Subscribe | UPI Odd Newsletter Subscribe May 17 (UPI) -- A mass hatching of lake flies on a Wisconsin lake was so dense it was picked up by a local TV station's weather radar. The radar image shared by WLUK-TV shows a large green mass over Lake Winnebago that analysts said was a swarm of millions of lake flies hatching. Advertisement Lake flies live only a few days and their larvae serve as a food source for Lake Winnebago's sturgeon, the station said. Local witnesses posted photos to social media showing gigantic swarms of lake flies after they flew out over land. Read More Swarm of migrating butterflies shows up on weather radar Swarm of termites shows up as cloud on weather radar