The Surprising Reason Minnesota Is Shutting Off Lights on Mississippi River Bridges

The next time you are driving across the Mississippi, take a look around. Some bridges across the land of 10,000 lakes are going dark over the next few weeks, and the reason is bugs. Here's why and where you'll find 'dark' bridges over the next few weeks.

Hatching Season Has Begun

The Minnesota Department of Transportation, or MnDOT, has announced that it will turn off the lights on a few bridges across the Mississippi River because the mayfly hatch has begun.

According to a news release from MnDOT:

Crews will begin turning off the overhead lights over the next few days on the Mississippi River bridges in Red Wing (Highway 63), Wabasha (Highway 60) and Winona (Highway 43). The lights will remain off until the hatching has subsided. Hatching can often last weeks. Mayflies are attracted to lights and having mayflies swarming on the bridges can create dangerous driving conditions.

The bridges will remain dark for a few weeks, as the mayfly hatch happens, and then the lights will go back on.

Mayflies in Minnesota

Mayflies are one of Minnesota's most fascinating, and sometimes frustrating, summer insects. Despite the headaches they can cause for drivers and homeowners, they're actually a sign of healthy lakes and rivers.

Mayflies are aquatic insects that spend most of their lives underwater. Depending on the species, they can live one to three years as nymphs in lakes and rivers before emerging as winged adults.

Sadly, the adults don't last very long. Sometimes just a day, other times as long as a week, as all they are looking to do is reproduce.

So Thick They Need Slow Plows

Some of Minnesota's largest mayfly hatches are so dense they can appear on weather radar. In extreme years, river towns have used snowplows and street sweepers to clear piles of dead mayflies from roads and sidewalks.

For most Minnesotans, mayflies are simply one of the signs that summer has truly arrived, along with mosquitoes, fishing season, and weekends at the lake.

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