Summer of mosquitoes in store for Ottawa, experts say

Weather conditions have created ideal breeding grounds for mosquitoes in the Ottawa area, according to experts.

Weather conditions have created ideal breeding grounds, experts say

A mosquito on someone's skin.
Experts say wet weather has left pools of standing water where mosquitoes can breed safe from predators. (CBC)

Bug experts are predicting a good summer for mosquitoes and a bad one for Ottawa-area residents, as weather conditions create ideal breeding grounds for the unpopular insects.

"The combination of this year being wet, on top of last year's drought, makes it look to me that this year is a good year for mosquitoes," said Davis Beresford, an associate professor of biology at Trent University who specializes in biting insects.

Beresford, who lives east of Peterborough, said he's already experiencing the abundance of mosquitoes whenever he steps out of his country home.

"I haven't seen anything like this in 15 years," said Beresford, who noted that conditions are similar in the Ottawa area.

He explained higher water levels in rivers, streams and ponds leave little puddles as they subside. Once those puddles become isolated from larger bodies of water, the mosquitoes can lay their eggs and thrive free from predators.

Beresford also noted dry weather from last year could mean fewer predators overall to eat the mosquitoes, notably dragonflies.

"There's a lot more mosquitoes, adult mosquitoes, in response to that," he said.

He predicted the worst time — that is, the best time for the mosquitoes — will begin now, taper off in July and August and pick up again in the fall.

Mark Ardis, scientific advisor at GDG Environment, agreed this summer "absolutely" could be a bad one for those trying to fend off the pesky little insects.

"We had a winter with a lot more snow, which translates into more of these vernal pools," he explained, "and because the water table is high that means that any rainfall event will cause pooling."

Someone holds a container of water and puts a dropper in to take a sample.
Researchers look for mosquito larvae in Ottawa in a 2017 file photo. (Jean Delisle/CBC)

He added the more than 40 local species of mosquitoes hatch and grow into adults at different times. Cooler temperatures could lead to springtime species living longer and joining their summertime relatives.

"You're going to get an overlap on different species."

Beresford agreed that's a possibility.

According to Ardis, climate change has also increased the range of some species, with three southern types now emerging in the Ottawa area. None are dangerous as transmitters of disease, however.

Reducing mosquito populations

Ardis works as project manager on a mosquito control project for the Kanata North ward.

The program uses a bacteria-based larvicide that attacks mosquitoes at the standing water where their larvae develop, aiming to reduce mosquito populations by 80 to 90 per cent.

Beresford advised residents to be aware of unknown or tucked away puddles of water that could accumulate around their homes, including in storm drains. 

He said DEET-based insect repellent remains the "gold standard" for warding off mosquitoes, though it's only necessary to put a small amount on the cuffs of clothing.

"A couple drops spread on the way you can put perfume on is ideal," he said. "It's not sunscreen."

Beresford also urged residents to avoid letting mosquitoes ruin their summer.

"The psychological health of being outside just far outweighs the irritation, in my opinion."


Arthur White-Crummey is a reporter at CBC Ottawa. He has previously worked as a reporter in Saskatchewan covering the courts, city hall and the provincial legislature. You can reach him at

With files from Sara Frizzell

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