hellgrammite

Dobsonfly male with long mandibles. Pat Porter.

Article author: Pat Porter
Most recently reviewed by: Blayne Reed & Ballinger (Vacant) (1970)

Common Name(s): dobsonfly, hellgrammite, toe biter

Description

Dobsonflies are not really flies (insects in the Order Diptera). They are in the Order Megaloptera along with the Alderflies and Fishflies, all of which have aquatic larvae. The adults are quite striking in appearance with membranous wings and bodies 1.9 to 2.4 inches long, and often covered by wings that are much longer. Wingspans are from 3.9 – 5.5 inches. Males have long, sickle-like mandibles used to hold females during mating or for self defense, and females have relatively short mandibles. It is not known whether adults feed during their 3-10 day lifespans, but some entomologists suggest that they do.

Larvae are equally striking and can be as long as 2 3/4 inches. They are aquatic and have both gills for breathing under water and spiracles for breathing on land. The larvae are commonly called hellgrammites and are sometimes sold as fish bait.

Origin and Distribution

There are some 30 species of dobsonflies in the New World, but only one in the United States, the eastern dobsonfly. There is some disagreement though, as the there are three western species in genus Corydalus, but these are currently included under species cornutus. Dobsonflies are also found in Asia, Africa and Australia.

: Male dobsonfly.

: Adult female, note the relatively short mandibles.

Habitat & Hosts

Dobsonfly larvae live in flowing water, often at the base of rocks in fast moving water. They feed on the larvae of other aquatic insect species living in the same location. Because they have gills they do not need to surface for air.

Life Cycle

Eggs are laid in masses on leaves and structures above flowing water, or on rocks at water’s edge. They are covered with a white substance that is said to help protect the eggs from overheating. Eggs hatch at night and first instar larvae drop or crawl to water and disperse. There are 10 – 12 larval instars (or stages), and it takes 1-3 years to complete development. Pupation occurs on land near the stream from which they emerged. Prepupae excavate small cells in moist soil then enter the pupal stage. Adults emerge 7-14 days later. Adult males live only a few days, and females as many as 10 days.

Management

If you live in the State of Texas, contact your local county agent or entomologist for management information. If you live outside of Texas, contact your local extension for management options.

Dobsonflies and hellgrammites are beneficial insects. They are a key component of the food chain for fish that live in the streams and rivers where they are found. The predatory nature of the larvae helps keep other species in check, including blackflies, a serious biting pest.