That's a fish fly. It means you're living in a healthy ecosystem

It's an unusual insect with spotted wings and a long tail. You've probably seen one fluttering around the Windsor-Essex area.

It's called a fish fly (sometimes called a shadfly or mayfly) — and you're likely to see lot more come mid-July if you live by a big body of water.

"They have one goal in their adult life — and that's to reproduce," said David Lowenstein, an entomologist at Michigan State University.

"I live about 20 kilometres from Lake St Clair. I'll never see a mayfly unless I go there," he said.

LISTEN: Entomologist David Lowenstein joins Windsor Morning

"People who live right on the lake... can see tens of thousands. Perhaps even millions of mayflies. We're talking significant numbers where they can become a nuisance for people on those brief nights where they're out in big numbers."

If you see a large number of fish flies, there's no need to worry, Lowenstein said. The insects are good news.

"Fish flies are a sign that water quality is really good. Fish flies only emerge in places that have clean water, good oxygen levels and not a lot of nutrient runoff."

He's got some tips for people who would rather limit the number of fish fly encounters they'll have this summer.

"If you know it's going to be a fish fly night, turn your porch lights off because they're attracted to light. That might reduce their numbers a bit. Keep your windows closed if you don't want them coming in."

Fish fly larvae live underwater for more than two years, feeding on algae and plants. In southern Ontario, they only come above water during the summer months to mate — and they die within days. Adult fish flies don't have mouths so they do not eat or bite people.