Why Were Mayflies Covering the Sidewalks of St. Paul this Morning

I saw a video on Facebook this morning of mayflies just COVERING the sidewalks, streets, and windowsills of St. Paul, Minnesota this morning! It was so nasty, I can't imagine having to walk or drive on all of those mayflies. But why were so many mayflies coating St. Paul this morning?

The Mayfly Life Cycle

Mayflies have a very odd lifecycle. The Minnesota DNR says 99% of a mayfly's life is spent as a nymph. Once the mayflies "hatch" they are subimago, which is just a stage in between a nymph and a mature adult mayfly. Then after a few days, they mature, become mayflies, and attack the nearby town. Ok, not really but because of how their "hatching" works, it sure seems like we're under attack.

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Why Were There So Many Mayflies in St. Paul this Morning?

Mayflies seem to synchronize when they "hatch" so that's why, if you're in an area where mayflies would live, you'll see swarms of mayflies and not just a few. The good thing is that adult mayflies have a super short life span. They rarely live longer than a month. The Minnesota DNR says they often live much less than a month. The super gross part about mayflies is that any little bump will usually cause them to "explode" as KARE 11 writes. You could just walk into a mayfly and it'll explode. Yep, nasty. So when they're covering the streets and you're stepping on them, you're shoes are going to be so gross.

A quick side note, even though mayflies are gross to us, they're an important part of the ecosystem. KARE 11 writes that they're food for "invertebrates, amphibians, reptiles, fish, birds and mammals" as nymphs. Adult mayflies are food for birds and bats.

Here's Why Mayflies Are Actually a Good Thing

Mayflies live "in almost all freshwater systems with adequate oxygen levels" according to the Minnesota DNR. Or in other words, they live in healthy bodies of freshwater. Basically, the one good thing that we can say about mayflies is that if you see lots of mayflies, that is usually a good indicator that the nearby body of freshwater is healthy.

Here's the video I saw on Facebook this morning from WCCO's Facebook page.