An opossum nicknamed Prairie Dog met a gruesome fate last fall in Key Largo, Fla., when it was squeezed to death and then swallowed whole by a massive, 12-foot-long Burmese python. But you could say it got revenge, thanks to an unusual accessory: a tracking collar that led scientists to its killer.
Prairie Dog was one of dozens of opossums and raccoons that scientists equipped with tracking collars as part of an ongoing study to try to understand how these mammals move across nature reserves on Key Largo, a 33-mile-long island off the coast of southern Florida. But the researchers also hoped that tracking potential prey could lead them to invasive Burmese pythons, which are relative newcomers to Key Largo but have wreaked havoc in the Everglades in mainland Florida for decades with their voracious appetites for mammals.
“A secret, underlying potential application was that [this initiative] could lead to python captures,” says Michael Cove, a conservation ecologist on the project and a research curator of mammalogy at the North Carolina Museum of Natural Sciences. “That was kind of a hope—not a hope that these animals get eaten but a hope that if they do, they lead to captures and removals.”
For Cove, the project stems from efforts to protect two species of rodent found only on Key Largo: the Key Largo woodrat (Neotoma floridana smalli) and the Key Largo cotton mouse (Peromyscus gossypinus allapaticola). Younger, smaller pythons eat both critters, which are considered endangered. And the rodents are intriguing beyond that endangered status: Key Largo woodrats build huge nests from dirt and sticks that can house generations of the animals. “They’re basically building these gigantic compost heaps within the forest, and then a ton of other species use those compost heaps as habitat or foraging grounds,” Cove says.
Cove and his colleagues hoped to determine if raccoons and opossums were eating the Key Largo woodrats and Key Largo cotton mice or otherwise competing with these rodents for the island’s limited resources—native fruits and nesting spots, for example. If so, the raccoons and opossums might have been getting a leg up from human residents putting out garbage and cat food that didn’t appeal to the native rodents. Or these animals’ urban excursions might have reduced stress on the local rodents. Scientists hoped that tracking the opossums and raccoons could determine which was the case.
If a collared opossum or raccoon happened to become a beacon pointing to a massive, invasive snake, well, far be it from the researchers to complain. That’s how, in November 2022, invasive species technician Joe Redinger and three of his colleagues found themselves hauling out of the ground the 12-foot, 62-pound snake that had eaten Prairie Dog the opossum.
The hours-long snake extraction was the culmination of weeks spent tracking the signal put out by Prairie Dog’s collar after an alert that the animal had stopped moving. The lengthy tracking process was necessary in part because pythons can hide in the Swiss-cheese-like local bedrock. “It takes a lot of patience; they’re incredibly difficult to find,” Redinger says of the snakes.
“They’re really well camouflaged; they blend in great with the leaf litter,” he adds, noting that he’s nearly stepped on more than one python in his work. “You can be right on top of these animals and not even know.”
But once Redinger and his colleagues had fished the snake out of its hiding spot and euthanized it, there was one fewer Burmese python—and because it was a mature female, some 60 fewer python eggs—in the delicate ecosystem of Key Largo.
The first credible report of a Burmese python on Key Largo was made in the mid-2000s, but exactly how many of the snakes have made their home on the island in the past couple of decades isn’t clear. “Population size estimates are some of the most important missing pieces as far as successful suppression of the Burmese python invasion,” said Jacquelyn Guzy, a population ecologist at the U.S. Geological Survey, who isn’t involved in the project but recently led a detailed review of pythons in Florida, in an e-mail to Scientific American. “So far there are no reliable python population estimates, and this includes for Key Largo.”
Cove noted that more snakes are observed on Key Largo every year but says the fact that there are still plenty of mammals on the island means the situation isn’t as dire as it could be. “We’re still relatively early in the invasion front,” he says. “There is still the potential for management before it’s too late.”
In fact, if the python invasion were more advanced, the collaring project wouldn’t have been possible because so few mammals would be left. Cove compared the situation with what’s happening in the Everglades, where the snakes have reigned for decades and have snapped up not just opossums and raccoons but also bobcats, rabbits and foxes: there aren’t enough mammals living in that ecosystem left to collar. But on Key Largo, midsize mammals are still abundant enough to study—hence the collaring.
Kelly Crandall, a master’s student in forestry at Southern Illinois University, who is gathering the mammalian data as part of her master’s degree project, was particularly interested in studying toxoplasmosis, a disease she knew raccoons and opossums might be picking up from the island’s feral cat population.
Scientists know that toxoplasmosis can cause animals of some species to become more reckless. So Crandall wondered if infection could make her study subjects more likely to become a snake’s lunch, even as she doubted pythons would ever have an opportunity to eat a collared animal.
“We had a lot of questions regarding if a python would and could eat a study animal,” Crandall says. She notes that the team has collared only perhaps 2 percent to 5 percent of the island’s total population of raccoons and opossums. “We didn’t know if they’d be running into big snakes,” Crandall says. “We didn’t know how many really large snakes that are taking down raccoons and opossums are on the landscape. I also had concerns about whether they would be deterred by the collar.”
But Prairie Dog isn’t the only collared mammal that has faced a python. In January an alert from a raccoon’s collar eventually led team members to a second large snake they were able to remove. In February a second opossum collar put out an alert, although project personnel tracked it and a few stray hairs down in a pile of snake poop, not a snake. Scientists think the python that snagged the opossum must have been about 16 feet long.
With three known encounters and two snakes out of the ecosystem, wildlife personnel want to expand the project and lean into the technique as a means of catching pythons, Cove says. But even on Key Largo, collaring prey will only ever be one of a suite of tactics experts use to try to keep pythons at bay.
“Python researchers generally subscribe to the same philosophy: there isn’t one golden method to remove pythons from the landscape,” says Guzy, the USGS ecologist. “Each has its limitations, and so the more tools we have at our disposal, the better.”
And every python removal counts, even to Crandall, who loses a hard-earned study animal when a python strikes. “These ideas ended up removing these two huge snakes from a really delicate ecosystem,” she says. “It feels amazing.”