Eastern Dobsonfly

The eastern dobsonfly, Corydalus cornutus, is the best-known dobsonfly species in North America and the one most anglers and stream-side hikers encounter. It ranges across much of the eastern half of the continent, from the Great Plains to the Atlantic coast, wherever swift, clean streams provide suitable larval habitat.

Males are unmistakable thanks to mandibles that can be nearly as long as the rest of the body, used in jousting matches with rival males rather than for biting prey. Females carry shorter, more powerful jaws capable of a noticeably firmer pinch.

The species' larval stage, the hellgrammite, is well known to freshwater fishermen as one of the most effective natural baits for bass and trout, a testament to how important these larvae are in the diets of stream fish.

• Large grayish-brown insect with long, smoky, net-veined wings folded roof-like over the abdomen
• Males: mandibles dramatically elongated, curved, and toothless-looking, often longer than the head and thorax combined
• Females: shorter, thicker mandibles capable of a stronger pinch
• Four spots (ocelli-like markings) sometimes visible near the base of the wings
• Larva (hellgrammite): dark, flattened, wormlike body with eight pairs of lateral filaments and terminal hooked prolegs
• Distinguished from other dobsonflies mainly by range and the specific proportions of the male's mandibles

Ranges through eastern and central North America, from southern Canada to the Gulf states, centered on regions with clean, rocky, well-oxygenated streams and rivers. Larvae live for one to three years beneath submerged stones in riffle zones; adults appear from late spring into summer and are commonly found resting near stream banks, bridges, and porch lights after dark.

Adults feed rarely, if at all, and devote their brief lives to finding mates; males compete for females by grappling with their elongated mandibles in tests of strength rather than combat meant to injure. The hellgrammite larva is an active nocturnal predator, crawling among stream-bottom rocks to hunt aquatic insect larvae and other small invertebrates, and it is itself a major prey item for game fish, making it a key link between invertebrate and fish communities.

Females deposit egg masses containing up to several thousand eggs on overhanging surfaces above the water. Newly hatched larvae fall or crawl into the stream and burrow among rocks, growing through numerous instars over one to three years. Full-grown hellgrammites leave the water to pupate in soil or under debris nearby, and emerge weeks later as short-lived winged adults that mate and lay eggs to complete the cycle.