The annual Lake Winnebago lake fly hatch is on! Swarms of the large, one-inch, harmless flies have invaded High Cliff State Park, Sherwood, creating one of the largest hatches in many years. / Rob Zimmer/Gannett Wisconsin Media
It started as a low, buzzing hum in the morning air, but as the sun rose higher in the clear blue sky, the rising temperatures stirred the Lake Winnebago lake fly population into a furious roar that enveloped the shoreline in many areas in clouds of swarming insects.
The annual lake fly hatch is on, a few weeks later than normal, but, according to some who are witness to the swarms every year about this time, heavier than they have seen in many years.
Cynthia Mueller, Wisconsin DNR naturalist at High Cliff State Park, said she hasn’t seen lake fly numbers this large in several seasons.
“The lake flies have landed,” she said. “That means food for incoming bird migrants and Winnebago lake sturgeon is plentiful for another spring season. The spring hatch usually shows up on the east shore of Lake Winnebago on or close to Mother’s Day weekend, but this year it is late. Every year we wonder if this will be a big year. Will it be a major hatch or will the winds blow the lake flies to the west shore.”
This year, it’s a major hatch, at least at High Cliff.
Clouds of newly hatched lake flies funneled up into the sky from below, the wind often spinning them into twister-like formations and swirls. The constant high-pitched hum of untold numbers of lake flies in flight can be heard for long distances.
As the lake flies swarm, hungry songbirds, such as purple martins, tree swallows, warblers, orioles and thrushes sweep through the skies, snatching the insects in flight. Peak warbler migration is timed to the hatch of the lake flies, providing these tiny birds with all the sustenance they need to make the return journey north into northern Wisconsin and Canada. Nesting birds already raising families take advantage of the abundant food source to feed their growing young.
As they begin to emerge from aquatic larvae, lake flies have one purpose-to find a mate. The characteristic mating flight, or dance, of the lake fly can be seen as the insects race forward and back through the air in rapid swings.
Soon after they mate, the insects will die. Most live just a day or two, though the hatch will persist for a week or more.
“Visitors to the park who have never experienced a lake fly hatch are often overwhelmed at what they see,” Mueller said. “The sheer number and loud humming is like something out of a Hitchcock movie! A misconception is that these large insects, that resemble mosquitoes, bite. The lake fly does not have the capability to sting or bite. They are harmless and only live for a short time. Just enough time to reproduce.”
Mueller loves to share this bizarre and one-of-a-kind experience with school groups who happen to stop by during the peak hatch season.
“The looks on kid’s faces when they exit buses on field trips during a lake fly hatch is priceless! I always hope that the teachers and parents are adventurous enough to allow the children to get off the bus, if even for five minutes, to experience the lake fly phenomenon. They will never forget it. It also makes for an important teachable moment and introduction to the many faces of Lake Winnebago’s ecosystem.”
Following the annual spring hatch, a smaller, secondary hatch often occurs during August.
— Rob Zimmer: 920-419-3734, email@example.com