Will the extreme winter cold wipe out ticks?
I’ve been asked on four different occasions recently, how tick populations will be impacted by the December/January below-zero cold.
Some of those asking had heard reports, apparently claiming that tick populations would be decimated, if not eradicated, by the prolonged period of extremely cold weather.
We’d all certainly welcome that. It’s probable that you or someone you know has been affected by ticks and/or by Lyme disease. And any downward pressure on tick populations is welcome.
But, the answer isn’t that simple. Extremely cold temperatures do have an impact on overwintering insects and insect-like critters. (Technically, ticks are not insects. They’re arachnids, like spiders.) But determining mortality rates based on winter weather conditions is anything but certain. The mechanisms that allow their survival are varied and complicated. So different groups will have different rates of survival.
Some ticks survive as eggs deposited before winter. Depending on the species, a single female tick may lay 3,000 to 8,000 eggs, after which she dies. Ticks in other stages of development also overwinter in the shelter and relative comfort of the soil or within leaf litter and ground clutter, where snow cover can actually provide additional protection from extremely cold temperatures and wind. Even when the air temperature lingers in the double digits below zero F, things that are covered with an insulating blanket of snow will remain much nearer to 32 degrees. In fact, the temperature beneath the snow, in many cases, will keep the soil from freezing. I’ve been told that just one foot of snow cover will completely protect the soil, and any organisms living within the soil, from the subzero air temperatures above the snow surface. And many experts believe that, even without snow, it takes a long period of bitterly cold weather to even have a chance of knocking tick populations back.
The rate of mortality greatly increases, however, with the combination of extremely cold conditions and liquid water. Overwintering insects and non-insects alike (i.e. ticks), must remain dry; insulated by the surrounding ice and snow; but not touching it.
A 2012 study co-authored by Rick Ostfeld; an ecologist at the Cary Institute of Ecosystem Studies in Millbrook (Dutchess County), examined the probability of tick mortality in winter conditions in both Millbrook and Syracuse. The study found that exposure to subzero temperatures increased mortality “only at super-cold temperatures. And it wasn’t a clear die-off; just an increased probability of dying.” Regardless of winter conditions, more than 80 percent of the ticks survived at both sites.
According to Peter Jentsch, an entomologist and Senior Extension Associate with Cornell Cooperative Extension’s Hudson Valley Lab in Highland, “most living things are able to survive environmental extremes if they have enough time to transition and acclimate to change.”
It’s interesting to note, too, that a 2010 study from the Journal of Clinical Investigation (www.jci.org/articles/view/42868) showed that some ticks developed a type of glycoprotein, a compound produced within their bodies, which works to help them survive the cold.
Some tick species overwinter on warm mammalian hosts; often moose or deer, but also black bears, dogs, and occasionally horses or cattle. They attach themselves to the animals’ fur. Then, during the winter months, to the hosts themselves; feeding and molting until spring arrives, at which time they drop to the ground, where the females lay their eggs.
New York state Integrated Pest Management Program Extension Support Specialist, Joellen Lampman, first looks at how extremely harsh weather conditions may impact mammals; small mammals, like mice, when considering the question of the recent frigid weather and how it will impact tick populations. In a recent IPM news article she writes, “Animals that have a harder time finding food are more likely to (in order of lessening consequences) die of starvation, succumb to other stresses such as disease or predation, fail to mate, give birth to fewer young, and give birth less often. In a nutshell, there should be fewer hosts, come spring. And fewer hosts eventually lead to fewer ticks.”
But there’s some bad news, too. Lampman writes, “During the time of high tick numbers and fewer small mammal hosts, each of us, and our companion animals, are at greater risk of coming into contact with questing (waiting on plants for a host) ticks. So, as soon as the temperatures rise into the mid-30s (and we know you will be out enjoying the veritable heat wave), ticks will be questing, and we need to steer clear of ticks and the diseases they carry — the IPM way.”
For more information, visit https://blogs.cornell.edu/nysipm/2017/10/10/steer-clear-of-ticks-and-the-diseases-they-carry.