OMAHA, Neb. (AP) — Swarms of mayflies have emerged from under water along the Missouri River and are caking windshields on stretches of road between Omaha and Kansas City, forcing drivers to pull over and clean up the mess. Mayflies spend 99% of their lives in water, but they rise when they become winged adults to take part in a mating swarm, the Omaha World-Herald reported . They quickly die after that. But the few days they spend mating are a nuisance.

“They are atrocious. They are horrid,” said Pam Frana, a membership specialist for the Nebraska City Tourism and Commerce Department. “Flooding brought those and stirred them up.” The mayflies are piling on windshields so much that Dominator Fuel in Rock Port, Missouri, sold out of windshield wiper fluid. Other gas stations report they’ve gone through twice the usual amount.

“The windshields are completely covered,” said Chandra McCarty, a cashier at Dominator. Mayflies may be an irritant to humans, but they’re a good source of food for fish and reptiles. The insects are drawn to light and have attracted frogs looking for a late-night feast. At the Rockport gas station, they’ve been seeing 30 to 40 a night. They sit in front of the doors, lured by the bugs. “They try to come up and come in,” McCarty said.

But there is a light at the end of the tunnel. “It used to be so bad people couldn’t see when they were driving,” said Andrew Wagner, who works in Hamburg, Iowa. “It’s getting a lot better since the flooding is going down.”

Urban entomologist Jody Green, an educator with the Lancaster County Extension Service, said mayfly hatches are actually a yearly event. “As an entomologist, I would relish seeing them, but I am sure it might even gross me out, too, if I couldn’t help but step and squish them,” Green said.