Know your ticks: American dog tick (Dermacentor variabilis)

Today I'm going to introduce you to a domestic tick that you've probably already encountered even if you didn't know its identity.

American dog ticks are large, reddish-to-greyish brown ticks that are fairly easy to spot. As their common name suggests, dogs are an important host for adult American dog ticks although this tick species is neither restricted to the US nor does it rely solely on dogs for the blood it needs to propel its lifecycle.

Adult dog ticks target a vast array of host species. They're happy to feed on badgers, bison, black bears, deer, eastern chipmunks, ground squirrels, horses, raccoons, opossums, porcupines, skunks, weasels, and others. (It's a long list.) They are also, sadly, rather keen on biting both dogs and humans. Immature dog ticks, on the other hand, generally stick to feeding on small mammal species such as deer mice, eastern chipmunks, meadow voles, red-backed voles, snowshoe hares and white-footed mice, but have also been known to latch onto cats and dogs.

Since dog ticks typically hang out in tall grasses and low brush along boundaries and margins (roadsides, trails, fences, hedge rows, and the points where wooded areas and fields meet), it's commonplace for dogs and people who stray off the beaten path to come into contact with them, which is a big part of the reason why this is the tick species most frequently submitted by the public to tick collection programs in this country. Dog ticks are also increasingly making themselves at home in urban spaces, making them more likely to be spotted.

Size of American dog tick in relation to other tick species found in Canada. Image courtesy of CDC

Although the bites of dog ticks are painless, these ticks are capable of transmitting several tick-borne illness that affect humans, including Q fever, Rocky Mountain spotted fever, tularemia, and Lyme disease. They have also been implicated in cases of tick paralysis in the US. However, it's important to note that it's considered rare for Canadians to pick up any of these infections from dog ticks. You're exceedingly more likely to acquire Lyme disease, for instance, from blacklegged ticks in all of Canada east of the Rocky Mountains than you are from dog ticks.

What makes the dog tick an important species in Canada isn't so much the diseases it can potentially transmit to humans, but the fact that it's ubiquitous and is the species Canadians are most likely to encounter. When we try to visualize what a tick looks like, this is the species we often call to mind. Ironically, it's also a species from which we don't have much to fear.

Where found: Abundant in southern Manitoba, northwestern Ontario, southeastern Saskatchewan and Nova Scotia. Locally abundant in southern Ontario and Quebec. Also found in Newfoundland, Prince Edward Island, and New Brunswick. Although ocassionally reported in BC, dog ticks are uncommon there. However, their range is continuing to expand northward and westward, particularly in Manitoba and Saskatchewan.

Originally published in The Lyme Report, Issue 14 in a slightly different form.
Photo: James Gathany / CDC