Reptiles
Green Iguana
Iguana iguana · also called common iguana, American iguana
The green iguana is a big, spiny, tree-living lizard from the American tropics. It is a committed vegetarian, an accomplished swimmer and climber, and — thanks to the pet trade — an invasive species causing real damage far outside its natural range.
Overview
Green iguanas live in lowland tropical forest from Mexico to South America and across the Caribbean, almost always near water. They spend the day high in the canopy basking and feeding, and they favour trees overhanging rivers so that a threat can be met by dropping straight into the water, where they swim well using the tail. Despite the name, adults range from green to grey-brown to orange, and old males often turn coppery in the breeding season.
A leaf-eating reptile
Most large lizards are carnivores; the green iguana is an obligate herbivore. It crops young leaves, shoots, flowers, and soft fruit with small serrated teeth and ferments the tough plant fibre in an enlarged hindgut populated by microbes — a digestive strategy more like a tortoise’s than a monitor lizard’s. Hatchlings eat some insects and, notably, the droppings of adults, which seed their guts with the microbes they need.
Distinctive features
- A dewlap, the large flap of skin under the chin, flared to look bigger to rivals and predators and to catch or shed heat.
- A crest of soft spines running down the neck and back.
- The parietal eye on the crown — a light-sensitive organ that helps detect aerial predators and keeps the body clock in step with the seasons.
- Loose folds of skin and powerful legs that let the animal survive long falls from the canopy.
Reproduction
In the dry season, males hold territories and display with head-bobs and dewlap extensions. After mating, the female travels to open, sunlit ground — sometimes a long way from her home range — and digs a burrow in which she lays 20 to 70 eggs, then leaves. The eggs hatch after 10 to 15 weeks and the young emerge together, staying in loose family groups for their first year, which is unusual among lizards.
Threats and invasions
In its native range the green iguana is classed as Least Concern but is hunted heavily for meat (it is called “bamboo chicken” in parts of Central America) and collected for export, and local populations have thinned.
Outside that range it is the opposite story. Pet iguanas released or escaped in Florida, Hawaii, Puerto Rico, and several islands have built booming wild populations that damage infrastructure with their burrows, strip gardens and crops, and outcompete native wildlife. Control programmes and unrestricted hunting have so far failed to reverse the spread.
Green Iguana: common questions
What is the iguana's "third eye"?
On the top of a green iguana's head, between the two normal eyes, is a pale scale covering a parietal eye — a simple light detector with a rudimentary lens and retina wired to the brain's pineal region. It cannot form images, but it senses changes in light and shadow, helping the iguana notice a bird of prey diving from above and helping regulate daily and seasonal rhythms. Many lizards, frogs, and fish have one.
Are green iguanas good pets?
They are widely sold cheaply as hatchlings but are one of the most frequently abandoned reptiles. A green iguana grows to nearly two metres, needs a room-sized enclosure with intense heat and UVB, lives for two decades, and males can become aggressive in the breeding season. Most pet iguanas die young from inadequate care, particularly metabolic bone disease from poor diet and lighting.
Why are iguanas a problem in Florida?
Escaped and released pets have established large wild populations in south Florida, where the climate suits them and they have few predators. They dig burrows that undermine seawalls, sidewalks, and canal banks, eat ornamental and native plants, and leave droppings around pools and docks. Florida encourages residents to remove them from their own property and allows year-round hunting on public land.
How do green iguanas survive falling out of trees?
Green iguanas spend most of their time in the canopy, often over water, and dropping is their standard escape from a predator. They can survive falls of 15 metres or more onto solid ground by flattening the body to slow the descent and absorbing the impact through strong limbs and a flexible ribcage. During Florida cold snaps, iguanas go torpid and lose their grip, and "falling iguana" advisories are issued.