The presence of large, often brightly colored iguanas has become a defining, yet unwelcome, characteristic of South Florida’s landscape. These reptiles, now a common sight basking on seawalls and foraging in manicured gardens, are not native residents but rather an invasive species that has established a robust population in the state. Understanding their current ubiquity requires looking back at the historical and logistical vectors that enabled these tropical lizards to travel hundreds of miles and successfully colonize a new continent. The story of the iguana in Florida is one of accidental introductions, an accommodating environment, and explosive population growth.
Identifying the Primary Invasive Species
The Green Iguana (Iguana iguana) is the most common invasive species established across South Florida. This species is naturally distributed throughout a vast range, stretching from Central America down to tropical parts of South America, and across some Eastern Caribbean islands. Its popularity in the exotic pet trade, combined with its adaptability, facilitated its establishment in the state.
The Black Spinytail Iguana (Ctenosaura similis) is also present and considered invasive, though it is less commonly encountered than its green counterpart. Native to Mexico and Central America, it shares the Green Iguana’s ability to thrive in Florida’s warm environment. Both species were introduced to Florida through human activity, not natural migration.
The Mechanisms of Initial Arrival
The establishment of iguanas is largely attributed to two distinct methods of transport. The first, and most significant, vector was the exotic pet trade that flourished in the mid-20th century. Green Iguanas were imported in massive numbers, with over a million individuals brought into the U.S. in a single year during the 1990s alone.
Iguanas sold as small pets often grew to five to seven feet, becoming too large and difficult for owners to manage. This resulted in intentional release or accidental escape. For example, an exotic pet dealer reportedly released over 300 iguanas in the Miami area in the 1960s. These initial releases created a foundational breeding population in urban areas like Miami-Dade, Broward, and Palm Beach counties.
The second method involved accidental transport, where iguanas acted as stowaways. They were inadvertently carried on cargo ships arriving from Central and South America or the Caribbean. Smaller populations may have also arrived on natural rafts of debris washed out to sea after major hurricanes. While the pet trade created the largest initial breeding groups, accidental transport augmented the feral population over time.
Environmental Factors Enabling Population Growth
Once a breeding population was established, Florida’s unique environmental conditions provided an accommodating habitat for iguanas to flourish. The state’s subtropical climate, characterized by mild winters, prevents the cold-related die-offs that would limit the northward spread of these tropical reptiles. While temperatures below 40 degrees Fahrenheit can cause them to become lethargic and fall from trees, these cold snaps are infrequent enough that they do not control population growth.
Urban and suburban areas of South Florida offer an unending food supply, primarily ornamental plants and landscaped vegetation consumed by the herbivorous iguanas. This constant food availability, combined with the mild climate, allows for extended breeding seasons. Female iguanas can lay up to 70 eggs per clutch, enabling rapid population growth.
Iguanas have few natural predators in Florida capable of controlling the large adult population. Adult iguanas are generally too big to be preyed upon by most native animals, though eggs and hatchlings are vulnerable. The lack of sustained predation pressure, coupled with climate and abundant food, has allowed populations to grow exponentially.
Current Geographic Spread and Control Efforts
Successful establishment has led to the spread of iguanas across the southern half of Florida, primarily along the coastlines. The densest concentrations are in the southeastern counties, including Miami-Dade, Broward, and Palm Beach, with populations expanding northward into central Florida. The network of canals and waterways throughout South Florida has aided their dispersal, as the reptiles are capable swimmers.
The population boom causes significant damage to both infrastructure and the natural ecosystem. Iguanas burrow, which can undermine seawalls, foundations, and sidewalks, requiring costly structural repairs. Their herbivorous diet also impacts native flora, including plants that are food sources for native species like the rare Miami blue butterfly.
Iguanas are not a protected species in Florida, except by anti-cruelty laws, so state agencies encourage homeowners to remove them from private property. Control strategies focus on humane removal, including trapping and euthanasia. The Florida Fish and Wildlife Conservation Commission has also restricted the sale and keeping of iguanas to limit future releases. The challenge remains immense, given the iguanas’ high reproductive rate and the scale of the established population.