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Vermont's Moose Population

How Winter Ticks Impact Northeast Kingdom Moose

What is a winter tick?

The winter tick (Dermacentor albipictus) is one of 15 species of tick found in Vermont. Unlike the more familiar black-legged ticks and American dog ticks, winter ticks complete their entire life cycle on a single host: moose. Members of this species find a moose in the fall and spend the winter on that animal before dropping off in the spring—hence the common name, winter tick.

Why have winter ticks become a problem for moose?

In high numbers, winter ticks can kill young moose and seriously impact the health of adults. But to reach these numbers, winter ticks need a dense local moose population with many potential hosts packed into a relatively small area of habitat.

In Vermont, winter ticks are only a significant problem in the Northeast Kingdom, where moose densities are high. While winter ticks can be found in small numbers on other mammals, the poor grooming practices of moose can result in them carrying tens of thousands of winter ticks. Moose’s natural protection against winter ticks is their reclusiveness. In most of Vermont, moose are dispersed enough that ticks do not multiply and spread fast enough to kill calves or reduce population health. But in areas of rich habitat like the Northeast Kingdom, large numbers of moose—generally more than one per square mile—concentrated in a relatively small area gives ticks the chance to spread to many vulnerable hosts.

Unlike other ticks which have expanded their range northward, winter ticks have been in Vermont for a long time. They were recorded on moose here in the 1980s and were likely present long before that. However, winter ticks are also benefiting from shorter winters as a result of climate change. Later snow in the fall allows winter ticks more time to find a host before winter, and lack of snow in the spring allows engorged female ticks to fall on bare ground, boosting their chances of surviving to reproduce.

Can moose or their habitat be treated to kill winter ticks?

This is a common and logical question. However, moose are not pets or livestock, and treating winter ticks by inoculating moose or the environment is not currently feasible. Research in this area is ongoing but far from being viable or practical in the field. Potential treatments like a fungus that targets winter ticks also do not address the key issue of moose abundance. As long as moose numbers in northeastern Vermont remain at high levels, winter ticks will increase again when treatments stop or when ticks develop immunity.

What can we do?

To achieve a healthy and sustainable moose population, we need to keep moose numbers in northeastern Vermont at a level that does not support large numbers of winter ticks. A carefully controlled hunt is the best—and perhaps only—way to achieve this goal.

An image of a cow moose in the forest.