With spring now officially transitioning to summer, I thought I would take this opportunity to talk about one of the more bizarre natives you can find while exploring the wilderness of Pennsylvania: the eastern dobsonfly. Dobsonflies are flying insects in the order Megaloptera (literally “large wing”), and they live up to that name well, with larger individuals having a wingspan of up to 5 inches across. In addition to their long wings, dobsonflies are also notable for the long, pincer-like mouthparts found on males. While intimidating, these jaws are incredibly weak and are completely harmless. Females, on the other hand, have much shorter, more robust jaws and can deliver a pretty powerful crunch, potentially breaking skin.
Fishers may be more familiar with the dobsonfly’s larval form, the hellgrammite (or the grampus, as it’s apparently called in some regions), which somewhat resembles a centipede and are often used as bait for bass fishing. Hellgrammites are aquatic larvae, living in fast flowing streams, breathing through the series of short, filamentous gills running along their slender abdomens. Similar to the adult female dobsonfly, hellgrammites have short, powerful jaws which they use to catch other aquatic invertebrates to feed on, and like their adult counterparts, these jaws are capable of drawing blood.
Life Cycle
The Eastern dobsonfly spends most of their life cycle as the larval hellgrammite, inhabiting creeks and streams where they are voracious predators that can feed on a wide range of aquatic invertebrates. After 2-3 years of feeding, hellgrammites will crawl onto land, find a covered location such as under a rock or log, and burrow into the ground to pupate. The adult dobsonfly emerges from their pupa 1-2 weeks later. Adult dobsonflies are incredibly short lived. Males typically survive for 3 days, while females can last up to 10 days. Adult dobsonflies do not feed.
Older literature states that the male uses their large mandibles to hold females in place while mating, but more recent studies of dobsonfly mating behavior found no evidence of this, although males were seen to place their mandibles on the female’s wings as part of their pre-mating ritual, as well as using their mandibles to fight other males for access to females. After mating, female dobsonflies lay egg masses on vegetation near rivers. These egg masses are white and hatch at night a couple weeks later, with freshly hatched larvae dropping to the ground and crawling to the stream.
Habitat
The eastern dobsonfly can be found across much of the eastern half of the United States. Hellgrammites can be found in fast flowing streams with low amounts of organic material, usually hunting for prey under rocks and stones. Because they require clean, highly oxygenated water to survive, hellgrammites are often used as an indicator of stream health. While adult dobsonflies typically stay near rivers and streams, they are attracted to lights and have been known to fly long distances from their larval habitats.
Because of their wide range, the life cycle of the eastern dobsonfly varies greatly regionally. In the south, dobsonflies can reach adulthood in about a year, as compared to in more northern states where they can remain larvae for up to 5 years before pupating. Additionally, the pupation behavior varies regionally, with hellgrammites emerging in spring or summer to pupate in some regions while in others they emerge in the fall and overwinter as pupae.
Scientific Vagaries 