Why Are Enormous, Alligator-Eating Pythons Invading Florida?

By Brian Resnick

Giant snakes are devastating the Everglade ecosystem. An expert explains how this became a problem, and what, if anything, we can do to stop it.

Mike Rochford, University of Florida

America has a border problem, but it's not the one you're thinking about. Foreign invaders arrive in this country quietly, often in shipping containers from Asia or as exotic pets. At first, small populations are hardly noticed. Then, when becomes apparent that these invaders have no natural enemies here, their numbers explode exponentially. 

America can't keep invasive plants and animals out of its ecosystems, and stories of their destruction continually appear in the news cycle. For the past few years, increasingly large swarms of Asian stink bugs have been destroying apple harvests in the fall. Streams, rivers, and lakes in the heartland are teeming with Asian Carp -- fish that routinely cause injury to boaters, jumping up from the water when provoked. There are also less visual stories concerning invasive species, such as Emerald Ash Borers, insects that have killed tens of millions of trees across the country in the past decade. In all, invasive species cost the U.S. $120 billion a year, both in damages and containment. 

And now Burmese pythons are capturing headlines. These snakes can grow to 16 feet and eat almost anything -- even alligators (click if you dare, it's a photo of an alligator carcass and a dead python that burst open while devouring it). Since 2003, as a new study in Proceedings of the National Academy of Sciences notes, the increase of the python population from just a few to perhaps a few thousand has been connected to declines of several native mammals. According to the study, observations of raccoons have declined 93 percent, bobcats by 87 percent, and possums by 98.9 percent. The Everglades are enormous -- nearly 4,000 square miles -- and it is difficult terrain to traverse. So it's hard to say how the pythons have affected rarer, quieter species such as egrets.

Recently, Michael Dorcas, professor of herpetology at Davidson College and lead author of the study, spoke with The Atlantic about how pythons became a problem, and what, if anything, we can do to stop them.

Do researchers have a sense of how quickly the python population is expanding?

We really don't. Basically, my answer to that is there are a lot of pythons out there. I found more pythons in the Everglades National Park than I found rat snakes, which are one of the more common species of snakes in the eastern United States.

Determining, or even estimating, how many snakes are out there is very difficult because snakes are very secretive. They remain inactive for much of the time, and to determine actual densities of snake populations requires mark-recapture studies. But all of the pythons that are captured in the park are actually removed from the park, so that precludes us from doing mark-recapture studies. I would certainly feel comfortable saying there are thousands of snakes, but there may be many orders of magnitude more than that.

People keep pet snakes all across the country. Why is it that they have found such a suitable home in Florida?

Certainly the climate and habitat is very suitable for these snakes there, or it appears to be. There are these vast areas of wilderness that, at least at one time, had abundant prey. The climate is subtropical, so it facilitates their survival and reproduction.

When did it become apparent that pythons were overtaking the Everglade ecosystem?

Pythons have been found in various places throughout the United States for a number of years and have been a mainstay of the reptile pet trade for decades. Pythons would turn up here and there, even in places like Charlotte, North Carolina, where I live now, and including the Everglades National Park, even back in the 1980s and 1990s. But it wasn't until the year 2000 that they were recognized as an established, reproducing population. Since that time, they have increased their numbers dramatically. If you compare the mammal populations to before they started proliferating to the mammal populations now, you see these drastic increases we report in our research article.

On Tuesday, the government announced that it will ban the importation and interstate transport of several python species. Is this too little too late?

That ban is certainly not going to effect the python population that is now in south Florida to any appreciable amount. There are thousands out there already.

It might prevent Burmese pythons from being released elsewhere in the U.S. where they might be able to survive, such as south Louisiana or south Texas. Then, it might help to prevent other species -- there are three other species on that ban that would be prevented from becoming established in south Florida.

What are some of the consequences for the Everglade ecosystem?

It is really hard to predict. The Everglades are a vast landscape, and consequently, are a complex ecosystem. So it is very difficult to make accurate predictions about having so many once-common mammal species removed from the park. But it is not unreasonable to assume that when you remove large numbers of once-common species from an ecosystem, there are going to be ecosystem-wide repercussions. That is a safe assumption.

There is a similar situation in Guam with brown tree snakes. Guam really didn't have any snakes at all. Snakes were introduced in the 1950s and within 30 years they were recognized as having devastated many of the native species. In Florida, we have a situation where we have an invasive snake, and within only 11 years of being recognized as established in a considerably more complex ecosystem, it appears to already have devastating impacts on the prey populations.

We've had numerous cases from around the world where top-apex predators have been removed or severely reduced. But here we have a case where a top predator has been added to an ecosystem, and it's certainly not unreasonable to assume that the ecosystem is going to respond in dramatic ways. But it is a really unique situation; there are really few cases like this.

Are there any pending solutions to this problem, biological or otherwise?

Our history of introducing one invasive species to control another is not real good. We had problems with that in the past so that is something you want to be extremely cautious about. People proposed, "Well let's have a disease that could wipe out all the pythons." But what if that wiped out all of the native snakes as well or other species? Then, we would have real problems. So developing some sort of biological control is certainly something that we want to be extremely cautious about. It is something that might hold promise, but we would want to proceed with extreme caution in that case.

There's nothing on the horizon that we know of that is really going to suppress python populations over the thousands of square miles that they now inhabit. You've got a vast landscape and much of it is very difficult to access by humans, and there aren't many roads through Everglades National Park. It makes it very difficult to develop techniques that could really reduce the overall population in any appreciable amount. It's a real challenge.

Giant pythons attacking alligators in Florida are a headline grabber, but are there other invasive species threats in the Everglades, or in the country at large, that should receive attention?

Pythons certainly get a lot of attention. They're giant snakes; people are fascinated by snakes, especially by giant ones. Invasive species are one of the major threats to biodiversity worldwide, and we literally spend billions of dollars every year managing invasive species such as fire ants, which may not get the press but certainly cause major problems.

It's extremely difficult to stop the influx of invasive species, and we're not even talking about things like bacteria and diseases that move around and cause problems. The old "an ounce of prevention is worth a pound of cure" certainly holds in this case with invasive species. It's certainly easier to prevent new species introductions in most cases than to deal with them after the fact. And in some cases, after the fact it is nearly impossible to deal with them.

This article available online at: