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The hills are alive in Northwest Connecticut, but it’s not all birdsong and snowdrops: the blacklegged tick has shaken off its winter torpor, and now crawls in droves through the understory, spreading disease and myths in equal measure.

Dr. Scott Williams, Chief Scientist and Head of the Department of Environmental Science and Forestry at the Connecticut Agricultural Experiment Station (CAES), a state organization spearheading research on tick-borne diseases, dismissed two commonly held misconceptions about the tiny, dangerous insect: “They don’t fly. They don’t drop out of trees.” Williams advised that rather than worry about the branches overhead, think low and keep your ankles covered. “They crawl up from the ground for the most part, or [from] a few inches off the ground.”

Demystifying tick behavior and pathogen transmission yields surprising insights into how to manage disease levels in our region: in a healthy forest, more ticks might actually equal less disease, Williams explained.

Debunking Myths

Blacklegged ticks (also widely known as deer ticks) and Lyme disease are commonly misunderstood components of the New England forest, starting with the illness’ origin story. Conspiracy theories abound speculating where it began, with an especially persistent and oft-debunked claim that it leaked from a government research facility on Plumb Island.

But reputable research has shown that the disease has been circulating in the northern hemisphere for millennia. One of the bacterium responsible for causing Lyme disease, Borrelia burgdorferi, was detected in Ötzi the Iceman, a 5,000 year-old mummy found in the Eastern Alps in the 1990s. A study conducted by the Yale School of Public Health in 2017 traced B. burgdorferi back to North American forests of 60,000 years ago, meaning the bacterium was resident in our woods long before the earliest human inhabitants arrived.

Closer to home

Deer ticks and Lyme disease are as Connecticut as New Haven pizza, with one of our picturesque coastal towns lending its name to the ailment after a cluster of cases there in the 1970s lead to its identification as a unique condition. The state remains positioned in the very heart of tick country, and the Icebox of Connecticut, which previously benefitted from the protection of its harsh winters, is losing its defenses as the cold season continues to warm up.

“We’re not trying to scare people from being outside, we’re trying to educate people on when the various stages [of ticks] are active – what’s tick habitat and what’s not,” Williams said. For instance, a field of high grass, commonly regarded as a tick haven, is actually largely inhospitable to the bugs, as they desiccate quickly in a dry environment. “That’s kind of a desert for ticks,” Williams explained.

The most “ticky” habitat “is really that edge where your lawn meets the forest,” he said, and when it comes to getting bitten, it’s often a matter of timing.

When to watch out

While adult deer ticks are active now, Williams explained that May, June, and early July are the months when most infections occur since that’s when both humans and the nymphal stage of deer ticks are likely to be active outdoors. Although the adult ticks wandering the undergrowth and brush now can certainly transmit the pathogen, it’s the nymphs that are “the really problematic guys,” Williams said, in part because they are small and hard to detect, and also because in spring, “human activity and tick activity in the nymphal stages coincide.”

A white-tailed deer in the forest. Photo: Mike Zarfos

Host competency and the dilution hypothesis

Active ticks, active humans, and an abundance of both yield higher bite rates, thus contributing to more infections. However, Williams explained that the species present in an ecosystem can have significant impacts on the spread of tick-borne pathogens to humans.

A surplus of white-tailed deer upon the landscape, for example, is often thought to correlate to more tick-borne illness. While a large deer population will often support a high concentration of ticks, deer are a “dead-end host” for the bacterium, meaning they don’t transfer the pathogen back into the ticks.

Mice, however, are “competent hosts.” The concept of host competency is the ability of a reservoir host species (animals that carry and spread disease-causing pathogens) to infect the ticks with pathogens, which small rodents are highly adept at whereas larger animals are less so. When deer are plentiful on a landscape, “you typically have high tick abundances with lower infections with the various pathogens,” Williams said.

The reservoir host species of B. burgdorferi that actually infects the ticks with the pathogen are small rodents, especially the white-footed mouse which is common to the Litchfield Hills. When fewer deer, and other medium sized mammals, are available, Williams explained that the ticks will then be forced to feed primarily on mice, which will support a smaller population of ticks within which the pathogen is much more concentrated.

CAES team conducts Lyme disease research with mice in Woodbury. Photo: Mike Zarfos

Healthy forests, healthy people

In a healthy ecosystem with a spectrum of animal species, ticks aren’t forced to rely on these highly competent hosts for a blood meal. Williams explained that this scenario, in a species-diverse forest, describes what disease ecologists call the dilution hypothesis: “with a diversity of animals, you’re going to see less infection in the ticks because they have so many options to feed.”

The loss of forest diversity can have the opposite effect, Williams said, which is happening across the Northeast due to development and the incursion of invasive species. Several years ago, Williams conducted research on the correlation of Japanese barberry, an invasive shrub, with tick populations; some of the work was done at Great Mountain Forest with the help of GMF forester Jody Bronson. The study found that the dense tangle of undergrowth created by the proliferation of the shrub caused a humid microclimate that not only provided great tick habitat, but enabled them to remain active throughout the day.

Normally, the moisture-dependent ticks might be inactive under a pile of leaves during the heat of the day, Williams said. But the microclimate created by the “monoculture” of invasive brush growth means ticks continue looking for a host “pretty much 24 hours a day.” He clarified that this was not specific to Japanese barberry, but any plant that grows in a monoculture tangle, “which is pretty much what invasives do in our neck of the woods.”

“What we’re trying to push is a healthy, diverse forest, and that’s very applicable to Great Mountain Forest,” Williams said. The goal, he continued, is responsible management: “If you have a healthy, diverse, well-managed forest, you’re going to have a diverse array of wildlife, and as a result you’re going to have a healthier tick population with lower pathogen infection. That’s kind of the bottom line.”