It's mayfly season in Minnesota, and it's totally gross

But a mayfly hatch is actually a good thing, we swear!
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Mayflies in St. Paul.

Mayflies in St. Paul.

St. Paul Saints broadcaster Andy Helwig, seemingly speaking for the entire city, put it well Wednesday.

"Yo St. Paul – what level of hell have we reached with all these bugs around tonight?" he tweeted. "More importantly, how can we make it stop?

The "bugs" Helwig is referring to are mayflies — small, flying insects with delicate wings and an extremely short adult lifespan that descend upon riverside towns and cities during many summers. It was St. Paul that bore the brunt of the most recent emergence.

(Video above submitted by Patrick Smith)

It is, undeniably, a little gross to be swarmed by countless flying insects. Especially when a snowplow is needed to clear them from the road

But a mayfly hatch (which can occur any time from May through September)  is actually an important, positive sign for the Mississippi River and other freshwater systems.

Mayflies spend most of their life as nymphs or larvae. They burrow into the sediment and feed on algae and bacteria. Eventually they emerge from the water, often in enormous bunches, as the insects we see (and get grossed out by) during the warmest months of the year. The adults will mate, lay their eggs and die within days or weeks.

Mayflies aren't just harmless to humans — they're actually a "a corner stone of the aquatic food web," the DNR says. Many animals, including invertebrates, amphibians, reptiles, fish, birds and mammals, eat the larvae; and birds and bats will happily snack on the adults, including following their death when tens of thousands may fall on to the surface of the water.

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Mayflies are also a sign of water quality. As Friends of the Mississippi River explains, there was serious concern in the 20th century when mayfly hatches stopped altogether. This happened because of pollutants in the water and lower oxygen levels, the MPCA says, which killed mayflies in droves, resulting in a collapse of local populations.

For 30 years, Friends of the Mississippi River says, mayflies were essentially absent from the Twin Cities, returning in 1987 after a concreted effort to minimize pollutants going into the water.

So yes, they're gross. But if you're seeing mayflies, you can have a bit more confidence in the quality of nearby waters.

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