Masked Biologist: Beware Of Falling Iguanas

Feb 10, 2020

We may have our share of challenges to face during Wisconsin winters, but at least we don’t have to deal with falling iguanas. That’s the topic the Masked Biologist chose for this week’s Wildlife Matters.

Oftentimes in the depths of winter, people’s thoughts may wander southward toward the tropics. For example, it is well known in the advertising world that effective commercials and marketing campaigns this time of year include some variation of sunshine, sea and sand. Even our stalwart Wisconsin residents will oftentimes seek out warmer climes, heading to Florida or Arizona this time of year in a behavior sometimes called snowbirding. And after all, if you wanted to go somewhere where you could walk around without a winter coat, or get in your car without first having to scrape your windshield, who could blame you? Winter brings with it a long list of hassles. Shoveling snow. Trying to keep the house warm. Running out of places to pile snow. Ice dams on roofs, increasing snow loads. Slippery sidewalks and icy parking lots. Short days, and long cold nights. But at least we don’t have iguanas.

Earlier this winter, Florida made the national news for a couple days because the national weather service issued an advisory warning that iguanas would be falling from trees. I used to spend a lot of time in Florida, and while their winter coincides with ours, I always think of the last couple of weeks of January as being the coldest. Sure, I would wear shorts and swim in the ocean, but my grandparents and most other Florida residents would wear warm jackets during this time. Florida’s native wildlife is not well equipped for prolonged cold periods, but has no trouble handling the occasional cold night. Even alligators, if the water forms a layer of ice, will let their nostrils freeze above the frozen lake surface so they can breathe, and their metabolism slows way down until the water warms again. But that is native wildlife. Florida has more than it’s share of nonnative exotic wildlife as well. They have pythons, monkeys, and a whole lot of green iguanas. These animals were probably introduced as people decided iguanas make good pets back in the late 1980s and 1990s. They are mostly vegetarians, eating some eggs as well, and are good diggers. They don’t really have natural predators in Florida, especially in and around human population centers where they thrive. They reproduce very quickly, and although they may not be as dangerous as pythons or carry as much disease as monkeys, they are still a serious problem for the ecosystem.

When the temperatures get down to 50 degrees or colder, the cold-blooded reptiles slow to a stop, and if they happen to be in a tree, they will lose their grip and drop to the ground. They are not frozen, nor are they dead. They are just cold, and so slow that they appear dead. Once the weather warms up, their metabolism increases, and off they go again. Large iguanas can reach 18” (plus the tail) and weigh upwards of 8-10 pounds. I don’t like it when I get hit with a tree branch, or an acorn. I would not like being hit by a solid reptile. Plus, then you have to decide—should I humanely dispatch it while I have it here, or do I let it live and wander off to reproduce and make a nuisance of itself? If the temperatures get cold enough, legitimately freezing, some of the iguanas will die off. Some will also be killed by the fall. However, the last time Florida had a good hard freeze that wiped out large numbers of iguanas, they rebounded very quickly and now there are more iguanas there than before. Iguanas can live for ten years, and have few legitimate predators, so the iguana problem in Florida will get worse before it improves.

The good news here, at least in the near future, is that we are unlikely to be grappling with an iguana problem any time soon. Our temperatures here routinely fall below 50, and the long winter would kill even the heartiest iguana. So, while you may be cursing the snow, and the ice, and the cold, be thankful – at least you don’t have falling iguanas.