Iguanas in Florida

Posted on by Andrew Furness

Three introduced species of iguana are found in South Florida. Two of these are common: The black spiny-tailed iguana (Ctenosaura similis) and the green iguana (Iguana iguana). A third, the western spiny-tailed iguana (Ctenosarua pectinata), is found in only a single location.

Evolutionary tree of the family Iguanidae (i.e. iguanas), modified from TimeTree.org. The scale bar at the bottom depicts millions of years before present. The species introduced to Florida are indicated with stars. The two more common species, discussed further below, are indicated with blue stars.

The species Ctenosaura similis goes by the common names black spiny-tailed iguana, black iguana, or black ctenosaur. I like the name ‘ctenosaur’ because it sounds like dinosaur, which I think is fitting given their Godzilla-like appearance (particularly large males). This large-bodied omnivorous species is native to Central America and Mexico. On several occasions, I have seen them while conducting fieldwork in Costa Rica. They tend to be found near the coast in environments modified by humans. I saw them on hotel lawns, basking on the metal roof of houses, and near brush piles. This species was introduced to South Florida in 1979, and has become established on the Gulf and Atlantic coasts. In South Florida, the black spiny-tailed iguana is not as widespread as the more familiar green iguana but can be locally abundant in certain areas.

The green iguana (Iguana iguana) has a widespread distribution ranging from Mexico to Brazil. This species was first introduced to Florida in the early 1960s and now has established populations throughout the southern half of the state. Green iguanas are herbivorous and can reach five feet in length. When people think of ‘iguana’ this is typically the species they are thinking of.

In Florida, these two species of introduced iguana occur together in certain places. One such place is Key Biscayne, a low-lying barrier island just south of Miami Beach. On several recent visits to Key Biscayne I saw hundreds of black spiny-tailed and green iguanas in several different habitats, even co-mingling together in mixed species flocks. While photographing these iguanas, I witnessed some novel feeding behavior and unusual prey items. I am currently writing up these observations as a natural history note for publication (I may highlight this in a future post). But for now, I wanted to include a set of photos depicting these iguanas in their habitat. All photos included below were taken in early September 2021 on Key Biscayne.

The Black spiny-tailed iguana (Ctenosaura similis)

Juveniles are actually green in color.
This individual, likely a male, had lost and regrown its tail.
A large male. Note the dewlap, a fold of loose skin hanging below the neck that is used in territorial displays.
A large male, pressed against the crub. Note the ‘spiny tail’ which gives rise to the common name for this species.
A male basking on the rocks.
Basking on the rocks with the ocean in the background.
A female (foreground) and male (looming in the background). Note the degree of sexual size dimorphism, with males substantially larger than females and with larger dorsal spines and dewlap.
Black spiny-tailed iguanas seemed to like basking on rocks, rock walls, and even the curb edge.
Black spiny-tailed iguanas on the beach. I think the open mouth may have been a means to cool down (i.e. panting).

The green iguana (Iguana iguana)

A horde of green iguanas.
I count 13 green iguanas.
Impressive dewlap. I found the variation in overall coloration amongst individuals interesting (i.e. bright green, blue-green, brown)
This large male appeared to have a dart sticking out of his body. It would have been very difficult for me to remove because when I approached from behind he turned his head to carefully keep watch and seemed ready to flee.

Black spiny-tailed and green iguanas together

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