How cold does it need to get before iguanas start falling out of trees in Florida?

A stunned baby iguana lies in the grass at Cherry Creek Park in Oakland Park, Fla., Jan. 22, 2020. (Joe Cavaretta/South Florida Sun-Sentinel via AP)

MIAMI — It's a South Florida phenomenon that draws amusement from across the country — when temperatures drop below a certain level, cold-stunned iguanas start falling out of trees.

While it may sound bizarre, it happens. And there's a scientific reason for it.

Although several iguana species live in Florida, the predominant one is the green iguana, native to Central and South America. According to the Florida Fish and Wildlife Conservation Commission, green iguanas are considered invasive in the state.

Like all reptiles, iguanas can't handle cold temperatures very well because they are cold-blooded, meaning they rely on external heat sources to regulate their body temperature.

They begin to get sluggish or lethargic once the temperature drops below 50 degrees Fahrenheit, said Zoo Miami Communications Director Ron Magill.

Once the temperature drops below the mid-40s, iguanas go into a dormant or cold-stunned state and sometimes fall out of trees where they perch. They appear to be dead, but they are not. They remain breathing with critical body functions still operating. Iguanas go into this cold-stunned state as a way of protecting themselves until the temperature warms back up above 50 degrees.

Zoo Miami Communications Director Ron Magill said cold weather effects on iguanas depends on the size of each specimen. The larger the iguana, the colder it can tolerate for longer periods, Magill said.

Adult male iguanas can reach 5 feet in length, and weigh up to 20 pounds.

Many iguanas in South Florida have adapted to going deep into burrows where they stay insulated from the cold. They also tend to live close to large bodies of water, which are usually warmer than the air temperatures, helping them survive short cold snaps.

The green iguana, the Mexican iguana, and the spinytail iguana were originally brought to South Florida from Central and South America.

They're considered an invasive species and they've become more than just a nuisance. The giant lizards have caused costly structural damage and even power outages. Iguanas have been seen eating gardens, getting into pools and even finding their way into toilets. They can also transmit salmonella to pets.

Experts say the iguana population is growing out of control and disrupting the lives of Florida's native wildlife, including gopher tortoises, sea turtles and burrowing owls.

In 2021, Florida banned having iguanas as pets. The giant lizards have almost no natural predators in the state; one female can lay up to about 70 eggs a year.

Iguanas, like all non-native, invasive species, are not protected in Florida except by anti-cruelty law and can be humanely killed with a landowner's permission.