It’s finally happened. Winter is over, for real this time. That means that in much of the United States, the forests are at their most inviting… and the ticks are out in force.
You’ve prepared for this. You’ve got your repellant and know to tuck your pants into your socks and do a tick check after you’ve been outdoors. But what should you pay attention to as you’re headed into tick country? Are there any places where you’re more likely to get bitten than others?
We know that dense, shrubby patches of vegetation tend to be tick magnets. But scientists are only just starting to understand how different plants and features of the landscape amass or repel ticks. If you want to minimize your chances of encountering these disease-ridden pests, though, there are a few things you can watch out for.
Avoid the aliens
Ticks tend to hang out in places where they are sheltered or where their animal hosts spend a lot of time. These preferences vary among different species. “Not all ticks are created equally,” says Rebecca Eisen, a research biologist at the Centers for Disease Control’s Division of Vector–Borne Infectious Diseases in Fort Collins, Colorado. Dog ticks, which can transmit tularemia and Rocky Mountain spotted fever, are often found in grasslands. Other ticks are more vulnerable to desiccation and prefer shady woodlands. These include the blacklegged ticks (also called deer ticks) that spread Lyme disease.
There’s evidence that some invasive plants may be particularly good places for ticks to await passing animals. That’s because invasive species tend to be ones that can overwhelm the competition and dominate the forest understory, says Scott Williams, an ecologist at the Connecticut Agricultural Experiment Station in New Haven. So these plants are often found growing in large thickets or tangles of vines that create a shady, humid shelter for ticks. This allows ticks to spend more time questing—a behavior in which the animals wait poised on the edge of a leaf or blade of grass with their front legs outstretched—without drying out.
One such offender is Japanese barberry, an ornamental shrub that was introduced to New England in the late 1800s and has since spread to 32 states. This plant offers a perfect storm of conditions that are ideal for blacklegged ticks, Williams says. Not only does it grow in dense infestations, but it is just the right height to give ticks a great perch from which to grab deer as they brush past. To make matters worse, barberry is “highly unpalatable” to deer, Williams says. “They’ll eat everything else in the forest except barberry, so the deer consume all the competition.”
Of course, native plants can and do harbor ticks as well. “People should beware of low growing and dense vegetation which will provide the same benefit to ticks,” Williams says. Still, native understory tends to be patchier than barberry stands, which makes it a more hostile environment for blacklegged ticks.
He and his colleagues have found greater numbers of blacklegged ticks in barberry stands than elsewhere in the forest. In areas where they removed Japanese barberry, the amount of ticks dropped sharply. This indicates that controlling nuisance plants like barberry could deprive ticks of shelter and expose them to harsh, sunny conditions more similar to those found in native understory. “We’re trying to figure out what is the best forest makeup to reduce ticks and pathogens,” Williams says.
However, the team also saw that as time passed, the plant began to creep back in and the ticks rebounded. So if we want to keep the blacklegged tick population down, we’ll have to give areas where Japanese barberry has been eliminated a touch-up every five or so years, Williams says.
Another plant that may increase our risk of getting a tickborne disease is Amur honeysuckle, a woody shrub native to Asia. In this case, the problem is not that the plant creates a refuge for ticks. But because deer graze on the plant and use it for shelter, Amur honeysuckle tends to accumulate ticks that have been feeding on them. Scientists have found that eradicating patches of honeysuckle in Missouri cut down on the numbers of lone star ticks—a “very aggressive” species that can transmit a serious condition called ehrlichiosis or render you allergic to red meat—in a given patch of forest.
Don't stop to smell the roses
You might also want to steer clear of multiflora rose. Native to eastern Asia, this plant was introduced for decoration and to prevent soil erosion and create living fences for cattle. It now grows in dense thickets across the mainland United States. Scientists recently reported in the journal Parasites & Vectors that ticks in forest fragments dominated by multiflora rose bushes were about twice as likely to be infected with the bacteria that cause Lyme disease, Borrelia burgdorferi, as those in uninvaded patches of forest.
This could be because areas that have been taken over by multiflora rose are more appealing to white-footed mice, says coauthor Solny Adalsteinsson, a staff scientist at the University of Washington in St. Louis’s Tyson Research Center. Once mice have been infected with B. burgdorferi, they are able to transmit it back to the next tick that feeds on them. This makes them a much better reservoir for the bacteria than other animals that ticks feed on, including deer. So where there are mice, the bacteria can flourish.
One way to combat B. burgdorferi could be to remove invasive roses and replant native understory, which provides better habitat for a wide range of animals, including ones like raccoons and possums that are poor hosts for the pathogen, Adalsteinsson says.
There is a twist, though—ticks tended to congregate on the rose bushes, yet the uninvaded patches of forest actually had three times more ticks overall. “The uninvaded forests, they don’t have much going on in the understory but they do have a thick leaf litter layer which is probably [even] more conducive for tick survival,” Adalsteinsson says.
This means your chances of encountering an infected tick are likely higher in forests that haven’t been overrun by multiflora rose, even though the pathogen is rarer in these areas, she says.
You can avoid the dense shrubberies where ticks gather by sticking to the center of the trail, but paying attention to how much leaf litter is on the ground is also a good idea. “They’re sneaky,” Adalsteinsson says. “All it takes is your shoe or your sock brushing by some leaf litter, and if there’s a tick waiting there they grab on.”
Traversing tick terrain
There are a few other features of the forest landscape you can keep an eye out for too. Adalsteinsson and her colleagues didn’t find very many blacklegged ticks right near streams. “Drying out is a huge risk, but if things are too wet then they risk getting infected by fungi as well,” she says. “Real close to the stream ticks are likely either washed away or the soil is just too wet to survive.” She’s also examined lone star ticks in the Missouri Ozarks, and saw that the pests were less plentiful on south-facing slopes. These areas received more sunlight, possibly making them too hot and dry for the ticks.
You may also want to be especially careful right as you’re beginning your trek. “The most likely place for me to pick up ticks is in the first five steps after I get out of my pickup truck on the edge of a forest,” says Matthew Ayres, an ecologist at Dartmouth College. He’s investigating whether ticks are indeed more abundant on the borders of a forest than within it. He suspects that ticks will be most densely concentrated in the bountiful shrubs and grasses that spring up where forests give way to meadowland.
There also seems to be a connection between blacklegged ticks and oak trees. Following mast years, when oaks produce a glut of acorns, the population of white-footed mice shoots up, causing the number of infected ticks in the forest to rise in turn. Ayres is now looking into whether more ticks can be found right in the vicinity of oak trees.
Another place where blacklegged ticks may build up are fallen logs where animals like mice and chipmunks nest. “You sometimes see little clusters of ticks around where you would have nests or where those small mammals are spending a lot of time,” Eisen says. “But that doesn’t mean that you won’t find a tick elsewhere.”
It’s also worth mentioning that ticks are only becoming more of a nuisance. The Centers for Disease Control reported last week that diseases transmitted by pests like ticks and mosquitoes are on the rise in the United States. Between 2004 and 2016, the number of cases of tickborne illnesses doubled and seven new tick-borne pathogens emerged in the country. There are likely a number of reasons for this, including a drop in deer hunting, warmer temperatures related to climate change, and ticks hitching a ride on travelers to get to new territory.
None of this means you should flee the forest and barricade yourself indoors. But where there is woodland, there will be ticks, and it’s best to assume the little suckers could be just about anywhere. Yes, some parts of the forest might be hotspots, and you can be extra careful about giving them a wide berth. Just make sure you also take all the usual precautions.