When does mosquito season start in the GTA?

Mosquito season in the Greater Toronto Area typically begins in late April when temperatures consistently exceed 10°C. Activity ramps up through May and reaches its peak in June and July. The season runs through September, with activity declining as temperatures drop in early fall.

What is the worst month for mosquitoes in Ontario?

June and July are the worst months for mosquitoes in Ontario and the GTA. Warm nights, frequent afternoon thunderstorms, and mature vegetation combine to create peak breeding conditions during these months. August remains highly active, with activity declining through September.

When is the best time to start mosquito treatment in the GTA?

The best time to start mosquito treatment in the GTA is the first week of May — before populations peak. Acting early catches the first generation of adults before they breed, reducing the overall population through the season. Waiting until mosquitoes become noticeably bothersome (typically mid-June) means populations have already been building for weeks.

When does mosquito season end in Ontario?

Mosquito season in Ontario effectively ends in late September to early October, when temperatures drop consistently below 10°C. Activity declines noticeably after Labour Day, though biting mosquitoes remain active through most of September. Homeowners who stop treatment in August often experience resurgent mosquito pressure through September.

How many mosquito treatments do I need per season in the GTA?

For continuous protection through the GTA mosquito season, 5 treatments spaced 21–28 days apart is the recommended schedule: early May, late May/early June, late June/early July, late July/early August, and late August/early September. Properties near ravines, rivers, or wetlands benefit most from the full 5-treatment program.

When do mosquitoes go away in Ontario?

Mosquitoes go away in Ontario in late September to early October, once overnight temperatures consistently drop below 10°C. Activity fades noticeably after Labour Day, but biting mosquitoes can linger through most of September, especially in mild falls or near ravines and wetlands. A hard frost ends adult activity for the year, though eggs overwinter in the soil and hatch again the following spring.

When do mosquitoes come out in Ontario?

Mosquitoes come out in Ontario in late April, when daytime temperatures start holding above 10°C, and populations build quickly through May. Overwintering eggs laid the previous fall hatch as soon as conditions warm and moisten, so a warm spring can bring the first mosquitoes out as early as the third week of April in the GTA.

What temperature do mosquitoes come out at?

Mosquitoes come out once air temperatures consistently reach about 10°C. Below that threshold, adults cannot fly effectively and larval development in the water nearly stalls. They become most active in warm, humid conditions above 20°C, which is why June and July are peak months in the GTA. A late-spring cold snap can temporarily push them back into sheltered resting spots.

Do mosquitoes come out in the rain?

Mosquitoes generally shelter during heavy rain because raindrops can knock them out of the air, but they come back out in force once it stops. Rain actually fuels mosquito season: every puddle, clogged gutter, and water-filled container becomes a breeding site, so populations often spike 7–10 days after a wet stretch. Warm, humid, still evenings right after rain are among the worst for biting.

Where do mosquitoes go during the day?

During the day mosquitoes rest in cool, shaded, humid spots to avoid drying out — tall grass, dense shrubs, under decks, in leaf litter, ivy, and thick vegetation around your yard. Most GTA mosquitoes feed at dawn and dusk, so they stay hidden through the midday heat and emerge to bite in the evening. This is exactly why professional barrier sprays target shaded resting vegetation rather than open lawn.

Mosquito Season Ontario: When They Come Out 2026

By Alex and The Mosquito Team

BuzzSkito Mosquito & Tick Control Specialists · Published March 20, 2026 · Updated July 12, 2026

Quick Answer

GTA mosquito season starts in late April, once daytime temperatures hold above 10°C, and biting peaks in June and July. The single best window to book your first treatment is the first week of May — before the first generation of adults breeds.

The first GTA mosquitoes emerge in late April, when temperatures consistently exceed 10°C.
Peak mosquito activity runs June through July, with heavy pressure continuing through August.
The season ends in late September to early October, once overnight temperatures drop below 10°C.
Below 10°C, adult mosquitoes cannot fly effectively and larval development nearly stalls.
Five treatments spaced 21–28 days apart, from early May to early September, provide continuous season coverage.
Populations often spike 7–10 days after a wet stretch, as every puddle becomes a breeding site.

— BuzzSkito, GTA mosquito & tick control · 150+ five-star Google reviews

This guide covers the exact mosquito season timeline for each GTA city, what temperature triggers mosquito activity, and how to time your protection. Part of our Ultimate Backyard Mosquito Control Guide. Want early-season coverage locked in? Book your first treatment with a free yard assessment — or see what GTA mosquito control costs first.

The Short Answer: GTA Mosquito Season 2026

First mosquitoes: Late April (when temperatures consistently exceed 10°C)
Season ramps up: Mid-May
Peak activity: June through July
Active season ends: Late September / early October
Best time to start treatment: First week of May

The Temperature Trigger: 10°C Is the Key Number

Mosquitoes become active when air temperatures consistently reach or exceed 10°C. Below this threshold, adult mosquitoes cannot fly effectively and larval development slows dramatically. This temperature threshold is why GTA mosquito season is compressed compared to warmer climates — but also why it can start surprisingly early in a warm spring.

Overwintering mosquito eggs, laid in moist soil the previous fall, begin to hatch as soon as temperatures and moisture conditions are right. In a warm spring, this can happen as early as the third week of April in the GTA.

The other end of the scale is what closes the season. Adults go dormant below 10°C and a sustained hard frost near -2°C kills the ones still flying — the full temperature table shows where each threshold sits and why the population still rebounds every May.

Month-by-Month Mosquito Activity in the GTA

April (Late): Season Begins

The first mosquitoes of the season emerge. Activity is low and limited to warm, sheltered areas. Homeowners near the Credit River, Humber River, or other waterways may notice the first mosquitoes earlier than others.

May: Rapid Population Growth

Mosquito populations grow quickly through May as temperatures warm and rainfall provides fresh breeding water. This is the ideal time to book your first treatment — acting before populations peak gives maximum protection.

June–July: Peak Season

June and July are the most active mosquito months in the GTA. Warm nights, frequent afternoon thunderstorms, and mature vegetation all contribute to peak breeding conditions. Without treatment, properties near water features can become essentially unusable in the evenings.

August: Sustained Pressure

Activity remains high through August. Rainfall events in late summer can spike populations even on properties that seemed well-protected earlier in the season.

September: Gradual Decline

Mosquito activity declines as temperatures drop, but biting continues through most of the month. Homeowners who stop treatment in August often regret it by Labour Day.

What to Do While You Wait for the Season (and Your First Treatment)

Booked your first barrier spray for early May but still getting bitten on a warm April evening? Or waiting for the truck between treatments? A portable repeller buys you a comfortable patio in the meantime. The best-known option in Canada is the Thermacell — a battery or fuel-powered device that creates a roughly 20 ft (15 sq m) zone of protection around a chair or table without sprays, sticky lotions, or citronella smoke.

It won’t protect an entire yard the way a professional barrier treatment does, but for a single seating area it’s the fastest same-day fix while the season warms up.

As an Amazon Associate, BuzzSkito earns from qualifying purchases. BuzzSkito only points to products we would genuinely use or recommend, at no extra cost to you.

As an Amazon Associate, BuzzSkito earns from qualifying purchases. Price shown on Amazon.ca, at no extra cost to you.

🏆 Our Top Pick for the Wait

8.5/10· BuzzSkito rating

Thermacell Mosquito Repeller

The fastest same-day fix while you wait for the season to warm up or for the truck between treatments. It creates a roughly 20 ft zone of protection around a chair or table — no sprays, sticky lotions, or citronella smoke. It won't protect a whole yard the way a professional barrier treatment does, but for a single seating area it's the most reliable portable option in Canada.

Pros

Creates a ~20 ft repellent zone in minutes
No sprays, lotions, or smoke
Portable — move it chair to chair

Cons

Covers one seating area, not a whole yard
Refill mats and fuel are consumables

Check price on Amazon.ca

Check Thermacell mosquito repeller prices on Amazon.ca →

Deciding between a Thermacell and other gadgets? Read our full breakdown of the best mosquito repellent devices in Canada, and if you’ve settled on the brand, our guide to where to buy a Thermacell in Canada covers models and pricing.

City-by-City: Which GTA Areas Have the Worst Mosquito Season?

Not all GTA locations experience the same mosquito pressure. The most heavily affected areas tend to be:

Mississauga — Credit River corridor, Rattray Marsh, and Credit Valley neighbourhoods experience the earliest and most intense activity
Toronto — Ravine-adjacent properties in Don Valley, Humber Valley, and High Park neighbourhoods
Hamilton — Cootes Paradise and escarpment areas see early and sustained activity
Oakville — Glen Abbey and Joshua Creek ravines, and the Bronte Creek corridor
Brampton — the Etobicoke Creek and Heart Lake corridors hold the shaded, damp cover mosquitoes rest in through the day
Markham — Rouge River valley and Milner Creek properties back onto the same kind of ravine habitat

The Case for Starting Treatment Early

The most common mistake GTA homeowners make is waiting too long to start mosquito treatment. By the time mosquitoes become noticeably bothersome (typically mid-June), populations have already been building for weeks. Starting treatment in the first week of May catches populations before they peak, giving barrier spray the best chance to reduce activity through the entire season.

The same timing logic applies to the standing water on your property. A BTI larvicide such as Mosquito Bits kills mosquito larvae in rain barrels, birdbaths, and clogged gutters before that first generation ever matures into biting adults — far easier than chasing those same mosquitoes around the yard in July.

Recommended 2026 GTA Mosquito Treatment Schedule

Treatment	Timing	Why
Treatment 1	Early May	Catch first-generation adults before populations build
Treatment 2	Late May / Early June	Bridge into peak season
Treatment 3	Late June / Early July	Cover peak activity period
Treatment 4	Late July / Early August	Maintain coverage through late summer
Treatment 5	Late August / Early September	Extend protection through September activity

When Does Mosquito Season Start in the GTA? (2026 Guide)