Eastern Dobsonfly (Corydalus cornutus)
The eastern dobsonfly is found in regions with fast-flowing streams where its aquatic larvae can develop. The larvae are called hellgrammites, the primary invertebrate predators in their habitat. So anglers use them as bait. The males of this species have intimidating large mandibles, and the adults are strong fliers.
- Species:C. cornutus
Description and Identification
The eastern dobsonfly is a large insect with a length of 140 mm and a wingspan of up to 125 mm. The females have short, strong mandibles the same size as the larvae, while those of the males are sickle-shaped and up to 40 mm long, half as long as their bodies. The antennae are segmented and long. The grayish translucent veined wings often have white dots. When the insect is at rest, its wings are folded flat over its back, extending beyond the abdomen.
Distribution: Eastern North America.
Habitat: Usually near unpolluted, swift-flowing streams.
Do They Bite/Sting: Yes.
Lifespan: 3 days for males and 8-10 days for females.
Predators: Stream fish, crayfish, birds, and bats
Behavior and Characteristics
The larvae hide under stones to catch and eat soft-bodied invertebrates.
The female can draw blood with its bite, while the male bite is not painful. But when threatened, both sexes raise their heads and extend their jaws in defense.
1. Egg Stage
The eggs are laid near the water’s edge on overhanging foliage or rocks. They are grey, cylindrical, and 1.4 mm long and 0.5 mm wide. They are laid in groups of around 1000 stacked in 3 layers. The female applies a clear protective fluid that dries white over the egg pile with the tip of its abdomen. The egg mass resembles a bird dropping.
2. Larva Stage
The eggs hatch at night after 2-3 weeks. The larvae or hellgrammites crawl or fall into the stream and make their way to a fast-flowing area with a stony bottom. They are light brown and covered with dark brown microspines. There are three pairs of legs in the thorax, each segment being covered by a hard, dark-colored dorsal plate. Lateral tactile filaments are present in the first 8 abdominal segments, while the first 7 additionally have tufts of tracheal gills. Spiracles are used for respiration both on land and in water. The abdominal tip has a couple of prolegs, each with a pair of terminal hooks (that help the larva to anchor in fast-flowing water) and a dorsal filament. They have powerful, sclerotised mandibles.
The hellgrammites grow slowly, molting 10-12 times and attaining a length of up to 90 mm. The bigger individuals are ferocious predators with well-developed jaws. They are ready to pupate after 1-3 years when they emerge from the water and travel some 15 m in search of a suitable location under a log, leaf, or leaf litter. There can be a mass emergence of the larvae at short intervals. Each one of them digs a hole in moist soil and prepares a small chamber with smooth walls. They pass through a prepupal stage of a few days before shedding their skin and pupating.
3. Pupa Stage
The orange pupa is covered with tiny bristles and has dark patches on the upper part of the abdomen. The developing limbs, antennae, and wings project from the pupal covering. In some areas, the pupae overwinter; in others, the adults come out in 7-14 days.
3. Adult Stage
After emerging, the adults dig their way to the surface. They don’t feed and live in dense vegetation near streams. They are most active at night and get attracted to lights. They die within a week of mating and laying eggs.
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