Dobsonfly

Dobsonflies (genus Corydalus) are among the largest flying insects in North America, instantly recognizable by their smoky, net-veined wings and, in males, a pair of sickle-shaped tusks that can rival the length of the body itself. Despite their fearsome appearance, adult dobsonflies live only a week or two, during which they rarely feed and exist mainly to mate.

The aquatic larvae, known as hellgrammites, spend one to several years hidden under stones in swift, oxygen-rich streams, where they are voracious predators of other aquatic invertebrates. Because hellgrammites require clean, well-aerated water, their presence is often taken as a sign of good stream health.

Adults are nocturnal and strongly attracted to porch and streetlights near waterways in summer, which is when most people encounter them.

• Very large, soft-bodied insect with two pairs of long, smoky-gray, net-veined wings held roof-like over the body at rest
• Males have enormously elongated, curved mandibles (tusks) that can exceed the length of the body
• Females have much shorter but stouter, pincer-like jaws
• Body is brownish-gray with a flattened head and long, segmented antennae
• Larvae (hellgrammites) are dark brown-black, wormlike, with strong legs, pincer jaws, and paired filaments along the abdomen ending in hooked prolegs
• Lookalikes: fishflies and alderflies are smaller relatives without the extreme mandibles

Found throughout much of North America wherever clean, rocky, fast-moving streams and rivers occur. Larvae live for one to several years under submerged rocks in riffles, while winged adults emerge in late spring through summer and stay close to the water's edge, often found clinging to bridge railings, tree trunks, or walls near lights at night.

Adult dobsonflies feed little or not at all, relying on energy reserves built up as larvae. Males use their oversized mandibles in ritualized combat with rival males and to grip females during mating rather than for capturing prey. The aquatic larvae are aggressive ambush predators, feeding on mayfly and stonefly nymphs, small crustaceans, and other invertebrates, and in turn serve as an important food source for fish, which is why anglers prize them as bait. Both larvae and adults are important links in freshwater and riparian food webs.

Females lay large chalky-white egg masses containing hundreds to thousands of eggs on surfaces overhanging water, such as rocks or bridge supports. Hatchlings drop into the stream and develop through many instars as hellgrammites, a stage that can last one to five years depending on species and conditions. Mature larvae crawl onto land to pupate in a chamber under logs, bark, or stones, emerging as winged adults that live only about a week to ten days, just long enough to mate and lay the next generation of eggs.