It’s happening again: the skies have darkened with the flapping of tiny wings, the sidewalks are crunchy, and that suspicious smell in the air? Yep—mayflies, or fishflies if you like. If you live along the Mississippi River or any large body of water in Wisconsin, Iowa, or Illinois, welcome to the annual mayfly invasion. It’s weird, it’s wild, and it’s already underway.
What Are Mayflies?
After my recent excursion to the Boundary Waters in Minnesota, our lodge host mentioned that they could see a Mayfly bloom several lakes away, which piqued my curiosity about why these insects often experience such explosive hatch events. Well, mayflies are aquatic insects that spend most of their lives underwater in the river as nymphs.
After a year (sometimes even two), they emerge all at once in a synchronized, short-lived swarm of fluttering wings and romance. Adult mayflies don’t eat or bite; they simply exist solely to mate, lay eggs, and die. Their lifespan out of water? Just 24 to 48 hours. Even crazier, we can see mayfly hatches on radar, which can occur anytime from March through August, depending on flooding, temperatures, and brood cycle.
Why Do They Swarm Everything?
The Mississippi River, all the way from its beginnings in Minnesota to Prairie du Chien, WI, down through Dubuque, IA, and off to Moline, IL, well, it offers the perfect conditions for mayflies. We’ve got some seriously healthy water that offers wide, slow-moving channels.
When the hatch hits, millions of mayflies launch skyward, then dive-bomb anything with a light source. Streetlights, gas stations, porch bulbs; heck, even car headlights become the hottest clubs on the riverfront, even if just for a day.
The results can sometimes be crazy! Bridges get shut down, like in Sabula, Iowa. Parking lots look snowed-in. You’ll sweep off your steps in the morning and do it again by lunch. Which leads us to everyone’s favorite part…
The Smelly Aftermath
As the mayflies complete their mission, they pile up and quickly begin to rot in that good old humid Tri-State heat. The smell? A mix of fish market, old shrimp, and heavy decay. The visuals? Piles of delicate wings and tiny carcasses blanket everything from sidewalks to boat docks. It’s gross, but it’s natural. Still, you’ll have to deal with it.
Survival Tips for Mayfly Season
- Lights Out: Keep exterior lights off at night, or switch to bug-friendly yellow bulbs.
- Cover Your Ride: Park in garages or use a tarp if you’re near the river.
- Gear Up to Clean: Brooms, leaf blowers, or even snow shovels work best for removal.
- Drive Cautiously: Bug-slick roads, especially on bridges, are a real hazard.
- Keep Some Perspective: It may be smelly and messy, but it’s a sign of a healthy river ecosystem, and that’s a GOOD thing!
So whether you’re grabbing coffee in La Crosse, heading to the marina in Muscatine, or just trying to take a stroll along the mighty Mississippi in the port of Dubuque, be prepared: the mayflies have landed (or will soon). And they always bring the whole swarm.
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