Know your ticks: Winter tick (Dermacentor albipictus)

The winter or moose tick (Dermacentor albipictus) is a large reddish-brown to grey-brown tick that's similar in appearance to other dermacentor tick species (American dog ticks, Rocky Mountain wood ticks) found in Canada and inhabits an extensive geographic area that includes every Canadian province and territory. The farthest north they've been found is southern Yukon. However, evidence suggests they are continuing to spread northward so that may soon change.

The winter tick is Canada's only one-host tick species, meaning that every developmental stage feeds on a single host. Although moose are its primary target, these ticks are occasionally found infesting bison, caribou, deer, elk, mountain sheep and other wildlife species. Horses and cattle that share pastures with members of the deer family are also sometimes targeted, as are predators and scavengers (coyotes, wolves) that feed on infested prey.

Winter ticks sometimes feed on humans, but there is no solid proof they transmit diseases to people. There is, however, some experimental evidence that suggests winter ticks have the potential to transmit the pathogens responsible for Rocky Mountain spotted fever (Rickettsia rickettsii) and/or anaplasmosis (Anaplasma marginale) to us, so conventional thinking on the subject could one day change as more data comes in.

Horses and cattle that become infested with winter ticks typically don't develop significant symptoms unless they fall prey to large numbers of them. Then the affected animals can experience hair loss and, in severe cases, major blood loss.

Winter ticks have their greatest impact on moose populations. Individual animals have been found infested with more than 100,000 ticks in a single season, with the most severe infestations typically arising in late winter and spring. In some years, such large numbers have died that moose may go extinct in Canada's hardest hit regions. Older and younger animals often get the worst of it and the degree to which they suffer is based on just how bad the infestation is. Death in severe infestations results from blood loss, weight loss or both.

Winter tick populations can fluctuate significantly from one year to the next for reasons that haven't yet been determined.

Photo by Madhu Shesharam on Unsplash.