The swarm is so dense, it almost looks like a blizzard instead of a bunch of mayflies.

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The Mayfly

If you aren't familiar with the mayfly it is a type of insect that you typically see around bodies of water.  Have you ever looked out over a lake and seen insects fluttering just off the water?  Typically those are mayflies.  Britannica describes mayflies as:

mayfly, (order Ephemeroptera), any member of a group of insects known for their extremely short life spans and emergence in large numbers in the summer months. Other common names for the winged stages are shadfly, sandfly, dayfly, fishfly, and drake. The aquatic immature stage, called a nymph or naiad, is widely distributed in freshwater, although a few species can tolerate the brackish water of marine estuaries.

How short are mayflies' lifespans?  Well pretty short, only about 1-2 days so you can imagine in that time they need to reproduce pretty quickly, which can at times, lead to swarms.

Unsettling Footage of Mayfly Swarm in Illinois

If you aren't following the All Bugs Go to Kevin group on Facebook, you are missing out on some seriously cool posts.  Recently a user named Phalesia P. posted some photos and videos of a mayfly swarm at a gas station in central Illinois.  The footage is absolutely wild, because if you were to glance quickly the swarm is so dense that it almost looks like a blizzard instead of insects.

Are Mayfly Swarms Something to Worry About?

In short, no.  The reason these bugs swarm is to, well, reproduce.   Entomology Today says that mayflies emerge from the water at the same time with the sole purpose of finding a mate and getting those eggs laid before their short-lived life span is up.   Mayflies are also attracted to light which can explain the swarm at this particular gas station in the video above.  Entomology Today says that while mayflies may seem like a nuisance, it's important to remember that having mayflies around is actually an indicator of clean freshwater, plus they are good for the ecosystem.

So if you see a mayfly swarm, while they may be a bit jarring, they're mostly harmless and will go away eventually.