Big bug die-off turns off the lights on some Mississippi bridges
By: Bill Strande, Dana Thiede (KARE11 News)
The cool spring followed by a rapid warm up in southeast Minnesota indicates a heavy, short-lived hatch this year. Oh, joy!
S E E D E D C O N T E N T
June 11, 2026 -- RED WING, Minn. — The lights on some Mississippi River bridges will be temporarily turned off due to an annual summer "circle-of-life" event.
Minnesota Department of Transportation (MnDOT) crews will begin turning off the overhead lights on the bridges in Red Wing (Highway 63), Wabasha (Highway 60), and Winona (Highway 43) over the next few days due to the annual mayfly hatch.
Mayflies are strongly attracted to artificial light. When they hatch, massive swarms can blanket bridge decks, creating slick and hazardous driving surfaces for drivers.
According to MnDOT, the lights will remain off until the hatching has subsided, a process that can often last for weeks.
There are four Mississippi River crossings within MnDOT's District 6 (southeast Minnesota). While three of the bridges will go dark, the Interstate 90 Dresbach bridge near La Crosse, Wisconsin, will keep its lights on. Transportation officials noted that the Dresbach bridge requires continuous lighting due to its interstate highway speeds, high traffic volumes, and the overall complexity of the interchange.
MnDOT has utilized this same light-reduction strategy during the mayfly season in previous years. Hatches can be so large that clouds of the bugs can show up on weather radar. When the insects die (winged adults only live for about a day), mayflies fall to the ground and it can leave a greasy coating on bridges, roads and paved trails. Some hatches or die-offs are so large that road crews have had to call in snowplows to remove the dead bugs.
Here are some facts about the mayfly to amaze and impress your friends:
- Mayflies can be found in almost all freshwater systems with adequate oxygen levels. Some species larvae burrow into the sediment, while others lead a more free-living life.
- Mayfly larvae feed on algae, fungi and decaying plant materials. Adult mayflies do not eat in many cases.
- Mayflies spend about 99% of their lives as nymphs. Those that do reach the adult stage rarely live for more than a month, often far less.
- In his pioneering biology text, History of Animals, Aristotle wrote about an insect called ephemeron, so named for its brief existence. Some modern biologists believe Aristotle was referring to the mayfly, which is famous for its extraordinarily brief adult life cycle.
- The presence of mayflies indicates that the body of water where they hatch is healthy.
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If you happen to be driving between La Crosse, WI, and Red Wing, MN, during the peak mayfly hatch, remember to NOT turn on the windshield wipers. Washer fluid doesn't cut through the greasy goo very well.
And don't wear your good shoes either.
I drove a moving van through the PA mountains once during the Red Monarch migration. As soon as we got out of the mountains we were flagged down by the State Police into a gas station where they power washed the front of the truck while we shopped in the convenience/gift shop.
It's an annual "thing".