Winter ticks threaten moose

by Matthew Robbins | January 22, 2024

Across this province and beyond, ticks are an increasingly troublesome reality for sportsmen and women. These little bloodsuckers are more than just annoying — they carry a host of ailments to which outdoor enthusiasts are especially vulnerable. Along much of their southernmost range, moose are struggling to adapt to the growing influence of ticks, and Ontario is no exception. 

Tick troubles

By and large, human-tick encounters involve one of two species: the dog tick (aka wood tick) or the black-legged tick (aka deer tick), the latter of which is responsible for a rising incidence of Lyme disease in humans. Despite their increasing prevalence, however, neither of these species appear to be an issue for moose.

Instead, the trouble for our iconic forest-giant comes almost exclusively from Dermacentor albipictus, otherwise known as the winter tick. These pesky parasites are slightly larger than other species of North American ticks and are considered unique for their use of a single host-animal. While most species of tick switch hosts during their various life stages, winter ticks catch a ride on an unsuspecting ungulate as larvae and remain there until the swollen females are ready to drop to the forest floor, lay their eggs, and die.

As a result of this prolonged parasitism, heavily infested host-animals like moose often experience severe blood loss, subsequent emaciation, and anemia. This may seem incredible, considering a tick’s diminutive size, but a heavily infested moose can hold more than 40,000 individual ticks at one time, each doing its small part to consume what amounts to an immense amount of blood over a season.

Severely infested moose also rub themselves on trees to alleviate irritation, often causing substantial hair loss. In extreme cases, moose can rub off so much hair that they appear almost entirely grey, earning them the unfortunate nickname “ghost moose.”

Changing seasons

Although Dermacentor albipictus is one of the heartier tick species, it is still hindered by the cold. Harsh winters tend to have adverse effects on tick reproduction. Warm conditions, on the other hand, often boost their numbers. Years with unusually short and mild winters can prompt a virtual explosion of ticks across the landscape. The problem is that years like this are becoming increasingly common.

“What we are seeing in some moose populations outside of Ontario is a pattern of severe and repeated tick outbreaks largely driven by changing winter conditions,” said former Ontario Federation of Anglers and Hunters Wildlife Biologist Dr. Keith Munro, who has been studying large ungulates like moose and deer for most of his career. “I have significant concerns about the tick situation worsening in Ontario over the coming years and foresee this becoming a challenge to our moose populations.”

Changing winter trends, due to climate change, have not only created ideal conditions for increased tick density, but for range expansion as well. In the last several decades, the winter tick’s northernmost range has jumped from 62° N (southern Yukon) in 1989 to 66° N (central Northwest Territories) in 2013.

Uncertain times

To be clear, winter ticks are not new to our province, and the full influence that a changing climate has had on Ontario’s winter tick populations (and subsequently on our moose) is not yet understood. However, trends elsewhere are cause for alarm, and there is little reason to believe that Ontario will be the exception.

In parts of the northern US, for instance, researchers have directly linked rapidly diminishing moose populations with near epidemic-levels of winter tick infestation. One study, published in the Canadian Journal of Zoology (2018), which focused on areas in western Maine and northern New Hampshire, encountered a staggering 70% winter/spring mortality in calf moose, 88% of which were attributed to these parasites. As for Canada, studies and surveys are ongoing throughout BC, Quebec, New Brunswick, and parts of Ontario.

Although we don’t yet know how this issue is playing out in our province, Ontario’s moose are already experiencing steep declines in many regions. The prospect of an additional stressor is indeed very bad news for our moose.

To make matters worse, possible solutions are running thin. As strange and unfortunate as it sounds, one of our only feasible tick-management options may be to reduce moose populations ourselves. Much like COVID-19, ticks do best where a high density of hosts exist, and there is evidence to suggest that a controlled reduction in moose numbers may end up increasing moose survival in the long run. Several US states, including Vermont and Maine, have already begun employing this approach.

Thankfully, the field of natural resource science is constantly changing. With advancements in research, more effective management solutions for this and other tick-related issues may one day exist. For our part, sportsmen and women can help by remaining vigilant in the out-of-doors.

“The public can play an important role in keeping management agencies up to date with potential issues,” said Munro, who now teaches at Fleming College. “If hunters start finding dead moose in the woods, especially in the winter or spring, it is important that they report it.”

To report a dead moose, moose with hair loss, or any other signs of tick-related stress, contact the Canadian Wildlife Health Cooperative at 866-673- 4781 or by email at

Originally published in the Jan.-Feb. 2023 issue of Ontario OUT of DOORS

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