Beware the falling iguanas in South Florida.

When temperatures dip into the 30s and 40s, people from West Palm Beach to Miami know to be on the lookout for reptiles stunned — but not necessarily killed — by the cold. They can come back to life again when it warms up.

In Boca Raton, Frank Cerabino, a Palm Beach Post columnist familiar with the critters, stepped outside and saw a bright green specimen by his pool on Thursday morning, feet up.

“It’s one of those ethical things: What do you do?” he said in an interview.

Iguanas, which can be as long as six feet, are not native to South Florida. They have proliferated in the subtropical heat, causing headaches for wildlife managers — and occasionally popping up in toilets. It took a prolonged cold spell to significantly reduce their population in 2010. (The same cold snap also resulted in the deaths of many invasive Burmese pythons.)

Iguanas climb up trees to roost at night, said Ron Magill, communications director for Zoo Miami.

“When the temperature goes down, they literally shut down, and they can no longer hold on to the trees,” he said. “Which is why you get this phenomenon in South Florida that it’s raining iguanas.” (Including on windshields.)