Why More Mosquitoes Are Showing Up in Canada

Why More Mosquitoes Are Showing Up in Canada
A female mosquito begins to bite the photographer's hand in a file photo. (Tom Ervin/Getty Images)
Doug Lett

It’s a part of summer in Canada that the tourism brochures don’t always tell you about—mosquitoes.

They can turn an otherwise idyllic summer evening into an indoor retreat.

And unfortunately, the problem might be getting a little worse.

That’s because a few more species of the blood-sucking pests are showing up in Canada—both by increased travel and through winters that tend to be slightly warmer.

“Most of that is likely to be in Ontario, and maybe the Maritimes,” said Sean Prager, an associate professor in the College of Agriculture at the University of Saskatchewan. “It's really the parts that are a little more southern. Because that's how they move in.”

Prager said in any given location, weather will be by far the biggest factor in mosquito populations. In warm weather with lots of rain, they will flourish.

He pointed to mosquito populations in his home community of Saskatoon as an example, which are about five times higher than normal.

“It’s all the rain,” he said. “They lay their eggs in or near water and their larvae are aquatic … and so when you get more rain, you get more pools of water either for them to lay eggs into or for larvae to live in.”

Conversely, he said, in a dry year, numbers will be lower.

But in the background, other factors are also slowly at work.

Because of increased global travel and slightly warmer winters, new species are hitching a ride into Canada. And finding once they get here, they can survive.

One of the better known, said Prager, is a species from Japan called aedes japonicus. It’s mostly limited to southern areas of eastern Canada.

“There’s also … one called aedes albopictus. That’s another invasive mosquito species … and all of these can actually transmit things. So they are problematic,” he said.

“So, it is the case that there are both introduced new species. And then also new species are able to live in places they couldn't live before. And then species that didn't live here, are starting to be able to move north. It's sort of like three things that are all happening,” said Prager.

He said while it is happening slowly, there are definitely more types of mosquitos in the country than there were 20 years ago. And that means when you go outside, you are slightly more likely to be slapping.

“It’s an array of things.”

Prager added that while there are about 80 species of mosquito, only a small percentage will bite people.

“So you don’t see them because they’re not really bothering people. Some of them are pretty rare.”

Some researchers have also suggested that as the pesticide DDT gradually breaks down over time in the environment, it is allowing mosquito populations to rise.

For example, a 2016 study from the University of California–Santa Cruz said the decay of DDT has allowed a rise in mosquito populations in New York, New Jersey, and California.
While DDT was phased out in Canada in the 1970s, studies have shown it can take decades to break down in the environment and breaks down more slowly in cooler climates like in Canada.
As for protecting yourself, Health Canada has a variety of suggestions on its website.

Tips include wearing long pants and sleeves when outside, along with shoes and socks, as well as using an approved insect repellent. In addition, the agency advises wearing loose-fitting clothes with tightly woven materials like nylon, which will help keep mosquitoes away from your skin.

It also recommends simple steps like getting rid of any standing water in your yard like puddles, keeping gutters clean, and storing containers like flowerpots upside down so water cannot collect in them.

“Since mosquitoes lay their eggs in still or standing water, even very small quantities of water can be a problem,” it said.

So while weather is by far the biggest factor in whether mosquitoes will drive you back into the house, there are also background trends that are making a bit of difference as well.

Doug Lett is a former news manager with both Global News and CTV, and has held a variety of other positions in the news industry.