A thick, massive band of mayflies traveling along the Mississippi River created a swarm so intense it became visible on National Weather Service radars on July 20, 2014.
Communities in the Upper Midwest experience this alarming phenomenon nearly every year. Mayflies are insects with short life spans that typically emerge in the summer. Typically found near areas of fresh water, the insects hatch in large quantities.
La Crosse, located along the Mississippi River, makes for a prime mayfly habitat. In addition, the northern part of the Mississippi River has more moderate temperatures, creating conditions favorable to the insects.
Radar from La Crosse, Wis., shows the throng of imposing bugs Sunday, July 20, 2014.
After hatching, the bugs began latching onto almost anything on Sunday night, blanketing buildings, cars and gas pumps.
Mayflies canvas the surface of a gas pump around Trempealeau, Wis. (Photo/NWS La Crosse)
Mayflies in Hokah, Minn., filled the skies Sunday night. (Photo/Instagram/laginapix)
As the bugs mobbed areas across Wisconsin and Minnesota, visibility became poor and slimy roads made for dangerous driving.
Pockets of mayflies were so dense with bugs that radars were able to pick up on the moving insects. (Photo/NWS La Crosse)
According to the Minneapolis Star Tribune, the pesky insects were the root of a Wisconsin car accident.
One woman was hospitalized late Sunday evening after her car was struck by a vehicle that lost control after slipping on the bug-covered roads.