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Photos taken by a man in Ohio show what appear to be thousands of mayflies. 

The photos were shared on Facebook with the caption: “Think the mayflies are bad in Catawba!”

WJW meteorologist Jenn Harcher said radar detected the mayfly invasion in the western basin at around 1 a.m. Thursday.

The little bugs arrived just recently in the Cleveland area. The bugs don’t bite. In fact,  they’re a sign of a healthy Lake Erie.

According to the Ohio State University, mayflies have been used as a key indicator of environmental health by agencies like the Ohio EPA to assess how Lake Erie and the other Great Lakes are faring over time.

They require very clean water to breed, and they begin their life cycle as larvae in lake sediments. They live there for about one year until the adult mayflies hatch into the swarms that arrive on shore, thanks to the wind, in late spring or early summer.

They’ll only be around for about a week or two.