Hellgrammite

Corydalus cornutus
Other Common Name
Eastern Dobsonfly Larva
Family

Corydalidae (dobsonflies and fishflies), in the order Megaloptera (alderflies, dobsonflies, fishflies)

Description

Hellgrammites are the larvae of eastern dobsonflies. They are aquatic, somewhat flattened, and usually some shade of dark brown, tan, or black. Some people think they look like centipedes. The head is equipped with a pair of large, sharp pincers that can deliver a painful bite. The thorax has 3 pairs of legs, each tipped with a tiny pair of pincers. The segmented abdomen has 8 pairs of pointed, leglike appendages along the sides, each with a cottony or hairy gill tuft at the base. There is a pair of hooked, leglike appendages at the hind tip; these help keep the animal from being swept away in the water current.

The winged adults, called dobsonflies, are large, soft bodied, usually a drab gray, black, or brown, with prominent pincers and long antennae. Wings with conspicuous veins, usually folded down the length of the body when at rest. Pincers (mandibles) of females rather stubby and capable of inflicting a painful bite. Mandibles of males very long, tusklike, and incapable of hurting people due to lack of leverage.

Key Identifiers
  • Aquatic, long-bodied, somewhat flattened.
  • Head with a pair of large, sharp pincers; can deliver a painful bite.
  • Usually dark brown, tan, or black.
  • Thorax with 3 pairs of legs, each tipped with a tiny pair of pincers.
  • Abdomen segmented, with 8 pairs of pointed, leglike appendages along the sides, each with a cottony or hairy gill tuft at the base.
  • Tip of abdomen with two leglike appendages, each bearing two claws.
  • Usually live under rocks in swift-flowing, large streams.
Size

Larva length: to about 4 inches.

Hellgrammite_9-9-16.jpg

Photo of a hellgrammite crawling among rocks in an aquarium.
Hellgrammite
The segmented abdomen of a hellgrammite has 8 pairs of pointed, leglike appendages along the sides, each with a fuzzy-looking gill tuft at the base.

Hellgrammite_9-10-16.jpg

Photo of a hellgrammite in an aquarium, side view.
Hellgrammite
Hellgrammites, the larvae of dobsonflies, can grow to be 4 inches long.

Hellgrammite_9-12-16.jpg

Photo of a hellgrammite in an aquarium.
Hellgrammite
This photo shows several identifying features of hellgrammites.

Hellgrammite_9-11-16.jpg

Photo of a hellgrammite in an aquarium, closeup on head.
Hellgrammite
Hellgrammites are predaceous and snatch nearly anything that swims or ambles by, including aquatic insects and small fish.

eastern_dobsonfly_11-08-12.jpg

Photo of eastern dobsonfly
Eastern Dobsonfly (Adult Female)
Habitat and conservation

Hellgrammites usually inhabit the swiftest sections of large streams and rivers and usually hide under rocks. Adults tend to stay near water and are most often seen in late spring and early summer. They are nocturnal and often attracted to electric lights. Dobsonflies are not venomous and the worst they can do is pinch you hard. These are long-lived insects. The larvae typically live for 2 or 3 years underwater before pupating and becoming winged adults.

Foods

The larvae are predaceous and snatch nearly anything that swims or ambles by, including other aquatic insects, small fish, and so on. The adults only live a few days or a week and do not eat during this stage.

Distribution in Missouri

Statewide.

Status

This is the only species of dobsonfly in eastern North America. Alderflies, dobsonflies, and fishflies used to be grouped in the order Neuroptera (“nerve-winged insects”) along with the lacewings and some other insects, but scientists have determined they are different enough to be classified in their own order, the Megaloptera (“large-winged insects”).

Life cycle

Egg masses are laid on branches or rocks next to streams. These masses resemble bird droppings, which protects them from predators. After hatching, the larvae crawl or fall into the water, where they spend the next 2 or 3 years. Once grown, they crawl out of the water, form a cocoon, and overwinter. They emerge in spring as adults and usually only live for a few days after that. The adults focus only on reproduction. The large tusks of the male are used for clasping the female during mating.

Human connections

The larvae (“devil scratchers” in Ozark dialect) are commonly used by anglers as bait. They should be grasped behind the head, lest they deliver a painful pinch. The enormous, imposing adults are rarely seen, since they are short-lived and nocturnal, but they are an awesome sight.

Ecosystem connections

Most of this insect’s life is spent underwater as a larva that preys upon smaller aquatic invertebrates. Meanwhile, there are plenty of fish that relish these larvae, which explains their hiding under rocks! The adults, once they have reproduced, become food for birds and other animals.