People aren't the only ones who like to escape from their hometowns; animals do, too, but with more serious consequences than being unable to speak a language.
Scientists classify any species that didn't originate from an environment as invasive. Simply put, it's something that doesn't belong. The introduction of a species like this throws off the balance of the ecosystem — and destroys it. "Some of them are very obvious, like invasive insects that destroy the dominant tree," says Daniel Simberloff, professor of environmental science at the University of Tennessee. "Others change fire cycles, [such as] invasive African grasses." Another well-known invasive species is the lionfish.