The Perfect Storm: Why There Are Suddenly So Many Ticks in Canada

In recent months, various media outlets have been reporting that Canada is anticipating an explosion of ticks this year thanks to a mild winter that has failed to kill off resident tick populations in many regions. As with everything related to Lyme disease, the situation is much more complicated than what's being reported.

That's not to say mild winters aren't playing a significant role. They most certainly are. Ticks are sturdy survivors. Experiments have been conducted in this country during which ticks have been frozen to temperatures below -10C. When warmed up again, they spring to life as if the freezing hadn't occurred.

As climate change continues to warm our winters to the point where temperatures no longer drop to the arctic lows that we've traditionally relied upon to keep tick populations in check, we'll inevitably see those populations both flourish and rapidly expand in the coming years. The current rate of expansion is estimated to be roughly 46 km per year with tick populations now pushing north of the Great Lakes. And there is no reason to believe that the expansion is going to slow in the coming years. It may even accelerate.

Still we are doing ourselves a disservice if we blame everything on climate change and fail to recognize that other factors are playing a role in the spread of tick populations across this country. Here are a few for you to consider.

Critical Mass & Migrating Birds
With breeding tick populations in the northeastern United States hitting critical mass, ticks need to migrate out of their traditional breeding grounds in record numbers in order to thrive. Birds have a long history of carrying ticks into southern Canada. Each year it's estimated they bring up to 175 million blacklegged ticks into the country in addition to the ones that already reside here. There was a time when cold temperatures meant that these hitchhiking ticks couldn't last the winter. That's no longer the case in an increasing number of areas which are now finding themselves playing host to both resident ticks and annual invaders. Got to love that.

Forest Fragmentation
Canada has been gifted with vast swaths of forests that for a variety of reasons we feel compelled to cut down. Certainly here in British Columbia, the logging of old growth and not so old growth forests is rampant, but the rest of the country isn't exactly innocent either. When we remove large numbers of mature trees we find ourselves left with exactly the sort of scrub that deer, mice, and other small mammals love to call home. The proliferation of these creatures causes a corresponding increase in the ticks that feed on them as well as any diseases those ticks may be carrying, including Lyme disease.

Suburban Sprawl
Our communities have a tendency to sprawl across wide open spaces in response to rising populations that see us building outwards instead of upwards. Areas at the edges of towns that until recently housed forests and fields are being cut down, paved over, and just generally reengineered so that we can build subdivisions in places where they have never been before. As a result, humans are increasingly coming in contact with the natural world and that world includes deer, mice, ticks and all of the lovely diseases they carry.

Declining Biodiversity
Humans, as a species, don't seem to care much for predators with the notable exception of ourselves. And there are days when that seems a bit iffy. As the number of top level predators decline, the prey they once hunted flourishes. Deer tend to proliferate in areas with few wolves and mice populations explode in regions where foxes are absent. The widespread decline of predators also has consequences for our health. Immature blacklegged ticks feed on mice and other small rodents. Mature blacklegged ticks feed on deer and other large mammals. The more deer and mice there are, the more support there is for the ticks that carry Lyme disease. And ultimately it's humans who end up paying the price.

Yes, acorns. Research has shown that two years following a bumper crop of acorns, cases of Lyme disease go through the roof. That's because all of those acorns provide mice with an abundance of food that causes their numbers to spike, which in turn causes tick populations to spike, and that eventually causes the number of humans infected with Lyme disease to spike. It takes about two years for the effect of all those acorns to work its way through nature to humans. And since there was a bumper crop of acorns two years ago, experts believe that this year will be a particularly nasty one for ticks transmitting Lyme infections to humans.

What It All Means
Keep in mind that the "acorn cycle" only really applies to eastern Canada, which is where the majority of this country's oak forests are located. But then it's also eastern Canada which is seeing the largest impact from ticks being carried into the country on migrating birds and which already had the largest numbers of resident tick populations. And it's also eastern Canada that had the mildest weather this past winter. (Those of us in southern BC froze our butts off.) So then it's not surprising that it's in eastern Canada where this year's tick explosion is expected to occur.

That's what's known as a perfect storm. It seems to me that there is no better time than the present for easterners to relocate west of Manitoba where things are expected to be a little bit calmer for the foreseeable future.

Picture of Vanessa FarnsworthVanessa Farnsworth is a British Columbia-based writer with an in-depth knowledge of Lyme disease. Her work has been published in magazines & journals across Canada and in the United States.
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