SOUTH ST. PAUL — When driving across the Mississippi River, it wasn’t a sudden burst of rain that battered the car window — it was a swarm of mayflies.

Ryan Repke, of Woodbury, saw that the mayflies were out and decided to make his annual stop at the Kwik Trip on Concord St. in South St. Paul. The mayflies gather on the corner gas pump, hundreds of winged bugs perching on the pump and surrounding area — and every year, Repke comes by to take a photo of them.

“Not every gas pump is bad; it’s just the corner gas pump that gets like that,” Repke said.

There have been various recent reports of swarms of mayflies in the Twin Cities. The insect spends about 99% of its life as a nymph until all emerge, often at once, during “the hatch” for mating, according to the Minnesota Department of Natural Resources. Adult mayflies live around a month, usually less.

According to Repke, the Interstate 494 bridge is usually bad, as mayflies are attracted to the big street lights. He said it’s been better this year because the lights on the bridge were turned off.

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“It sounded like rain or hail, they were just splattering all over my car,” Repke said of crossing the bridge in previous years.

Mayflies are delicate insects with triangle-shaped wings that stand vertical when they land. They can be found in almost all freshwater habitats, including the Mississippi.

According to the DNR, mayflies are important to the food chain and serve as a good indicator for environmental distress. They are a big source of food for bats, birds and then fish as they die and lie on water surfaces.

Mayflies are also very sensitive insects, easily affected by chemicals and toxins in the water, the DNR said. Although driving through a swarm of mayflies can be an unpleasant experience, it is an indicator of a healthy aquatic ecosystem.