Eastern Dobsonfly

Photo of eastern dobsonfly
Scientific Name
Corydalus cornutus
Corydalidae (dobsonflies and fishflies), in the order Megaloptera (alderflies, dobsonflies, fishflies)

Eastern dobsonfly adults are large, soft bodied, usually a drab gray, black, or brown, with prominent pincers and long antennae. The wings have conspicuous veins and are usually folded down the length of the body when at rest. The pincers (mandibles) of females are rather stubby and are capable of inflicting a painful bite. The mandibles of males are very long, tusklike, and incapable of hurting people due to lack of leverage.

Larvae, called hellgrammites, are aquatic, somewhat flattened, and usually some shade of black, brown, or tan. Some people think they look like centipedes. The head is equipped with a pair of sharp pincers that can deliver a painful bite. The thorax has 3 pairs of legs. The segmented abdomen has 8 pairs of leglike appendages extending from the sides, each with a cottony or hairy gill tuft at the base. There is a pair of hooked, leglike appendages at the hind tip; these help keep the animal from being swept away in the water current.

Similar species: Fishflies are in the same family and can be large and easily confused with female dobsonflies. Male fishflies, however, don't have the huge tusks, and males of many fishflies have pectinate (comblike or feathery) antennae. Females of the two groups can be distinguished by the more prominent pincers of female dobsonflies, and by their distinctively shaped pronotums (the necklike section just behind the head).

Other Common Names
Hellgrammite (larva)
Adult length: can exceed 3½ inches, with wingspan up to about 5 inches; larval length: 2-3 inches.
Where To Find
image of Eastern Dobsonfly Hellgrammite Distribution Map

Adults tend to stay near water and are most often seen in late spring and early summer. They are nocturnal and often attracted to electric lights. As adults, only the females are capable of delivering a painful bite. However, when molested, both sexes will raise their heads and spread their jaws defensively. Dobsonflies are not venomous and the worst they can do is pinch you.

The larvae usually inhabit the swiftest sections of large streams and rivers and usually hide under rocks.

The larvae are predaceous and snatch nearly anything that swims or ambles by, including other aquatic insects, small fish, and so on.

The adults only live a few days or a week. Despite their fierce-looking pincers, adults don't usually eat at this stage, having gained all their nourishment as aquatic larvae. But they can pinch you if you molest them.

This is the only species of dobsonfly in eastern North America. Alderflies, dobsonflies, and fishflies used to be grouped in the order Neuroptera (“nerve-winged insects”) along with the lacewings and some other insects, but scientists have determined they are different enough to be classified in their own order, the Megaloptera (“large-winged insects”).
Life Cycle
Dobsonflies are long-lived insects. The larvae typically live for 2 or 3 years underwater before pupating and becoming winged adults. Egg masses are laid on branches or rocks next to streams. These masses resemble bird droppings, which protects them from predators. After hatching, the larvae crawl or fall into the water, where they spend the next 2 or 3 years. Once grown, they crawl out of the water, form a cocoon, and overwinter. They emerge in spring as adults and usually only live for a few days after that. The adults focus only on reproduction. The large tusks of the male are used for clasping the female during mating.
The larvae (“devil scratchers” in Ozark dialect) are commonly used by anglers as bait. They should be grasped behind the head, lest they deliver a painful pinch. The enormous, imposing adults are rarely seen, since they are short-lived and nocturnal, but they are an awesome sight.
Most of this insect’s life is spent underwater as a larva that preys upon smaller aquatic invertebrates. Meanwhile, there are plenty of fish that relish these larvae, which explains their hiding under rocks! The adults, once they have reproduced, become food for birds and other animals.
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Similar Species
About Land Invertebrates in Missouri
Invertebrates are animals without backbones, including earthworms, slugs, snails, and arthropods. Arthropods—invertebrates with “jointed legs” — are a group of invertebrates that includes crayfish, shrimp, millipedes, centipedes, mites, spiders, and insects. There may be as many as 10 million species of insects alive on earth today, and they probably constitute more than 90 percent all animal species.