Mayfly swarm so massive, it shows up on radar

ByMatt Deicke WLS logo
Tuesday, July 29, 2014

Over the course of the past week, residents surrounding the Upper Mississippi River Valley are being afflicted by massive swarms of mayflies of Old Testament proportions. The mayflies hatched all at once, in such a vast cloud, it was captured on radar by the National Weather Service at around 8:45 pm on July 20th.

National Weather Service / NOAA

And again, four days later.

National Weather Service / NOAA

These are not baby mayflies, but full blown, one-inch long adults. The 'hatch' refers to the nymphal mayflies hatching out of their final molt, or cocoon, and emerging as adults. Think of it as graduation day, and these barely legal young guns are out for summer. Often, an entire population will hatch at once, blacking out the skies in a massive swarm cloud for a few days of the year. And because they are attracted to light, you can bet to find the swarms in just about every part of local civilization.

Mayflies may congregate onto roads and lit surfaces in large piles, even up to 2 feet high. Reportedly, roads in the nearby area are coated in crushed bug slime, and even one three-vehicle accident in Wisconsin has been attributed to the insect epidemic.

Residents of the afflicted areas posted photos on Reddit:

"You can't even get to your vehicle without a Mayfly massacre occurring."


Near La Crosse, WI.

TrynnaFindaBalance / Reddit

Thankfully, mayfly adults don't live for longer than about a day.

However, despite the fact that adults live such a short lifespan, the preceding nymphal lifecycle of a mayfly can take up to two years before maturity. Once they are adults, their digestive system and mouth parts are merely vestigial, and useless, so its last remaining day of life is purely spent on copulating and reproducing before their immediate death. Watch this video below of a mayfly giving birth, and its eggs hatching in under a minute.

Mayfly eggs hatching a minute after being laid.

So what's for lunch today? Let us know in comments below.