FORT LAUDERDALE, Fla. — When temperatures drop, so do green iguanas — from the trees. But evolution, it seems, could be robbing South Floridians of a tradition as common as checking the heat index on New Year’s Day.
Research shows that in recent years, several species of lizards have grown more tolerant of cold temperatures. It’s a discovery with big implications for Florida, where bouts of cool weather keep invasive iguanas contained to the southern regions of the state and helps keep populations under control.
It also could mean fewer images on social media and TV news of iguanas lying on their backs under trees, legs in the air, stunned until the warm sunshine gets their bodies moving again.
As recently as four years ago, most of South Florida’s most common species of lizards could tolerate temperatures between 46 and 52 degrees. Now, they hold up in temperatures as low as 44 degrees, according to a study done by a researcher at Washington University in St. Louis.
That means it’s possible that iguanas could expand their territory beyond their normal stomping grounds of Miami-Dade, Broward and Palm Beach counties.
“The potential is they could spread farther and disperse farther, so that’s why it’s interesting to Florida, specifically” said James Stroud, the research associate who conducted the study and did his doctoral work at Florida International University.
That’s bad news considering iguanas are invasive, propagate profusely and wreak havoc on homes, gardens, sidewalks, pool decks, seawalls, boats and anywhere else they eat and, well, poop. They’re so destructive, the state of Florida issued a call for homeowners to kill them. (It later clarified the statement, saying it’s best to call a professional to do the deed.)
Iguanas fall out of trees during cool weather because they’re cold-blooded and tropical. Low temperatures cause them to become sluggish and, in some cases, immobile. If it happens while they’re sleeping in trees, they often fall to the ground. They’re cold-stunned, not usually dead — they spring back into action once temperatures warm again if the fall from the tree doesn’t kill them.
It happened this past January, raining iguanas when temperatures in parts of South Florida fell to 39 degrees, the coldest air in about a decade. It also happened in January of 2018.
Stroud and his colleagues studied six lizard species common in South Florida — one that’s native (the American green anole), three Caribbean lizards that are not native (one each from Puerto Rico, Cuba and Hispaniola), the northeast tropical gecko, and the brown basilisk lizard.
Iguanas weren’t included because they were too big to fit into the refrigerator-like device used to study the chilled lizards. But Stroud said he believes the results apply to iguanas, too.
Blake Wilkins, co-owner of Hollywood-based Redline Iguana Removal, said the discovery doesn’t surprise him. While collecting iguanas during last January’s cold spell, he saw signs that iguanas might be warming up to the cold.
“I noticed a lot of them were actually in