The winter tick, scientifically known as Dermacentor albipictus, is an external parasite that feeds exclusively on blood. These organisms are sometimes called “moose ticks” and are found throughout much of North America, ranging from Canada down to the southern United States. Winter ticks are distinct from the more commonly known blacklegged (deer) tick because of their life cycle and feeding habits.
The Unique One-Host Feeding Strategy
The winter tick is classified as a “one-host tick,” meaning it spends its entire parasitic phase on a single animal, unlike other ticks that find a new host for each life stage. Larvae hatch on the ground in late summer and climb onto vegetation to wait for a passing host in the fall. Once attached, the tick remains there through the winter, molting from a larva into a nymph, and then into an adult.
The tick takes three blood meals while on the host—one as a larva, one as a nymph, and a final one as an adult female. This sustained feeding occurs from approximately October to March or April. The adult female, now fully engorged, drops off the host in the spring to lay thousands of eggs on the ground, after which she dies.
Primary Hosts and Preferred Meals
The winter tick’s sustenance comes primarily from the blood of large North American ungulates. These hooved mammals are the most frequent targets, including moose, elk, caribou, and white-tailed deer. Ticks infest the animals that are most active in areas with large numbers of questing larvae, showing no strong preference for one species.
Moose (Alces alces) are the most affected primary host, often carrying tens of thousands of ticks. This concentration is partly due to the timing of the moose breeding season, which coincides with the larvae’s peak questing period in the fall. Domestic animals, including cattle and horses, can also be hosts. Incidental hosts like coyotes and black bears may occasionally acquire winter ticks, but they are not the main source of blood meals.
Consequences of Mass Feeding on Hosts
The continuous, mass feeding of winter ticks creates severe health issues for their hosts, particularly moose. A single moose can be infested with up to 100,000 ticks, which collectively draw an immense amount of blood throughout the winter months. This severe blood loss can lead to acute anemia and metabolic imbalance, weakening the animal during a time when food is scarce.
The constant irritation from the ticks causes the host to groom excessively by rubbing and scratching. This behavior leads to significant hair loss, sometimes removing large patches of the protective winter coat. Moose with extensive hair loss are often referred to as “ghost moose” because the pale undercoat or bare skin is exposed. The loss of insulation makes them vulnerable to hypothermia and exhaustion, which can ultimately result in death, especially for calves.