Dobsonfly: Large brown bark-colored bug with huge pinchers

The Dobsonfly is attracted to lights at night so it’s not unusual to see an adult in front of the East Lansing Wild Birds Unlimited store from May until August. The first one I saw was at least a couple inches long with long scary looking pinchers coming out his mouth. Yesterday I took a photo of this female after I moved her from the front door to a nearby tree.

The dobsonfly spends two to three years of its life as a predaceous larva called hellgrammitein streams and rivers. When Hellgrammites get full-sized, they crawl from the water and find a safe spot to overwinter in a coccoon. The following summer, the adult Eastern Dobsonfly will emerge only to mate. They live just a few days and don’t eat.

The adult males have huge, ferocious looking jaws, which are used for nothing else but clasping the female during courtship. The adult females have much smaller looking mandibles. After the adult dobsonflies mate, the female lays eggs on a branch or on rocks near a stream. Between 100 and 1,000 eggs are laid in a mass with a white substance over it. The eggs resemble bird droppings, which may protect them from predators.

Hellgrammites, after they hatch, will either fall into the stream from an overhanging branch, or crawl to the water and the process starts all over again. There are over 220 species of dobsonflies found throughout the Americas and Asia, as well as South Africa. They are sensitive to contaminates in the water and a good indicator that the water is clean.

Sources: 

1. http://www.fcps.edu/islandcreekes/ecology/dobsonfly.htm

2. Insects of the North Woods by Jeffrey Hahn

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