Were mosquitos bugging you more than usual this summer? Blame the rain

If it felt like mosquitoes were been particularly bad this summer — and hanging around for longer — it might not be in your head.

Some prairie cities saw a mosquito population boom earlier this summer, with some stores in Manitoba, Saskatchewan and Alberta running out of bug spray entirely due to high demand. 

Data collected by the City of Edmonton showed the number of mosquitoes in the city was 15 times higher in July compared to the same time last year.

“While these do not represent record high mosquito numbers for our region, they are a stark contrast to the previous two summer seasons, which can magnify public perception,” said Peter Daly, a biological sciences technologist at the City of Edmonton.

Saskatoon and Winnipeg also saw higher numbers of mosquitoes in July compared to last year, according to data from those cities. 

In southern Ontario, experts say the record rainfall parts of the region saw this summer is likely to blame for the mosquito boom, and why they’re still causing itchy red welts well into September. 

Fiona Hunter, a medical and veterinary entomology professor at Brock University, said this summer, southern Ontario has seen greater numbers of the Ochlerotatus trivittatus species compared to other years. 

Ochlerotatus trivittatus is known as a floodwater mosquito that lays its eggs in low-lying areas filled with water, so the amount of rain southern Ontario has seen this year has created ideal conditions for them, she said. 

“Think about all the rain we’ve had in southern Ontario this year. Soggy fields, low spots in lawns, roadside depressions and other poorly drained areas have repeatedly filled with water,” she said. 

“That creates lots of potential habitat for this particular mosquito, and probably helps explain why we’re seeing so many of them this year.”

The species is known to be a very persistent biter, she said. 

“So I suspect people are simply coming into contact with this species more often this year, which may be part of the reason mosquitoes seem especially bad right now.”

The torrential downpour that pummelled the Greater Toronto Area and many other communities across southern and southwestern Ontario also may have triggered the hatching of a whole bunch of dormant mosquito eggs, said Rosalind Murray, an assistant professor of biology at the University of Toronto. 

“And so we might see a little bit of a blip where we have a bit of a boom, especially in places that have major flood flooding like Toronto,” she told CBC Radio’s Metro Morning. 

WATCH | Wet weather extends mosquito season:

Mosquito season stretches into September after wet summer in Ottawa

Thanks to heavy rainfall this summer, Ottawa is still seeing high numbers of mosquitoes, even though residents are ready to leave them behind. The CBC’s Jenna Legge reports.

Colder temps will drive populations down 

But as soon as the region starts to see colder overnight temperatures, the mosquitoes won’t be an issue anymore.

“They don’t do very well when it’s extremely hot, they can dry out. They also are going to die immediately once it gets cold,” Murray said. 

“Once we start seeing those really cool nighttime temperatures, like below 10 C, we should start to see them peter out. And as soon as we have a frost, they’ll be gone.”

That’s what Alberta has seen happen after a recent cold snap, said Ken Fry, an entomology instructor at Olds College in Olds, Alta. 

Edmonton and Calgary experienced a particularly bad mosquito season earlier this summer, driven by a large amount of rainfall early on in the year. 

But then, he said, mosquito populations “pretty much crashed” due to colder temperatures in recent weeks.  

Daly said Edmonton has already seen numbers drop for the most dominant local mosquito species, Aedes vexans, but added that since the city has had a warm fall so far, “we’ve yet to see quite as precipitous drop in their numbers as some other years. “

Fry said the critters might make a reappearance as temperatures are expected to climb back to 20 C or higher over the next week in the region. 

“But we won’t have the populations, I don’t think, anywhere near close to what central Canada is experiencing.”