Does Winter Fend Off Ticks?

As fall turns to winter, customers might assume that they can forget about outdoor pests until spring returns. What they don’t realize is that many tick species, and especially the blacklegged (deer) tick, can remain active all winter long.

It makes sense that ticks could be active until the first hard frost but whether they remain active throughout the winter depends on the tick species, your location and how cold the winters get. For instance, in northern California and southern Oregon, adults of the western blacklegged tick, Ixodes pacificus, were found to be most abundant during cooler seasons. This western vector of Lyme disease is most active from fall to spring with numbers peaking in mid to late winter. Western blacklegged ticks are driven primarily by higher moisture in winter, not cooler temperatures.

The eastern vector of Lyme disease, Ixodes scapularis, the blacklegged tick, is most active during warm weather months, but can remain active all winter unless the temperature approaches freezing or there is snow cover. Even these periods of inactivity are usually short-lived because the ticks will resume activity as soon as conditions warm up a bit or snow melts. For freezing temperatures to kill most ticks, there must be a sustained number of days below 10 degrees Fahrenheit.

Fall weather may mean ticks are even more active as they begin a frantic search for a host animal whose body heat and blood will allow them to survive the winter. Those that fail to find a host before cold weather are forced to spend the winter in protected places and they may not survive. Typical overwintering sites for ticks are in lawns under leaf litter, in garden debris, in thick shrubbery under bark or under snow cover.

IMPACT ON DISEASE TRANSMISSION. It’s easy to see how global warming or climate change can be a factor affecting the life cycle of ticks. Blacklegged ticks have a two-year life cycle so there are times when two or more stages overlap. October is a key month in the blacklegged tick’s life cycle. If fall weather remains warm and allows ticks to extend their host-searching, more ticks will find hosts and will survive the winter.

As winters get warmer, there are fewer extended cold spells that will kill overwintering ticks. More ticks surviving the winter means more ticks looking for hosts in the spring. That means more infected ticks to transmit Lyme disease or other diseases. The take home message is that there is really no time of the year when you can assume that ticks (and Lyme disease) are not factors. People and pets still need some level of protection, even in winter.

The authors are well-known industry consultants and co-owners of Pinto & Associates.