Every year, “The Tick Guy” Thomas Mather is asked if the tick season will be bad, and his answer is always yes.
“Most tick experts will say, ‘Oh, they’re probably going to be bad,’ and they will never be wrong, because to the average person, one tick is a bad tick year,” said Mather, director of the University of Rhode Island’s Center for Vector-Borne Disease.
This year, however, does not seem to be a one-tick-per-person year. Media headlines last month announced the worst start to a New England tick season in a decade when the Centers for Disease Control and Prevention’s Tick Bite Data Tracker counted 168 out of every 100,000 emergency room visits related to tick bites. Nationally, the rate hit 104 per 100,000 emergency room visits, the highest in nine years. The alarm bells of a bad tick season are ringing.
Since Lyme disease first appeared in the 1970s, New England has remained an epicenter for ticks and tick-borne diseases. But the prominence and range of Lyme-carrying black-legged ticks and alpha-gal harboring lone star ticks have grown exponentially in just the past decade. In Rhode Island and southern Massachusetts, Mather found the ratio of black-legged ticks jumped from 50-to-1 to 3-to-1. Black-legged ticks have pushed into areas of Canada and Maine much faster than ecologists typically observe in species migrations.
“Ticks are winning,” Mather said.
The rise in the severity of the tick season seemingly coincides with hotter summers, warm snaps in winter and more humid stretches. But changing climate is only one piece of the puzzle, and Mather notes it’s not the main factor. Rather, these ticks are hitching a ride on their favorite feast, the white-tailed deer, to new areas of New England.
Combined with favorable weather, these diseased arachnids have the perfect conditions to create a public health crisis.
“Every white-tailed deer basically represents a big piece of breeding real estate for a tick,” said Stephen Rich, University of Massachusetts Amherst professor of microbiology and executive director of the New England Center of Excellence in Vector-borne Diseases. “There’s now like this fertile ground, vis-à-vis the white-tailed deer, that spread across New England, and the tick can now go places that they couldn’t go before.”
Hitching a ride
According to MassWildlife, a healthy deer density is about 12 to 18 deer per square mile. But in some parts of the state, the density is much higher. In Martha’s Vineyard and Nantucket, where tick-borne illness rates are edging toward a state of emergency, the deer population is 55 to 85 deer per square mile.
There are now more deer than when European settlers first arrived at Plymouth Rock, Rich said. Populations of lone star and black-legged ticks nearly disappeared in the 1800s, when colonists clear-cut New England forests and destroyed deer habitat. But as the forests grew back, so did the deer population — and eventually, the ticks returned as well. This time, however, the landscape was far more favorable to them.
“Deer don’t like big, open forests. They like the forest edge. That’s what they like to munch on,” Rich said. “And that’s the way we manage our properties now, with tree lines. Deer love it.”
Massachusetts has begun to explore ways to empower hunters, the last remaining predator of deer in the state. Just last month, Gov. Maura Healey filed legislation to allow hunting on Sundays, expand crossbow hunting season and shrink minimum setback distances for bow hunting and falconry.
Western Massachusetts’ population of hunters is the reason the region remains in the deer density sweet spot. However, experts say the solution cannot ride on hunters alone. Places like Martha’s Vineyard simply have too many deer.
“It’s a bloodbath,” Rich said. “You would just have to kill so many animals, and it’s just not going to happen. No one’s got the stomach for it. So we have to think of alternatives.”
Instead, scientists are experimenting with tick preventatives used for pets. If deer eat baited food like corn treated with oral acaricide, their blood would become poisonous to ticks. Early studies have shown reductions in tick density, particularly in the pin-sized nymphs known to carry Lyme disease at higher rates. The actual impact on wild deer populations, and the potential dangers of the strategy, require more study
Beating the heat
Just as the landscape now caters to the deer’s lunch preferences, New England’s climate shifts in the tick’s favor. It is not just the change in winter weather — in fact, ticks survive well under a layer of snow. A study from the University of Maine found that black-legged tick overwinter survival did not significantly vary across the state despite the pests’ higher abundance in southern Maine.
“The reality is that when you’ve got a foot of snow on top of the ground, not to mention the leaf litter and other abiotic features of the environment, you’ve got some pretty decent insulation on the tick so they’re not actually getting exposed to those coldest temperatures,” said Allison Gardner, associate professor of Arthropod Vector Biology at the University of Maine and co-author of the study.
Ticks do not like extremes, Rich said. If the weather is too cold or too hot, these cold-blooded critters crawl into a layer of leaves, twigs and bark that covers the forest floor. This leaf litter provides insulation and moisture to keep the tick alive.
“Black-legged ticks are very susceptible to drying out,” Mather said. “That’s why they hang out in the shady recesses of the wooded edge or into the woods. The leaf litter provides a higher degree of humidity than out in the middle of a lawn.”
Warmer temperatures will bring out the ticks, but they begin to dry out almost immediately. Mather’s lab discovered humidity below 82% for over eight hours is likely fatal.
“These ticks come out like gangbusters the last week or two of May and they could be active all the way into August,” Mather said. “It depends on how many of those sub 82% eight hour days there are, because any one of those and they start to die.”
Temperature data and climate modeling paint New England summers as increasingly warm and wet with heavier but infrequent storms. Warmer air holds more water, pushing humidity levels higher and keeping ticks comfortable outside.
However, Mather said that muggy days do not mean favorable tick conditions. The southern United States, where humidity feels high, actually has drier conditions for the ticks compared to New England because of the temperature. Nor does humidity explain the recent explosion in the lone star tick population, which relies less on humidity than its black-legged cousin.
“There are some spots that you could point to in New England and say there weren’t ticks here 10 years ago. Now there are ticks there,” Rich said. “We know the climate’s changing, and so there’s a temptation to think, that must be driving this. [But] we don’t know to what extent temperature change may be driving these expansions.”
The early alarms
While climate change alone cannot predict a bad tick season, it might explain the high rate of tick-related emergency room visits cataloged by the CDC. The secret: it’s not the number of ticks, but their early appearance.
“I’ve been seeing ticks already this April in Maine, which I can assure you, I was not seeing 10 years ago when I first moved here,” Gardner said. “So it’s a very real change that’s taking place on a reasonably short time scale.”
Gardner has been analyzing a 30-year data set with one of her graduate students and they’ve noticed the ticks’ biological clock has shifted. Tick activity now begins sooner, expanding the tick season.
“The time that we’re really concerned with from the perspective of tick-borne disease transmission and human health is how long do the ticks have to encounter a human,” she said. “If they’re sitting in the soil underneath the foot of snow, maybe they’re surviving. But it’s not time that pathogen transmission is taking place, because no one is going to encounter that tick.”
Tick season usually peaks from April to June and again in October and November. But Rich said people can get bitten by ticks year-round now. As soon as the temperature hits 45 degrees Fahrenheit, the pests come out and there’s a risk of finding them.
Because ticks are winning, experts say playing defense is more important than ever. For tips on tick safety, refer to Project ITCH or tickreport.com.
