Vineyarders may think a stroll in woods during these cold winter days would be an activity without the hazard of ticks. It would be a mistaken assumption.
Cold doesn’t necessarily kill off ticks, and “as soon as the temperatures get above freezing, they activate,” Larry Dapsis, Barnstable County entomologist, said. Dapsis said ticks harbor the chemical glycerol, which has similar properties to ethylene glycol, the key component of automotive antifreeze. The glycerol in their bodies makes them resistant to freezing, he said.
“[It] prevents ice crystal formation in cells, which is detrimental to tissue health.”
Dapsis pointed out that it’s the black-legged tick, a.k.a. the deer tick, that can be found questing for hosts in winter. The dog tick and the lone star tick present only a three-season threat, he said.
When he worked for Ocean Spray, Dapsis recalled regularly traveling to Wisconsin, where weeks of -25° Fahrenheit were “not unusual,” and nevertheless the deer tick population of the state was robust, he said, and Lyme “quite endemic.”
“They do indeed withstand Wisconsin winters,” Susan Paskewitz, chair of the University of Wisconsin department of entomology and director of the Midwest Center of Excellence for Vector-Borne Disease, wrote in an email.
“They are able to overwinter under the snow layer and down in the top few inches of the leaf litter. One of my colleagues says that when you remove the leaf litter and snow cover, you can see a measurable reduction in overwintering success, so it is clear that insulation is important.”
Paskewitz affirmed deer tick antifreeze capability. “In terms of the biochemical mechanisms: We know that black-legged ticks produce something that is similar to antifreeze glycoproteins from other organisms, and there is one report that [indicates] when a tick makes more of this molecule, it is able to survive longer in colder temperatures,” she wrote. “We also know a bit about the physiology: Ticks can go into a type of metabolic and developmental slowdown and period of inactivity called diapause, that is the result of hormonal changes in response to seasonal indicators (shorter day length and/or colder temperatures).”
“Ticks lived through the ice age, that’s what I tell people,” Dapsis said. Tickwise, a snowstorm is a good thing, he pointed out.
“They’re not going to tunnel up through snow,” he said. But under trees or shrubs with no snowpack, they can emerge and bite even if snow is elsewhere on the ground, he added.
Dick Johnson, biologist for the Dukes County Tick Program, said he’s routinely walked in the Menemsha Hills this winter and not encountered ticks. However, others across the Island have told him they’ve gotten ticks on themselves or their pets this winter. In general, he said, he’s getting more and more inquiries about winter tick activity.
Earlier in January, after brushing against a huckleberry patch on the edge of a driveway, a Times reporter found a tick crawling up his pant leg. It was sent to the University of Massachusetts Laboratory of Medical Zoology for testing, and was identified as a partially fed adult deer tick, negative for several pathogens including Lyme.
Dapsis recommends wearing permethrin-treated clothing year-round to stave off ticks.
Tick researcher Sam Telford, director of the New England Regional Biosafety Laboratory, told The Times ticks won’t been seen in any great numbers in frosty weather. “Yes, a few might be seen, and there may actually be spots where there are more than expected … but you should remember that the landscape is not homogeneous and that there are little pockets here and there that might be warmer,” he wrote. “The sunny side of a trail as opposed to the shady side of a trail comes to mind. As for Wisconsin ticks, note that they are long adapted to much colder conditions, and it is likely that there is a genetic basis for this, so what [Dr. Paskewitz] sees there is not necessarily applicable here.”
Telford went on to write that when more cold-hardy ticks share genetic material through mating, some evidence suggests the offspring may inherit the durability.
“Long ago, a student of mine did an interesting experiment in looking at the capacity of larval and nymphal deer ticks to molt after a blood meal, when the engorged ticks were held at three different temperatures, 18°C, 20°C and 22°C,” he wrote. “Subadult ticks from Quabbin and Ipswich were used. Those from Quabbin had no problem molting at all temperatures, whereas those from Ipswich took twice as long as they normally do at 20°C, and did not molt at 18°C. When the parent ticks were crossed, the offspring had an intermediate response — there was good normal molting at 20°C, some at 18° and all at 22°C. Sadly, the work was never published because it was one trial, and it took two years to see the results. We moved on to other more important things. But over the years, ticks have been adapting to colder temperatures and moving northward. My guess is that most of the ticks in coastal areas would not do well if they were transplanted into Western Massachusetts.”