Corydalus cornutus

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Geographic Range

Corydalus cornutus is found in or near the rivers and streams of eastern North America. (Evans and Neunzig, 1996; McCafferty, 1983)

Habitat

The eggs of Corydalus cornutus are laid tree branches, rocks, or other structures that are over or immediately adjacent to moving water. The larvae live on the bottoms of fast-moving (well-oxygenated) streams and rivers, climbing over gravel, cobbles, sand, soft sediments, and organic debris. They are not usually found on living aquatic plants. Dobsonflies pupate on land, usually hidden in muddy soil or decaying wood near a streambank. Adults tend to stay near to streams, mating occurs on the ground or on vegetation.

  • Aquatic Biomes
  • benthic
  • rivers and streams

Physical Description

Dobsonfly larvae, sometimes called hellgrammites, are flattened and elongate, dark brown in color, with a segmented body. They have a wide head with strong biting mouthparts, 3 pairs of thoracic legs, and a eight pairs lateral filaments, one to a segment, down each side of the body, each with a gill tuft at the base of the filament. They are distinguished from stonefly (Plecoptera) larvae by the pair of prolegs at the hind end of the abdomen, each of which has two terminal hooks. Fully-grown larvae may be as long as 90 mm.

Pupae and adults have large mandibles, also a wide head, and an elongate abdomen. Adults are tan or light brown, with darker mottling, and are up to 75 mm long. They have two pairs of large, strongly-veined wings. The forewings are translucent grey-brown, with darker markings, especially on the veins. At rest they are held folded over the back, in a roof-like arrangment. The mandibles of adult males are extremely long (up to half the body length, and horn-like. (Evans and Neunzig, 1996; McCafferty, 1983)

  • Range length
    90 (high) mm
    3.54 (high) in

Development

This is a holometabolous species, with four life stages: egg, larva, pupa, and adult. The eggs, pupae, and adults breath air and live on land. The larvae are aquatic, and take their oxygen from the water. Nearly all feeding and growth occurs in the larval stage, which may molt as many as 10 times as it grows. Larval development is strongly affected by temperature: larvae in colder climates and colder streams take longer to grow (sometimes spending two winters in the larval stage before) and may be larger when they transform. (Anderson, 2003; Evans and Neunzig, 1996; McCafferty, 1983)

Reproduction

Adults mate within days of emergence, in late spring or summer. Mating occurs near streams, on the ground or on vegetation. Males may use their elongate mandibles in contests with other males. They also use them in courtship and mating behavior with females. (Anderson, 2003; Evans and Neunzig, 1996; McCafferty, 1983)

Female dobsonflies lay eggs very soon after mating. They produce up to three masses of eggs, usually on the undersides of leaves, branches, or other structures over-hanging a stream. Each mass may contain as many as 1000 eggs, laid in 1-5 layers and covered with a white protective material. Eggs incubate for 2-3 weeks before the new larvae hatch and drop or crawl to water.

The life-cycle of this species is strongly affected by temperature -- in the southern part of the range they can complete a generation in less than a year, but further north it may take 2-3 years. Adults only live for a few days -- females die after laying their eggs. (Anderson, 2003)

  • Breeding season
    Dobsonflies mate and lay eggs in spring and summer.
  • Range eggs per season
    3000 (high)
  • Range age at sexual or reproductive maturity (female)
    1 to 3 years
  • Range age at sexual or reproductive maturity (male)
    1 to 3 years

Only parental investment is in choosing egg-laying site, and provisioning eggs. (Anderson, 2003)

  • Parental Investment
  • pre-fertilization
    • provisioning

Lifespan/Longevity

Corydalus cornutus takes one to three years to complete its life-cycle. (Anderson, 2003; McCafferty, 1983)

  • Range lifespan
    Status: wild
    3 (high) years

Behavior

Corydalus cornutus larvae and adults are most active in twilight or at night. Except for mating, they are not social. Larvae mostly crawl, but can swim forward or backward by undulation. Adults are sometimes attracted to artifical lights at night, and may fly some distance from their emergence site. (Anderson, 2003; Evans and Neunzig, 1996; McCafferty, 1983)

Communication and Perception

Hellgrammites, the larval stage of Corydalus cornutus, probably rely mainly on touch and chemical sensing to locate prey. They do have eyes though and can at least detect motion and shadow.

Adult male dobsonflies have scent glands on their abdomen that apparently play some role in mating. They also lay their mandibles over females when courting them, so touch is relevant too. (Anderson, 2003; McCafferty, 1983)

Food Habits

Hellgrammites, the larvae of Corydalus cornutus and other corydalids, are active predators that feed on a wide variety of small stream invertebrates, including insects and other arthropods, small worms, and small molluscs. They are generalists, whose diet choices probably reflect relative abundance of different prey types rather than specialization. They are known to particularly feed on blackfly larvae (Simuliidae) and the larvae of net-spinning caddisflies (several familiies in the Trichoptera) and mayflies (Ephemeroptera).

Adults are not believed to take solid food. Females are reported to feed on nectar from flowers, males are not believed to eat at all. (Anderson, 2003; Evans and Neunzig, 1996; McCafferty, 1983)

  • Animal Foods
  • insects
  • mollusks
  • aquatic or marine worms
  • aquatic crustaceans
  • Plant Foods
  • nectar

Predation

Corydalus cornutus avoids predators by limiting its activity in daylight, by hiding, and by biting in self-defense if necessary. Adults and larvae are cryptically colored. We have no information on specific predator species. Stream fish eat them, and probably some crayfish. Birds and bats are probably natural enemies of adult dobsonflies. (Anderson, 2003; Evans and Neunzig, 1996; McCafferty, 1983)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

This species is a mid-level predator, feeding on smaller animals, but also fed upon by larger predators. In small stream where fish are small or rare, large hellgrammites may be some of the largest predators in the water.

Some very small parasitoid wasp species in the genus Trichogramma are known to lay their eggs in the eggs of Corydalus cornutus. The wasp larvae consume the host egg, and emerge as adult wasps. (Anderson, 2003; Evans and Neunzig, 1996; McCafferty, 1983)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

This species is sometimes used as bait by fishermen. It is also a natural enemy of some insects pests, especially blackflies. (McCafferty, 1983)

Economic Importance for Humans: Negative

Though people are sometimes frightened by the large size and fierce appearance of adult dobsonflies, they are quite harmless. The larvae can deliver a painful bite in self-defense.

Conservation Status

This species is wide-spread. It is not generally considered in need of special conservation protection. (Anderson, 2003; Evans and Neunzig, 1996; McCafferty, 1983)

Contributors

George Hammond (author), Animal Diversity Web.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

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benthic

Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

crepuscular

active at dawn and dusk

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

fertilization

union of egg and spermatozoan

freshwater

mainly lives in water that is not salty.

insectivore

An animal that eats mainly insects or spiders.

internal fertilization

fertilization takes place within the female's body

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

semelparous

offspring are all produced in a single group (litter, clutch, etc.), after which the parent usually dies. Semelparous organisms often only live through a single season/year (or other periodic change in conditions) but may live for many seasons. In both cases reproduction occurs as a single investment of energy in offspring, with no future chance for investment in reproduction.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

sexual ornamentation

one of the sexes (usually males) has special physical structures used in courting the other sex or fighting the same sex. For example: antlers, elongated tails, special spurs.

solitary

lives alone

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

visual

uses sight to communicate

References

Anderson, N. 2003. Megaloptera (Alderflies, Dobsonflies). Pp. 700-703 in V Resh, R Cardé, eds. Encyclopedia of Insects. New York City, New York, USA: Academic Press.

Evans, E., H. Neunzig. 1996. Megaloptera and Aquatic Neuroptera. Pp. 298-308 in R Merritt, K Cummins, eds. An Introduction to the Aquatic Insects of North America. Dubuque, Iowa, USA: Kendall/Hunt Publishing Company.

McCafferty, W. 1983. Aquatic Entomology: The Fishermen's and Ecologists' Illustrated Guide to Insects and Their Relatives. Boston, Massachusetts, USA: Jones and Bartlett Publishers, Inc..