It sounded like a joke when the news first hit in 2000: Giant Burmese pythons were invading the Everglades. Now scientists have measured the real impact of the arrival of this voracious species, and the news is troubling.

In areas where the pythons have established themselves, marsh rabbits and foxes can no longer be found. Sightings of raccoons are down 99.3%, opossums 98.9% and white-tailed deer 94.1%, according to a paper out Monday in the Proceedings of the National Academy of Sciences.

This is an example of how regulation is critical for preserving the environment.