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Nature

Good Natured in St. Charles: Giant dobsonflies live exciting double lives

I can still remember my first dobsonfly.

The date was July 2002. The place, Red Oak Nature Center in North Aurora. The insect was contained within a two-quart Tupperware bowl – with holes poked in the lid for ventilation. The woman carrying it clearly was unsettled, her voice quavering as she described how the “alien” creature had landed on her screen door. Her father and two children nodded solemnly as she recounted the discovery and capture of “E.T.”

The creature did not resemble our “regular” bugs. It measured nearly 5 inches in length, and its long, vein-streaked wings were speckled with small white dots – perhaps stardust, and proof of the insect’s intergalactic trek, the children said.

But its most conspicuous feature was a pair of enormous jaws, or mandibles – thick and pointed.

It took some convincing, but we finally got the family to agree to take their “extraterrestrial” bug home, put it back on the screen where they found it, and let it get down to business – namely, making more of its own species: Corydalus cornutus, also known as the eastern dobsonfly.

Found on land as adults, dobsonflies spend the majority of their lifespan as larvae, underwater. This phase lasts so long – two or three years in our area, and up to five in cold or intermittent streams – that the larvae even have their own names. Most commonly called hellgrammites, they’re also known as toe-biters, go-devils and sometimes conniption bugs. The larvae have prominent, powerful mandibles.

Prowling the depths of rivers and streams, they consume their fair share of underwater insects, but are, in turn, consumed by a fair share of fish, including smallmouth bass and panfish such as crappie and bluegill.

They also have a sensitive side: Hellgrammites are vulnerable to pollution. They breathe through delicate, tufted tracheal gills, structures that are easily fouled by chemicals or too much sediment.

Sad to say, we don’t see a lot of hellgrammites – or dobsonflies – here in the TriCities. So when one shows up, it’s noteworthy. Just as I still remember my first dobsonfly from years ago, I’m probably not going to forget the larva that we found more recently. As big as my pinkie, with pinching jaws shaped liked sickles, the young insect was plucked from a rushing riffle in Ferson Creek by a group of park district nature campers. We placed the larva temporarily in a white dish pan to observe its movements.

Without any rocks to cling to or hide under, the creature quickly latched onto the nearest object it could find, which happened to be a large rusty crayfish (that is, Orconectes rusticus). The crayfish shot backward across the pan and dislodged the conniption bug, which then proceeded to have a conniption of its own.

Flailing about the pan, the hellgrammite gave us brief glimpses of its intricate underparts – those gills, which are adapted to well-oxygenated waters; and two sets of hooks, which it uses to cling to the underside of rocks in streams. And then there were those mandibles – so powerful in this life stage and designed to crush prey (everything from fish and tadpoles to invertebrates such as caddisfly larvae and small crayfish).

Knowing how rare hellgrammites are in our area, we decided we didn’t want to stress the little guy/gal out anymore than we already had, so back to its riffle it went.

Moments later, we found what was probably our toe-biter’s relative – an adult dobsonfly clinging to some vegetation. A couple of kids shrieked, and one initially refused to get close. But our oohs and aahs eventually inspired even the most squeamish of the group to move in for a closer look.

This individual, a male, possessed a set of long mandibles that looked like vintage ice tongs – imposing, but so large as to be completely useless save for one important function: attracting female dobsonflies.

As adults, dobsonflies live just a short time – a few days to a week or so, depending on fat stores – and likely don’t feed. Their sole purpose is to find a mate and allow the circle of life to begin again. The males’ enormous mandibles serve as an indication of fitness for breeding, with bigger meaning better. Not wanting to disrupt the cycle, we took some photos, wished the insect well, and went on our merry way.

With any luck, the dobsonfly we found was successful in his mating mission and has gone where all good go-devils go, up to that Big Riffle in the Sky.

His offspring will live on though, as will his presence in the kids’ summer camp memories. Years from now, I bet they’ll still remember their first dobsonfly.

Pam Erickson Otto is the manager of nature programs and interpretive services at the Hickory Knolls Discovery Center, a facility of the St. Charles Park District. She can be reached at 630-513-4346 or potto@stcparks.org. Feedback on this column can be sent to editorial@kcchronicle.com.

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