WHERE are ticks during Winter?
We know that tick activity drops (though tick bites can still happen in winter!) during winter months in cold climates. But what’s really happening—are the ticks still alive? Where are they?
Where are ticks during winter?
In mild climates like the West Coast of the U.S., ticks will remain active throughout the year. In winter months in colder and snowier regions, tick activity will vary by species and behavior, starting with basic divisions in how each species chooses and interacts with hosts.
Nidicolous ticks (ticks that live in or around the burrow or other shelter of their preferred host) tend to behave as they do throughout the rest of the year. Since many have adapted to the activity of their preferred host and feed intermittently when that host is in the burrow and inactive, these nidicoles may not see much interruption in their life cycle. This is especially true in warmer climates and among nidicolous ticks that parasitize hosts that do not migrate or have dormant seasons. These ticks bite humans infrequently, so this year-round cycle is not always noticeable to us.
Non-nidicolous multi-host ticks—which include most of the hard ticks of medical concern like the deer tick (Ixodes scapularis) and other species—will typically seek out insulating materials like leaf litter and other materials to protect themselves from freezing and desiccation. Depending on whether or not the tick fed before unfavorable weather set in, it may enter one of a few states of dormancy.
Dormant ticks
Note: dormancy, hibernation, diapause, and related concepts may be a topic of debate among wildlife biologists. Tick ecology will vary by species, region, and even individuals. Comments on species exceptions or suggested reading are always welcome!
Tick “dormancy” isn’t a simple topic if we are concerned about accuracy in description—and as a result an accurate assessment of how easy it is to interrupt that dormancy so the tick becomes a risk to humans and other animals again. One useful categorization lets us divide developmental diapause and behavioral diapause. Although this may oversimplify an important aspect of tick ecology for those who study it (please forgive the simplification, and keep up the good work!), it can map onto fed and unfed ticks in a way that is useful for estimating risk of tick-borne disease for the public.
Developmental diapause: this type of dormancy applies to ticks that have had a blood meal and are delaying the activity that the blood meal will allow. For replete (fully fed) larvae and nymphs, this would mean ecdysis or the process of “molting” from one stage to the next (larva to nymph, nymph to adult). In the case of replete adult female ticks, the next stage would be developing and laying eggs. Both ecdysis and oviposition (egg-laying) are extremely energy-intense activities, and if ticks determine that the next life stage may have a low chance of finding a host to feed on, that change may be suspended to preserve calories and hydration until conditions improve. The exact processes are not fully understood yet, but developmental diapause is most likely regulated by hormones, and the ecdysis or oviposition activity can resume once the tick determines that it is safer to do so (e.g. the return of spring and summer).
Behavioral diapause: this describes a suspension or deferral of host-seeking or “questing” behavior by an unfed tick that needs a blood meal to support the next life stage. Every questing event is a calculated risk taken by a tick; individual ticks need to weigh the energy and hydration costs of questing against the likelihood of finding a host and blood meal. These calculations are complicated and vary widely by species, but most often include temperature, humidity, and photoperiod (hours of daylight per day). These factors can directly affect the tick’s health, especially by desiccating or drying out the tick before they encounter a host, or may change the daily behavior of the tick’s preferred animal hosts which may be less active in winter. Ticks in behavioral diapause may be assessing these conditions on a regular basis, which is why a few days of mild weather in a northern climate may bring out hungry ticks!
If you are bitten by a tick during the winter or any other time of year, visit TickReport.com to arrange identification and testing for over 20 different tick-borne pathogens.
Suggested reading:
If you would like to dig deeper into some of the technical aspects of tick diapause, a good first stop is the 2016 review cited and linked below: