Horrific writhing masses of gross flies have been spotted in Ontario, but not seeing them in summer would actually be a cause for concern.

Fish flies, also called shadflies or mayflies, swarm Ontario towns in summertime, mobbing cars and sidewalks and are difficult to deter even with a leafblower at full blast.

Though species of mayflies exist worldwide, there's nothing like the specific fear of these aquatic insects coating vehicles and garage doors, which continues to traumatize kids in Ontario.

Here in Southwestern Ontario we have fish flies, they suck! pic.twitter.com/2rr1a2Kmdw

— Rob Earl (@Robdissident) March 21, 2022

Attracted to light in the dark, they typically swarm lakeside towns, and can be especially prominent for a period of a few weeks, usually around June.

#ShadFlies (#MayFlies) are out along the #OttawaRiver this evening.

Not as bad as #Prescott #Ontario where they are as bad as a thick fog . . .

— John Zwicker 🇨🇦 (@JohnZwicker1) July 5, 2022

They're attracted to light in the dark which has even led some people to try to take matters into their own hands by disabling public street lights.

Springtime around Lake Ontario, you come inside covered in mayflies.

— Kirin_A_W🏳️‍⚧️ (@Kirin_Mags) March 12, 2022

Though they cling to absolutely everything in the creepiest way, not seeing them would actually be a cause for concern as they're a sign of healthy lakes. Lots of mayflies are a sign of a healthy ecosystem, and are a protein source for fish and birds. 

They emerge from the lakes and are attracted to lakeside communities mainly by lights. Though they may be annoying and kind of freaky in their large numbers, they're totally harmless, and only have a lifespan of a couple days.