Will Florida's Burmese pythons move north? How far?

For one thing, the subfreezing temperatures were highly unusual for the region. For another, some studies indicate that the temperatures a snake experiences during its first year determine how it regulates its body temperature for the rest of its life. Snakes born in the area might fare better than snakes transplanted in as adults.

Finally, the pythons that survived the longest were the ones that crawled into underground cavities at night, and Dorcas wonders whether they might have fared even better outside the enclosure.

"There are certainly in South Carolina much deeper retreats that they could have found if they were out in the wild, such as armadillo burrows," Dorcas said. “If we provided deeper refugia, well, would they have survived? We certainly had snakes that survived a long time and were finally killed by the extreme cold snap we had in January. But snakes had survived many nights where it got below freezing.”

Florida cold snap

The same cold snap that killed the South Carolina transplants also killed many Burmese pythons in the Everglades. Nine of 10 radio-tagged pythons there died, researchers reported in another Biological Invasions paper, published online in June. That sounds like a good proportion, but extrapolating to a population of thousands leaves plenty of snake survivors, said Skip Snow, a wildlife biologist based at Everglades National Park who contributed with Dorcas and others to the study.

In the months since the cold snap, adults and 24 hatchlings have been spotted in the wild, according to Snow. That's about the same number of hatchlings found by this time last year, so clearly the wintry weather didn't set the population back much. Whether the surviving pythons have genetically based adaptations to the cold is unknown, but if so, said Dorcas, "then we just had a major selection event for cold-tolerant pythons."

What it all means for the pythons' ability to invade farther north remains to be seen, but Snow takes the long view: "The snakes are going to tell us. They're clearly here, and they're breeding and they're established and they're going to tell us over the years and over the decades just what they can put up with and how far they can go."

If Snow doesn’t sound very hopeful that the snakes can be eradicated, it's because they're so secretive, and the Everglades are vast, largely inaccessible, and full of hiding places. "We have no proven eradication tools for introduced reptiles anywhere in the world, really. It's never been done, and we have no studies to go to, that say: 'Yep, if you do these things you can eradicate an introduced reptile.' Our toolbox is empty of proven tools," he said.

Not that he and other managers aren't trying. The current strategy focuses on containing the pythons' range, stubbing out isolated populations, and targeting areas where pythons are particularly destructive, such as near bird colonies.

Public involvement is also key. The latest tactic on that front is a new smartphone app that serves as a field guide to the region's big reptiles. Eventually the public will be able to transmit sightings, photos and GPS data to help authorities track invaders.

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