December 10, 2018
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‘Bone-chilling’ weather unlikely to kill off ticks before spring, researchers say

Maine Medical Center Research Institute | BDN
Maine Medical Center Research Institute | BDN

With sub-zero temperatures lingering in the Northeast, and a blizzard approaching, some Maine residents have been wondering if this might impact the tick population.

While the idea of a milder tick season is alluring, Maine tick experts agree that it’s unlikely this cold spell will cause any significant decline in Maine’s tick population.

“From what we’re finding, even with these persistent below-zero temperatures, it’s staying 25, 30, as high as 35 degrees down close to the ground,” said Griffin Dill, coordinator for the tick identification program at the University of Maine Cooperative Extension Pest Management Office. “It’s still relatively warm under there … If we have the ticks covered by leaves and covered by a foot or so of snow, chances are, even with these persistent cold temperatures, they’ll be relatively unharmed.”

If Maine wasn’t covered in snow, it’d be another story, Dill said.

“If the ticks were completely exposed, these temperatures of zero or 5 below or 10 below would certainly be sufficient to kill a number of ticks,” Dill said.

Scientists in southern Maine are currently at the tail end of the three-year study to learn more about how cold temperatures, snow cover and leaf litter affect tick mortality in the winter. The study is being conducted by the Maine Medical Center Research Institute in cooperation with the Connecticut Agricultural Experiment Station at sites in Cape Elizabeth and Connecticut.

“The big question we have is how beneficial is a heavy snowpack to ticks,” said Charles “Chuck” Lubelczyk, a field biologist for the Maine Medical Center Research Institute’s Lyme and Vector-Borne Disease Laboratory.

For the study, scientists are using deer ticks, which are a species of big concern in Maine because of their ability to transfer diseases to people and pets, including Lyme disease, anaplasmosis, babesiosis and Powassan virus.

“We have these ticks seeded out in enclosures,” Lubelczyk explained, “and we go out and certain ones get shoveled after snowstorms while others don’t.”

In addition, some of the enclosures are covered with leaf litter, while others are not. Leaf litter also can contribute to warmer temperatures at the ground level.

“Some studies have indicated leaf litter may be even more important than snowpack alone,” Dill said.

“Come spring, we’ll see how many have died,” Lubelczyk said.

It’s that simple. But for the first two years of the study, the weather wasn’t ideal.

“Last year and the year before were pretty mild winters,” Lubelczyk said. “We didn’t have very cold temperatures and not a lot of snowfall. This year has turned out to be probably the best year of the study because we’ve had bone-chilling temps and plenty of snow on the ground.”

From the first two years of the study, the winter tick mortality in the study area in Cape Elizabeth was significantly higher than in the study area in Connecticut, and snowpack and leaf litter appeared to help ticks survive.

“It looks like both snow and leaf litter had insulating value, and from what I can tell from the Maine data, it looks like what’s making the most difference in the survival of the ticks is the leaf litter,” said Susan Elias, a research associate at the Maine Medical Center Research Institute.

While the study focuses on the deer tick, there are 14 different tick species that have been found in Maine, including a species known as the “winter tick,” which plague moose throughout the state. Some species are hardier than others, and scientists are continually learning about their biology and the diseases they carry.

For example, Dill conducted a study in the fall to learn more about the activity of deer ticks, and he found that deer ticks in Old Town, Orono, Veazie and Stockton Springs were actively seeking hosts in temperatures as low as 35 degrees Fahrenheit.

“Above 40 [degrees], the activity level was virtually unchanged from when it was 50, 55, 60 degrees earlier in the month,” Dill said. “Once it got below 40, it certainly dropped off, but I was still collecting ticks here and there.”

To learn more about ticks in Maine and to stay up to date on the most recent tick studies, visit the University of Maine Cooperative Extension Integrated Pest Management website at extension.umaine.edu/ipm and the Maine Medical Center Research Institute Lyme and Vector-Borne Disease Laboratory website at mmcri.org/ns/?page_id=1090.

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