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The Eastern Dobsonfly

Although male dobsonflies (Corydalus cornutus) have the most impressive mouthparts, it is the relatively small-mandibled females that can deliver a painful bite when carelessly handled.
Although male dobsonflies (Corydalus cornutus) have the most impressive mouthparts, it is the relatively small-mandibled females that can deliver a painful bite when carelessly handled.

Entomologist Dr. Art Evans and VPM producer Steve Clark talk about their experiences with dobsonflies and about the natural history of these impressive insects.

SC:  I'm Steve Clark with Dr. Art Evans, entomologist, and this is What’s Bugging You.  I remember the first time I encountered a dobsonfly.  I was a motorcycle rider in those days.

AE:  Were you?

SC:  Yeah, and I stopped at a, at a convenience store.  It was on the Smith River out in Henry County.

AE:  Yeah.

SC:  Those bright lights from the convenience store had drawn in all kinds of insects, including this huge prehistoric looking male with big pincers.  And I thought I'd discovered a new species because I'd never seen anything that could match that.

AE:  I clearly remember the first dobsonfly I ever saw, and that was in Arizona up near the Verde River. And we had our black lights out and several of these came in.  They were all females.  The females have shorter and much more powerful jaws.  They're the ones that actually bite, and I discovered that the hard way. 

SC:  Uh oh.  (laughing)

AE:  I picked one up and realized just how nimble they were.  And this thing kind of reached around over her shoulder and nipped me on the skin in between my fingers, and it really hurt.  A couple of listeners have sent photos of dobsonflies and want to know what they are, so I thought this would be a good opportunity to talk about them.  The males have those great big mandibles used as part of their mating ritual.  They're part of a, a courtship thing where they'll lay them across the wings of the female and they may have jousting contests with other males.  Have you ever heard of hellgrammites?

SC:  I have.  They use them as bait.

AE:  Yeah, hellgrammites are the larvae, and they are about three to four inches in length when they're fully grown, and they have these long filamentous gills on the sides of their abdomen that look like legs.  They sort of resemble a centipede in the water.  And they're nocturnal; during the day they remain hidden under rocks.  Bass fishermen use them as bait.  Studies on the preferred diets of fish show that fish hardly ever eat them in the wild, and that's probably because the hellgrammite spends most of its time hidden under rocks.  The hellgrammites themselves are predators.  They eat small aquatic insects.

SC:  Are the dobsonflies soft-bodied?

AE:  Yes, they have four wings that are approximately the same size and shape.  They're in their own order of insects, the megaloptera, which means giant-winged insects, so they're aptly named.  And they have other relatives too in that order.  Fish flies, the males and females look very similar to one another in terms of their mouth parts.  The dobsonfly is one of the largest insects in North America, and it's one of the largest insects in eastern North America, save for the giant silk moths,  like luna moths and cecropias and polyphemus and that sort of thing.  They’re an impressive beast.  When the hellgrammites are ready to pupate, they crawl out of the water, and they will dig a chamber in the moist sand.  They all come out within a couple of days of one another, and apparently they're reported to come out during thunderstorms.  And there's some speculation that the actual sound of thunder is what triggers their emergence.

SC:  That's interesting.

AE:  And then once the adults emerge, they're readily attracted to light.  So they're very commonly seen around storefronts and streetlights, especially along rivers and streams.

SC:  That’s exactly where my convenience store was.

AE:  Or a convenience store.

SC:  Dr. Art Evans is a research associate at the Virginia Museum of Natural History, right down where I saw my flies.

AE:  That’s right.

SC:  You’ll find photos, audio, and links to the museum and Art’s Facebook page at our brand new website address, vpm.org/bugs.

Dr. Arthur V. Evans teams up with VPM Radio producer Steve Clark for a weekly feature, “What’s Bugging You?,” which airs during NPR’s Morning Edition. The program takes its name from another of Evans’ books “What’s Bugging You – A Fond Look at the Animals We Love to Hate.”

Tune in each Tuesday at 8:45 a.m. or at 5:44 p.m. on VPM News