So many mayflies have emanated from the Mississippi River that they are actually showing up on weather radar.

The National Weather Service in La Crosse captured the insects on radar Sunday as they began leaving the Mississippi River. The cloud of mayflies is so big that it looks like a large raincloud on the radar.

If you look at the radar image above, you might notice a variety of different colors. The yellow in the middle of the picture is actually showing the flies beginning to emerge from the Mississippi River. As the flies begin to swarm and move north, the color on the radar turns green. Finally, the blue color shows the flies dispersing.

According to the National Weather Service website: “The radar detected the flies about 845 pm, emanating from the river (the source) with echo values similar to that of light-moderate rain (35-40 dBZ). With a general south-to-north wind flow above the surface, the mayflies quickly moved north once in the air. As the flies dispersed moving north-northeast, they also gained altitude with some of the echo being detected as far north as Black River Falls and as high as 2500 feet above ground.”

After the mayflies moved away from the river, they started swarming over everything. The National Weather Service website features a number of pictures taken by a variety of people that show the insects covering cars, buildings, and gas pumps. Be sure to check them out!


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