Fishflies Dobsonflies and Alderflies: Megaloptera

Physical characteristics: Adults measure up to 2 inches (50 millimeters) in length, with wingspans up to 5.5 inches (140 millimeters). The larvae, known as hellgrammites, are 2.6 inches (65 millimeters) long. The head is almost circular, and the first section of the thorax is slightly narrower than the head. The wings are see-through gray with dark veins and white spots. The jaws of the male are half as long as the body. They are curved and pointed at the tips and held crossing each other. The jaws of the female are shorter.

Geographic range: Eastern dobsonflies live east of the Rocky Mountains in the United States and Canada.

The male eastern dobsonfly uses its big jaw as a weapon against other males when battling over females. (©Ken Thomas/Photo Researchers, Inc. Reproduced by permission.)

Habitat: The hellgrammites live in fast-flowing streams. The adults are found resting on streamside vegetation.

Diet: The hellgrammites eat small insect larvae, crustaceans, clams, and worms. Adult females drink various fluids, but the males do not drink or eat.

Behavior and reproduction: Adults are active at night during the summer and are sometimes attracted to lights. They are seldom seen during the day, spending most of their time hidden under leaves high up in trees. The larvae usually crawl on the bottom of the stream. Sometimes they move like a snake, swimming forward and backward in the water.

Males use their big jaws as weapons against other males over females. Courtship behavior is limited but does include fluttering of the wings. Females lay one hundred to one thousand eggs in round masses on rocks, branches, and other objects close to the water. Each mass is coated with a chalky, whitish substance. The larvae drop into the water or crawl to the nearby stream. They take two to three years to reach the pupal stage. Mature larvae crawl out of the water to dig their pupal chambers beneath logs and rocks along the shore.

Eastern dobsonflies and people: Fishermen use hellgrammites as bait for trout, largemouth bass, catfish, and other fishes. Eastern dobsonflies also help control populations of aquatic pest insects such as the Asian tiger mosquito.

Conservation status: This species is not listed as endangered or threatened. ∎