Though they are not endemic to Puerto Rico, green iguanas  have flourished here due to the absence of natural predators. They were introduced to Puerto Rico through the exotic pet trade and today are considered an invasive species, so much so that in a few decades the 4 million strong population now outnumbers the entire population of Puerto Rico. It is common to see them in trees, mangroves and near the side of the roads.
Known colloquially in Puerto Rico as gallina de palo, which loosely translates to “chicken of the trees”, these herbivores can grow to about 1.5 meters in length, though they can reach lengths of up to 2 meters and can live between 10 to 15 years in the wild.
In some countries of Central and South America, green iguanas are part of the local cuisine, which is why they are protected by laws that regulate their hunting. Because they are such a popular part of the diet in some areas and are much sought-after by the exotic pet trade, they are listed in the CITES  Appendix II (Convention on International Trade in Endangered Species of Wild Fauna and Flora), which means that, even though they aren't quite considered an endangered species, trade has to be controlled in order to make sure their numbers don't go down too much.
In Puerto Rico, some people have decided to hunt the iguanas for free in order to help farmers protect their crops. A group called Los iguaneros de Aguada  not only hunts them, but also encourages people to try them as food, showing how to prepare and safely cook the meat.
Some environmentalists have formed teams of volunteers to help control the population of green iguanas in natural reserves. Because one female can lay as much as 75 eggs —more than 90% of which will hatch successfully— the best way to do this is to harvest the eggs from the nest, thereby eliminating it altogether.
This short three-and-a-quarter-minute documentary  produced by National Geographic shows biologist Rafael Joglar and environmental interpreter Carlos Rodríguez explaining why the green iguana is such a serious problem in Puerto Rico. Carlos Rodríguez sums up the scope of the work that must be done to successfully control the population in the Las cabezas de San Juan Natural Reserve:
We've eliminated since the year 2008 to the present approximately 13,000 eggs from the population. That's a big number, but this is something that we're gonna have to do for the next 15, maybe 20 years.
You can see the full video below: