Puerto Rico’s iguana problem started, in all likelihood, with a few pets released into the wild. Those outcasts met and bred, and soon their progeny, feral and ravenous, started moving around the island, following the coastline at first, but about 10 years ago, they started moving inland. Initially, iguanas were considered a novelty. But in just a few years, populations went from scattered to dense, and from nuisance to environmental catastrophe. There is no part of the island where you won’t find the invaders gauchly lounging in trees, but they are particularly troublesome in the countryside, where they eat or damage as much as a quarter of the crops. And in a United States territory that’s teetering on the brink of economic collapse, any reduction of its export business is taken seriously. The favorite foods of iguanas are banana, papaya, and melon.