Mayflies descend upon Wisconsin gas station. It’s actually a good sign, experts say

A swarm of mayflies descended upon a Wisconsin gas station — again.

But their annual appearance is actually a good sign, experts say.

Photos obtained by WSAW of the BP gas station in Nekoosa captured what appear to be millions of mayflies crawling and flying over the fuel pumps and parking lot.

Employees told the news outlet that drivers pulled into the gas station and immediately left at the sight.

This isn’t the first time the gas station along the Wisconsin River has been covered in mayflies. In July 2017, the Wisconsin Rapids Tribune reported a “black cloud” of mayflies at the BP and nearby McDonald’s sent customers scrambling inside for cover.

The newspaper obtained video of that year’s swarm.

According to the University of Wisconsin - Milwaukee, mayflies have some of the most “primitive” insect characteristics, and fossils indicate they’ve been around about 300 million years.

But their life span is fleeting. Though mayflies live as larvae in the water for about a year, they emerge as adults for about a day at the most, according to The National Wildlife Federation.

That’s why mounds of dead mayflies appear in the aftermath. At the BP gas station in Nekoosa, employees told WSAW it took them four hours to use a leaf blower and broom to remove the dead insects.

They are harmless to humans, “but some people are allergic to large quantities of mayfly” parts, University of Wisconsin - Milwaukee said.

Because mayflies are sensitive to changes in water quality, a large swarm of them is actually a good sign of healthy rivers and streams free of pollution, according to the University of Wisconsin - Milwaukee.

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