Across the southeastern United States, a quiet biological upheaval is unfolding as giant reptiles spread into new territory and show signs of adapting to colder weather that once held them in check. Biologists warn that these changes, driven by both evolution and behavior, could lock invasive species into the landscape and reshape ecosystems already stressed by development and climate change. The alarm is growing as experts document Burmese pythons, Argentine black and white tegus, and other large reptiles surviving cold snaps that used to be lethal.
The spectacle is jarring: iguanas dropping from trees in a freeze while other invaders hunker down, ride out the chill, and emerge ready to keep hunting native wildlife. I see in this contrast a preview of which species will dominate a warming, more volatile South, and why scientists are racing to understand how quickly these animals are changing.
Cold-resistant pythons and the new reptile frontier
For years, the assumption among wildlife managers was that Florida’s periodic cold spells would at least slow the spread of Burmese pythons. That confidence is eroding as researchers document snakes that appear to be adapting to lower temperatures, both through behavior and physiology. Experts have warned that there is a clear potential for behavioral shifts and even genetic changes that enhance cold tolerance in these large reptiles, a concern underscored by reporting that highlights how experts alarmed by Burmese python behavior see a pathway for the snakes to push beyond their current range.
Those warnings now sit alongside evidence that Burmese pythons in Florida are already enduring conditions that once would have killed them. Coverage of the latest Arctic blast notes that Burmese pythons in Florida have reportedly adapted to endure colder temperatures, even as other reptiles succumb to the chill. When a species that can reach more than 5 meters in length and prey on everything from wading birds to deer begins to shrug off freezes, the ecological stakes extend far beyond one state’s borders. I see this as the leading edge of a broader reptile frontier, where the line between “too cold” and “just right” is shifting north.
Argentine tegus: South American predators built for the cold
If Burmese pythons are the headline-grabbing invaders, Argentine black and white tegus are the stealth operators, already engineered by evolution to handle cooler climates. These South American lizards, which can grow more than a meter long, have established breeding populations across south Florida and are now showing up in new counties. Local reporting has described how Argentine black and are spreading across Florida, with warnings that Argentine tegus are in Florida communities that never expected to host a South American predator.
Part of what makes these lizards so formidable is that they are not tropical specialists. In their native range, Argentine black and white tegus experience seasonal cool periods, and they bring that hardiness with them. Wildlife agencies emphasize that Tegus can brumate, a reptile form of hibernation, during colder months, which increases their likelihood of survival across entire states. That ability to retreat underground, slow their metabolism, and wait out bad weather is precisely the trait that could let them leapfrog northward as winters become milder and more erratic.
From Florida backyards to the broader Southeast
Florida has become the proving ground for how quickly these animals can colonize new landscapes. In several coastal and inland counties, residents are learning that the big lizard in the yard is not a familiar iguana but an invasive predator. Detailed explainers stress that the Invasive Argentine tegu is not a Florida iguana at all, but an Argentine species that spends much of its time on the ground, digs extensive burrows, and is a strong swimmer, traits that help it exploit everything from suburban lots to wetlands.
Scientists tracking the spread warn that this is not just a Florida story. One report notes that Argentine black and white tegus have already been detected from the Florida Keys to Alabama, Georgia and the Carolinas, a footprint that hints at how quickly they can move when conditions are favorable. Another account underscores that South American predators are spreading across south Florida, with University of Florida agriculture experts noting that some populations have been established in the wild for a decade. I read those timelines as a warning that by the time the public notices a new reptile in the neighborhood, it may already be deeply entrenched.
Cold snaps expose a split-screen reptile reality
The recent cold snap across Florida created a surreal split-screen: some reptiles dropping helplessly from trees, others quietly surviving underground. Video from South Florida showed Residents across South Florida waking up on a Sunday to iguanas lying on roads after a cold snap left the reptiles in a cold-stunned state. Wildlife officials explained that when temperatures drop quickly, iguanas lose muscle control and can fall from trees, a dramatic but often temporary paralysis that has become a familiar winter spectacle in South Florida.
Authorities have tried to turn that vulnerability into an opportunity for control. During the latest freeze, Florida officials temporarily allowed people to capture and drop off cold-stunned iguanas, noting that the animals can die from bacterial infections if left untreated or unmanaged. Residents responded in force, and one local account described how, during the cold snap, people helped capture more than 900 invasive iguanas without permits, with organizers calling it “a big deal” because Florida residents are trying to use the cold weather to remove an invasive species. In stark contrast, tegus and pythons that can brumate or find insulated refuges are far less exposed during these events, which means cold snaps may selectively knock back some invaders while leaving the most cold-tolerant ones relatively unscathed.
Climate change, shifting ranges, and what comes next
Behind these local dramas is a larger climate story. As winters across the United States trend warmer on average but punctuated by sharp cold blasts, the map of where reptiles and other wildlife can survive is being redrawn. Biologists have already documented how Armadillos moving north across the U.S. are a sign of global warming, with regions that were once too cold for the small mammal to survive now becoming habitable. If a relatively fragile mammal can expand its range this way, it is not hard to imagine what large, adaptable reptiles might do as cold barriers weaken.
At the same time, extreme cold events still matter, especially for native species that have not evolved the same tricks as their invasive competitors. The Florida Fish and Wildlife Conservation Commission has warned that Iguanas in a cold-stunned state can still pose risks and that rapid temperature swings stress many wildlife species, not just the invaders. I see a troubling feedback loop: climate change opens new territory for cold-tolerant reptiles, human trade and pet releases seed those landscapes with species like Argentine tegus and Burmese pythons, and then erratic weather events periodically cull the least adapted animals, effectively favoring the hardiest survivors. The result is a cohort of giant reptiles that are not only spreading, but evolving and behaving in ways that make them even harder to stop.
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