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These giant lizards have a reptile superpower that may help them thrive from Florida to North Carolina

Close-up photo of an argentine black and white tegu lizard approaching the camera.
Lida Thornley/NCARK
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An Argentine black and white tegu. This species can grow up to four feet long.

Argentine black and white tegu lizards seem to break a lot of reptile rules. They’re smart enough to recognize individual humans. They’re big, up to four feet long from nose to intricately patterned tail. And they’re not entirely cold-blooded, a remarkable adaptation that has biologists intrigued… and conservationists scared.

Native to South America, Argentine tegu populations are rapidly expanding in Florida as the descendants of escaped pet lizards gain a foothold in the wild. Ecologists fear that the tegu’s ability to regulate its body temperature, unique among reptiles, could help it survive North Carolina winters and become established here. The prospect is so concerning that the state Wildlife Resources Commission has banned Argentine tegu sales and imports, effective August 1, after only a handful of sightings statewide.

They are actually able to elevate their temperature slightly above ambient conditions. This may give them a competitive advantage for being able to invade further north than we originally predicted.
Amy Yackel-Adams, a research ecologist with the U.S. Geological Survey

The first sign that these giant lizards can regulate their body temperature was discovered in 2016. Researchers at São Paulo State University noticed that tegus were sometimes considerably warmer than their environments.

Unlike other reptiles, which closely match the temperature of their surroundings, tegus could stay warm for days in cool weather, possibly thanks to a weirdly fast metabolism that sometimes looked more like a mammal’s than a typical lizard’s. More recent research in the Everglades found that invasive tegus are almost always warmer than their surroundings year-round.

“They are actually able to elevate their temperature slightly above ambient conditions,” explains Amy Yackel-Adams, a research ecologist with the U.S. Geological Survey who contributed to the Everglades study. “This may give them a competitive advantage for being able to invade further north than we originally predicted.”

Adding to concerns that they could become established in North Carolina, tegus can sometimes survive in considerably colder parts of the country than they currently inhabit.

In a study of tegus’ ability to adapt to colder temperatures, researchers kept the lizards outside through the winter in Auburn, Alabama, more than a hundred miles north of Florida. Not every tegu survived, but those that did nearly doubled in weight by the end of a full year. Monthly low temperatures in Auburn are colder than in Wilmington year-round.

Their ability to handle cool winters may be one reason these lizards are thriving in Florida, but it’s not the only one. Nor is it the only reason they make ecologists’ blood run cold.

A bar graph of the number of tegu lizards captured in Florida from 2012-2019. Over this time period, the total lizards trapped per year increases from 178 in 2012 to 1452 in 2019.
National Park Service
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Tegus removed in Florida by Florida Fish and Wildlife Conservation Commission (FWC), University of Florida (UF), National Park Service (NPS) and United States Geological Survey (USGS) through trapping.

Tegus are remarkably adaptable, which, in Florida, has made them both successful and ecologically harmful. Tegus thrive in forests, plains, scrublands, wetlands, and even suburbs. “They are amazing predators,” says Jeff Hall, herpetologist with the North Carolina Wildlife Resources Commission.

“They pretty much eat anything they can fit in their mouth.”

Tegus will go after anything from fruit to snakes, turtles, and baby raccoons. Of particular concern to conservationists, they also eat a lot of eggs, which can have a huge impact on native reptiles and ground-nesting birds.

Many reptile keepers remain unconvinced that tegus could ever become established in North Carolina. Tegu owner and president pro tempore of the North Carolina Association of Reptile Keepers Adam Wulf describes the new restrictions on tegus as “wildly unnecessary,” saying that the experience of tegu keepers shows that they require much warmer temperatures than can be sustained in North Carolina.

“It’s pretty firmly established that the Argentine tegus do in fact need a very hot basking spot, and they need it pretty regularly,” Wulf says. “Is it conceivable that one or two could overwinter here or there? Maybe? But I would really strongly doubt that based on our climate.”

It’s hard to convince anyone of a problem before it starts, and in this case, state officials think that tegus pose a sufficient risk to impose a ban. So far, there has been only one recorded instance of a tegu managing to survive a North Carolina winter – an unusual case of a tegu hiding out in the warm pipes under a plant nursery.

“But,” Hall asks, “how many instances like that does it take before you end up with an introduced population? And once you have an introduced population, how difficult is it to wipe that population out? I don’t know. I really don’t want to find out.”

Want to learn more about giant tegus and other species? CREEP is a podcast about creatures invading our space, and changing the world around us, presented by WUNC and the North Carolina Museum of Natural Sciences. Listen and subscribe wherever you get your podcasts.

Sophia Friesen is a science writer and WUNC’s 2022 AAAS Mass Media Fellow. Before working with WUNC, they wrote for science news outlets including Massive Science, preLights, and the Berkeley Science Review, covering everything from wildfire mitigation to pterosaur flight abilities.
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