring mimics bumblebees. “The better to get close to you, my dear….” Robber flies even sport a “mustache” called a mystax which makes them look like villains – but of course, they’re really just playing their role of keeping nature in balance.

So, it pays to explore with eyes, binoculars and cameras on an early summer morning. Nature’s always ready to teach us something new and strange!