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.
Communication Channels: tactile ; chemical
Other Communication Modes: pheromones
Perception Channels: visual ; tactile ; chemical
This species is wide-spread. It is not generally considered in need of special conservation protection.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
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
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.
This species is sometimes used as bait by fishermen. It is also a natural enemy of some insects pests, especially blackflies.
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.
Commensal/Parasitic Species:
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.
Animal Foods: insects; mollusks; aquatic or marine worms; aquatic crustaceans
Plant Foods: nectar
Primary Diet: carnivore (Insectivore )
Corydalus cornutus is found in or near the rivers and streams of eastern North America.
Biogeographic Regions: nearctic (Native )
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
Corydalus cornutus takes one to three years to complete its life-cycle.
Range lifespan
Status: wild: 3 (high) years.
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.
Range length: 90 (high) mm.
Sexual Dimorphism: ornamentation
Other Physical Features: ectothermic ; bilateral symmetry
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
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.
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.
Key Reproductive Features: semelparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); oviparous
Only parental investment is in choosing egg-laying site, and provisioning eggs.
Parental Investment: pre-fertilization (Provisioning)
The eastern dobsonfly, Corydalus cornutus, is a large insect in the Corydalidae family. It is found in eastern North America in regions with fast-flowing streams where its aquatic larvae develop. These are known as hellgrammites and are among the top invertebrate predators in the streams in which they live. They are used by anglers as bait.[1]
The eastern dobsonfly is found in most of eastern North America. It is usually found near the swift flowing, unpolluted streams in which its larvae develop.[1]
The origin of the word "dobsonfly" is unclear. John Henry Comstock used the term in reference to this species in his 1897 book Insect Life,[2] but did not explain it. He also mentioned that anglers use the word "hellgrammite" for the aquatic larvae they used as bait, but the origin of this term is also unknown.[3] These common names are still widely used for this and other species of corydalids, and essentially all that is known is that the earliest recorded uses appear to originate in the southern Appalachian region of the US (Kentucky, Tennessee, Virginia, West Virginia), where there were other archaic regional names and variants such as "helgamite", "hojack", "go-devil", and "grampus" (or "crampuss"), all with no definitive source or etymology.[4] The latter name, "grampus", was used in the same region for a large aquatic salamander, the hellbender, that lives in the same habitat.[4]
The eggs are grey and cylindrical, about 1.4 millimetres long and 0.5 millimetres wide. They are laid in groups of about 1,000, stacked in three layers. The pile of eggs is protected by a clear fluid which dries white and is applied by the female with the tip of her abdomen. The egg mass is said to look rather like a bird dropping.[5]
The larvae are light brown with a covering of tiny dark brown microspines. The thorax has three pairs of legs and each segment is covered by a tough, dark-coloured dorsal plate.[6] The first eight abdominal segments have lateral tactile filaments and the first seven have tracheal gills in tufts.[7] The larvae also have spiracles 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 and powerful.[1]
The pupae 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.[1]
The adult dobsonfly is a large insect up to 140 millimetres long with a wingspan of up to 125 millimetres.[8] 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.[1] 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.[9]
Dobsonfly eggs are usually laid close to the water's edge on a rock or overhanging foliage and hatch at night one to 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.[10] They grow slowly, shedding their skins ten to twelve times and reaching a length of up to ninety millimeters. 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.[11] There may be a mass emergence of hellgrammites within a few days of each other.[12] 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 [1] but in other areas they overwinter as pupae.[13] 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.[1]
The eastern dobsonfly, Corydalus cornutus, is a large insect in the Corydalidae family. It is found in eastern North America in regions with fast-flowing streams where its aquatic larvae develop. These are known as hellgrammites and are among the top invertebrate predators in the streams in which they live. They are used by anglers as bait.
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