As tick season approaches, experts warn that Illinois residents should be even more wary as the type of ticks in the state increases and the season lengthens.

Researchers discovered the Asian longhorned tick — an invasive species native to Japan, Korea and parts of China and Russia — in Illinois in April. First reported in the United States in 2017, the tick has since spread to 20 states.

“The role that this tick will play in the transmission of infections in humans is yet to be determined,” the Illinois Department of Public Health said in a recent statement.

But the U.S. Centers for Disease Control and Prevention says the tick is not likely to increase the spread of Lyme disease or cause a significant nuisance for humans. Instead, according to Mark Ernst, a veterinarian with the Illinois Department of Agriculture, the longhorned tick is most likely to affect cattle.

Though the longhorned tick generally targets cattle, Maureen Murray, assistant director of the Urban Wildlife Institute at Lincoln Park Zoo, said Chicago residents should be on the lookout for other types of ticks.

Tick patterns tend to vary significantly from year to year, Murray said, but one consistency has been a movement in tick season.

“We’re seeing less severe winters, which might lead to more ticks,” Murray said. “Fewer ticks die during the winter, and ticks can be active sooner in the spring, just because it warms up faster.”

Chris Stone, a medical entomologist at the Illinois Natural History Survey, said he suspects climate change is affecting the types of ticks in Illinois in a few different ways.

First, he said, warmer winters may be encouraging ticks to migrate. His lab has found the Gulf Coast tick, a tick that was once limited to the southern United States, across southern Illinois, he said. The tick can cause rickettsial disease, a type of Rocky Mountain spotted fever, in humans, which can cause fever, vomiting and even death.

“With particularly the winters getting milder, which is one of the main changes we’ve seen in Illinois over the past several decades, that could affect species and allow them to spread further north,” Stone said.

Murray urged Chicago residents not to fall for the common misconception that ticks are a rural problem. Chicagoans can come into contact with Gulf Coast ticks, deer ticks and other types of the disease-prone insects. Her institute has been doing surveys of Chicago green spaces since 2017 and has collected more than 1,000 ticks from different areas in the city over that time period.

“It’s really important to spend time outside and connect with nature in the city,” Murray said. “But we just want to make sure that people are aware that they could encounter ticks, and that there are straightforward steps for preventing tick bites.”

People should check themselves for ticks every time they exit a green space, she added.

Cattle producers also need to be vigilant, according to Ernst.

The longhorned tick can carry a disease that particularly affects pregnant cattle and calves, causing them to become anemic, weak and lethargic. There is no effective and approved treatment for the disease, Ernst said, so it can spread rapidly among surviving animals.

“We urge our cattle producers to check around their ears, under their tail, in their brisket areas, and look for large numbers of really small ticks,” Ernst said. “They’re only about the size of a sesame seed and can get up to the size of a pea when they’re engorged.”

Longhorned ticks also pose a particular threat because of their sheer numbers, he said.

“Female insects do not need a male in order to reproduce and can lay up to 2,000 eggs at a time,” Ernst said. “So it doesn’t take long for an area to become pretty well-saturated with this type of a tick.”

Becky Smith, an associate professor of epidemiology at the University of Illinois College of Veterinary Medicine, teaches the public how to identify, prevent and treat tick-borne diseases.

Cattle have been affected by the disease in places like Australia, New Zealand and Pakistan, she said. So far, there has only been one affected cow in the United States, but scientists have proven ticks can carry the disease in labs in the United States, she said.

“The biggest concern is for the beef industry and for the sheep industry as well,” Smith said. “One female can produce thousands of eggs, and the real concern is if you get a really strong infestation, a calf can die from blood loss.”

Smith added that people should be particularly aware of the risks of any kind of tick bite.

“Ticks are expanding their range,” Smith said. “They’re moving into a lot of places, and Illinois is at the frontline of that. We’re getting more ticks everywhere. We’ve seen a tenfold increase in the number of tick-borne illnesses. It’s time to be aware.”