Dobsonflies are large insects known for their substantial bodies and often large, net-veined wings, with some species reaching wingspans of over 18 cm. They are a subfamily, Corydalinae, belonging to the Megaloptera order, which also includes fishflies and alderflies. Despite their imposing appearance, adult dobsonflies are generally weak fliers.
Aquatic Habitats of Larvae
Dobsonfly larvae, commonly known as hellgrammites, are aquatic and inhabit freshwater environments for up to four years. They prefer clean, well-oxygenated water, often found in fast-flowing streams and rivers. Hellgrammites reside along rocky bottoms, seeking shelter under stones, logs, and other debris. Their presence often indicates good water quality, as they are sensitive to pollutants.
These larvae are predatory, ambushing smaller aquatic insects like mayfly nymphs, caddisfly larvae, and stonefly nymphs amidst riffles. Their strong, pincer-like jaws enable them to capture prey and hold themselves against strong currents. Hellgrammites breathe through abdominal lateral filaments and tracheal gills, though they also possess spiracles that allow them to take in air when out of water. When mature, hellgrammites leave their aquatic habitat to pupate in damp soil, moss, or decaying vegetation near the water’s edge.
Terrestrial Habitats of Adults
Adult dobsonflies emerge from their pupal chambers in late spring or early summer for a brief terrestrial phase. Their lifespan as adults is short, lasting only a few days to two weeks, primarily focused on reproduction. Adults are found near the aquatic environments where their larval development occurred, such as along the banks of rivers and streams.
These nocturnal insects rest during the day, hiding under leaves in the canopy or clinging to structures like bridges and tree trunks near water sources. At night, adult dobsonflies are attracted to lights, making them more visible around human-inhabited areas like campgrounds and lighted parking lots. While males possess long, sickle-shaped mandibles, they are primarily used for mating displays and are not capable of inflicting painful bites, unlike the shorter, more powerful jaws of females and larvae.
Global Presence
Dobsonflies have a widespread global distribution, found across the Americas, Asia, and South Africa. In the Americas, dobsonflies of the Corydalus lineage are distributed from southern Canada to northern Argentina and southeastern Brazil. The Eastern Dobsonfly (Corydalus cornutus), for instance, is found throughout much of eastern North America, extending from Canada to Mexico, typically east of the Continental Divide.
Asian species, including the Protohermes, Nevromus, and Acanthacorydalis lineages, are distributed from Northwest India to Southeast Asia, China, and Japan. The monotypic genus Chloroniella is unique to South Africa. While dobsonflies are found in both temperate and tropical regions, their presence is closely tied to the availability of clean, flowing aquatic habitats required by their larval stage. Their geographic range correlates with mountainous formations and areas with warm climates and higher precipitation rates, which support the necessary freshwater ecosystems.