Ticks in Ontario

Written by Phillip George · Last updated: July 24, 2026

Ticks in Ontario: what to actually watch for

Ontario is the province where blacklegged ticks have spread the fastest, and it now carries the largest reported burden of Lyme disease in Canada. This guide focuses on what that means on the ground: which ticks you are likely to meet, where and when the risk is highest, and exactly what to do if one bites you. For live maps and official case counts, use the Ontario links near the bottom of the page.

Key takeaways for Ontario

• One tick drives almost all disease risk: the blacklegged tick (Ixodes scapularis), also called the deer tick, transmits Lyme disease and three other reportable illnesses in Ontario.
• Risk areas keep expanding: Public Health Ontario has added new "established risk areas" every year since 2015. In 2025 alone, 13 new areas were added across 6 of Ontario's 34 public health units.
• Timing matters as much as place: the tiny summer nymphs (May–July) cause the most human infections because they are so easy to miss before they have fed.

Which ticks you'll actually encounter

Ontario is home to several tick species, but for practical purposes two matter most:

• Blacklegged / deer tick (Ixodes scapularis) — the only widespread Ontario tick that regularly transmits disease to people. Adults are reddish-brown with a solid dark shield; unfed nymphs are about the size of a poppy seed. This is the species behind Ontario's Lyme, anaplasmosis, babesiosis, and Powassan cases.
• American dog tick (Dermacentor variabilis) — common in meadows and along trail edges, larger, and brown with pale silvery mottling on its shield. It is a nuisance biter but is not a meaningful Lyme vector in Ontario.

Other species, including the lone star tick, occasionally turn up on Ontario hosts — usually carried in by migratory birds — but are not considered established across the province. If you are unsure what you found, submit a photo to eTick (below) rather than guessing.

Sources: Public Health Ontario — Lyme disease; Ontario.ca — Tick-borne diseases.

Where risk is highest

Blacklegged ticks are most established across southern and eastern Ontario, and the map keeps growing. Long-standing hotspots include the eastern Ontario corridor (Ottawa, Kingston, the Thousand Islands and the Rideau Valley), Prince Edward County, the north shore of Lake Erie (Long Point, Turkey Point, Rondeau), the Niagara region, and pockets in the northwest near the Manitoba border. Because "established risk area" boundaries are redrawn each year, it is safest to treat all of southern Ontario as potential tick habitat and check the current Public Health Ontario map for your specific area.

When ticks are active

Blacklegged ticks in Ontario can be active any time the ground is not frozen and temperatures rise above roughly 4 °C — which increasingly includes mild stretches in late winter and early spring.

• Spring and fall: adult ticks quest for larger hosts. Adults are big enough to notice on skin or clothing.
• Late spring to midsummer (May–July): nymphs are active. These poppy-seed-sized ticks cause most human Lyme cases precisely because they are so easily overlooked.

Tick-borne diseases reported in Ontario

Ontario lists four tick-borne illnesses as Diseases of Public Health Significance, all spread by the blacklegged tick:

• Lyme disease — by far the most common; watch for an expanding rash and flu-like symptoms.
• Anaplasmosis — increasing in Ontario; causes fever, headache, and muscle aches.
• Babesiosis — a malaria-like parasite of red blood cells; more serious for people who are immunocompromised or have no spleen.
• Powassan virus infection — rare but potentially severe, with no specific antiviral treatment.

For symptoms and timelines, see our tick-borne disease symptoms in humans guide.

Source: Ontario.ca — Tick-borne diseases.

Found a tick in Ontario? Do this

1. Remove it promptly with fine-tipped tweezers — follow our step-by-step tick removal guide. Avoid matches, nail polish, or petroleum jelly.
2. Identify it for free: upload clear photos to eTick.ca, a national platform run by Bishop's University with Public Health Agency of Canada funding. A regional expert usually replies within 24 hours with the species and health guidance.
3. Record the date and location of the bite, and watch for symptoms over the following days to weeks.
4. Contact a healthcare provider or your local public health unit if you develop a rash, fever, or other symptoms — and ask about post-exposure options if the tick was attached in a known Lyme risk area.

Official Ontario resources

• Public Health Ontario — Lyme disease (risk-area maps and guidance)
• Public Health Ontario — Vector-Borne Disease Tool (interactive case counts and blacklegged tick risk-area maps, updated weekly May–October)
• Ontario.ca — Tick-borne diseases
• eTick.ca — submit a tick photo for identification
• Public Health Agency of Canada — Lyme disease

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