Where do mosquitoes go in winter in Ontario?

They do not go anywhere — they overwinter in place. Depending on the species, mosquitoes survive an Ontario winter as cold-hardy eggs waiting in dry soil, as mated adult females hibernating in a dormant state called diapause, or as larvae resting at the bottom of unfrozen water. Common shelters for diapausing females include culverts, sewers, hollow logs, animal burrows, sheds, garages, crawl spaces, and basements.

Do mosquitoes die in winter?

Most individual mosquitoes you see in summer do die by fall — all the males and most of the females live only a few weeks. But the species survives. Mated Culex and Anopheles females that entered diapause survive the winter, and Aedes species survive as frost-tolerant eggs. So the population is not wiped out by cold; it simply pauses and waits for spring.

What do mosquitoes do in winter?

They enter diapause, a hormone-driven dormancy similar to hibernation. Triggered by shortening daylight and falling temperatures in fall, diapausing female mosquitoes stop seeking blood, build up fat reserves, slow their metabolism almost to a standstill, and shelter in a protected spot. They produce cryoprotectant compounds like glycerol that act as a natural antifreeze, letting them survive months of cold until spring.

What temperature kills mosquitoes or stops them?

Mosquitoes become sluggish and mostly stop flying once sustained temperatures drop below about 10°C (50°F). Below roughly 15°C their activity, biting, and breeding slow sharply. Cold itself does not reliably kill overwintering mosquitoes, because diapausing females and Aedes eggs are cold-adapted and produce antifreeze compounds. A hard, sustained deep freeze can kill some exposed individuals, but sheltered females and buried eggs routinely survive an Ontario winter.

At what temperature do mosquitoes come back and become active?

Overwintered mosquitoes wake and resume activity when temperatures stay above about 10°C (50°F), with biting and breeding ramping up above 15–20°C. In the GTA that typically means the first mosquitoes reappear in April, with the season building through May and peaking in June and July. Longer spring days and spring meltwater are the cues that end diapause and hatch overwintered eggs.

Where do mosquitoes hide during the winter?

Diapausing female mosquitoes seek dark, humid, frost-protected shelter: storm sewers, culverts, hollow trees and logs, rodent and animal burrows, leaf litter, wood piles, and human structures such as sheds, garages, crawl spaces, unheated basements, and attics. Aedes eggs, by contrast, are not hidden in shelters — they sit glued to the walls of dry containers, tree holes, and low spots that will flood in spring.

Why do mosquitoes come back in May in Ontario?

Two things happen in spring. Overwintered Culex and Anopheles females emerge from shelter, take a first blood meal, and lay the first eggs of the year. At the same time, Aedes eggs that survived winter in dry low spots hatch as soon as snowmelt and spring rain flood them. Together these produce the first generation, which is why mosquitoes seem to appear all at once in late April and May.

Can mosquitoes survive freezing temperatures?

Yes. Overwintering Aedes eggs tolerate freezing and can survive well below 0°C, and diapausing adult females survive subfreezing conditions in sheltered spots thanks to glycerol and other cryoprotectants that lower the temperature at which their tissues freeze. This cold tolerance is exactly why a harsh Ontario winter does not eliminate next summer’s mosquitoes.

Where Do Mosquitoes Go in Winter? (Ontario Explained)

Mosquito group	Overwinters as	Where	What wakes it
Culex (e.g. C. pipiens — West Nile vector)	Mated adult female in diapause	Sewers, culverts, sheds, basements, crawl spaces	Sustained warmth above ~10°C + longer days
Anopheles	Mated adult female in diapause	Hollow logs, animal burrows, structures	Spring warmth; first blood meal
Aedes / floodwater mosquitoes	Cold-hardy eggs (frost-tolerant)	Dry soil, tree holes, container walls, low spots	Spring meltwater and rain flooding the eggs
Coquillettidia / some others	Larvae	Attached to plant roots in unfrozen water	Water warming in late spring
All male mosquitoes	Do not overwinter	—	They die in fall (lifespan ~1–2 weeks)

By Alex and The Mosquito Team

BuzzSkito Mosquito & Tick Control Specialists · Published July 12, 2026

Three Ways Mosquitoes Beat the Cold

People assume the first hard frost ends the mosquito problem for good. It doesn’t. The individual mosquitoes biting you in July are gone by October, but the species has three separate survival strategies that carry it through an Ontario winter and straight into next spring.

1. Hibernating adult females (diapause). This is the strategy of Culex mosquitoes — including Culex pipiens, the main West Nile virus carrier in Ontario — and Anopheles. In late summer, mated females stop laying eggs, gorge on plant sugars to build fat, and slip into a protected shelter. Only mated females do this; every male dies in the fall. These females don’t breed over winter — they simply survive, then lay the first eggs of the year in spring.

2. Cold-hardy eggs. Aedes mosquitoes (including the aggressive daytime-biting floodwater species) take a completely different approach. The female glues her eggs to the dry sides of tree holes, containers, tires, clogged gutters, and low spots in the yard. Those eggs are frost-tolerant — they can survive freezing and months of cold, then hatch the moment spring meltwater or rain floods them. The eggs, not the adults, are what carry the population through winter.

3. Overwintering larvae. A few species ride out winter as larvae, dormant at the bottom of ponds and marshes or attached to plant roots in water that never fully freezes. They resume development once the water warms in late spring.

Diapause: A Mosquito’s Version of Hibernation

Diapause is not just “getting sleepy in the cold.” It is a programmed dormancy triggered mainly by shortening daylight in late summer and early fall, reinforced by dropping temperatures. Once a female mosquito reads those cues, her body changes: she stops seeking blood, her ovaries pause, her metabolism slows to a crawl, and she stockpiles fat to live on for months.

Crucially, diapausing mosquitoes also produce cryoprotectants — compounds such as glycerol that behave like a natural antifreeze, lowering the temperature at which their tissues would freeze and rupture. This is why a cold snap that would kill an active summer mosquito doesn’t reliably kill a hibernating one. The female is chemically and behaviourally built to survive subfreezing conditions in her sheltered spot.

What Temperature Stops — and Wakes — Mosquitoes

Mosquito activity is governed by temperature more than by the calendar. Here are the practical thresholds for the GTA:

Temperature	What mosquitoes do
Below ~10°C (50°F)	Flight mostly stops; adults become sluggish. Diapause conditions.
10–15°C	Overwintered females stir; limited activity, little biting.
15–20°C	Biting and egg-laying begin; first generation gets going.
Above 20°C	Peak activity and fast breeding — the summer swarm.

Notice what’s missing: a “kill” temperature. Cold pauses mosquitoes; it doesn’t dependably kill the overwintering ones. Sheltered diapausing females and buried Aedes eggs are cold-adapted, so even a brutal Ontario winter leaves plenty of survivors to restart the population. The takeaway isn’t “wait for winter to solve it” — it’s that the reset button never really gets pressed.

Why Mosquitoes Come Back in May

The spring rebound happens on two fronts at once. First, the overwintered Culex and Anopheles females leave their shelters as the weather warms, take a first blood meal, and lay the season’s first batch of eggs. Second, the frost-hardy Aedes eggs that spent winter glued to dry surfaces hatch as soon as snowmelt and spring rain flood the low spots they were laid in.

Both waves land within a few weeks of each other, which is why mosquitoes seem to appear “out of nowhere” in late April and May. From there it compounds fast: each female lays 100–300 eggs, a generation completes in as little as 8–10 days in warm weather, and populations climb steadily toward the June–July peak. For the full GTA timeline, see our guide on when mosquito season starts in the GTA.

What Winter Survival Means for Spring Yard Prep

If mosquitoes overwinter right in your yard, the smartest thing you can do is deny that first generation the water it needs — before it ever hatches. A little work in April pays off for the entire season:

Drain standing water early. Snowmelt pools, clogged gutters, tarps, buckets, planters, tires, and toys are where overwintered Aedes eggs hatch and where the first Culex females lay. Empty or cover them before the yard warms up. Our list of hidden mosquito breeding spots shows the ones most people miss.
Clear leaf litter and yard debris. Damp leaf piles, wood stacks, and overgrown edges give diapausing females somewhere to shelter and hold the humidity mosquitoes love.
Refresh or flush water features weekly. Bird baths, plant saucers, and unfiltered ponds turn into nurseries the moment the water warms.
Book barrier treatment early. Starting a professional mosquito control program at the start of the season targets the first emerging generation, so populations never get the running start that makes July miserable.

You can’t change the fact that mosquitoes survive winter — but you can decide how big a head start they get in spring. The homeowners who prep in April, not July, are the ones enjoying their yards during peak season.

Where Do Mosquitoes Go in Winter? (Ontario Explained)