The Eastern Dobsonfly

Dobsonfly

A Dobsonfly is any insect of the subfamily Corydalinae, part of the megalopteran family Corydalidae. There are over 220 species of dobsonflies. Dobsonflies are found throughout the Americas and Asia, as well as South Africa...

, Corydalus cornutus, is a large insect in the Corydalidae

Corydalidae

The family Corydalidae contains the megalopterous insects known as dobsonflies and fishflies. Making up about one dozen genera, they occur primarily throughout the Northern Hemisphere, both temperate and tropical, and South America....

 family. It is found in eastern North America in regions with fast-flowing streams where its aquatic

Aquatic

Aquatic means relating to water; living in or near water or taking place in waterAquatic may also refer to:* Aquatic animal, either vertebrate or invertebrate, which lives in water for most or all of its life...

 larva

Larva

A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...

e develop. These are known as hellgrammites and are the top invertebrate

Invertebrate

An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...

 predator

Predation

In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...

s in the streams in which they live. They are used by anglers as bait.

Distribution

The dobsonfly is found in most of the eastern side of North America, in a range extending from Mexico to Canada. It is usually found near the swift flowing, unpolluted streams in which its larvae develop.

Description

The eggs

Egg (biology)

An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...

 are grey, cylindrical, about 1.4 millimetres long and 0.5 millimetres wide. They are laid in groups of about 1,000 eggs, stacked in three layers. The pile of eggs is protected by a clear fluid which dries to a white colour and is applied by the female with the tip of her abdomen. The whole egg mass looks rather like a bird dropping.

The larvae are light brown with a covering of tiny dark brown microspines. The thorax

Thorax (insect anatomy)

The thorax is the mid section of the insect body. It holds the head, legs, wings and abdomen. It is also called mesosoma in other arthropods....

 has three pairs of legs and each segment is covered by a tough, dark-coloured dorsal plate. The first eight abdominal

Abdomen

In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...

 segments have lateral tactile filaments and the first seven have tracheal gill

Gill

A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...

s in tufts. The larvae also have spiracle

Spiracle

Spiracles are openings on the surface of some animals that usually lead to respiratory systems.-Vertebrates:The spiracle is a small hole behind each eye that opens to the mouth in some fishes. In the primitive jawless fish the first gill opening immediately behind the mouth is essentially similar...

s allowing them to breathe on land as well as in the water. At the tip of the abdomen there are two prolegs, each with a dorsal filament and a pair of terminal hooks which enables the larva to anchor itself in fast-flowing water. The mandibles are sclerotised

Sclerotin

Sclerotin is a component of the cuticles of various Arthropoda, most particularly insects. It is formed by cross-linking members of particular classes of protein molecules, a biochemical process called sclerotization, but technically. The resulting material adds physical stiffness to the toughness...

 and powerful.

The pupa

Pupa

A pupa is the life stage of some insects undergoing transformation. The pupal stage is found only in holometabolous insects, those that undergo a complete metamorphosis, going through four life stages; embryo, larva, pupa and imago...

e are orange in colour with dark patches on the upper side of the abdomen and are covered with minute bristles. The developing limbs, wings and antennae project outside the pupal covering.

The adult dobsonfly is a large insect up to 140 millimetres long with a wingspan of up to 125 millimetres. The female has short powerful mandibles of a similar size to those of the larva while the mandibles of the male are sickle-shaped and up to 40 millimetres long, half as long as the body. The antennae are long and segmented and the greyish translucent, many veined wings are often mottled with white dots. When at rest the wings are folded flat over the insect's back and extend beyond the abdomen.

Life cycle

Dobsonfly eggs are usually laid close to the water's edge on a rock or overhanging foliage and hatch at night, one or two weeks later. The newly emerged larvae fall or crawl into the stream and make their way to a fast flowing section with a stony bottom. They are called hellgrammites and they hide under stones, catching and eating soft-bodied invertebrates. They grow slowly, shedding their skins ten to twelve times and reaching a length of up to ninety millimetres. The larger hellgrammites are fearsome predators with well-developed jaws. After one to three years and when ready to pupate, they emerge from the water and travel up to fifteen metres looking for a suitable location under a rock, log or leaf litter. There may be a mass emergence of hellgrammites within a few days of each other. Each one digs a hole in moist soil and prepares a small, smooth walled chamber, and after a prepupal stage of a few days, sheds their skin and pupates. In some areas the adults emerge in seven to fourteen days but in other areas they overwinter as pupae. On emerging, they dig their way to the surface. They are not thought to feed as adults but spend their time in dense vegetation near streams. They are most active at night and are attracted by lights. They mate and lay their eggs, usually dying within a week.

In the Appalachians, children catch these for fishing bait as a test of courage, working their fingers into the mud under rocks until a hellgrammite bites, then grabbing the creature with the other hand and throwing it into a jar. A less painful way to catch them is to stretch a mesh net across a narrow point in the stream, forcing the net to the bottom, then have others upstream turn over rocks and disturb the creek bottom, forcing the hellgrammites into the streamflow so they are carried into the net, whence they can be plucked and put into bait buckets.