Green Iguana

Basking green iguana（圖片來源：Cayambe，採用 CC BY-SA 3.0 授權）

The green iguana (Iguana iguana) is a large lizard with an exceptionally wide distribution, native to Central and South America and the Caribbean, ranging from southern Mexico to Brazil and Paraguay, and extending across numerous islands. In the wild, this species primarily inhabits the canopy layer of tropical forests and is a highly arboreal reptile. Juveniles usually remain on lower branches, whereas adults prefer higher positions, allowing efficient basking and broad environmental surveillance. They are also closely associated with water, being strong swimmers; when threatened, they will readily leap into water and can even dive to evade predators.

In natural habitats, green iguanas are diurnal. They actively bask in the early morning and midday to regulate body temperature. When ambient temperatures drop too low, they lose mobility and may even become temporarily immobilized, a phenomenon that has led to the well-known “falling iguanas” incidents reported in Florida's invasive populations. Their primary diet consists of leaves, flowers, and fruits. Although they may occasionally consume insects, bird eggs, or small vertebrates, this typically occurs incidentally while feeding on plants.

Green iguanas can reach considerable size. Adults commonly measure 1.2 to 1.7 meters in total length, with some exceeding 2 meters and weighing over 8 kilograms. Males are generally more robust than females and possess prominent dorsal spines, a dewlap, and femoral pores. These features are closely linked to behavior; during the breeding season, males display dominance through head bobbing, dewlap extension, and tail movements. They also possess acute vision and a specialized parietal eye, enabling detection of light changes and overhead movement, which aids in predator awareness. In terms of lifespan, wild individuals typically live around 8 years, whereas those maintained under optimal captive conditions may reach 15 to over 20 years.

In their life history, females excavate nests exceeding 1 meter in depth during the breeding season and lay between 20 and 70 eggs per clutch. The incubation period lasts 90 to 120 days. Hatchlings are highly independent, yet during their first year, juvenile males often form groups and exhibit cooperative defensive behavior, a rare phenomenon among reptiles.

Green iguana on a tree（圖片來源：Charles J. Sharp，採用 CC BY-SA 4.0 授權）

Housing Requirements in Captivity

Because green iguanas are tropical arboreal animals, captive environments must closely replicate their natural habitat. Juveniles may temporarily be housed in enclosures measuring 100 cm × 45 cm × 45 cm, but their rapid growth means they often exceed 1 meter in length within a year. As a result, adult iguanas almost always require custom-built enclosures. Ideally, the enclosure should be at least twice the animal's body length in length, equal in width, and no less than 1.8 meters in height to provide sufficient climbing space. The environment must include thick, sturdy branches, along with hiding areas and platforms to simulate basking on elevated branches.

Daytime ambient temperatures should be maintained between 26 and 35°C, with a designated basking area of 38 to 43°C. Nighttime temperatures should not fall below 23°C. Lighting must include full-spectrum UVB, provided for 10 to 12 hours daily to enable vitamin D3 synthesis and prevent skeletal disorders. UVB bulbs should be replaced every 6 months, as ultraviolet output declines even if visible light remains.

Humidity should be maintained between 70% and 90%, supporting respiration, shedding, and hydration. A large shallow water container should be provided for soaking, and the enclosure should be misted daily. Suitable substrates include paper, grass mats, or alfalfa pellets; wood chips and sand should be avoided due to the risk of ingestion and intestinal blockage. Spot cleaning of feces and food residues should be performed daily, with full disinfection conducted weekly.

Feeding Conditions

Although occasional animal matter consumption has been observed, captive green iguanas must be maintained on a strictly herbivorous diet. Their digestive system is specialized for processing high-fiber plant material, and high-protein diets can lead to kidney failure and premature death. An optimal diet consists of 70% dark leafy greens, 20% other vegetables, and 10% fruit. Suitable leafy greens include dandelion greens, kale, turnip greens, and mustard greens. Additional items may include squash, carrots, and green beans. Fruits such as mango, banana, and strawberry should be provided sparingly, mainly as occasional treats.

Because green iguanas do not chew but swallow food whole, all items must be finely chopped to prevent choking. Food should be provided daily, preferably in the morning, as digestion depends on daytime heat and light. Uneaten food must be removed within 10 hours to prevent spoilage.

Nutritional supplementation is essential. Calcium powder with vitamin D3 and calcium without D3 should be alternated on food, along with reptile multivitamins provided 1 to 2 times per week. This helps maintain an appropriate calcium-to-phosphorus ratio of approximately 2:1 and prevents metabolic bone disease. Water should be supplied both through a drinking container and soaking, with clean warm water replaced daily.

Breeding Conditions

In captivity, green iguanas typically reach sexual maturity at 3 to 4 years of age. During the breeding season, males develop more vivid orange-red coloration and display strong territorial behavior, potentially becoming aggressive toward humans or other individuals. If breeding is not intended, it is advisable to house males and females separately or consider sterilization.

If egg-laying occurs, an appropriate nesting site must be provided immediately, typically consisting of moist soil or sand with a depth of at least 50 cm. Without suitable conditions, females may retain eggs, which poses a serious health risk. Incubation requires 90 to 120 days at temperatures of 29 to 33°C. Artificial incubation can be performed using a controlled incubator with appropriate humidity. After laying, females generally provide no parental care, and hatchlings are fully independent, requiring appropriately sized enclosures and finely chopped vegetables from birth.

For most keepers, breeding is not an ideal option. A single clutch can produce dozens of offspring, and without sufficient space and resources, this can easily lead to abandonment. Owners should carefully evaluate their capacity and seek professional assistance or licensed animal rescue organizations when necessary.

亞成年綠鬛蜥（圖片來源：Frank van de Putte，採用 CC BY 3.0 授權）

Preventing Invasive Spread

Green iguanas are considered invasive in many regions worldwide. Established populations have been reported in Florida, Puerto Rico, Hawaii, and even Taiwan. These populations often originate from escaped or released pets and can cause significant ecological damage, including predation on bird eggs, destruction of crops, competition with native species, and impacts on endangered species. In Florida, they have been documented consuming plants required by endangered butterflies and burrowing into infrastructure such as dams and levees, leading to serious environmental issues.

Owners must take full responsibility and should never release green iguanas into the wild. If care is no longer possible, animals should be transferred to legal shelters or qualified keepers. Even a seemingly harmless pet can establish breeding populations in non-native environments and lead to severe ecological consequences.

Author: Shui-Ye You