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

With thousands of Burmese pythons and other giant invasive snakes devastating wildlife in the Florida Everglades, the hottest question on many minds is: How far north could they go?

New research shows the snakes can withstand surprisingly cold temperatures, leaving open the possibility that their range could extend hundreds of miles northward.

Burmese pythons have been crawling amok in South Florida since at least the mid-1990s. The population's forerunners were probably released by pet owners daunted by the prospect of maintaining a predator that can grow to 20 feet (6 meters) long and weigh 200 pounds (90 kilograms).

No one knows exactly how many there are now, but estimates put their numbers in the thousands or tens of thousands. The pythons have been devouring local wildlife, indulging in mega-meals like deer, bobcats and alligators, as well as endangered species like the woodstork and the Key Largo woodrat.

So far the Burmese python invasion is restricted to Florida's southern tip, but scientists have been debating whether it could spread to more temperate parts of the United States. After all, the species' native range includes the foothills of the Himalayas, so it is no stranger to cold. One alarming study by the U.S. Geological Survey in 2008 predicted the pythons could find suitable climate in about a third of the United States, as far north as Washington, D.C.

How cold can you go?

To test those predictions, researchers recently brought 10 adult male pythons from the Everglades to South Carolina, to see whether they could survive the cooler climate. After implanting a radio transmitter and a temperature logger in each snake, the researchers let them loose in June 2009 in a snake-proof outdoor enclosure.

All 10 pythons did well through the summer and fall, and even survived 12 December nights that were no warmer than 41 degrees Fahrenheit (5 degrees Celsius). Then, in January, the region was plunged into an extremely unusual cold spell. With temperatures dipping below freezing at night for long stretches, the 10 snakes died, according to a paper published in September online in the journal Biological Invasions.

Still, said study leader Michael Dorcas of Davidson College in North Carolina, "there certainly is a possibility that pythons could survive in South Carolina and possibly even farther north."

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