As winters get warmer, ticks of several kinds are flourishing. Deer ticks, known for transmitting Lyme disease, are moving farther north. The longhorned tick, which came from overseas, has gained a foothold on the East Coast and begun moving west. Gulf Coast ticks have made it to states like Connecticut and Indiana. The lone star tick, which can make people allergic to red meat, is fanning outfrom the South and has been found as far as Canada.
And even in places long accustomed to them, ticks are becoming more numerous and active for longer stretches of each year.
Marc Lame, an entomologist and clinical professor emeritus at Indiana University’s School of Public and Environmental Affairs, put it simply: “There are more and different types of ticks around than there used to be, and I don’t see that stopping anytime soon.”
The spread of individual species can be difficult to track. The longhorned tick, for example, was not identified in the United States until 2017, but a recent study confirmed that it was here as early as 2010.
But there is evidence they are traveling across North America quickly: On its northern front in Canada, the deer tick — also known as the blacklegged tick — is believed to be extending its range more than 20 miles per year, said Catherine Bouchard, a research scientist at the Public Health Agency of Canada.
The movement of the lone star and longhorned ticks particularly worries Laura Goodman, an assistant professor in Cornell’s Department of Public and Ecosystem Health, because it takes so few to establish themselves in a new place. Both can breed in huge numbers — a single longhorned tick can lay 2,000 eggs. Female longhorned ticks can even reproduce alone, essentially cloning themselves through a process called parthenogenesis.
Some ticks are also behaving differently. Dr. Bouchard said that when she began studying deer ticks in southern Quebec around 2007, they stopped looking for someone to bite by October. Now, it is not unusual for her to see them in December.
Is this because of climate change?
Yes, in large part.
There are other factors at play, such as deer populations recovering along the East Coast after years of decline. But “there’s a clear scientific consensus that climate change is playing a role,” said Michael Dietze, who leads Boston University’s Ecological Forecasting Lab.
Because temperatures are rising, ticks and the animals they travel on — like deer and mice — are likelier to survive winters, and new territory is becoming hospitable.
Climate change also explains why ticks are emerging earlier in the spring and staying active later in the fall: They can be active whenever the temperature is above about 39 degrees Fahrenheit.