Originally published in the Cannon Falls Beacon on August 1, 2018.
I’d never seen one before. They only live in the Eastern United States and, as a transplant from Southern California, when this big guy crawled out from the rock I was standing on after I turned on my barn’s well faucet I took a wary step back and gasped a huge “What IS that?” to myself.
The “that” turned out to be a 2.5-inch long hellgrammite, the devilish-looking larval offspring of the quite impressive Dobsonfly.
The name hellgrammite alone sounds bizarre enough to be humorous, and any fan of the monster film Tremors might laugh as they recollect the giant Graboids of the 1990 cult classic. However, the fictional underground monsters share enough similarities with hellgrammites that one may begin to think the larva were the inspiration for the film in the first place. Bizarre, indeed.
An angry, 2.5-inch hellgrammite poses on a leaf. Photo: Jessica Woken.
First, like the Tremors monsters, hellgrammites have seriously oversized mandibles. Clearly, one ought to stay away from that end! I did just that with my specimen and was able to pick it up, chopsticks style, and bring it inside for a quick photoshoot. A little research proved my instinct correct: The hellgrammite’s mandibles are strong enough to break skin and, in some cases, draw blood.
Second—and this was quickly observed during my chopsticking maneuvers—hellgrammites have ridiculously limber bodies. My specimen was able to twist and bend his body into fantastic coils in order to evade and bite at my makeshift chopsticks. Surely that kind of mobility helps in satisfying their voracious predatory appetites, the third item on our comparisons list.
Like graboids, hellgrammites pretty much eat anything of appropriate size that moves. They snatch aquatic insects, worms, other larva, and even small minnows or froglings as a meal.
Fourth, a combination of 6 legs and 8 or more tufted projections run the length of the hellgrammite’s body, helping it to maneuver both in water and on land. (Graboids had rows of spikes along their snaky lengths that helped them move through soil.) And maneuver it did! The hellgrammite I caught was adept in moving both forward and reverse, running at the same (and quick) speed in either direction.
After finding these bugs are aquatic, I was surprised that the insect had been so agile on dry land. The only time hellgrammites emerge from water is when they’re on their way to dig a burrow in preparation for pupation or when they’re disturbed, as was the case in my situation. Oops.
But, alas, as fun as it may have been to compare the two, that is where the hellgrammite and graboid similarities end.
Instead of being a danger to humans like the famed Hollywood monsters I jestfully compare them to, hellgrammites actually pose a number of benefits to us humans. They’re adored by anglers and fishermen because they make excellent bait. They’re known by ecologists to be indicators of the health of waterways: Where there are hellgrammites, life flourishes, because the Dobsonfly larva can only survive in clean, well-oxygenated water. Finally, hellgrammites are known to eat the aquatic larva of mosquitos, something anyone who lives in Minnesota can well appreciate and be thankful for.
A male Dobsonfly lands on a photographer’s camera, showing off its impressive size. Photo: Creative Commons. Pavel Kirillov, July 14, 2013.
Forgetting everything else, mature Dobsonflies are simply magnificent. At about 5 inches long, females look like a larger version of their hellgrammite selves but with a pair of huge wings to glide them along. Males are equally aerial and are additionally fitted with a pair of 2-3” mandibles that can’t be missed by any eye, trained or not in the entomological sciences. Despite their tremendous size and intimidating presentation, Dobsonflies are harmless to humans unless provoked, in which case both the larva (hellgrammites) and female adults should be given a wide birth as their mandibles can do painful damage. The poor male, however stunning his display, is really more bark than bite: He cannot create enough leverage with his lengthy jaws to cause much, if any, pain.
If you spot these insects in flight consider yourself blessed: Adult Dobsonflies only live for about a week before dying and, though they aren’t rare insects, their very brief adult lifespans and nocturnal natures make them hard to find.
Furthermore, Minnesota is about as far westward as the Eastern Dobsonfly will travel, making a sighting in Cannon Falls or the surrounding local wild even more, well, bizarre.