The green iguana, Iguana iguana, is a large lizard native to Central America, South America, and parts of the Caribbean. Males can reach over five feet in length. In Florida, the species is not native and is classified as an invasive species. Since their first appearance, these lizards have established widespread, self-sustaining populations, primarily due to human activity.
The Dual Mechanisms of Arrival
The establishment of green iguanas in Florida is linked to two distinct pathways of human-mediated transport and release. The most significant mechanism was the exotic pet trade, which saw thousands of iguanas legally imported into the United States. Owners often purchased these reptiles when they were small but were unprepared for their rapid growth and specialized care requirements.
This led to widespread intentional or unintentional releases, often when the iguanas grew too large or became difficult to handle. Breeding populations began to appear in the 1960s in South Florida following escapes and deliberate releases. For example, an incident in 1964 involved the release of over 300 iguanas near Hialeah. These released individuals formed the initial founder populations that began to reproduce in the wild.
A secondary mechanism for introduction was accidental transport via commercial cargo. Iguanas and their eggs sometimes arrived as stowaways in shipments of fruit, nursery material, or on boats traveling from their native range in the Caribbean or Central America. While these individuals may have contributed to localized populations, the primary source of the established population is overwhelmingly attributed to releases stemming from the pet trade.
Environmental Factors Driving Establishment
Once introduced, the iguanas were able to survive because the South Florida environment closely mimics their native tropical habitat. The region’s warm, subtropical climate provides the long, frost-free seasons necessary for these reptiles to maintain active metabolism and successfully reproduce year-round. This climate is the most important factor allowing for the species’ permanent establishment.
The iguanas also found an unending supply of food in their new environment, as they are primarily herbivorous. They readily consume the abundant ornamental and cultivated vegetation found in urban and suburban landscapes, feeding on leaves, flowers, and fruits. This consistent food source, coupled with a lack of predation pressure on adults, created ideal conditions for population growth.
While predators such as raccoons, opossums, and native birds prey on juvenile iguanas and eggs, few natural predators are large enough to effectively control the adult population. The absence of control on larger, breeding individuals allows the population to grow exponentially. This combination of a favorable climate, plentiful food, and limited adult predation enabled the iguanas to establish a successful, self-sustaining population.
Geographic Spread and Density
The initial breeding populations were concentrated in the southeastern portion of the state, particularly in Miami-Dade, Broward, and Palm Beach counties, as well as the Florida Keys. The species is highly sensitive to cold, which acts as a natural barrier limiting their northward expansion. During cold snaps, iguanas enter a state of torpor, often falling from trees, which highlights the temperature limit of their range.
Within their established range, iguanas have reached high densities in human-modified habitats. They are frequently found along the network of canals, waterways, and urban infrastructure, often basking on seawalls and docks. Their burrowing behavior, necessary for nesting and shelter, is concentrated along these water bodies. This results in localized population densities that can exceed several hundred individuals per hectare. The successful colonization of these urban corridors has allowed the population to become naturalized and permanently integrated into the South Florida landscape.