In the 1980s, a small number of pet Burmese pythons were released into the Florida wilderness. The slithering snakes have since proliferated throughout the southern part of the state, and they are eating their way through populations of birds and mammals, including some that are endangered. As Bopha Phorn reports for ABC News, a team of researchers recently discovered an additional threat to Florida’s biodiversity: a number of Burmese pythons running loose in the state are hybrid species, which could make them even more resilient than their non-hybrid cousins.

Scientists from the United States Geological Survey and the Everglades National Park analyzed tissue from the tails of around 400 Burmese pythons that were captured in Florida between 2001 and 2012. The team wanted to learn more about the invasive species in order to better understand Florida’s Burmese pythons and the acute threat they pose to the state’s wildlife.

Native to Southeast Asia, Burmese pythons can grow up to 23 feet long and weigh 200 pounds. According to the USGS, these hulking snakes are now distributed across more than a thousand square miles of south Florida, including the entire Everglades National Park. In July of this year, Michael Kirkland, an invasive animal biologist at South Florida Water Management District, told Deutsche Welle that his agency has recorded a “a 99 percent reduction of fur-bearing animals” in the Everglades due to ravenous Burmese pythons.

“They are now preying on wading birds and even the occasional alligator,” Kirkland added.

Like other invasive species, Burmese pythons have disrupted delicate food chain balances in an area where they do not belong. And the problem may be more complex than scientists previously realized.

When researchers involved in the new study analyzed tissue samples from Florida snakes, they discovered that some animals assumed to be Burmese pythons were also carrying DNA from another type of snake. Writing in the journal Ecology and Evolution, the team reveals that 13 of the 400-odd snakes had genetic signatures of the Indian rock python in their mitochondrial DNA, which is inherited from the mother.

The two snakes likely hybridized long before the Burmese python became pervasive in Florida; according to the study authors, the inter-breeding probably happened in their native ranges or in captivity. But Margaret Hunter, lead author of the new report, tells the Guardian’s Richard Luscombe that the results of the study are nevertheless worrisome.

“When two species come together they each have a unique set of genetic traits and characteristics they use to increase their survival and their unique habitats and environments,” she explains.

Indian rock pythons, for instance, are smaller and faster than Burmese pythons. And while Burmese pythons prefer to dwell in jungles and grassy marshes, Indian rock pythons thrive on higher and drier ground.

“You bring these different traits together and sometimes the best of those traits will be selected in the offspring,” Hunter tells Luscombe. “That allows for the best of both worlds in the Everglades, it helps them to adapt to this new ecosystem potentially more rapidly.”

When it comes to controlling invasive species, knowing thine enemy is key. Wildlife experts have tried to curtail invasive snake populations in Florida in a number of ways, such as implementing civilian hunting initiatives and training dogs sniff out Burmese pythons. But the “cryptic nature of these snakes has limited detection and control efforts,” the study authors write. Having a more thorough understanding of the genetic makeup of invasive snakes, they add, “can inform management decisions and help to guide targeted removal efforts.”