Fishflies Pay Annual Visit to the Waterfront

It's that wonderful time of year when people are out enjoying the year's longest days and plenty of boating, fishing and other fun-in-the-sun activities.

To waterfront residents and merchants, it's also time for the annual onshore visit of millions of fishflies, which emerge from the surface of the lake and can be seen by the thousands under streetlamps, at windows and clustered all over brightly lit business establishments.

According to Mike Thomas, a research biologist at the Michigan Department of Natural Resources (DNR) Lake St. Clair Fisheries Research Station, the fishfly season begins in early to mid-June, typically building to a peak in late June to early July and then tapering off.

“There can be some hatch going on all the way into late in July … That's the term people use when the adults are emerging from the lake,” Thomas said. “That's the life stage that people are seeing around streetlights and on their houses, (which is) the adult life stage of the mayfly.

He added that while humans know them for flying around street lights, they are aquatic insects.

“A portion of the insect's life is spent in the lake, burrowing in the bottom sediment of the lake, and they are in that form for up to two years,” he explained. “And then they mature, emerge from the bottom of the lake and come to the surface, and the larval stage transforms into the adult—that's the winged stage.”

Thomas notes the fishfly is actually a type of mayfly called the burrowing mayfly, because they start their life in the bottom of the lake.

“They fly to shore, they hang out on the trees for a 24-hour period, and then they're ready to perform their mating (act)--the next night, they will swarm, do the mating dance and the females will go back out to the lake and lay their eggs and the cycle starts again,” he said. “It's the 24 hours when they are onshore that they're really obvious … they are especially attracted to light. It tends to draw them in, and they can really accumulate and if they don't get cleaned up they can become real smelly.”

Annoying as they can be, fishflies have their upside.

Thomas notes they are a plentiful food source for yellow perch, bass and walleye. And they're a feast for birds.

The annual hatch of adult mayflies is also an indication of a lake's good water quality because the burrowing larvae require water with an adequate oxygen content to survive.

“The birds are just feeding on them like crazy ... it's kind of a neat convergence of the aquatic ecosystem and the terrestrial ecosystem,” he said.

Businesses near the lakeshore cope until the cycle winds down.

Ann Miller, whose son Chip Miller owns , said the flies congregate in large numbers on the doors and windows, making it necessary to clean them off daily.

“It's a mess. You're always stepping on them,” she commented. “You try to keep the lights down as much as possible.”