The Green Iguana (Iguana iguana) is a large, non-native lizard and invasive species in Florida. Its presence causes significant ecological and structural problems, damaging residential landscaping and native flora, and undermining infrastructure like seawalls and sidewalks with extensive burrows. The establishment of this tropical lizard in the Sunshine State is rooted in human activity.
Native Range and Environmental Factors
The green iguana is naturally found from central Mexico south through Central America to Paraguay and central Brazil, including adjacent Caribbean islands. These arboreal lizards spend most of their time high in the tree canopy and thrive in tropical and subtropical environments, particularly near water sources. Their native habitat is characterized by warm temperatures and high humidity.
Florida’s subtropical climate, especially in the southernmost counties, perfectly mimics the iguana’s native conditions. The lack of prolonged, deep freezing temperatures is the most important environmental factor allowing the species to flourish. Iguanas are cold-blooded, and cold weather naturally limits their northern expansion by inducing torpor. South Florida provides the necessary year-round warmth, abundant rainfall, and lush vegetation for continuous activity, feeding, and breeding cycles.
The Role of the Pet Trade in Initial Introduction
The primary mechanism for the green iguana’s introduction into Florida was the booming exotic pet trade, which began decades ago. Green iguanas remain popular pet reptiles imported into the United States due to their attractive appearance and manageable size when young. For example, approximately 800,000 iguanas were imported into the U.S. in 1995 alone.
Feral populations were established through two main human-mediated pathways: accidental escape and intentional release. Accidental escapes occurred when poorly secured captive animals wandered away from enclosures. Hurricanes and severe storms also contributed to escapes by damaging outdoor cages, particularly in coastal areas.
The most significant contribution came from the intentional release of unwanted pets. Juvenile iguanas are small and easy to care for, but they grow quickly, reaching lengths over five feet and becoming aggressive as they mature. Unable or unwilling to care for a large, demanding lizard, owners often released them into parks, canals, or wooded areas.
The first documented sightings of free-living iguanas occurred in the Miami area in the early 1960s. A notable early event involved a pet dealer reportedly releasing over 300 iguanas in Miami-Dade County in 1964 because they had grown too large to sell, instantly creating a substantial breeding population. This pattern continued throughout the 1970s and 1980s, concentrated primarily in the urbanized areas of Miami-Dade, Broward, and Palm Beach counties, which served as the initial epicenters for the species’ establishment.
Biological Mechanisms of Establishment and Spread
Once introduced, the iguanas’ biological traits allowed them to transition rapidly from isolated escapees to established, self-sustaining populations. A significant factor is their high reproductive success. Female iguanas produce large clutch sizes, typically laying between 20 and 70 eggs in a single nesting event.
The breeding season occurs between December and April, with hatchlings emerging during the summer when food is abundant. Females dig extensive burrows in sandy soil, often along seawalls and canal banks, to create secure nesting chambers. Young iguanas reach sexual maturity quickly, with males maturing as early as 16 months and females by about two years, leading to rapid population growth.
The absence of natural predators capable of controlling adult iguana populations also contributed to their success. While juveniles face predation from native animals like raccoons and birds, mature adults have few local threats. This lack of population checks allows for high survival rates and exponential growth.
Iguanas are also highly adept at dispersal, allowing them to expand their range throughout South Florida. They are excellent swimmers and can travel long distances in water, aiding their spread across canals, rivers, and between the Florida Keys. The extensive network of human infrastructure, including canals, levees, and utility corridors, acts as a highway system for terrestrial travel, facilitating movement into new territories. Another element is secondary introductions, where individuals are inadvertently transported as stowaways in nursery plants, cargo, or vehicles, establishing new, localized populations.