Species Spotlight: Lake Flies!

These flies have wing lengths around 6 mm, and bodies as long as 13 mm. When they emerge to create mating swarms, adults live for only 3 – 11 days. Since they do not have functional mouthparts, they do not bite or even eat! The location and size of swarms are highly dependent on the wind, and are often concentrated on areas that contrast with the background. Females lay masses of eggs on the water surface, which then absorb water and sink to the lake bottom. These eggs hatch shortly after and become midge larvae. The larvae undergo 4 stages, the first of which is free swimming. During the following three stages, the larvae make and live in a tube, collecting food at the bottom of the lake. Then the lake flies emerge in May or late summer and start the cycle over again.

Many species eat lake fly larvae and adults are therefore very important for the food web in Lake Winnebago. In fact, lake fly larvae help support the sturgeon population and contribute to our large self-sustaining lake sturgeon population. Other fish species eat the larvae stages and birds including purple martins and warblers eat the flying adults. Though the large hatching event can be a nuisance for us, they are critical for the food webs of the Winnebago Lakes. Remember, though they can be very annoying, they only last about 2 weeks! Their impact on the rest of the system lasts for much longer.