You can find all sorts of exotic and terrifying-looking creepy-crawlies in Ontario, but sometimes even just your common backyard varieties of bugs are enough to tap into that subconscious fear of insects shared by many.

For anyone living near Ontario's Great Lakes, there's a good chance you're familiar with the annual midge season. However, that's not the only winged insect that you can find in masses, littering local shores with its dead and dying.

Mayflies, or ephemeroptera, are often known as "shadflies" or "fishflies" here in Canada, but regardless of what you call them, wriggling masses of these flying insects are probably congregating around a body of water near you.

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One Reddit user from Southern Ontario came across what they described as a "mass grave" of these insects, and took to the internet for an explanation.

"On a walk last night I found 100s of thousands of these flying things that were dead or dying," the user wrote. "Who are they and what could cause such a mass grave? It was near a street light and river. I assume they flocked to the light."

What lead to this mass slaughter of these poor guys?!?!
byu/randomacceptablename inwhatsthisbug

Despite the name, mayflies hatch from spring to fall. Their massive numbers have proven both a tourist draw and a hindrance.

Swarms of mayflies have already caused plenty of discomfort in the Great Lakes region this season, including an incident captured at the Cedar Point amusement Park across Lake Erie in Ohio back in June, where rollercoaster riders had to contend with swarms of the insects.

@vor3807 #insane #may #flies #cedarpoint #fypage #fy #fly @NBC @FOX Weather @NewsNation ♬ original sound - Vor

While the mass of bugs is unsettling to say the least, one user explained that mayflies are an indicator species, and the presence of many mayflies — even dead and dying ones — is a "very good sign" and an indication of healthy water quality.

"Their nymphs can only survive in clear, healthy water," the commenter explained. "They have fine, feathery gills that get easily choked by sediment. So, while the mass swarms and die-offs may be a nuisance to humans in the short-term, ultimately, it's good they're doing so well."