Recently while leaving for work in the early morning, I observed an amazing insect on the side of my house. It was a female Eastern Dobsonfly, Corydalus cornutus.
Dobsonflies are not really flies (insects in the Order Diptera). They are in the Order Megaloptera along with the Alderflies and Fishflies, all of which have an aquatic larval life stage.
Rarely seen, adult Dobson Flies are short lived with males living about three days and females living around 8-10 days. Adults are quite large, with wing spans reaching up to five inches in length. Male Dobson flies have long “tusk like” mandibles used for self-defense, courtship, and mating, while the female’s mandibles are much shorter. Coloring of adults can vary from gray to dark brown.
Larvae, commonly called Hellgrammites, are impressive predators and can grow up to 2 3/4 inches. Hellgrammites are aquatic and have both gills for breathing underwater and spiracles for breathing on land. These critters are prized and sold as bait in some parts. Handle them with care, as they will deliver a painful bite!
Hellgrammites live in flowing water, under rocks and on snags. They are top invertebrate predators and feed on other aquatic insect larvae and even small fish.
Eggs are laid on rocks, structures, and leaves near flowing water. Some say the egg masses resemble bird droppings which may protect them from predation. Once hatched, usually at night, the larvae fall or crawl into the water, where they will spend 1-3 years developing through 10-12 larval stages. Pupation occurs on land in moist soil or under a rock or log. Dobsonflies and Hellgrammites are important insects in the food chain. Hellgrammites are indicators of clean water, so get out on the stream and flip some rocks to see if you can find some.
By Dave Keane
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