Sunday, July 19, 2020

Nature: Hellgrammites, dobsonflies both fearful, fascinating

A male dobsonfly displays its formidable mandibles/Jim McCormac
(additional image at end of column)

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

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