The short answer
June, for Lyme disease risk in Ontario. That’s when nymph-stage ticks are most active and hardest to detect. October is the second peak, with adult blacklegged ticks.
Two peaks, not one
Ontario’s tick season has a bimodal pattern. The first and more dangerous peak hits in June and July, when nymph-stage blacklegged ticks are most active. Nymphs are about the size of a poppy seed, which makes them very hard to spot on your dog (or yourself). Public Health Ontario reports that roughly 70% of all Lyme disease cases in the province fall between June and August.
The second peak arrives in October and November. This is when adult blacklegged ticks are most active. Adults are larger and easier to find, but they thrive in cool, humid fall weather. They actually struggle in hot, dry summer conditions, so autumn is their sweet spot.
What this means in Oakville
In the Halton Region, blacklegged ticks are well established. They become active whenever temperatures stay above 4 degrees Celsius, which means encounters are possible from early March through late November in a typical year. Those walks along Bronte Creek or through Lions Valley Park carry real tick risk from spring through fall.
Climate change is stretching this window further. The Globe and Mail reported that Canada’s tick seasons are getting longer, and ticks are appearing in areas where they previously weren’t found. Year-round tick prevention is becoming the standard recommendation rather than just seasonal coverage.
If we had to pick one single month: June. The nymphs are tiny, the Lyme transmission risk is at its peak, and most people aren’t thinking about ticks yet because it doesn’t feel like “tick season.” But honestly, if your dog is outside between March and November in Ontario, prevention should be running.
For what to do about ticks in your yard, the best time to treat is mid-May to early June, timed to that nymph peak.
Key takeaways
- June is the worst month for Lyme disease risk in Ontario because of tiny, hard to detect nymph ticks.
- October is the second peak, with adult blacklegged ticks thriving in cool, humid conditions.
- 70% of Ontario Lyme disease cases occur between June and August.
- Blacklegged ticks are active whenever it’s above 4 degrees Celsius. In the Halton area, that’s roughly March through November.
- Climate change is making tick seasons longer across Ontario.
References
- Public Health Ontario. “Let’s Talk About Ticks.” publichealthontario.ca
- Tick Talk Canada. “Seasonality of Ticks.” ticktalkcanada.com
- CBC News. “Fall is Peak Season for Blacklegged Ticks.” cbc.ca
- The Globe and Mail. “Canada’s Tick Seasons Are Getting Worse.” theglobeandmail.com
- Ontario Government. “Protect Yourself From Tick Bites.” news.ontario.ca