Caiman crocodilus is native from southern Mexico to northern South America and is the most numerous crocodilian in the Americas. Its tolerance of degraded and artificial habitat, combined with a fast reproductive rate, makes it an effective coloniser.
Large numbers were imported into the United States as pets during the 1950s and 1960s, when hatchlings sold for very little. Animals discarded as they grew established themselves in the canal systems of Miami-Dade County, and reproduction there has been documented since the 1970s. Introduced populations have also been reported in Puerto Rico and Cuba. Florida's cold snaps limit northward spread, which is one reason the population has stayed localised rather than expanding through the peninsula.
The species also shows a general crocodilian trait plainly: sex is set by incubation temperature, not by sex chromosomes. Less settled is the ecological effect of the Florida population. Predation on native fish and competition with juvenile alligators are plausible but have not been quantified.