One of the largest insects that we see here in Minnesota is the eastern dobsonfly. The male dobsonfly measures around five and a half inches from the tips of their pincers to the ends of their wings. It is easy to tell the difference between male and female dobsonflies by the length of their mandibles. Males, like the one above have long mandibles, up to an inch long, where the females have short mandibles. The males use their long mandibles as a display in mating. Finding a mate quickly is important to a dobsonfly as they only live about seven days as an adult. Eggs are laid in groups of 1000 near the water on a rock or over hanging vegetation.
After a week or two the larva emerge from the eggs and crawl of fall into the water. They move to an area of fast moving water with a rocky bottom. Hiding under the rocks they feed on the larva of other aquatic insects. Hellgrammites, as they are called live 2 to 3 years under the water and can grow to 2 to 3 inches long. As they grow the hellgramites shed their skin with about 10 to 12 instars before they are ready to pupate. When the time comes they crawl out of the river and find a spot under a rock, log or some leaves and make a cocoon. Here in Minnesota they will stay in the cocoon over the winter and the following spring will emerge and dig their way to the surface where they will have one week to find a mate and reproduce. This hellgrammite did not appear to make it.