Turns out, opossums may not actually like eating ticks

This story was originally published in March 2022.

It’s not that Griffin Dill has anything against opossums. The director of the University of Maine Tick Lab just wants to set the record straight: North America’s only marsupial is not a tick-eating machine gobbling up thousands of the parasites in a single meal.

In fact, it turns out ticks are not even part of an opossum regular diet.

The idea that opossums consumed an abundance of ticks really helped the animal’s reputation, Dill said, since many people consider the animals nothing more than large vermin and pests. But he said people can get a false sense of security if they rely on opossums as a tick management control tool on their property.

“I don’t want to impune the poor opussums because they have gotten a bad rap in the past,” Dill said. “But it is important to understand what is and what is not happening in terms of ticks.”

That’s especially important in Maine where ticks have been on the increase in recent years, including the deer tick that carries the dangerous Lyme disease.

The most common opossum in North America is the Virginia opossum, and there are members of that species in southern Maine.

Dill said the idea of a single opossum eating thousands of ticks in a single week dates back to a study conducted by the Cary Institute of Ecosystem Studies in 2009.

According to Dill, researchers placed several adult small mammals, including opossums, in cages and then placed a hundred or so larval ticks in there with them.

“They waited several days and then counted how many ticks had fed and dropped off the animals,” Dill said. “When it came to the opossums they only found a few ticks meaning the opossums had eaten the rest.”

The researchers then did some math, extrapolated the numbers and came to the conclusion that a single opossum in the wild routinely ate between 5,000 and 6,000 ticks a week.

“It’s gotten spun through social media into opossums being tick vacuums running through the landscape gobbling up on every tick they see,” Dill said. “It’s really taken on a life of its own.”

But a 2021 peer-reviewed study by Cecilia Hennessy and Kaitlyn Hild of the division of math and sciences at Eureka College titled “Are Virginia opossums really ecological traps for ticks? Groundtruthing laboratory observations” attempts to debunk the opossum tick-eating behavior.

After analyzing the stomach contents of 32 wild opossums from central Illinois, the researchers did not find a single tick or tick body part. A subsequent search of scientific literature on the diets of opossums failed to back up the 2009 study.

“We conclude that ticks are not a preferred diet item for Virginia opossums,” Hild and Hennessy said in the abstract of their study. “Considering that wildlife unconditioned to laboratory conditions may exhibit non-typical behaviors, we recommend that lab-based studies of wildlife behavior be groundtruthed with studies based in natural conditions.”

What’s worse, Dill said opossums can carry certain pathogens, including the one that causes Equine protozoal myeloencephalitis — or EPM — that affects the central nervous system of horses.

“I’m not saying we should go back in time when we looked down on opossums,” Dill said. “But like any wildlife species there are a number of things they do carry that should not be encouraged and when it comes to ticks, opossums are not the silver bullet people want them to be.”