Return of massive swarms of insects to Ontario and all sorts of creepy, strange, and terrifying reptiles can be found in Ontario.

But sometimes, common backyard insect species are enough to take advantage of this unconscious fear of insects that many share.

For anyone living near the Great Lakes in Ontario, there’s a good chance you’re familiar with the annual fly season.

However, this is not the only winged insect you can find in swarms, as local beaches are scattered with their dead and dying.

The mayfly, or ephemeroptera, is often referred to as “shadflies” or “fishflies” here in Canada, but regardless of what you call it, it's likely shimmering clusters of these flying insects will gather around a body of water near you.

A Reddit user from Southern Ontario encountered what they described as a “mass grave” for these insects and took to the internet for an explanation.

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

Despite the name, the flies hatch from spring to fall. Their huge numbers have proven to be a tourist attraction and an obstacle.

Swarms of mayflies have already caused quite a disturbance in the Great Lakes region this season, including an incident captured at Cedar Point amusement park across the lake in Ohio in June, where roller coaster riders had to deal with swarms of insects.

While the insect mass is concerning at the very least, one user clarified that mayflies are an indicator species, and the presence of many mayflies—even the dead and dying—is a “very good sign” and an indicator of healthy water quality.

The commentator explained, “Their nymphs can only survive in clear, healthy water.”