Nature: Hellgrammites, dobsonflies both fearful, fascinating

A male dobsonfly displays its formidable mandibles/Jim McCormac

(additional image at end of column)

Columbus Dispatch

July 19, 2020

NATURE
Jim McCormac

One of our strangest insects begins life in largish, powdery-white masses of eggs pasted to structures overhanging streams. They might adorn rocks, logs or even bridges. This spring, I saw dozens glued to the underside of a bridge traversing a Scioto County stream.

Eventually, odd-looking larvae bust from these natal enclosures and drop into the stream below. Known as hellgrammites, the predatory larvae will grow to formidable size. For up to three years these gilled, strictly aquatic juveniles will lurk among the stream cobble, snapping up and eating lesser beasts.

Ultimately, a hellgrammite can reach 3 inches in length. It resembles a centipede, and the business end is capped with formidable pincers. A big one, mishandled, can give an attention-getting nip.

Fierce as they are, some fish have a sweet tooth for hellgrammites and snap them up. Wily fishermen willing to work for their bait use this knowledge to their advantage.

When triggered by some reproductive cue, the hellgrammite emerges from the water and seeks a sheltered spot to form its pupal chamber. This will most likely be in moist soil under a log or rock.

After three or four weeks of undergoing a major reorganization of tissues, an utterly different looking insect will emerge.

The adult stage is known as a dobsonfly, and what a bug it is. Its body is 2 inches or more in length, and the outstretched wings might span 5 inches. Long segmented antennae wave from the head like chitinous bullwhips. The female has short but brutishly powerful pincers that can give a nip to rival the juvenile hellgrammite form.

But the male dobsonfly is truly the stuff of nightmares for the entomophobe. Its greatly elongated mandibles are about an 1½ inches in length. These scimitar-shaped appendages look like they could slice your finger off, if not eviscerate you.

It’s a male dobsonfly pictured with this column. A group of us were engaged in nocturnal field work at the Highlands Nature Sanctuary in Highland County on June 26. We had set up a series of brightly illuminated sheets that are effective at luring moths.

Many other insects are attracted to the lights, including dobsonflies. We were pleased to have the male stop by, as they are seen far less than females — probably because the males live for only three days or so, while females might live to the ripe old age of 10 days.

To test the male’s pinching abilities, I stuck my finger between its mandibles. Yawn. It did clamp down, but the long flimsy mandibles can’t generate much pressure and there was little pain. Several female dobsonflies had also come to our lights, but I didn’t try the pinch test with them. I’ll take others’ word that the girls pack a punch.

Dobsonflies tell an environmental story, and their presence can only be considered a positive. The larval-stage hellgrammites are quite sensitive to water-quality degradation. Thus, they occur in healthier streams, and good water quality is a plus for everyone.

Cool as dobsonflies are, I suppose for many people its best that they stay out of sight and out of mind.

Naturalist Jim McCormac writes a column for The Dispatch on the first, third and fifth Sundays of the month. He also writes about nature at www.jimmccormac.blogspot.com.

Male (L) and female dobsonfly/Jim McCormac

Dobsonfly: Bit of a horrorshow, this one

Ah, the legendary hellgrammite, many a bass fisherman's dream bait. This multi-legged larva looks like a mini dragon, and has a powerful set of pinchers to boot. Mishandle one of these aquatic beasts, and it'll nip you, too. I caught this one on a darter-hunting expedition in Big Darby Creek a few years back. Hellgrammites are strictly aquatic, and lurk in the substrate of streams, capturing whatever they can. Ugly as this insect may be, their presence is in a waterway is a nice thing - hellgrammites are indicators of good water quality.

If you are an entomophobe, you'll not find the dobsonfly any more appealing than its hellgrammite larval stage. Corydalus cornutus is a whopper of a bug, and males such as the one in this photo measure several inches in length.

We lured a few of these beasts to our lights last week in Adams County. We were after moths, but they're not the only critters attracted to bright lights at night, and I was pleased to spot this bruiser on the wall. It's a male dobsonfly, as can easily be told by the incredibly long scimitar-shaped mandibles (females' mandibles are much shorter). They use the swordlike mandibles for self defense, and typically fly suddenly at a person invading their space, quickly thrusting each mandible deep into the person's eyes. With an abrupt reversal of its flight coupled with a fierce jerk of the mandibles, the dobsonfly rips the victim's eyes from the sockets, and flies off to feed them to its mate.

Just kidding. Ferocious as the dobsonfly may appear, it is actually utterly harmless. While one may try to give a pinch with its mandibles if mistreated, they're too long and flimsy to gain much purchase, and would cause no harm. All visual bark and no real bite.

We were intrigued to see this Carolina mantis sneaking up on the huge dobsonfly. I watched this drama for a while, my camera's video function at the ready, hoping the mantid would attack. It bobbed, weaved, cocked its pointy triangular head, waved its legs and swayed side to side, but wouldn't get any closer to the dobsonfly than this. Fierce as the mantids are, this dobsonfly was apparently too much and the would-be predator chickened out. Can't say as I blame it.