Dobsonfly

 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.

King Bug

The eastern dobsonfly is the one of the largest insects that we have in this area. Their large size, about 5 inches long from the tip of the wings to the tip of the mandibles, as well as their impressive tusks, especially on the males, have earned them the nickname of "King Bug". They spend much of their life underwater in their larval stage, hellgrammites. As hellgrammites they spend most of their time under rocks at the bottom of their watery home hunting other insect larvae.

You can tell that this is a female because she has short mandibles. The males can have mandibles that are up to about one inch long. They use these long mandibles for courtship displays and for holding on to their mates. Because they are so long the mandibles of the male do not have enough force to break a persons skin the females shorter mandibles however can lead to a painful bite. I photographed this dobsonfly at the Snake River.