LA CROSSE, WI (WTAQ) - The annual onslaught of mayflies began this week along the Mississippi River in the La Crosse region.
The National Weather Service caught a swarm of them on radar, as they drifted north in the same pattern as the wind.
The radar showed yellow spots directly over the Mississippi, as the mayflies came out of the water.
Radar maps showed the swarm as being green while drifting north, and then blue as the flies dispersed.
Officials said the large bands of mayflies looked like thunderstorms on the radar.
The initial band showed up last Sunday night. A second and smaller swarm came and went Thursday night.
(Story courtesy of Wheeler News Service)