Sunday wasn't a good day for bug-haters. Fortunately, the swarm didn't decide to stay.
The National Weather Service detects several swarms every year, usually during June to August, so this one was right on schedule. Water and air temperatures have been recently on the cooler side, though, so Sunday's swarm was the first big event for summer this year. The weather service's radar caught the swarm as mayflies were emerging from the Mississippi River before drifting north with the wind.
"Almost every night in the summer, there's some sense on the radar that there's something coming off the river. We don't know what kind of bug it is until we have people calling or saying, ‘Oh my gosh, there's mayflies all in the La Crosse area,' " shared National Weather Service Science and Operations Officer, Dan Baumgardt.
Calling it a hatching may be inaccurate, though. It was simply mayflies emerging to shed exoskeletons and mate, lay eggs and then die, all of which happened within 48 hours. Unless they got killed. Mayflies are attracted to light so it's common for a swarm to be found on bridges and roads, putting them at risk of getting run over.
But mayflies aren't the only ones at risk when they come out. Crushed mayflies are slippery because of the substance covering the eggs of the females, so they can be dangerous to drivers on the road. The swarm last Sunday was the reason for a three-car accident that left two people with injuries.
When it's time to mate, mayflies take to sky. Females lay eggs in water, dying shortly afterward along with the males. Eggs fall to the bottom and can hatch within hours or several weeks after being laid, depending on the species, and the cycle starts anew. After hatching, mayflies spend a year in the mud in the river before spending the last two days of their lives on the surface.
Mayflies are sensitive to pollutants so they are great indicators of water quality in the river, according to U.S. Fish and Wildlife Service biologist Mark Steingraeber.
This means that while Sunday's hatching may be a big inconvenience, it at least points out that the Mississippi River is still in good condition. In the 1920s, mayflies disappeared from an area south of the Twin Cities. They didn't reappear until 1978 when effects of the Clean Water Act started to be felt.
