Mayfly hatch so large it showed up on weather radar...

http://www.cbsnews.com/pictures/mayf...ota-wisconsin/

On the evening of July 20, 2014 mayflies hatched along along the Mississippi river between Minnesota and Wisconsin in such great numbers that they were picked up by radar resembling light rain. the hatch began around 8:35pm. According to the National Weather Service: "this particular emergence was that of the larger black/brown Bilineata species. The radar loop below shows the reflected radar energy (reflectivity) from 8:35 pm to just after midnight. The higher the values (greens to yellows) indicate greater concentrations of flies. Note how the swarm is carried northward over time."

The mayfly emergence on the Mississippi was down for years with pollution, but with the river being cleaned up some, the mayfies are back. They emerge for only a few nights, and then they are gone again until the next year. Some nights the local governments plow them off the bridge decks with snowplows. Driving in several inches of mayflies is dangerous.