Climate change is pushing ticks into new habitats across southern Canada, and experts say the blood-sucking pests will keep advancing.
Disease-carrying ticks were barely on Canada’s radar until the 1990s, but scientists say various species are travelling north from the United States at a rate of 35 to 55 kilometres per year.
“Where the vast majority of the Canadian population lives, which is near the American border, are all in areas that are already climatically suitable for tick populations,” said Katie Clow, an assistant professor in the department of population medicine at the University of Guelph. “Likely, the invasion process is just going to continue to sort of fill that ecological niche.”
Clow says parts of southern Canada that do not yet have ticks will likely see them emerge over the coming decade.
Lyme Disease, transmitted to humans by blacklegged ticks, or deer ticks, first appeared in southern Ontario in 1989. Blacklegged ticks, which can also cause Powassan virus in very rare cases, have since made inroads in every other province.
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They’ve also been found in Alberta and Saskatchewan, though the Prairies more commonly see dog ticks, which are less of a concern but can, in very rare cases, cause Rocky Mountain spotted fever.
Canada now has more than 40 species of ticks, according to Health Canada, including a handful that bring serious health concerns.
The lone star tick, which is common in the U.S. and researchers say has been found in small numbers across Canada, can cause humans to develop a severe red meat allergy. The Asian longhorned tick, which can cause serious disease in cattle, has also been creeping northward in the U.S., stirring up fears among Canadian farmers.
Clow says it’s more a question of “when” than “if” these species will establish themselves in Canada.
“We’ve seen places where they’ve never encountered ticks before [like] north of Toronto, up towards cottage country, where now ticks are a much higher burden,” Clow said. “I think that that has surprised a lot of people, because for decades they weren’t there.”
In Saskatchewan, researchers say the pests have been especially bad this spring. Montreal has logged a record-high number of Lyme disease cases.
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There are no hard stats on the number of ticks in Canada in any given year, but eTick.ca, which tracks species through submitted photos from Canadians, says it has vetted more than 95,000 tick photos.
The Public Health Agency of Canada has tracked an exponential increase in Lyme disease cases from 2009 to 2025, though experts say its numbers are likely an undercount and the agency has changed its surveillance case definition over time. PHAC’s preliminary count for 2025 is 7,105 cases. In 2009, its count was 144.
Lyme disease causes common symptoms such as fever, fatigue and a “bull’s-eye” rash. If untreated, it can cause severe joint, heart and nervous system complications. Clow says blacklegged ticks are most worrying in their nymph, or “teenage,” stage, when they are smaller and harder to see. That stage tends to peak in June and early July.
The tick proliferation has caught many Canadians off guard, to the point that some have spread an unfounded theory that the bugs are being dropped from planes in a nefarious plot to infect people. That claim that appeared on an online conspiracy forum and was amplified in a TikTok video with more than 205,000 views.
But researchers say the spread of ticks has been predictable, given climate change patterns over the last several decades.
“Previously our climate was just too cold, there wouldn’t be enough warm time for them to be active, and they would starve out,” Clow said.
Clow says millions of ticks come in every year on migratory birds, and many also come attached to deer and rodents. For those ticks to feed, reproduce and sustain themselves, they need summers that are long and warm enough — conditions that did not previously exist.
Ticks are resilient and can even survive winter cold snaps under leaf layers, as long as they have sufficient warmth throughout the year, Clow says.
“A cold winter will unfortunately not kill off our tick populations, but our earlier springs and longer summers are allowing them to reproduce.”
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That means some species are becoming a problem year-round, rather than just in the peak of summer.
They’re also becoming more noticeable in the suburbs, where housing developments are increasingly being built into wooded areas, causing “forest fragmentation” that increases populations of deer and rodents and allows ticks to thrive.
Negar Elmieh, a scientist with the National Collaborating Centre for Environmental Health at the B.C. Centre for Disease Control, says weather patterns can have various effects on tick populations — a heat dome with sustained temperatures over 40 C can kill them off, for example — but the trend over time is that populations are increasing.
She says research has shown a northward expansion, particularly along riverbeds and paths where deer and other host animals can easily migrate.
“What we’re seeing in general is that with climate change, you’re seeing more animals migrate further northwards, and with that comes the ticks,” she said.
Elmieh says it’s the “new norm” that Canadians will see “more and more ticks.”
Researchers say it’s important for Canadians to continue doing outdoor activities, but to add precautions to their routines.
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That means everything from managing your own property with clear pathways and landscaping, to wearing long sleeves and light-coloured clothing, tucking pants into socks and spraying DEET when going into tick-prone areas.
Elmieh also recommends checking your body for ticks after you’ve been outside. She says showering will remove ticks that have not yet attached, and ticks that may be left on clothes can be killed by putting them through the dryer.
