Lake of the flies is feast for migrating songbirds
SHERWOOD, Wis. — One sign of spring in Wisconsin is here, a few weeks later than normal but perhaps more robust than usual.
The annual lake fly hatch is on, and Cynthia Mueller, a naturalist at High Cliff State Park on the shores of Lake Winnebago, said she hasn't seen numbers this large in several seasons.
"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," she said. "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?"
The hatch of the adult Chironomus spp. is a bane to people for only a few weeks but a boon for fish and fowl, similar to lovebug mating season in May and late summer in the South. Following the lake flies' spring hatch, a smaller, secondary hatch occurs in August.
These lake flies started life at the end of this past summer as a mass of eggs on the surface of Lake Winnebago, the result of matings from that secondary hatch. The eggs then sunk to the bottom of the shallow lake — it is 21 feet at its deepest — hatched into larvae and burrowed into the lake's mud to feed and wait out the winter.
When water temperatures warm sufficiently, the larvae transform into pupae, swim to the surface of the lake and emerge as adults.
On Monday, 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 could 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 emerge, lake flies have one purpose — to find a mate. The lake fly's characteristic mating flight, or dance, 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."
Lake flies may look like mosquitoes but they don't bite; one of their names is non-biting midges.
"The lake fly does not have the capability to sting or bite," Mueller said. "They are harmless and only live for a short time, just enough time to reproduce."
Mueller loves to share this bizarre experience with school groups that 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," she said. "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."