Not venomous · Native to Mexico and Central America · Invasive in Florida

Black spiny-tailed iguana

Ctenosaura similis (Gray, 1831)

Also called black iguana, black ctenosaur
Data updated October 2026

Gray black spiny-tailed iguana with dark bands basking on white rocks beside the sea
Fig. 1 — Adult basking on coastal rocks. The tail is ringed with rows of spiny scales.
Pale gray black spiny-tailed iguana with bold black bands and a crest of pale spines on a mossy rock
Fig. 2 — Bold black bands on a pale body; a low crest of spines runs along the back.

At a glance

A large, fast, ground-dwelling iguana native from Mexico to Panama. A population started from three released pets on Gasparilla Island has spread along Florida’s coasts, where it digs under buildings and eats eggs and young of native wildlife.

01

Identification

Adults are gray, tan or nearly black, with several dark bands across the back. Hatchlings are pale tan to gray with brown net-like markings, and within a few months turn bright green with brown, black and gold marks. The best feature is the tail: it carries rings of sharp, pointed scales. Unlike the green iguana, there is no large round scale at the back of the jaw.

  1. 01Spiny tail rings. Rows of sharp, pointed scales circle the tail.
  2. 02Dark bands. Dark bars cross a gray to tan back.
  3. 03No round cheek scale. The jaw lacks the large round scale of the green iguana.

Commonly confused with

02

Size

01 ft2 ft3 ft4 ft5 ft6 ft7 ft8 ft Large adult · about 4 ft (1.2 m)

Adults can grow longer than 4 feet (1.2 m) including the tail, though it is shorter than the green iguana. Males are larger than females, with stockier heads and a taller crest. Hatchlings are about 6 inches (15 cm) long.

03

Range & habitat

Close view of a tan spiny-tailed iguana’s head resting on a rock
Fig. 3 — Rocky ground with crevices and burrows gives this iguana basking spots and shelter.

The black spiny-tailed iguana is native from Mexico to Panama.

In Florida it is established along much of the southern Gulf Coast, the south Atlantic coast and in the Florida Keys. The Gulf Coast population began on Gasparilla Island, where a resident released three pet iguanas brought from Mexico between the late 1970s and early 1980s. By 2003 they had spread across the island and onto the mainland. It favors rocky ground, canal banks and urban areas, and it digs burrows under rocks, logs, sidewalks, seawalls and building foundations.

State guide: Florida

04

Diet & predators

Young black spiny-tailed iguanas eat almost only insects and other small invertebrates. Adults eat more plants, including flowers and leaves of ornamental plants, but they also take small mammals, birds and bird eggs, hatchling sea turtles, young gopher tortoises and other lizards.

Feeds on

  • Leaves and flowers
  • Insects
  • Bird eggs and nestlings
  • Hatchling sea turtles and young tortoises
Dandelion flower and leaves
Food — flowers and leaves.
House cricket
Food — insects, especially for young iguanas.

05

Behavior & seasons

This is a ground-dwelling, day-active lizard that basks in the open and runs to a burrow when disturbed. In Florida it moves into gopher tortoise burrows and has been documented evicting young tortoises from them. Where no burrow is available, it digs its own.

06

Reproduction

Females can breed at about two years old. On Gasparilla Island each female lays one clutch a year in early summer, and hatchlings appear in late summer. Clutches there average about 30 eggs, and up to 82 eggs have been found in a single Florida female.

07

Conservation

In its native range the species is widespread and considered Least Concern.

In Florida it is invasive. It damages buildings and seawalls by burrowing, eats landscaping, fouls docks and pools, and preys on protected wildlife such as gopher tortoises, sea turtle hatchlings and the eggs of beach-nesting birds. Since 2008, more than 15,000 have been removed from the Charlotte County part of Gasparilla Island, but eradication is unlikely. Releasing pets into the wild is illegal.

Keep reading

Sources

Data updated October 2026 · How we build these pages