Dobsonfly

dobsonfly, any of a group of insects in the subfamily Corydalinae (order Megaloptera) that are usually large and have four net-veined wings of similar size and shape. Dobsonflies are found in North and South America, Asia, Australia, and Africa. Nine genera of dobsonflies, containing several dozen species, are recognized. Together, they comprise four lineages: Protohermes, Neuromus, Corydalus, and Chloroniella.

Dobsonflies are characterized by a long cylindrical body with short legs. Males often possess well-developed mandibles, which in some species are used in fighting and defense. The larvae, sometimes known as hellgrammites or toe-biters, are aquatic and are eaten by fish, especially bass; they often are used as fish bait by anglers. Mature larvae migrate from their freshwater habitat to wet soil, moss, or decaying vegetation near the water to form pupal cells from which adults emerge. Megaloptera larvae are an important component of the macroinvertebrate fauna of streams and serve as biotic environmental indicators because of their high intolerance of water pollution.

Among the best-described dobsonflies are those of the Corydalus lineage, which includes the widely known eastern dobsonfly (Corydalus cornutus), a large insect with a body length of about 5 cm (about 2 inches) and a wingspread of about 13 cm (5 inches). The jaws (or mandibles) are considerably larger in the male than in the female and are characteristic of the insect’s sexual dimorphism. They may exceed 2.5 cm (1 inch) in the male. Females of C. cornutus lay up to about 3,000 eggs in whitish clusters, typically on rocks near streams. After the eggs hatch, the young larvae crawl to the water and mature there in two or three years. The larvae are blackish in colour and live beneath stones in rapidly flowing streams. Large, older larvae, which may be up to 8 cm (3.15 inches) long, have strong biting mouthparts and are ferocious predators on other aquatic insects and small invertebrates.

Larvae of Platyneuromus dobsonflies, which occur in Mexico and Central America, are found in habitats similar to those of Corydalus. Adult Platyneuromus also are similar in appearance to Corydalus but are distinguished by the presence of postocular flanges (plates behind the eyes). In areas where the two genera occur together, they may segregate by altitude, with Platyneuromus generally preferring middle to high elevations and Corydalus occupying low to middle elevations. Dobsonflies of the genus Chloronia, also in the Corydalus lineage, are distinguished from other corydalids by the bright yellow colour of adults.