Lake fly's life cycle benefits birds, gardens

Despite the lake breeze, the fog doesn't shift. It remains in place, even as the wind stiffens. This is no ordinary fog. The lake fly hatch on Lake Winnebago has begun.

Like everything else this odd spring of 2010, the annual emergence of millions, perhaps trillions of lake flies arrived some two to three weeks early. In most years, the hatch occurs right around Mother's Day during the second week of May. The bulk of lake flies appear to be hatching this week, resulting in vast swarms of the inch-long midges all around the big lake.

Due to strong east-to-northeast winds for several consecutive days, the largest swarms of lake flies are especially concentrated from Oshkosh south to Fond du lac on the west shore.

Walking along the shore at Asylum Park north of Oshkosh was a surreal experience one recent evening. Newly emerged lake flies bubbled from the grasses and reeds in ever-thickening swarms as the afternoon sun warmed their bodies. The air vibrated and hummed with the wingbeats of untold numbers of insects in flight.

Shoreline trees and shrubs, just beginning to bud into leaf, stood cloaked with roosting flies, neatly arranged in orderly fashion along every stem, twig and leaf. Clinging tight against the buffeting lake breeze, the lake flies carefully timed their leaps into aerial flight.

The birds were ready for them.

Tree swallows, purple martins and red-winged blackbirds relish lake fly season, providing the birds with a bounty of fresh insects as their nesting season begins. Sometimes a parent doesn't even need to leave the nest to gather food for the young, just snatching the overabundant insects on the wing as they pass by or rest on the branches or the nest itself.

Normally, the lake fly hatch is synchronized with the arrival of thousands of migrating songbirds, such as warblers, orioles, tanagers and thrushes. Millions of swarming lake flies, in perfect timing courtesy of Mother Nature, emerge from their aquatic larval stage each spring. For about 10 days or so, the hatch remains at peak intensity.

A secondary hatch, much smaller and hardly noticeable, occurs later in summer.

As afternoon grew into evening, the swarming lake flies continued to build in number and intensity. The air buzzed with the frenzy. As far as I could see, a brown fog danced over the treetops, rising continually from the ground below.

For many lakeshore residents, the annual lake fly hatch is an accepted tradition and minor inconvenience to be expected and tolerated. Still, many Fox Cities residents have never experienced the full brunt of lake fly season at its best.

Watching the swarms closely, you will quickly see a pattern. No matter how random and restless their numbers may appear, the insects fly in a simple, characteristic pattern, rapidly front to back like a pendulum. This is their mating dance. The sole purpose of the adult lake fly is to pair up and mate.

As they begin to die soon after mating, Lake Winnebago's churning waves begin to pile up massive drifts of lake fly carcasses along shore. In more than 10 years in my small cottage on the lake south of Neenah, I quickly grew to appreciate the value of this rich, all natural fertilizer in my garden.

Drifts of dead insects, a foot thick or more accumulate rapidly along shore. As the peak hatch begins to wane, the lake flies pile up along sidewalks, roadsides and shorelines, sometimes requiring a snow shovel to clear them away.

Many longtime residents of the area still make the trek to the lakeshore annually, five-gallon buckets in tow, to collect this free and beneficial resource.

Robert Zimmer is a freelance outdoors writer based in Appleton and a longtime volunteer at Gordon Bubolz Nature Preserve. He can be reached at This e-mail address is being protected from spambots. You need JavaScript enabled to view it