The winter tick (Dermacentor albipictus) is a mite that mostly attacks moose. It differs from other ticks in terms of its impressive size (blood-swollen adult females measuring up to 15 millimetres). Parasitism of moose by the winter tick is a natural phenomenon that occurs in many regions of Québec, but infestations are currently reported more frequently in the regions located south of the fleuve Saint-Laurent.
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Wildlife at risk
Winter ticks feed on ungulate blood, particularly cervids. They mainly affect moose and to a lesser extent elk. They may be found on white-tailed deer, but their presence does not usually cause significant problems in this species. The impact of winter ticks on caribou in natural habitats remains little known.
Winter ticks can be observed on other animal species (domestic or wild), but this parasite causes little damage to these other species.
Signs of the parasite’s presence
The winter tick can be found in tens of thousands on a single moose. It causes several problems such as:
hair loss and appearance of wounds;
weight loss and poor physical condition;
abnormal behaviour (confusion or presence outside of its natural habitat).
Life cycle and persistence in the environment
In the fall, ticks climb the vegetation and are barely visible to the naked eye. Perched in clusters at a height of about 1.25 m, they hold onto nearby animals. In the fur of the animals, they feed on the blood of their host and gradually continue their development, in nymphs and then in adults. After mating in late winter, blood-swollen females drop to the ground to lay eggs and die. Eggs hatch in the summer and the cycle starts again. Ticks do not stay on moose in the summer.
Moose densities and climatic conditions are two factors that allow ticks to multiply. High moose densities would increase the likelihood of tick larvae finding a host to spend the winter on. In areas with high moose densities, it is normal for several affected animals to be observed.
Climatic conditions play an important role in the evolution of tick populations. Early or snow-free spring supports the survival of females that lay eggs on the ground. Warm summer temperatures allow more tick eggs to reach the larval stage. In the fall, mild temperatures extend the time ticks can hold onto their hosts before they are paralyzed by the cold or buried in snow.
Pest control treatments are available to control ticks on domestic animals (e.g. livestock) or on captive wildlife. They are not worth considering for moose in the wild. The safety and efficacy of pest control products for moose is unknown. No products are registered by Health Canada for this species. The sale of pest control products to control winter tick in moose is illegal.
Protection and prevention
Risk for wildlife health
In Québec, the number of moose infested with winter tick has increased in recent years. It is too early to determine whether the abundance of ticks we observe will continue year after year or whether, in the longer term, this parasite will have a significant effect on the moose population. At this time, the results of aerial moose inventories and hunting harvest data show no impact.
In addition, meat from winter tick-infested moose is safe to eat. Ticks do not transmit disease to moose when they feed on their blood. In the fall, at the time of hunting, ticks are in the early stages of development and do not yet cause any signs of disease in moose.
Research and surveillance
Since 2012, a collection of winter tick count data from a sample of moose harvested for hunting in the fall has been conducted annually. Several wildlife partners are involved. The goal is to track annual tick infestation fluctuations and better estimate the parasite’s geographic distribution.