Canadians who packed away their insect repellent earlier this year are discovering that mosquito season is far from over, with the persistent pests remaining active across southern and eastern Ontario, Nova Scotia, and other parts of Eastern Canada due to unusually mild autumn temperatures, The Canadian Press reported on November 4, 2026.
El Nino Extends Warm Weather Across Canada
Mosquitoes typically thrive in warm, humid conditions. This year’s strong El Nino phenomenon has extended those environments by keeping temperatures elevated well into the fall. Bill Merryfield, a research scientist at Environment and Climate Change Canada, noted that the weather event usually brings mild late-year conditions to the country, but this cycle is proving exceptional.
This year’s event is truly exceptional because this warming has already exceeded three degrees, which is well above that of any previous event and is expected to go even higher before the usual peak of El Nino in November or December,
Merryfield said, describing Pacific Ocean temperatures linked to the system.
Merryfield added that coast-to-coast warmth may reflect a new normal
for Canadian autumns and winters as global temperatures climb. That would consist of warmer-than-usual temperatures coast to coast,
Merryfield said.
Freezing Temperatures Required to End the Season
The insects continue to bite because autumn weather has failed to trigger the deep freezes needed to curb their populations. Laura Ferguson, an assistant professor in the biology department at Acadia University, studies how ticks and mosquitoes react to environmental shifts.
As long as those mosquitoes haven’t been exposed to temperatures low enough … so cold that it damages them and kills them, then they’ll just stick around,
Ferguson said.
Ferguson explained that overnight conditions must drop below freezing for a sustained period to affect the insects. In Toronto, which recorded mosquito activity into late October, temperatures lingered in the low 20s during the final week of the month and the first week of November. Data from The Weather Network indicates Toronto has not recorded a freezing temperature since May 3.
Researchers Monitor Super El Nino Effects on Winter Mosquito Survival
Researchers are monitoring how the super El Nino will impact mosquito survival over the winter and what population sizes will emerge next spring, especially across Canada’s 80 diverse mosquito species. Researchers are still waiting to see how this year’s super
El Nino will affect mosquito populations next year during warmer seasons. Ferguson noted that a warmer winter could lead to a longer active season next year if spring arrives early or autumn stays warm.
We think we’re seeing some evidence of that,
Ferguson said regarding expectations of a longer active season.
Extended life spans for mosquitoes also heighten concerns regarding disease transmission if unusual weather patterns lead to a boom in their populations, alongside the bites and itching that follows. Marc Avramov, a Carleton University PhD candidate focusing on mosquito-borne illnesses such as West Nile virus and eastern equine encephalitis, said prolonged seasons keep infection risks active.
We stop worrying about that as soon as those colder fall conditions start appearing,
Avramov said. He also warned that sustained mild weather could eventually allow new mosquito species capable of winter adaptation to enter Canada and introduce emerging diseases.
Frequently Asked Questions About Extended Mosquito Activity
How long do mosquitoes typically stay active in Canada?
Mosquito activity usually subsides as soon as regular autumn frost sets in across the country, but unusually strong El Nino conditions have kept insects biting into November in parts of Ontario and Nova Scotia.
What temperature kills adult mosquitoes?
According to Acadia University Laura Ferguson, overnight temperatures must dip below freezing for a consistent period to damage and kill the insects.
Which diseases are researchers watching for in Canada?
Carleton University PhD candidate Marc Avramov monitors mosquito-borne illnesses including West Nile virus and eastern equine encephalitis, noting that prolonged warm seasons extend the window for potential virus transmission.