Having more pythons in Florida is actually increasing the rat population because they're killing the other predators, scientists warn

• Burmese pythons are killing off mammals that would normally keep Florida's rat population in check.
• A new study found that parts of the Florida Everglades were becoming overrun with rats as a result.

Florida's Burmese pythons have been known to prey on birds, reptiles, deer, and even alligators. But one thing they don't seem to have a taste for is cotton rats.

And the rats are thriving because of it.

The wildlife ecologist Robert McCleery told LiveScience that cotton rats "dominate the community" in parts of the Florida Everglades where pythons were prevalent.

McCleery and a team of colleagues measured this unusual relationship between python prevalence and cotton-rat population in a new study published in the Journal of Mammalogy.

Pythons are helping cotton rats take over

For the study, McCleery and his colleagues tracked 115 rats using radio transmitters attached to regions with high and low python populations.

They found that death rates for cotton rats were similar in both regions and that the pythons were responsible for only about 12% of rat deaths.

Instead, what was killing and consuming most of the rats were the usual suspects: birds of prey, mammals, and other reptiles. The plot twist here is that pythons are snacking on the same animals that enjoy cotton-rat dinners.

Scientists warned that the number of predators cotton rats face was declining and would likely continue to do so if Florida's invasive-python problem persisted.

Florida has a serious invasive-python problem

Burmese pythons aren't native to Florida and actually hail from Southeast Asia.

They became pests in Florida when people brought them overseas during the exotic-pet-trade industry in the 1980s and then later released them into the wild. The snake's numbers have been steadily growing ever since.

It's gotten so bad that Florida holds an annual Python challenge that awards thousands of dollars and cash prizes to people who can catch and humanely kill the most pythons.

Florida's python infestation has thrown the state's delicate ecosystems off-balance and has led to severe declines in mammalian populations, including raccoons, opossums, bobcats, foxes, and cottontail and marsh rabbits.

The US Geological Survey said the snakes were "one of the most concerning invasive species in Everglades National Park."

And McCleery said his team was seeing the rippling effects cascade down the food chain.

The lack of predators like foxes to hunt cotton rats "helps explain why mammal communities in python-invaded portions of the Greater Everglades Ecosystem are increasingly dominated by cotton rats and other rodents," the researchers wrote in the study.

Cotton rats carry concerning diseases

While this seems like good news for Florida rodents, it could spell bad news for residents because rats are notorious for carrying nasty diseases that can infect humans.

Let's say, for example, that a mosquito bites an infected cotton rat and then feasts on your blood — you could become infected. And the diseases that cotton rats can carry are not fun. They include hantaviruses and the Everglades virus.

Correction: June 9, 2023 — An earlier version of this story misspelled the name of the journal that published the study involving pythons and cotton rats. It's the Journal of Mammalogy.