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invasive pythons in the united states

9 march 2013

I knew that a population of pythons had become established in South Florida – it's hard to surf the Web for any length of time without seeing video of them. What I didn't realize till I read Michael Dorcas and John Willson's Invasive Pythons of the United States is just how recent a development this is, or just how many pythons have installed themselves, or how little science knows about them.

There may, at this writing, be 100,000 or more Burmese pythons in the Everglades. That is just a lot of biomass. It's generally conceded that the founding pythons of this population were escaped or released pets, though the details will forever be obscure. Obscure as well is a key question: what have these pythons been eating, to replace so much existing animal mass with their snaky selves?

Pythons eat birds and mammals – mostly rats, which would not seem to be a bad thing. But they will eat any bird or mammal that presents itself, without consulting the Endangered Species list. The endangered Key Largo woodrat might go extinct from python predation, and while "Key Largo woodrat" doesn't sound like something we'd particularly miss, one should never assume that a species here and a species there can disappear from the ecosystem without cascading effects and irrevocable losses to the planet.

Pythons rarely eat other reptiles. One exception is alligators, another Floridian pest. (Of course, in what sounds like a python proverb, sometimes the alligator eats the python.) I have no idea how many Floridians would like to replace annoying backyard alligators with annoying backyard pythons. I'd prefer the pythons, frankly, but many people are afraid of any kind of snake, much less one that could crush the life out of them.

Still, pythons rarely attack people in the wild. Most python casualties are killed by their own pets, who confuse them with the food they've come to associate with their keepers. They're quite capable of killing an unaided human – even more so a frail or young one – but their default mode is "run away." Dorcas and Willson explain that this is one reason it's so hard for science to get a grasp of python ecology in Florida. Pythons are secretive, and they are well-camouflaged; they head for the deepest recesses of the Everglades, and if you don't positively see one crossing a road at night, you are unlikely ever to see one at all.

Are they headed our way? (Unless of course you're reading this in South Florida and they already are your way.) Scientists aren't even real sure about that. Dorcas and Willson print several maps of potential python ranges in the United States. The conservative ones have the snakes dotted here and there in subtropical habitats like their current range and the lower Rio Grande Valley. But research suggests that many Asian pythons live in quite temperate parts of their continent, and we're not quite sure whether the American pythons can adapt like them, or are already so adapted. The most liberal guesses have pythons able to live in most of the old Confederacy.

Dorcas and Willson took some Florida pythons to an "enclosure" in South Carolina (clearly not having seen Jurassic Park before trying this). They lost them to a freeze. It's just one study, but suggests that pythons aren't about to spill out of Florida northwards. Ironically, development threatens python habitats in Asia, endangering them in many places there even as they flourish in Florida. But they have not made inroads in metropolitan Miami (see "run away from humans," above). And I'd reckon their northern march might be stymied by the belt of building that seems to span the peninsula uninterruptedly from Tampa to Orlando and beyond.

Too bad, in some ways. I'd kind of like to have pythons in my neighborhood – at least till I think of them eating my cat Whisper Wilson.

Dorcas, Michael E., and John D. Willson. Invasive Pythons in the United States: Ecology of an introduced predator. Athens: University of Georgia Press, 2011.