Many of us think, or at least hope, that ticks die off after the first hard frost. Unfortunately, that’s not so. In fact, the adult blacklegged (deer) ticks that spread Lyme disease begin their prime feeding activity just about the time of the first frost. That’s because their main host animals are deer and deer are actively moving around in the fall. But if deer aren’t around, blacklegged ticks will attach to people or pets anytime the temperature is above freezing.

Winter Might Slow Some Ticks Down, But They’re Not Out!

The level of winter activity also depends on the tick. American dog ticks and lone star ticks are relatively inactive in fall and winter. Blacklegged ticks decrease activity only when the temperature drops below 35 degrees F. or the ground is snow-covered, but they quickly recover when things warm up just a little. For freezing temperatures to actually kill ticks, there must be a sustained number of days below 10 degrees F. This happens less often as our winters, in general, are warmer than they used to be. Even then, any tick that has attached to a deer will be kept warm by the animal’s body heat and will easily survive a cold snap.

In New Hampshire and Massachusetts, we even have a tick called the “winter tick,” Dermacentor albipictus, that looks like and is closely related to the American dog tick. This tick is not active in the summer and usually does not bite people. It is, however, doing a number on the populations of moose in our region since it feeds on them from fall until the end of May (see Ticks Are a Factor in the Decline of New Hampshire Moose.) While this particular winter tick is not a problem for people, other ticks that spread disease can be a concern even in winter. 

Lyme Disease Ticks Are a Threat Year-Round

What this means is that you can’t really let down your guard when it comes to ticks and the possibility of tick-transmitted diseases. You can take a small breath though because, in the Northeast, the risk of Lyme disease is lowest from late December to late March. This is due not so much to the weather as it is to the complicated life cycle of the blacklegged tick. The nymphal stage of the tick is responsible for most transmitted cases of Lyme disease, but by late fall the nymphs have molted into adult ticks to spend the winter.

For more on the life cycle of the blacklegged tick:

• It’s Still Prime Time for Lyme Disease
• Look Out! Ticks Are Already Active!