Lake Flies

Lakefly Swarm

Like an invading air force over Menominee Park, Oshkosh, Lake Flies have recently risen from Lake Winnebago and take to the skies solely of the purpose of mating. 

The Lake Flies (Chironomus plumosus) of Lake Winnebago are an amazing sight.  When they hatch they can hatch by the billions releasing a swarm of insects that can be visible on weather radar.   These swarms can be a real pain for those living on or near the lake, as tens of thousands rest on trees, shrubs and grasses.

Lake flies off the larger Lake Winnebago System have one major hatch in spring, and another on a much smaller scale in summer.  Although small in comparison to the spring hatch it can still be quite impressive.

Luckily the lake flies don’t bite.  The have only one mission in their adult life, and that is to reproduce, there is no time for feeding.  In a few days the new emerged lake fly adult is dead.  During the short time of the hatch resident and migrating birds will feast on the flies.  For many it is a welcome meal that will help the birds recover from migration, or to continue their journey north.  Birds from fly catches, swallows, robins, gulls, crows and geese will eat them.

Under the water fish will eat the adults as they emerge, lay eggs and die, but the larvae are eaten year round.  The larva from a large portion of the diet of Lake Sturgeon (Acipenser fulvescens).   The lakes and river of the Fox/Wolf/Winnebago System have the largest population of these fish in the world, and one of the greatest sturgeon fisheries of any species.  The fish can grow to an excesses of 200 lbs and live for a century.  The lake sturgeon will spend much of their long life on the bottom sucking up the larvae with their long tube-like mouths, a sort of aquatic vacuum cleaner.  Many other important game fish eat the larva too.

lakeflies on radar

A swarm of lakeflies that have risen out of Lake Winnebago are clearly visible on this radar image.

Local legend say the lake flies were imported by a Russian professor  at the university (or Russian of some other profession)  to feed the sturgeon, and that is not true.  Sediment cores show the flies have been here for hundreds of years.  These sediments are packed with the hard heads of the larva which do not decay quickly.   The legend probably originates because incredibly numerous animals and plants are often non-native invasive, but in the case of the lake fly it is as native as the lake itself.


Lake Winnebago Lake Fly

Close up of one of the Lake Flies (Chironomus plumosus) of Lake Winnebago


Lake Flies belong to insect family Chironomidae and are also known as chironomids or non-biting midges.  Lake Fly is a generic term that can refer to any number of other chironomids, or insects in other families.

This is a short introduction to the Lake Winnebago Lake Fly, more to come soon.

8 Responses to Lake Flies

  1. Winston says:

    Can anyone tell me how far inland the lake flies come as I am looking to move near the lake. Thanks

    • Andrew Sabai says:

      Lake Flies typically only show up in numbers a few blocks from the lake, but that depends on the wind and what you think is too many lakeflies. I live about a mile from the lake and we might see a dozen caught in spiderwebs, or crawling around during the mating season.

  2. Valerie Goehler says:

    I believe the university professor story would be about Dr. Shapiro from UW Oshkosh. Years ago he studied the lake flies, but of course didn’t help with hatching them in the lake. I believe he was looking to see if Lake Winnebago was the only lake where these flies would survive, as you don’t find them on closely located Lake Butte Des Morts.

  3. Dale says:

    How long does a hatch typically last.

  4. Greg says:

    Very interesting! Growing up on the lake I didn’t realize all that. Do you know where the sediment core samples were taken from? I’m a local that was told that a professor brought them from Africa to feed the fish and they got out of hand.

    • Andrew Sabai says:

      They have taken cores all around the lake for many studies over the years. I wonder how some of these stories get started, perhaps it is like the children’s game telephone. It starts out as fact, but gets a little changed every time time story is repeated.

  5. Frank Lawatsch says:

    Are Winnebago Lake Flies the same as mayflies that hatch in many Minnesota lakes?

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