The iguanas most frequently encountered in Puerto Rico are not native to the island, having established themselves as a widespread invasive species. The massive population of Green Iguanas (Iguana iguana) is now a fixture of the local landscape, particularly in urban and coastal areas. However, this fact often overshadows the existence of a truly native iguana species, a critically endangered animal whose survival is threatened by its invasive relative and other factors. The story of the iguana in Puerto Rico is therefore one of two extremes: an unchecked invasive population and a fragile, protected native one.
Differentiating Invasive and Native Iguana Species
The Green Iguana (Iguana iguana) is the large, common lizard seen basking on fences and roadsides across the main island. This species is native to Central and South America, but its ability to thrive in Puerto Rico’s tropical climate has allowed its population to explode. Densities are far higher than in its native range, sometimes reaching over 200 individuals per hectare in certain areas.
The island’s only native iguana is the Mona Island Iguana (Cyclura stejnegeri), a protected species endemic to the small, uninhabited Mona Island, west of the main island. Unlike the invasive Green Iguana, the Mona Island Iguana is a rock iguana, a large, terrestrial reptile that is critically endangered. This species is distinguishable by its gray to olive-green color, heavy build, and the presence of small, horn-like scales on the snouts of males. The total wild population of this native species is estimated to be only a few thousand mature individuals.
The Green Iguana’s Establishment and Spread
The introduction of the Green Iguana to Puerto Rico began in the 1970s, primarily through the exotic pet trade. Escapes, accidental cargo shipments, and intentional releases by owners are considered the primary vectors that led to the establishment of wild populations. The tropical environment provided an ideal setting for these reptiles to proliferate, as the climate mimics their native habitat.
A lack of natural predators for adult iguanas on the island is a significant factor contributing to their success. In their native range, they face over 40 different predator species, but in Puerto Rico, they are virtually unhindered once they reach maturity. This absence of population control, combined with a highly successful reproductive strategy, allowed for exponential growth. Females can lay large clutches of eggs, often exceeding 40 eggs per nest, with a hatchling viability rate recorded at over 90 percent.
The resulting population boom led to conservative estimates of over four million iguanas on the island by 2012, a number that far exceeds the human population. This rapid expansion has been further supported by the iguanas’ preference for disturbed and modified habitats, such as coastal mangroves, canals, and areas near human infrastructure. The abundance of resources and the favorable conditions have cemented the Green Iguana’s status as a dominant invasive species across the main island.
Ecological and Infrastructural Damage
The unchecked growth of the Green Iguana population has led to two categories of severe consequences: ecological harm and infrastructural damage. Ecologically, the iguanas’ herbivorous diet means they consume the flowers and buds of native plants, which can disrupt the reproduction of local flora and reduce the available nectar for native pollinators like hummingbirds and bats. They also compete directly with native wildlife for resources, including the rare Mona Island Iguana.
In terms of physical damage, the iguanas’ nesting habits cause widespread erosion and structural instability. Females dig extensive burrows in loose soil to lay their eggs, which can undermine the foundations of infrastructure. This burrowing activity translates into significant maintenance costs and poses a threat to public safety.
- Roads
- Sidewalks
- Seawalls
- Canal banks
Iguanas also cause significant economic disruption by damaging agricultural crops, with farmers reporting losses of valuable produce, particularly squash and pumpkin. Furthermore, the iguanas’ habit of basking on utility poles and electrical substations frequently leads to short circuits and power outages. This behavior causes costly damage to the electrical grid.
Current Management and Control Strategies
Due to the extensive damage they cause, the Green Iguana is classified as an invasive pest species by the Puerto Rico Department of Natural and Environmental Resources (DNER). This classification means the species has no protection under local wildlife laws, and control measures are actively encouraged to mitigate the negative impacts. The most effective strategy for population control focuses on disrupting the reproductive cycle by harvesting eggs and destroying nests.
Various public and private initiatives promote the humane culling of the animals, which can be legally hunted year-round. This is necessary because the sheer number of iguanas and their high reproductive success makes eradication virtually impossible. Some local groups have attempted to encourage the consumption of iguana meat as a way to incentivize population control, though public health concerns regarding Salmonella transmission remain a factor.
Government agencies also utilize targeted removal programs and habitat modification in protected natural reserves and sensitive infrastructural areas. Despite these efforts, the Green Iguana remains deeply entrenched, requiring continuous, systematic management to reduce its numbers and limit the ongoing ecological and economic damage it inflicts upon the island.