Only a small fraction of Florida's Burmese python population survived the January 2010 cold snap. (Photo courtesy of Mark Conlin via Alamy)
Fifteen years ago, a cold snap froze much of Florida’s wildlife, including many of the state’s invasive Burmese pythons (Python bivittatus). But in this excerpt from Slither: How Nature’s Most Maligned Creatures Illuminate Our World (Gand Central Publishing, 2025), science writer Steven Hall shows that a subset of these pythons was genetically able to survive the cold, fueling a rapid evolution that may have helped the invasive snakes expand their range across North America.
In early January 2010, a historic and prolonged freeze gripped the southeastern United States, reaching as far as the subtropical Everglades. Temperatures hovered around 50 degrees Fahrenheit (10 degrees Celsius) for 48 hours; on January 11, thermometers in South Florida dropped to 24.8 degrees Fahrenheit (minus 4 degrees Celsius). Many remember it, if they remember it at all, for the frozen iguanas that fell from trees and the photos of citrus trees covered in icicles, as if some Minnesota winter carnival had been smuggled into the Deep South.
Yet for wildlife and invasive species experts, the Big Freeze was the start of a massive, unplanned experiment.
The immediate impact on the Burmese python population was clear. Dead snakes littered roadsides; frozen specimens were found in underground burrows; and as far north as South Carolina, at the famous “Where’s Waldo?” python enclosure, all 10 snakes died during a regional cold snap.
The researchers attributed the mass die-off to “maladaptive behavior”; many snakes tried to bask in the sun outside despite the frigid temperatures, rather than seek warmth in underground or aquatic shelters. Python “takes” — trappings by hunters that served as a rough proxy for the overall population — peaked in 2009 in the national park but plummeted by nearly fivefold over the next two to three years. At first, this seemed like good news.
But population numbers were still low, and the “models” were just that: models. Genes are where biology meets environmental challenges, and that’s where geneticists come in. They were less interested in the many snakes that died than in the few that survived.
Like all snakes, Burmese pythons rely on environmental warmth, lacking the ability to generate their own metabolic heat, so they must develop behavioral or physiological adaptations to survive life-threatening cold conditions that are not found in their native range. As a U.S. Geological Survey (USGS) review noted, “some of the southern Florida population survived” the 2010 event, “and these snakes and their offspring make up the current population.”
Sourse: www.livescience.com
