To ward off bloodsuckers, some mammals turn to plants, ants and each other as natural tick repellents
AS THE WORLD HEATS UP and their habitat expands, ticks—the bloodsucking parasites known for transmitting Lyme disease and spotted fevers harmful to humans and other mammals—are thriving. But some wildlife have ways of keeping ticks at bay that scientists are just starting to understand.
Take American black and brown bears. Perhaps their most charismatic behavior, standing on their hind legs and wriggling against a tree, leaves behind a signature scent that lets other bears know they were there and likely helps them scratch hard-to-reach spots. Now scientists may have found another reason: rubbing on tick repellent.
When a bear rubs against trees, particularly conifers, the trees release pungent, sticky resins and saps—especially if the bear clawed through the bark first. Those goos can get stuck in fur and on skin, providing a physical—and potentially a chemical—barrier against parasites, including ticks.
To test this idea, Agnès Blaise, a Ph.D. student in biology at France’s University of Strasbourg who published her research in Journal of Zoology earlier this year, put ticks in tubes with two smelly substances derived from trees: beech tar and turpentine. The ticks high-tailed it away from the stink, suggesting tree resins and saps might help bears naturally stay tick-free.
“We are not the only animals that can self-medicate,” Blaise says. “An antiparasitic effect … could explain why bears are doing this, in spite of it being very energy-demanding and time-consuming.”
If bears are the frontier of repellent research, primates are old-school. Over decades, scientists have observed more than 40 primate species rubbing various smelly substances on themselves or otherwise self-medicating. Capuchin monkeys, macaques and owl monkeys have used everything from onions to pepper leaves to citrus fruits. Studies have shown that pungent oils lingering on fur can send ticks scurrying.
Many monkeys have another advantage in the fight against parasites: social grooming. In addition to physically removing ticks and other parasites from each other, monkeys have been observed rubbing citrus on each other’s backs. As largely solitary animals, bears don’t have that luxury. “They have to find their own solutions,” Blaise says. Mice and voles, which represent significant tick reservoirs in the United States, rely on copious self-grooming to rid themselves of ticks, too.
Monkeys and some birds may seek tick-repelling chemicals in a surprising source: ants—specifically members of the Formicidae family, including carpenter ants—that release formic acid as a defense mechanism. In a behavior called “anting,” monkeys destroy the ants’ nest on the ground, prompting a horde of ants to scurry out and attack.
“The monkeys just start rubbing themselves with ants,” says Tiago Falótico, a primatology fellow at Brazil’s University of São Paulo. Falótico’s research has shown that formic acid repels ticks, providing a potential explanation for anting. Monkeys also use millipedes, which release tick-repelling chemicals called benzoquinones.
Other researchers have observed passerine birds, such as starlings and grackles, lying in ant nests and crushing the ants into their feathers. Like monkeys, this avian order also rubs citrus and other smelly substances into their feathers.
“They look sort of nuts when they’re doing it,” says Dale Clayton, a biologist at the University of Utah. Ticks are less of a concern for many birds that spend little time on the ground, so the behavior also could target other ectoparasites or bacteria, according to Clayton.
“We don’t know a lot about these behaviors, frankly,” he says. “Maybe 200 [bird] species do this crazy behavior, when they’re totally vulnerable to predators. It must be worth it for them.”
Backyard birds might not worry too much about ticks, but their predators do. Domestic cats and other pets that go outside should be treated with tick-repellent medicine, but a favorite cat snack can help. Nicoletta Faraone, a biochemist at Canada’s Acadia University, found that essential oils in catnip can repel ticks.
“But don’t put on catnip to avoid ticks while you’re hiking!” she warns. Big cats, including mountain lions, are attracted to the plant, too.
Not all wildlife have safe and efficient remedies. Across the Upper Midwest and New England, moose have been hit hard by ticks, and biologists are struggling to help. “These moose get such heavy loads of ticks—70,000 or more—that their blood supply is pretty much drained,” says Michelle Carstensen, a wildlife health specialist for the state of Minnesota. While a robust adult can withstand a hefty tick load, a younger or infirm moose doesn’t have a chance.
What’s more, scratching—a moose’s one known tool—“might even make things worse, because they’ll be dealing with hair loss,” Carstensen says. Moose need a thick, warm coat to survive winters. If they rub it away, “they become anemic, and then hypothermic, and then they die,” she says.
Scientists know even less about risks and potential treatments among canids such as foxes, coyotes and wolves. That blind spot could be due to canids’ reputation as nuisance animals, according to Hannah Tiffin, an entomologist specializing in ticks at Pennsylvania State University. She says that’s an important knowledge gap we need to fill.
“With suburban encroachment, as humans expand into wild landscapes, we’re going to have more of that overlap between people and tick-bearing animals,” Tiffin says.
Rebecca Dzombak is a writer and editor with a Ph.D. in earth and environmental sciences.
A new storymap connects the dots between extreme weather and climate change and illustrates the harm these disasters inflict on communities and wildlife.Learn More
Take the Clean Earth Challenge and help make the planet a happier, healthier place.Learn More
Promoting more-inclusive outdoor experiences for allRead More
A groundbreaking bipartisan bill aims to address the looming wildlife crisis before it's too late, while creating sorely needed jobs.Read More
More than one-third of U.S. fish and wildlife species are at risk of extinction in the coming decades. We're on the ground in seven regions across the country, collaborating with 52 state and territory affiliates to reverse the crisis and ensure wildlife thrive.