The Perfect Storm: Florida’s Subtropical Climate Makes an Ideal Home for Invasive Iguanas

While most areas in the United States are more temperate and don’t make great homes for most species of iguana, Florida is something of an anomaly. The state’s subtropical climate makes it warm and humid year-round, and therefore an ideal home to many species of reptiles, amphibians, and other animals we usually see in distant, isolated rainforests and on tropical islands.

Unfortunately, not one species of “Florida” iguana—there are three—is native to the state. While these large lizards have become icons of sorts for the state, they are highly invasive nuisances, wreaking havoc on Florida’s flora and fauna and causing serious damage to both man-made and natural structures.

A few species of skink, a species of lizard, are native to the Sunshine State, but none of them are as recognizable as its most famous lizard resident, the green iguana (Iguana iguana). Not only is the green iguana a non-native species, but it has also become such a nuisance, in 2021 it was added to Florida’s Prohibited Nonnative Species List along with two other invasive lizard species, the Nile monitor (Varanus niloticus) and the Argentine black and white tegu (Salvator merianae). There is no doubt that these reptiles are a nuisance, but it is not an excuse to torture them. They are protected under Florida’s anti-cruelty laws, although they can be humanely killed year-round without a permit or hunting license on 32 Fish and Wildlife Conservation Commission–managed lands.

Lesser known and not as widely distributed as the green iguana are two species of spiny iguana: the Mexican spiny-tailed iguana (Ctenosaura acanthura) and the black spiny-tailed iguana (Ctenosaura similis). People brought these creatures to Florida’s shores from nearby islands via cargo ships and independent releases throughout the 1960s and 1970s. Eventually, their populations exploded, most notably that of the green iguana, in large part because Florida just happens to be a hospitable place for iguanas, with its warm, humid weather and diverse plant and animal life.

As we look at each of these species in a bit more detail, we’ll be able to understand why they are so damaging to Florida’s ecosystems, exactly how each one was introduced to the area, and what sort of measures state officials are taking to reverse their environmental impact as humanely as possible.

Green Iguanas

The most widespread iguana species in Florida by far is the majestic and docile yet tragically destructive green iguana. Although many Floridians mistakenly believe green iguanas are native to the state, the species is highly invasive. 

These large, handsome lizards are easily recognizable due to their vibrant green (and sometimes red, orange, and blue) coloration, tall spikes extending down their spines, and outgoing, friendly temperaments. Adult green iguanas commonly reach 5 or more feet in length and can weigh over 15 pounds.

It certainly seems like these iguanas have existed in Florida for centuries due to their seemingly ubiquitous presence. However, they’ve only been in the Sunshine State since the mid-1960s. Florida’s first green iguanas likely hitched rides on Cuban cargo ships transporting goods to Florida in the 1960s.

Soon after their arrival, the herbivorous lizards reproduced rapidly and quickly established themselves throughout South and Central Florida. They indiscriminately began feeding on all manner of both widespread and endangered plants in the state, in turn also disturbing various native wildlife populations.

Today, green iguanas are everywhere throughout the state, even in northern Florida where temperatures are cooler. Although the state has since incentivized the culling of green iguanas and using them for meat, the species’ numbers continue to grow. Green iguanas are extremely prolific breeders like the other two iguanas discussed here. In fact, they are capable of laying massive clutches of 40-plus eggs at a time. Currently, researchers estimate there are more than 20,000 green iguanas living in Florida.

Mexican Spiny-Tailed Iguanas

The Mexican spiny-tailed iguana, as you may have guessed, is native to western Mexico and parts of Central America. Nowadays, it inhabits parts of South and Central Florida. These large, brownish-grey lizards partially get their name from the rows of short, rough spines on their tails. The typical Mexican spiny-tailed iguana grows to be between 4 and 5 feet long and weighs between 5 and 15 pounds. While they prefer eating plants, these iguanas are opportunistic omnivores and will dine on insects, small birds, reptile eggs, and even other lizards.

Local environmental scientists believe this iguana was introduced to South Florida mostly via independent releases in the 1970s. Basically, a small number of irresponsible reptile owners released a few of their iguanas into the wild, and the rest is history.

Over time, those few independently released iguanas found each other and reproduced with one another. Mexican spiny-tailed iguanas are especially prolific breeders. Females are able to produce several clutches after a single successful copulation. In fact, each individual clutch usually consists of more than 45 eggs. This resulted in a fast and significant uptick in their numbers. By the time Florida’s environmental agencies could intervene, there were thousands of them living throughout multiple South Florida counties. 

Black Spiny-Tailed Iguanas

A few isolated independent releases introduced another spiny iguana species to South Florida back in 1978. The black spiny-tailed iguana causes significant damage to buildings and other man-made and natural structures with their large, elaborate burrows. They can dig surprisingly quickly with their long claws and muscular limbs, and their feces and urine create quite a mess in the process.

The species is originally native to parts of Mexico, Central America, and a few islands in the Caribbean. They are large, stocky iguanas that are mostly grey or black in color with long, spined tails and long snouts. Most individuals have some vertical grey and black striping across their bellies and tails. Like most spiny-tailed iguana species, these lizards often reach 5-plus feet in length and can weigh 10-plus pounds as adults.

While they prefer eating plants, these iguanas are opportunistic omnivores and will gladly snack on insects, arachnids, and the eggs of birds and other reptiles, and occasionally other lizards. They indiscriminately eat any plant material they can get their claws on. This includes not only various shoots, leaves, and vines but also tropical fruit and vegetable crops.

While neither the Mexican nor the black spiny-tailed iguanas are on the Prohibited Nonnative Species List, meaning they cannot be humanely killed, the state of Florida does have measures in place to address these invasive species’ destruction. Through the South Region Volunteer Program within the state’s Fish and Wildlife Conservation Commission, volunteers can “assist with trapping and removing iguanas from areas” where the state-threatened Florida Burrowing owl is present. These iguanas and owls shelter and nest in burrows, and the owls are usually on the losing end of their encounters.

Various measures have been taken by Florida’s government and environmental agencies to diminish these species’ populations. However, these persistent iguanas remain numerous today, with their numbers reaching well into the tens of thousands.