As ticks expand throughout the state, experts say prevention remains key

Climate change and deer overpopulation likely playing a role

A Lone Star tick.

Twice a year, ecologists at the Lake County Health Department visit five natural areas throughout the county and drag a large white cloth across vegetation and over the forest floor. They’re hoping to find some ticks.

In an effort to monitor the types of ticks in the area – and the diseases they carry – the department regularly collects samples and sends them downstate to a lab for testing. It’s a practice that is becoming routine for more and more county health departments.

That’s because there’s growing evidence that tick species in Illinois are expanding in range and although it’s a challenge to detect year-to-year population increases, cases of tick-borne diseases in the state have seen an undeniable rise over the past two decades.

Scientists say the reasons for these trends are varied, with climate change and deer overpopulation likely playing a role. In response, researchers and health departments have buffed up surveillance of the arachnid, but awareness and prevention remain the best defense against it, they said.

“Ticks are pretty hardy. It’s difficult to control their population size,” said Alana Bartolai, the ecological services program coordinator at the Lake County Health Department. “We do the monitoring side to understand what is out there and to help our medical providers understand what’s out there as well. But a lot of our communication is geared toward how people can prevent it themselves.”

At-home prevention is paramount, Bartolai said. Part of what makes tick populations so hard to control otherwise is their reliance on other mammals that are similarly difficult to control, such as mice and deer.

With Illinois deer easily exceeding their ecological capacity because of mild winters, abundant food sources and a lack of natural predators, ticks tend to thrive along with them.

At the same time, ticks are part of incredibly complex systems and deer populations are just one piece of the puzzle, medical entomologist Chris Stone said.

“It’s probably really a mix of different factors of changes in the environment, animal populations and then, in some cases, climate can certainly play a role,” he said.

For instance, the invasive Gulf Coast tick has been found to be much more prevalent in southern Illinois than had been realized, and the tick seems to be slowly traveling north amid more mild winter temperatures. About three years ago, the Gulf Coast tick was first reported in DuPage County – the farthest north it had ever been sighted.

Other environmental changes, such as habitat fragmentation, may be the cause for the expansion of other tick species. Stone said lone star ticks, for instance, are being found farther north and are perhaps moving from the south upward, while the blacklegged tick has been spreading farther into central and possibly southern Illinois.

“There’s also some evidence that this might actually just be kind of a reinvasion, and in the late 18th and early 19th century, [ticks] were actually sort of widespread in this area,” Stone said. “As a result of forest clearing and deer removal, they might have been driven out and now we could be seeing a reinvasion.”

Stone directs the Medical Entomology Lab at the Illinois Natural History Survey, which researches and surveils mosquitoes and ticks in close collaboration with the state and county health departments.

When Bartolai’s team collects samples in Lake County, they go to Champaign, where the lab is based on the University of Illinois campus. Although the lab previously focused mainly on mosquitoes, it began working on ticks about five years ago.

The lab’s tick surveillance work can be seen on an online map maintained by the Illinois Department of Public Health. Created with data collected by the lab, the map shows where in the state different tick species are established or have been reported. The map also indicates in which counties different tick-borne diseases have been detected. It can be found at

Beginning in March and tapering off in the fall, tick season is in full swing, but Bartolai said people shouldn’t be afraid to go outside.

“We want people to enjoy outdoor resources, and we have a lot of really great ones. It’s just about taking some preparation and steps when you do go outside,” she said. “I always tell people: Knowledge is also power.”

The four steps of protection against ticks are dress, defend, check and remove. That means wearing long sleeves and pants, using insect repellent, checking your body after being outdoors and promptly removing ticks with tweezers if they’re found on you, your children or your pets.

For information on how people can best defend against both mosquito and ticks bites, the Lake County Health Department has resources at

Jenny Whidden is a climate change and environment writer working with the Daily Herald through a partnership with Report For America supported by The Nature Conservancy. To help support her work with a tax-deductible donation, visit