Smithsonian National Zoological Park l Friends of the National Zoo



Green Iguana

Order: Squamata
Family: Iguanidae
Genus/species: Iguana iguana

The green iguana can weigh up to 18 pounds (8 kg) and can reach a length of five to seven feet (1.5 to 2 m). This iguana has a long body covered with soft leathery scales, a long tail and short legs. Its hard, long tail is used as a weapon and for balance when climbing. It has a greenish-gray color and can change color slightly (but not nearly as well as some lizards, such as chameleons). Female and juvenile male iguanas are a much brighter green than an adult male. It has feet with five very long toes with sharp claws on the ends, used especially for climbing. The iguana has a row of spines that extend along its back from the base of its head all the way to the tip of its tail, descending in size from head to tail. It also has a dorsal crest at the base of its head and a dewlap underneath its chin. The iguana also has a row of sharp serrated teeth.

The male iguana is larger than the female and has a larger dewlap as well. The male may develop a dorsal crest as high as three inches (8 cm). He has broader jowls and a bulge behind the cloacal vent, which contains the hemipenes. It is often hard to tell the sex of juvenile iguanas until these characteristics develop. Another way to tell sex is through femoral pore secretions. During breeding months, secretory activity peaks, and at that time, the dominant breeding males produce more secretion than subordinates and females. Juvenile males that perform visual displays have significantly larger pores than those who do not display. Because of this, it is believed that there is a relationship between social dominance and secretion levels. Femoral pores are also a good way to identify related species. Related species have secretions that are more similar than distantly related species.

The green iguana is a social species; groups can be found basking and foraging together in trees. The male iguana is typically more aggressive and territorial than the female. They exhibit male-male aggression and a male may injure another iguana in attempts for the alpha position, the best basking perch, the biggest territory, or access to females. Young males who are not yet ready to challenge mature males for territories may hang out with dominant males but are always watchful for signs of aggression.

Distribution and Habitat
The geographic range of the green iguana is from Central to South America and on smaller West Indian islands.

Green iguanas are both arboreal and terrestrial. They live in the light-shade mosaic of trees along rivers, lakes and mangrove swamps, as well as in relatively open, arid areas if food resources are sufficient.

Diet in the Wild
The green iguana is basically herbivorous. The green iguana spends most of its activity cycle resting, not feeding and foraging like carnivorous lizards. When foraging, the iguana returns to the same foraging site day after day. Its food intake decreases when it changes foraging sites. It gets water from catching rain and condensation on the flowers and leaves of trees, but most comes from the food it eats. It occasionally eats insects along with the vegetation. In the spring the iguana eats leaves of plants in the bean family that are high in protein. A young iguana eats mostly insects. The young are small and potential prey for larger predators including larger iguanas.

Zoo Diet
They are fed salad, which includes, kale, sweet potatoes, carrots and romaine lettuce.

The seasonal reproductive cycle is correlated with rainfall. The mating season usually occurs in the fall, which is the first half of the dry season, and only lasts a couple of weeks. During mating season the male becomes more aggressive. When green iguanas mate, the male bites down on the body of the female so that their cloacas are next to one another. He then everts his hemipenes and attempts to force them inside the female to deposit his sperm. The male iguana relies on color and display to attract mates. Displays include dewlap extensions, head-bobbing and/or pushups. Outside of the mating season iguanas appear to be much less mobile; they spend most of their time resting. Female iguanas seem to choose mates directly based on male phenotypes. Females aggregate in the mating territories of the largest males and preferentially mate with them.

After mating females lay their eggs during the second half of the dry season. The female iguana carries her eggs for two months. Female iguanas usually build nests widely separated from one another in areas with sandy soil. Females use moderately straight terrestrial paths to move from their home site to the nest. After seven days spent at the nest site, nearly the identical path is used to travel back to the home site. Females may migrate as far as 1.8 miles (3 km) to find a suitable nesting site.

Hatching occurs anywhere from two months before the onset of the rainy season to very early in the rainy season, usually in May. This ensures that hatchlings can take advantage of a long growing period before entering the dry season again. The female iguana lays eggs whether they have been fertilized or not. She lays a group of eggs, called a "clutch", which can be as small as 12 or as large as 30. In the wild only about 35 percent of these eggs survive due to predators, incorrect incubation, or some other kind of hazard. After 90 days, baby iguanas hatch. These one foot (30 cm) long juveniles disperse rapidly after hatching. The juvenile is bright green and vulnerable to predators. The iguana may be sexually mature at 16 months of age and at least nine inches (23 cm) snout-vent length.

Life Span
With proper care a captive iguana can live for 20 years.

The green iguana is listed as threatened and on CITES Appendix II. The main cause is destruction of the rain forests and demands of the wildlife and pet trade. In attempts to conserve this species, exporters and importers of iguanas are required to obtain permits to move them across country borders. However, once they are in the United States, it is legal for someone to buy them. The pet trade industry has put a great demand on the iguana; 800,000 iguanas were imported into the U.S. in 1995 alone.

Another step that is being taken to conserve this species and meet these demands is the formation of captive farming operations, based in the country of origin and designed strictly for breeding iguanas as pets. This may have a negative effect on the genetic diversity of the species, as they are being mass-produced. As iguanas are bred in a captive area, they lose their phenotypic and genetic diversity, as cattle do when they are raised on a farm.

Green iguanas are hunted for meat in the tropics, however this does not seem to have much effect on numbers. Iguana meat is less commonly eaten because it is considered a low class food in most areas, but some indigenous people may depend heavily on it.

Fun Facts
Iguana eggs are sold as a novelty food. They are boiled in salt water and sold at more than twice the price of chicken eggs by weight. This species is also used as a favorite bait for catching crocodilians.

The two prominent nostrils are used to expel a saline solution to regulate its body's salt level.

The green iguana is a wonderful swimmer. It holds its legs close beside it and uses its tail to propel itself through the water. An iguana can stay under water comfortably for up to 30 minutes.