Not long ago, I went on a walk with some friends through a field near my house in upstate New York. When we stopped for a break, something moving on my pants caught my eye. There were about a dozen reddish-brown ticks crawling up my legs. I looked closer and found ticks tangled in my socks, latched on to the insides of my shoes, hanging by hooked legs to the backs of my knees. The big ones, American dog ticks, were easy to spot, but the little ones, blacklegged nymph ticks the size of poppy seeds, were harder to find. I was still pulling them off of me days later.
Northeasterners are used to coexisting with ticks, but this season has felt unusually intense. An unofficial survey of my friends unearthed some horrifying anecdotes. A landscape designer said she had been bitten by more ticks this year than ever before. The owner of a local wine shop pulled a tick out of his hair at the Atlanta airport that had somehow managed to accompany him on the plane ride south. One guy is living with the (possibly permanent) trauma of finding a tick attached to his nipple.
The anecdotal evidence for a busy tick year is corroborated by data, Richard Ostfeld, a disease ecologist at the Cary Institute of Ecosystem Studies in Millbrook, New York, said. It's still too early in the season to say exactly how this year stacks up compared to previous years, but early returns indicate that there has been an explosion of ticks this spring. "All these people complaining of a horrendous year," Ostfeld said, "they're actually right."
The tick boom isn't exclusive to the Northeast. Tom Mather, an entomologist at the University of Rhode Island and director of a tick awareness program called TickEncounter, said he's seen an uptick in reports of American dog tick sightings and bites around the country this year. TickEncounter, which crowdsources tick data from people all over the U.S., shows American dog tick submissions were up 30 percent in April compared to March, about 10 or 15 percent higher than usual. "They're having a good year so far," Mather told Grist.
Jean Tsao, an associate professor of disease ecology at Michigan State University, said she's noticed more ticks this season, too. When she talks to colleagues in Michigan, Wisconsin, Maine, and even Quebec, Canada, she hears the same story: "It's a big year."
American dog ticks are big and noticeable, which is why, when people report encounters with ticks, Mather said, they're often reporting dog ticks. In the Northeast, where the risk of tick-borne illness is extremely high, the most dangerous ticks out and about right now are tiny blacklegged ticks in the nymph stage, the second stage of the blacklegged tick's three-stage, two-year life cycle. Nymphs typically emerge from hibernation in May, reach their peak around Memorial Day weekend, and stay highly active until July, right when Americans are heading out for some outdoor fun.
"Nymphs are really hungry when they emerge," Ostfeld said. "And they do look like they are at a peak this year." That's a big public health problem. Blacklegged nymphs carry Lyme disease, which can cause joint pain, weakness in limbs, and flulike symptoms in humans. And they're even harder to see than adult blacklegged ticks. It doesn't take long — about 36 to 48 hours — for an attached tick to infect a human host with Lyme. As a result, folks who contract Lyme usually experience symptom onset around this time of year.
There are a number of reasons for this year's tick boom, including climate change. Climate change is making the "shoulder seasons," spring and fall, warmer, which means longer feeding seasons for ticks. And rising temperatures are making it possible for ticks to shift their ranges all over the U.S. The lone star tick, an aggressive tick whose bite can cause humans to develop a severe allergic reaction to red meat, has been steadily making its way north from the southern U.S. for several years. Warming winter temperatures could be giving ticks a boost too, Tsao said. "It definitely seems that a mild winter helps their survivorship," she said. Urbanization and the fragmentation of forests also play a role, as do rodents and deer, which do a great job of picking up ticks in one place and dropping them off in another.
The main reason blacklegged ticks are booming in the Northeast this year has to do with acorns, Ostfeld said. In 2019, oak trees unloaded a big crop of acorns onto forest floors across vast swaths of the Eastern Seaboard. The plethora of hardy tree nuts was a boon for rodents of all kinds — especially mice, which are major carriers of Lyme disease. Rodents survived well that winter and got a jump-start on spring breeding in 2020. When baby blacklegged ticks hatched that summer, they had no shortage of mice to feed on. A year later, those baby larval ticks are molting into nymph ticks — the ticks posing a risk to so many of us this summer.
Climate change has an indirect effect on these big acorn years, or "masting events," too, Ostfeld said. Research shows that oak trees are able to produce lots of acorns when they can photosynthesize and store a lot of carbon. Longer growing seasons, in addition to the warmer and wetter conditions we're getting in the Northeast, help oaks do that. And storing carbon is even easier to do when atmospheric carbon is at record-high levels. "If it's really warm and wet, the oak trees can come to a point where they can let loose with a large bumper crop of acorns sooner and probably a bigger bumper crop," Ostfeld said. "So there is some evidence for a climate signal on the ability of oak trees to make bumper crops of acorns."
Some amount of global warming might be baked in, but tick-borne illnesses are not inevitable. When going outside, experts recommend wearing long, light-colored pants, teaming up with a buddy for daily tick checks, and avoiding tall grass when possible. I also recommend protecting your nipples at all times.