A perfect swarm: Wet spring, no frost make ideal conditions for mosquito boom

If you feel like you've been shooing, swatting and scratching more often this spring, you aren't crazy.

According to one expert, the Ottawa area has seen the perfect conditions for an absolute onslaught of mosquitoes. 

Winter in the region was both warmer and drier than usual, with Ottawa seeing 102.5 centimetres of snow between December 2023 and March 2024 — less than one-third of the levels during the same period one year earlier.

Normally, those dry conditions would lead to fewer mosquitoes, since there would be no standing water for breeding. But then the skies opened, with 166.1 millimetres of precipitation falling between April and May, similar weather to the year before. 

That filled up ponds and created puddles, the perfect places for the insects to breed, according to David Beresford, an associate professor at Trent University's biology department and school of the environment.

When you add in the lack of a spring frost that typically kills off a bunch of bugs and a quick surge in temperatures, the mosquito population was bound to boom, Beresford said. 

"In warm weather, they grow fast. In cooler weather, they grow slowly," he said, adding it only takes a small puddle for them to thrive.

Even a watery footprint left in the grass will do, he added.

"That's brilliant mosquito habitat because there's nothing in there that's going to eat them."

As long as puddles stick around and stay warm for a week or so, that's enough time for mosquitoes to go from egg to adult, Beresford said.

Since an individual mosquito's chance of survival is very low, their strategy is to lay hordes of eggs — and they can do that in spades when conditions are on their side. 

'Even the dogs can't stand it'

Living in the rural village of Clarence Creek in Clarence-Rockland, Ont., Alexis Brisson is used to having mosquitoes around.

But the conditions locally are the worst he's ever seen.

"You can't go outside without getting absolutely swarmed — us and our animals, actually. Even the dogs can't stand it," he said.

"For the first time this year, we bit the bullet and we decided to hire a company to come and spray the property. Because we literally could not see any other solution."

Brisson said that's helped, but he and his girlfriend still need to spray themselves and use other equipment to keep the bugs at bay. 

'Quite tenacious'

On the trail networks around Ottawa, it's no better. 

"I would say they're bad this year," said Anita Grace, a member of the Rideau Trail Association 

"I'm used to hiking in all weathers and [with] all bugs, so I wear long sleeves and pants and put on bug spray, wear bug jackets. But even with all that, they seem to be quite tenacious this year."

Grace said she's also had worse reactions to bites this year, something she thinks might be attributed to a different type of mosquito being more common in the Ottawa area.

Beresford said different types of mosquitoes can travel to other areas to find food. For instance, if you spot larger ones with stripes, they could be from the genus Aedes — and they pack a mean bite, he said. 

"They could be from some place that's a couple kilometres away. They're happy to make the trip to get blood in the evening or in the morning and go back to lay eggs," he said. 

Beresford said the region might get some relief if the summer heats up and the rain stops, although that comes with the risk of drought.