In the 1930s, a Florida cruise boat operator named Colonel Tooey (Colonel was in fact his first name) had a grand idea for jazzing up his tours. He decided to deposit six rhesus macaques on a man-made island near Silver Springs, hoping to entice tourists with the promise of monkey sightings. What he did not appear to know, however, is that rhesus macaques can swim.

Tooey’s star attractions quickly hightailed it into Silver Springs State Park, where they established a troop that now numbers around 300 individuals. The monkeys are cute and popular with tourists. They are invasive and about a quarter of their population is infected with the herpes B virus. Now, according to Anne Schindler of First Coast News, their population appears to be expanding.

The macaques were already known to range beyond the limits of Silver Springs State Park, but recently, for the first time, they were spotted in Jacksonville, nearly 100 miles away in the northeastern part of the state. “Florida Fish and Wildlife Conservation Commission (FWC) officials call the reports credible,” First Coast News reports, “a likely expansion of the feral monkey population in Central Florida.”

Though they are typically skittish around people, the macaques have been known to get aggressive. In 2017, parts of Silver Springs State Park had to be shut down because the monkeys were getting tetchy about human visitors. According to Carlos E. Medina of the Ocala Star-Banner, there is concern that a continued increase in the macaque population will mean more chances of interactions and conflicts with humans—which is disconcerting, in part, because of the monkeys’ herpes problem.

Macaques shed the virus in their saliva, urine and feces, reports Hannah Knowles of the Washington Post. Humans can contract herpes B from infected monkeys through scratches, bites, or contact with an infected animal’s nose or mouth. If untreated, the disease can lead to brain damage or even death—but according to the CDC, “B virus infections in people are rare.” Since 1932, there have been only 50 people with documented herpes B cases in the country, 21 of whom died.

“Hundreds of bites and scratches occur every year in monkey facilities in the United States,” the CDC notes, “but people rarely get infected with B virus.”

Steve Johnson, a University of Florida wildlife ecologist, tells First Coast News that the concern about herpes B transmission from macaques comes down to “low risk, high consequence.” A more pressing worry, perhaps, is the possible impact of the monkeys on the native environment. In the 1970s, rhesus macaques decimated red mangroves in the Florida Keys, “leading to massive vegetation loss and shoreline erosion,” according to the FWC. Between 1984 and 2012, around 1,000 of Florida’s feral monkeys were removed or sterilized as part of a state-sanctioned initiative—one that abruptly came to a halt when the public discovered that the trapped monkeys were being sold for biomedical research.

Since then, the FWC has prohibited the feeding of wild monkeys, but there are no population control efforts currently in place, according to First Coast News. Sterilizing the monkeys is expensive, and culling them is unpalatable. So officials are facing what Johnson describes as a “lose-lose situation.”

“It’s not an issue if it’s catching pythons,” he tells the Ocala Star-Banner, referencing the invasive Burmese pythons that Florida hunters are encouraged to “humanely kill.” “No one cares about snakes. When it’s a furry, charismatic animal, it makes it different.”

But letting the macaques proliferate unchecked is not a viable option, either. “Unless there is some management action by the state to curtail their numbers,” Johnson says, “it’s going to create a situation where they will be forced to take more drastic action due to a serious incident.”