Managing Some Invasive Plants Might Reduce Blacklegged Ticks

This article is part of The State of Science, a series featuring science stories from public radio stations across the United States. This story, by Lexi Krupp, was originally published by Vermont Public.

In much of the eastern US, October and November usher in an autumn peak of the blacklegged tick season.

For years, researchers have noticed that these ticks, also called deer ticks, are more abundant on certain invasive plant species, like Japanese barberry, that create dense thickets in the forest understory. 

Now, a group of scientists in Vermont and Maine is investigating how managing these plants might decrease the number of blacklegged ticks—and the risk of people developing tick-borne illnesses, like Lyme disease and Babesiosis. After getting a $1.8 million grant from the National Science Foundation, they’re hoping to come up with guidance for landowners.

Over the next five years, Dr. Allie Gardner, a medical entomologist at the University of Maine, and other researchers will survey tick numbers and test out different management techniques at around 30 locations on private and public land in northern New England. Then, they’ll train landowners on best practices for managing ticks and invasive species.

“We can do all the ecological research we want on the problem, but if we are not able to translate our findings into recommendations, ultimately we are not going to make any headway,” says Gardner, the lead researcher on the project.

It’s not entirely clear why ticks are more likely to be found on some invasive species compared to native plants, but there are several theories.

“The humidity levels around Japanese barberry seems kind of ideal for ticks,” says Dr. Kristen Ross, a restoration ecologist at Vermont State University and a collaborator on the project. “They like it not too rainy and not too dry.”

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Tangled thickets of barberry in a forest’s understory also provide cover for white-footed mice, a main host of blacklegged ticks.

“They can hide in these really dense infestations and it’s very hard for natural predators of mice to get in because the invasive plant infestations are so thick,” Gardner adds.

She thinks there might be more blacklegged ticks on other common invasives that can become a monoculture in the forest understory, like honeysuckle and buckthorn. 

“We really haven’t actively looked for it before,” she says.

Other researchers, like Dr. Thomas Mather, a tick ecologist at the University of Rhode Island, point out there are many variables that determine where blacklegged ticks show up on the landscape, and invasive plants are just one of them.

“I would argue I could find lots of places now with non-invasive plants that have lots and lots of ticks as well. So I’m slightly a skeptic,” says Mather, who is not involved in the project. 

He thinks the link that’s been documented between species like barberry and blacklegged ticks might be overblown. “If you were to look at people’s interpretation of those studies, you would think, ‘Oh, as soon as you go over to a barberry, instead of those little red berries, they’re going to be raining ticks on you.’ It’s not that way.” 

And removing invasive species is not going to eliminate ticks entirely. 

“There is this question of, how much of a reduction does there need to be before you see a reduced risk [of disease],” says Dr. Bill Landesman, a tick ecologist and collaborator on the project, also at Vermont State University.

Other strategies, like doing tick checks or using chemical controls might ultimately be a more efficient way to manage the risk of disease than invasive species removal, according to Mather.

“The effort to manage that is huge compared to simpler things that also work, like spraying insecticides,” he says. 

For her part, Gardner hopes the research will spread awareness of the possible link between invasives and blacklegged ticks, and perhaps give people another reason to manage some of the invasive species on their property.

“We know that there’s an intense dislike of invasive plants, and, similarly, of ticks,” she says.

“We’re looking for win-wins.”