Mayfly Swarm Wreaks Havoc in Upper Midwest

Mayfly Swarm Wreaks Havoc in Upper Midwest

 

Some Wisconsin and Minnesota Residents Have a Big Cleanup Job; Overwhelmed Car Washes

 

 

By Andrea Gallo in the Wall Street Journal

 

Some Wisconsin and Minnesota residents had a big cleanup job this week after a huge swarm of mayflies emerged from the Mississippi River, blanketing light posts, making roadways slick and lighting up radar screens.

At least one traffic accident was blamed on the infestation that lasted only a few hours Sunday evening while the bugs conducted their frenzied annual mating ritual.

Kwik Trip gas stations in Red Wing, Minn., are still recovering from the mayflies, which flocked to windows, price signs, parking-lot lights and fuel pumps, officials said. Vehicles have been coming nonstop to the Kwik Trip's carwash since Sunday, leaving it reeking of dead bugs.

"The Mississippi River is a great asset but we don't need the smell of it in the carwash," said David Ring, Kwik Trip's community-relations coordinator.

Similar swarms could show up in other regions as water temperatures reach optimal temperatures for different varieties of the bugs. The right temperature triggers the newly winged adult mayflies to emerge en masse from the water. The bugs are usually all dead within a few days.

"Their only function as adults is to disperse and to mate and to reproduce and lay eggs," said Arwin Provonsha, a retired Purdue University faculty member and mayfly expert.

On Sunday night, swirls of green, yellow and blue splashed across radar screens at the National Weather Service in La Crosse, Wis., as though a rainstorm were pelting the region on an otherwise clear night.

Dan Baumgardt, science and operations officer for the weather service in La Crosse, said the swarm's size indicates another one from the same species probably won't happen again in the region this summer.

Drivers on Sunday evening struggled through the bevy of bugs as they coated vehicles' headlights. The layer of mayflies underneath their tires caused a three-car accident on the Highway 63 bridge that connects Hager City, Wis., and Red Wing, officials said. One passenger went to the hospital to be treated for injuries, according to the Pierce County Sheriff's Office.

Mr. Provonsha said the bugs were more intense in decades past. Snowplows had to remove 3-foot-high piles of mayflies from roadways and bridges. But the bugs disappeared once pollution became a problem in water that they liked to inhabit.

The mayflies, which don't bite or sting, returned once the water became less polluted. Indeed, the bugs are considered a good indication of water quality, as well as a friend to fishermen.

"This is peak fly-fishing time because mayflies have landed on the water surface to lay eggs," Mr. Provonsha said.