Geographic Range
Corydalus cornutus
is found in or near the rivers and streams of eastern North America.
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.
- Habitat Regions
- temperate
- freshwater
- Aquatic Biomes
- benthic
- rivers and streams
- Other Habitat Features
- riparian
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.
- Other Physical Features
- ectothermic
- bilateral symmetry
- Sexual Dimorphism
- ornamentation
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.
- Development - Life Cycle
- metamorphosis
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.
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.
- Key Reproductive Features
- semelparous
- seasonal breeding
- gonochoric/gonochoristic/dioecious (sexes separate)
- sexual
- fertilization
- oviparous
Only parental investment is in choosing egg-laying site, and provisioning eggs.
- Parental Investment
-
pre-fertilization
- provisioning
Lifespan/Longevity
Corydalus cornutus
takes one to three years to complete its life-cycle.
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.
- Key Behaviors
- natatorial
- nocturnal
- crepuscular
- motile
- sedentary
- solitary
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.
- Other Communication Modes
- pheromones
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.
- Primary Diet
- carnivore
- 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.
- 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.
- parasitoid wasp species in Trichogramma
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
.
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.
Additional Links
Contributors
George Hammond (author), Animal Diversity Web.
- 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.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- 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).
- freshwater
-
mainly lives in water that is not salty.
- 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.
- riparian
-
Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).
- 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.
- 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.
- 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.
- seasonal breeding
-
breeding is confined to a particular season
- sexual
-
reproduction that includes combining the genetic contribution of two individuals, a male and a female
- fertilization
-
union of egg and spermatozoan
- internal fertilization
-
fertilization takes place within the female's body
- oviparous
-
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
- natatorial
-
specialized for swimming
- nocturnal
-
active during the night
- crepuscular
-
active at dawn and dusk
- motile
-
having the capacity to move from one place to another.
- sedentary
-
remains in the same area
- solitary
-
lives alone
- tactile
-
uses touch to communicate
- chemical
-
uses smells or other chemicals to communicate
- pheromones
-
chemicals released into air or water that are detected by and responded to by other animals of the same species
- visual
-
uses sight to communicate
- tactile
-
uses touch to communicate
- chemical
-
uses smells or other chemicals to communicate
- 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.
- carnivore
-
an animal that mainly eats meat
- insectivore
-
An animal that eats mainly insects or spiders.
- ectothermic
-
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
- 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.
References
Anderson, N. 2003. Megaloptera (Alderflies, Dobsonflies). Pp. 700-703 in Encyclopedia of Insects . New York City, New York, USA: Academic Press.
Evans, E., H. Neunzig. 1996. Megaloptera and Aquatic Neuroptera. Pp. 298-308 in 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..