Colleen KottkeWisconsin State Farmer
While the brood emergence of the long-awaited cicadas is grabbing news headlines, folks living along the shores of Lake Winnebago and the banks of the Mississippi River in western Wisconsin are preparing for a different regularly scheduled appearance of winged insects that will coat the sides of their homes, fences, vehicles and lawns.
Watching a softball game the other night at Lakeside Park in Fond du Lac, this reporter overheard a conversation between two local residents lamenting the onset of the annual swarm of lake flies.
"What do you expect when you live next to Lake Winnebago?" one spectator complained. "Those mayflies are enough to drive you crazy. I can't even take the dog out for a walk!"
It's not uncommon for people to confuse mayflies with lake flies (a species of midge). After all, they both appear in cloud-like swarms in the warmer months of the year and emerge from bodies of water. But what do these often misidentified insects share in common and how are they different?
Both are out of sight most of their lives
Like the cicada, mayflies and lake flies spend most of their life cycle hidden out of sight. While young cicadas, called nymphs, attach themselves to tree roots and suck tree sap for nearly 17 years before emerging, mayfly and midge larvae live in the sediment of streams or muddy, silt-bottomed rivers and lakes, eating decaying plant matter.
"These insects spend over 99% of their life cycle in the water as juveniles, feeding and growing and developing. When they emerge as adults, they are really short-lived," said PJ Liesch, director of the University of Wisconsin-Madison’s Insect Diagnostic Lab
Midges emerge around mid-to-late May, while mayflies prefer to hatch in warmer water temperatures and emerge a month later.
Once they become adults, it's easy to see that the mayfly is larger than the midge with a pronounced tail and distinct large wings which give it an ephemeral-like appearance, Liesch said. The male and female midge differ in appearance, with the male being larger and having fuzzy antennae.
Those freaked out by "lake flies" almost always attribute their fear to the insect resembling a "big mosquito." Liesch says both the midge and mayfly are harmless — neither have a mouth with which to eat or bite humans.
After spending most of their lives seeking nourishment, these aquatic insects take to the sky with only one aim.
"It's a mad dash for them to find a mate," said Liesch, adding that the lifespan of the mayfly is anywhere from 12 to 24 hours. The midge, on the other hand, completes its full life cycle in about two weeks.
The chances of finding a mate in that swirling cloud are pretty good. Once that goal has been achieved, the males goes on to breed multiple times before dying as the female returns to the water to lay her eggs — numbering between 5,000 to 10,000 — for the next fleeting generation.
Abundant insects contribute to ecosystem in a big way
The humming, undulating clouds of millions of insects may be off-putting to humans, but these swarms delight the wildlife that consumes them. Observers parking along Lake Winnebago at dusk are entertained as bats, swallows and martins glide above the surface, eating their fill of the insects.
Wisconsin Department of Natural Resources water management specialistScott Koehnke told the Appleton Post-Crescent that around 60% of the lake sturgeon's diet is made up of lake flies, helping to nourish Lake Winnebago's sturgeon population.
Liesch said swarms of freshly hatched mayflies over Lake Erie and along the Mississippi River are so massive and thick that the National Weather Service radar can detect them.
About 95% of the flies will be eaten before they die off. Those who escape being devoured in the air or water also play an important role.
"Once they die, they're going to break down and the nutrients are going to return to the ecosystem around you," Liesch said. "Think of it as free lawn fertilizer."
The abundance of mayflies and midges as well as other aquatic insects can also serve as an indicator of water quality.
"There are some species that are relatively tolerant of pollution and polluted conditions," Liesch said. "Then on the other end of the spectrum, there are those that are very sensitive. You can go out, collect and survey the insects that are present as a way to gauge the water quality in a given body of water."
Don't let these flies bug you
Unlike mosquitoes that bite, spread disease and tend to wear out their welcome by late summer, Liesch says mayflies and midges are to be tolerated during their brief lifespans.
"I can understand if you're trying to have a cookout in your backyard that they may be an annoyance, but they're pretty harmless," he said.
Trevor Kamholz, an employee at Ardy & Ed's drive-in, located on the south side of Oshkosh near Lake Winnebago, says the lake flies haven't impacted business.
"They're around for a month or so and tend to coat the outside of the building. I just go outside and spray them off with water," Kamholz said.
Liesch advises against using chemical sprays to eradicate the insects. He notes that certain kinds of lighting may attract the flies.
"Their vision is slightly different than ours in terms of the wavelengths they can detect. Yellowish or sodium vapor lights tend to not be as attractive to nighttime flying insects," he said. "However, some of the newer LED lights seem to draw them in."
The wind may also play a role in whether or not the latest swarm will concentrate in your neighborhood. As lake flies tend to be weak flyers, they are at the mercy of the wind.
Koehnke told the Post-Crescent that wind direction and intensity at the time of the hatch may determine where they congregate.
The worst swarms of the flies are typically found in High Cliff State Park and Menasha due to the prevailing south and southwest winds blowing the flies across Lake Winnebago,he said.
