What Do Iguanas Eat in the Wild? A Leafy Herbivore Diet

What do green iguanas eat in the wild?

The green iguana lives in tropical forests from Mexico to South America, mostly in trees close to rivers and coasts. It feeds where it lives, browsing on the foliage of the canopy and of shrubs and vines below.

Its natural diet includes:

• Leaves, the bulk of the diet, especially young, tender leaves that are easier to digest.
• Flowers and flower buds, which are rich in sugars and water.
• Fruit, eaten when trees are in season, such as the wild hog plum (Spondias mombin), a favorite in Panama.
• Shoots and new growth, which contain more protein than old leaves.

Green iguanas have been recorded eating more than 100 plant species. Their choices change with the seasons, depending on which trees are leafing, flowering or fruiting.

How do iguanas eat their food?

Iguanas do not chew in the way mammals do. Their teeth are small, flat and leaf-shaped, with fine serrations along the edges like a bread knife. The iguana uses them to slice or tear off bites of leaf, which it swallows with little chewing. The teeth are replaced throughout life as they wear down.

The tongue helps the iguana handle food and also picks up chemical cues. Iguanas often touch leaves with the tip of the tongue before eating, which may help them identify suitable plants.

How can iguanas digest leaves?

Leaves are full of cellulose, a tough fiber that no vertebrate can digest on its own. Green iguanas solve this problem the same way cows and horses do, by hosting microbes that break down fiber for them. In iguanas this fermentation happens in the hindgut, an enlarged section at the end of the intestine.

Inside the hindgut, bacteria and other microbes ferment the plant material and release fatty acids that the iguana absorbs for energy. Folds in the gut slow the food down and give the microbes time to work. Warmth matters as well: iguanas digest best when their bodies are warm from basking, which is one reason they spend so much time in the sun.

This system lets green iguanas live on a diet that would starve many other lizards. It also means they need to eat large amounts of food, because leaves contain relatively little energy per bite.

How do baby iguanas get their gut bacteria?

Iguanas are not born with the microbes they need. Hatchlings acquire them by eating the droppings of older iguanas, a behavior called coprophagy. Studies of wild green iguanas in Panama found that young iguanas seek out soil and droppings from adults soon after hatching, picking up the bacteria that let them digest leaves.

Living in groups during their first year may make this easier, as young iguanas stay near one another and near older animals. Without these microbes, a young iguana could not digest its leafy diet efficiently.

Do wild iguanas ever eat meat?

Rarely. Wild green iguanas have occasionally been seen eating grasshoppers, tree snails, bird eggs, nestlings and carrion. Some of these items are probably swallowed by accident along with leaves, and others are opportunistic snacks.

Biologists generally regard the green iguana as a true herbivore. Its teeth, gut and microbes are all specialized for plants, and animal food is a minor and irregular part of what it eats.

How do iguanas get rid of extra salt?

A plant diet brings its own chemical problem. Leaves contain a lot of potassium and other salts, and the iguana’s kidneys cannot make urine concentrated enough to remove all of it. Instead, green iguanas have a salt gland in the nose that removes extra salts from the blood. The iguana expels the salty fluid with a short snort or “sneeze,” sometimes leaving white crusts around the nostrils.

Their relative the marine iguana of the Galápagos uses the same trick on a larger scale, since it eats salty seaweed. Read more in Why do marine iguanas sneeze?.

What do iguanas eat where they are invasive?

Where green iguanas have been introduced, they eat whatever suitable plants are available. In South Florida that includes hibiscus, orchids, roses, fruit and many vegetables, as well as native plants of conservation concern. Their appetite for garden plants and nursery stock is one reason they are considered an invasive species; see Are iguanas invasive in Florida?.