Mosquitoes emerge 'all at once' in Ottawa after spring melt, warm spell

CBC

18-05-2025

A heavy snow melt and a snap warm spell have caused mosquitoes to emerge "all at once" in Ottawa, according to an expert in biting insects.
David Beresford, a professor of biology at Trent University, said a steady supply of melting snow in eastern Ontario has left behind plenty of standing and still water — the preferred place for mosquitoes to lay their eggs.
The young start growing as larvae in the water, he said, but recent warm temperatures would have pushed them to emerge.
"It's different when we get that warm weather. It feels like they've come on all at once," Beresford said. "You'll go along and it'll be nothing, and then suddenly there's clouds of mosquitoes."
The current crop of mosquitoes matured in a "big pulse," he said, and now are wasting no time finding something to eat.
"When the females emerge — now they want blood," he said. "They're not going to hang around waiting for this. They're going to be looking for people to bite as soon as they get out of that water."
Numbers difficult to predict
Last May, Beresford said the Ottawa area had the perfect conditions for an "absolute onslaught" of mosquitoes.
Looking back, however, reality didn't end up meeting expectations, he said. A dry period meant mosquitoes had "pretty well disappeared" by mid-summer, he said.
"It's hard to know what's going to happen after that first pulse in the spring," he said.
As well as drought, overly wet conditions can threaten mosquito populations, Beresford said, as overflowing ponds may introduce predators like beetles and other insects into the puddles where mosquitos have laid eggs.
Regardless of the trends, the number of mosquitoes may vary significantly between neighbourhoods, with potential breeding grounds ranging from clogged eavestroughs to waterlogged holes in trees, Beresford said.
Climate change could shift season
Climate change could alter both the length and makeup of Canada's mosquito season, according to Robert Anderson, a research entomologist with the Canadian Museum of Nature.
Canada is currently home to 82 species of mosquito, Anderson said, but a warming climate could draw new species north as well as encourage an earlier emergence for those already here.
As for this spring, Anderson said he hasn't noticed anything especially unusual about the mosquitoes.
"It's just a part of living in Canada," he said.