Dead Mayflies Pile Up in Welch, Minnesota

The swarm only lasts about 24 hours before the insects die

WELCH, Minn. — Mayfly season has produced an unusual sight in Welch, Minnesota.

Mounds of dead mayflies resembling piles of mulch littered the lock and dam on the Mississippi River.

Every summer, millions of mayflies lay their eggs on the river in Minnesota and Wisconsin, creating a swarm that’s big enough to be seen on weather radar.

The swarm only lasts about 24 hours before the insects die.

The quick infestations can cause serious problems including vehicle crashes.

Once the swarm dies, there is an all-you-can-eat buffet on the surface of lakes and rivers for fish and birds.

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