Green Iguana, Iguana iguana
Green Iguana, Iguana iguana. Photograph taken in the coastal area of Southeast Florida, December 2020. A non-native that has established a significant population, presumable via terrarium releases and they are now considered to be highly invasive. Photograph courtesy of Ben Cantrell, San Diego, California.
Green Iguana, Iguana iguana. Photographs taken in Zihuantanejo, Guerrero, March 2019. Photographs courtesy of Ron Woheau, Zihuantanejo. Identifications courtesy of Gary Nafis, Californiaherps.com.
Green Iguana, Iguana iguana. Photograph taken in a residential community, Boca Raton, Florida, December 2023. Photograph courtesy of Dean Oquist, Boca Raton, Florida.
Green Iguana, Iguana iguana. Underwater photograph taken in Zihuantanejo, Guerrero, March 2018. Photograph courtesy of Ron Woheau, Zihuantanejo. Can you imagine having an encounter with one of these that is six feet long in waters known to contain crocodiles!
Green Iguana, Iguana iguana. Photograph taken of captive iguanas in the Los Cabos area of Baja California Sur, December 2019. Photograph courtesy of Dr. Tom Bartol, Carlsbad, California.
The Green Iguana, Iguana iguana, is a member of the Iguanidae family that includes Iguanas, Chuckwallas, and their prehistoric relatives. The Iguanidae family consists of seven hundred members placed in forty genera. There are two species in the Iguana genus. They are also known as the American Iguana and the Common Green Iguana. The Green Iguana is known in Mexico as “Gallina de Palo”, with males known as “Goorobo” or “Ministro” and juveniles as “Iguanita” or “Gorrobito”.
The Green Iguana is the largest species in the Iguanidae family. They vary in body size from 7.7 cm (3.0 inches) snout-to-vent length (SVL) in neonates to more than 50 cm (20 inches) SVL in adult males, with a total length of almost 2 meters (6 feet 6 inches) including their long, tapering tail. They have a row of thin, enlarged dorsal spines that extend along the top of their back from their neck to the end of their tail and assist in predation avoidance. Their limbs are robust with long claws on their toes. They have a few small horns on their snout that lie between their eyes and nostrils. Their teeth are sharp and diamond-shaped with serrated edges. Additionally, all of their teeth are roughly the same size and shape. Their tail is long and robust with wide black bands. They possess a large dewlap that can be extended when an individual is basking to assist in body temperature control, or when they interact amongst themselves in courtship and territorial displays. Several small horns lie between their mouth and their dewlap. Green Iguanas have excellent long-range vision but cannot see well in low light environments. They have a third “eye” directly on top of their head that is not a true eye, rather, it is a sense organ that assists in body maintenance and can detect predation from above. Green Iguanas change in color as they mature. Neonates are normally a brilliant green color with an aquamarine bar over their anterior limbs and dark pigmentation on their eyelids. Juveniles are typically light-green in color. Adults are a dark green and males take on an orange hue in the reproductive season. They also change in color during the day, being darker in the morning to absorb more heat from the sun, and lighter in color in the afternoon to reflect the sun’s heat. In general, their coloration will typically mimic their jungle background. In Mexico, Green Iguanas generally appear with an orange cast. They display sexual dimorphism with males being larger and more brightly colored with various hues of black, blue, green, lavender, orange, and pink. Additionally, males possess taller dorsal spines and large very pronounced jowls. Males also display more dominant behaviors such as head bobbing and tail whipping. The sex of a juvenile is difficult to determine because both sexes possess enlarged, circular, and highly visible sub-tympanic, or helmet, scales that are found on both of their cheeks. These scales can be puffed out to intimidate potential predators.
Green Iguanas are territorial and perch themselves high in the tropical forest canopies, establishing home ranges that are approximately 5,017 square meters (6,000 square yards). Considerable overlap between male and female territories is maintained. During the mating season, dominant males reduce the size of their territories significantly. Males are capable of copulating only once a day, producing a competition among females during the reproductive season for access to dominant males, in addition to the normal male-male competition for access to females. Females also compete amongst themselves for access to partially completed nest burrows in areas where they nest in aggregation. Green Iguanas are oviparous and their reproductive cycle is tightly correlated to the tropical wet and dry seasons. Mating is polygynandrous and males establish reproductive territories at the beginning of the dry season. Courtship behavior of males includes head bobbing, extension and retraction of the dewlap, and nuzzling or biting a female’s neck. Dominant males may also mark rocks, branches, and females with a waxy pheromone-containing substance secreted from their femoral pores. Females return annually to historical nesting sites and may migrate up to 3 kilometers (1.9 miles) to get there. Nesting occurs in communal nesting sites where females construct simple, shallow burrows. Each female guards the entrance to her burrow for several days after nesting. Gravid females arriving at a nesting site will extend existing burrows, developing a complex burrow system with interconnected tunnels and several escape routes. During mating, the male approaches the female and climbs on her back, straddling her. To restrain his mate, the male bites the female’s shoulder with his teeth, sometimes causing wounds. The male then pairs his cloacal vent with the female’s and inserts one of his hemipenes into her cloaca. Copulation can last for several minutes. Females can save sperm for several years, allowing them to fertilize eggs at a much later time. Eggs take 59 to 84 days to develop before they are laid. Females oviposit at times that allow the eggs to begin hatching near the onset of the rainy season, a time when new leaves are abundant and easier for neonates to digest. Over a 3-day period, females lay 9 to 71 cream colored eggs. Eggs measure approximately 1.54 cm in diameter and 3.5 cm to 4.0 cm in length. Incubation lasts between 90 and 120 days. Hatchlings rip the egg open using a special egg tooth, called a caruncle, that falls off shortly after hatching. After the eggs are laid, there is no direct parental investment in the young, who emerge fully independent. Egg mortality rates are exceedingly high and primarily result from natural environmental causes (heat, desiccation, floods) and raids by birds, snakes and terrestrial animals. It is estimated that at least 95% of the hatchlings fail to survive their first year. Juveniles often form small groups for enhanced protection. They grow rapidly within their first three years to become 1.0 kg (2 lb 3 oz) adults. The Green Iguana has a life span of eight years in the wild and twenty years in captivity.
Green Iguanas are diurnal and ectothermic, with their body temperature being dependent on their environment. They thrive in locations that have temperatures between 25oC (77oF) and 35oC (95oF). Green Iguanas interact among themselves using visual signals, chemical secretions produced by their femoral glands, and via direct physical fights among members of the same sex. In addition to reproductive fights, they will also fight (puff up their body, hiss, bob their head at the aggressor, lash their tail, bite, use claws, etc.) over basking locations, as basking plays an important role in raising their body temperatures. Green Iguanas are agile climbers and primarily arboreal, only descending to the ground for reproduction. They prefer to reside in trees above water, diving into the water and swimming away as needed to avoid predation. They also have the ability to fall up to 15 meters (50 feet) and land on hard surfaces unhurt. In addition to these strategies to avoid predation, they are also able to shed a large portion of their tail to distract predators, allowing the rest of the animal to escape. Their tail will grow back within a year, however, the regrown tail is not as long as the original tail. Green Iguanas are primarily herbivores, consuming upwards of 500 different species of plants. Their diet is supplemented on a limited basis by small amounts of carrion or invertebrates. Juveniles require high protein diets and consume lots of insects and spiders. Adults consume low phosphorus and high calcium, leafy diets. They are preyed upon by caiman, crocodiles, and fish while swimming and by other lizards, birds, snakes, and mammals while in their terrestrial habitat. When threatened, the Green Iguana will initially freeze in place and then, as needed, will flee utilizing one of numerous pre-planned escape routes.
The Green Iguana are found from sea level up to elevations of 1,000 meters (3,280 feet). They occupy a variety of habitats including tropical rainforests, dry forests, gallery forests, savannahs with few trees, and even xeric islands with exclusively shrub vegetation.
From a conservation perspective the Green Iguana is currently considered to be of Least Concern with a widespread distribution, large population size, and invasive range expansion. Additionally, this species has healthy populations found in several protected areas across multiple countries. They are threatened by habitat destruction caused by urban development and the conversion of land for grazing. The Green Iguana is also used for human consumption. Their meat and eggs have been consumed in numerous countries for centuries but at present, their population levels have dropped in many areas and they are no longer sustainable. Their hides are used for for leather products. Additionally, they are acquired for use as tourist attractions in resort areas. They are vulnerable to overharvesting because adults are conspicuous during mating season and females are easy to capture while nesting. The legal international pet market for juvenile Green Iguanas is enormous and estimated to be at 4.5 million individuals per year. It is likely that businesses, such as iguana farms, supplement their stocks with individuals from natural populations. The illegal Iguana pet trade is also large but difficult to document. Green Iguanas are popular due to their calm disposition and bright colors. However, they their maintenance is very labor intensive and the majority of Green Iguanas in captivity die within two years. In some parts of the United States, they are considered to be a non-native nuisance and an invasive pest, and ownership has been banned. They are currently the focus of farming efforts as a source of human food and to help supplement native populations. Some cultures worship Green Iguanas and depict them in their art. Although they are large in stature and visually intimidating, Green Iguanas present no known threat to humans.