Burmese pythons are being spotted farther and farther north in Florida and could reach other states, experts warn. 'It really does feel like an alien invasion,' one scientist said.

• Burmese pythons are an incredibly destructive invasive species in Florida.
• Since they first came to Florida, more snakes have turned up in counties farther and farther north.
• Warming temperatures from climate change could help pythons spread beyond Florida.

Donnie Darko was deep underground in a pipe, but his transmitter was giving off a faint signal that researchers picked up from a plane and tracked to a tree nursery.

An equipment operator dug up the pipe, and out fell Donnie and a female python.

Donnie is just one of the scout snakes Ian Bartoszek, a biologist with the Conservancy of Southwest Florida, uses to try and find other Burmese pythons.

Pythons are so good at hiding, so destructive, and such a perfect fit for Florida's climate that it's only taken a few decades for a small population to become "one of the most intractable invasive-species management issues across the globe," according to a recent United States Geological Survey review.

Because of the snakes' versatility, both in diet and habitat, and their cryptic nature, they're thriving in difficult-to-access areas of the Florida Everglades and may be impossible to eradicate, the survey found.

"It really does feel like an alien invasion," Bartoszek said. Given the right conditions, that invasion could spread to other states.

How Burmese pythons got from Asia to Florida

The first definitive recording of a Burmese python in the Florida Everglades was in 1979.

"They originally got here through the pet trade," Melissa Miller said, with over 300,000 snakes imported from Thailand, Myanmar, and Vietnam.

The animals either escaped, or their owners let them loose when they became too big to handle. Miller coordinates the invasive species research program for the University of Florida Croc Docs laboratory.

Throughout the 1980s and '90s, researchers thought the occasional python sighting was due to isolated escaped or released pets.

It wasn't until the early 2000s that they realized snakes were breeding in the wild. By then, it was too late.

Florida's subtropical climate, its many ports of entry for a flourishing pet trade, and the ecological marvel of the Everglades constituted the perfect ingredients for establishing a growing population of Burmese pythons, Bartoszek said.

Pythons are on the move and no one knows how far they'll go

Every year, "we're just seeing them show up in counties further and further to the north," Bartoszek said.

A radiotagged snake showed it could travel about a mile a day, and people have seen pythons swimming 15 miles offshore.

Since the 1990s, they've spread from the southernmost tip of the Florida peninsula to over 100 miles away.

But exactly how far north pythons live in Florida is unclear as is how they're spreading — whether it's from wild populations migrating or local pet releases.

They range at least as far as Lake Okeechobee in central Florida through an island in the Florida Keys, about 130 miles away.

Models predict pythons could possibly spread anywhere from the entire lower third of the continent all the way up to the Pacific Northwest — to states like Oregon, Washington, and Idaho — and Canada.

It would take decades for that kind of dispersal, and a confluence of other factors, like a lack of extremely low temperatures and better cold adaption for the snakes.

When they do travel, canals and deep-water levees may also make it easier for the snakes to get around.

"There's potential that they could help the pythons disperse," Miller said. "It could act as a bit of a python highway, but we don't know that right now."

How pythons could adapt to survive colder temps farther north

While the snakes don't fare well in freezing temperatures, it doesn't always kill them.

Florida's population bounced back after a 2010 cold spell. Those that lived through it might be better adapted to lower temperatures.

"Those individuals, when they reproduce with other individuals that survived potentially could propagate a more cold-tolerant gene," Miller said.

Warmer global temperatures combined with the pythons' ability to find refuge in underground holes could open up northern latitudes for the snakes.

Ten years ago, Bartoszek said, he would've said Burmese pythons are a Florida problem. "Then I just developed this mantra over the years of don't underestimate the Burmese python," he said. They're extremely versatile and adaptable.

Plus, there's the human element. People releasing pet snakes could establish them in other states.

"Hopefully pythons will be a cautionary tale for folks to not release pets into the wild and to make sure that pets are secure from accidental release," Miller said.

Because once they got a toehold, the pythons start decimating the local wildlife.

Pythons eat everything, and a lot of it

Burmese pythons have a generalist diet, meaning they eat just about anything, from mammals to birds to reptiles.

Researchers have linked the presence of the pythons to huge declines in mammal species in Florida.

In parts of the Everglades National Park, raccoon, opossum, and bobcat populations shrank by 87% or more, and marsh rabbits, cottontail rabbits, and foxes disappeared.

"It's just next level, the effect they're having on our wildlife," Bartoszek said.

Some of the largest pythons found in Florida include a 215-pound female with over 100 eggs inside and a 19-foot snake. During necropsies, Bartoszek said he's seen the remains of white-tailed deer.

Hatchlings can slither out their eggs already as long as 2 feet. Once they're fully grown, they have little to fear from other predators. "That's their evolutionary secret weapon is they can get really big really quick," Bartoszek said.

Catch them if you can

You might think a 15-foot snake would be easy to find. But their black-and-brown splotches on tan coloring helps them blend in with leaves, bark, mud, and just about anywhere else they want to hide.

And that's when they're above ground and not hiding in turtle holes or swimming through canals.

"Their probability of detection is less than 1%," Miller said. "If you go out searching for a python, it's going to be very unlikely that you're going to find one."

It makes python hunters' jobs very difficult. While state-regulated programs have removed over 13,700 snakes from the Florida Everglades, they're usually the ones found near roads and canal levees.

Most of the areas where pythons live are more than half a mile from a road, like in sawgrass marshes.

"If you can imagine hiking and climbing at the same time," she said. "You're just basically into muck up to your thighs and trying to pull yourself on sawgrass and cattail clumps to make any forward progression."

More remote pythons require a scout snake, like Donnie.

For the past 10 years, Bartoszek has been tracking pythons with radiotelemetry tags. Currently, he has about 40 male snakes, or scout snakes, that he closely follows from November to April. That's breeding season.

"They have sensory abilities that we can only imagine," Bartoszek said. "How they find each other is likely pheromones and chemical trails."

The scouts lead the team to egg-filled females. They've removed over 1,000 snakes and 10,000 eggs in the past decade that otherwise would've been impossible to find, Bartoszek said.

Miller is also using radio-tagged snakes to learn more about where pythons prefer to lay eggs. "It's kind of a win-win because you're removing pythons at the same time you're getting to do these more long-term studies," she said.

The biggest question researchers need to answer is how many Burmese pythons are actually in Florida at the moment. Without that information, it's impossible to know whether elimination efforts are succeeding.

Scent dogs, snake traps, drones, toxic bait, and genetic engineering have all been used or proposed as ways of helping remove pythons from Florida.

But, the USGS review found, current methods aren't sufficient to eradicate the population. And that means they could continue to expand both their numbers and distribution.