July signals the midpoint of summer, but it also signals the pending invasion of mayflies in the La Crosse area.
When the weather gets warm enough the insects hatch at various spots along the Mississippi River, and for a few weeks they call La Crosse home.
Though they may be a nuisance to some they serve as a valuable member of the ecosystem by providing a gauge of the health and cleanliness of area waterways.
"Mayflies can’t live in highly polluted water," Visitor Services Manager at the Upper Mississippi National Fish and Wildlife Refuge Hallie Rasmussen elaborates, "Pollution takes oxygen out of the water and mayflies can’t live in water that doesn’t have a lot of oxygen in it. So when we see a big mayfly hatch we know the river is doing good, we know that the river quality and the water quality is good," Rasmussen adds.
Mayflies also serve as a food source for many different animals throughout their life cycle.
"When they’re emerging as mayfly nymphs they provide food for those fish, and when they actually emerge out of the water they become food for the birds and the bats. So they are a really large food source for the fish that live in the river and the birds and bats around the area too," Rasmussen explains.
Rasmussen continues to say they have seen multiple hatches already this season, and expect to see smaller hatches in the upcoming days.