dobsonfly, common name for a group of insects of the order Megaloptera, found throughout E North America. The adults may be 5 in. (12.7 cm) long; the male has mandibles half as long as the body. They are soft-bodied insects with a fluttery flight, and are largely nocturnal. Despite their strong jaws, the adults probably do not eat, living only long enough to lay large egg masses near water. The large aquatic larvae, called hellgrammites and much used by fishermen as bait, feed on aquatic insects for three years and then emerge to pupate on land. The closely related alderflies differ from the dobsonflies in their smaller size and diurnal habits. Dobsonflies are classified in the phylum Arthropoda, class Insecta, order Neuroptera, family Corydalidae.