Burmese Pythons in the Everglades

by Michael Sarill (ELP 2016) | Director, Project Noah, USA

As of February 2013, scientists estimate anywhere between 30,000 and 150,000 Burmese Pythons exist in South Florida. As you may have suspected, Burmese Pythons are not native to Florida. They are native to Southeast Asia and south China. 

The problem? The pythons are completely decimating populations of native wildlife. A study conducted by Michael Dorcas, a herpetologist at Davidson College in North Carolina in 2011 documented “severe declines” in mammal sightings. The 2003 to 2011 surveys compare mammal sightings to data from surveys conducted in 1996 and 1997 – before the python was breeding in the wild. 

As the population of pythons has spiraled upwards in the last decade, mammal observations have declined by the following percentages: 

  • ​87.5% bobcat decline 
  • 94.1% white-tailed deer decline
  • 98.9% opossum decline 
  • 99.3% raccoon decline 
  • 100% rabbit decline 
  • 100% fox decline 

Not a single rabbit or fox sighting was found. Furthermore, the impact of the invasive species on rare animals is unknown. It’s unclear whether or not the python is consuming the Florida panther. It’s quite possible, as these snakes eat leopards in their native habitat of Southeast Asia. 

As per above, the pythons aren’t picky eaters. They will often eat any animal they can find. Even large numbers of birds are being consumed. Over 25% of the pythons found in the Everglades contain bird remains.

The above-listed mammals simply have no instinctive defense or fear from a large carnivorous snake. As a result, they fall easy prey. Before the Burmese Python in early 2000, the last large snake to live in this region was 16 million years ago, when a boa-like snake became extinct.

The study does report that certain animals, like turtles, may thrive as a result of this ecological distortion. Raccoons routinely prey upon turtle eggs. With severe declines in raccoon population, turtles have the potential to grow at a higher rate. Of course, this argument assumes the python doesn’t eventually turn on the turtle as food sources dwindle. 

In addition to the above report, the National Academy of Sciences published a separate report suggesting bird and coyote populations are also threatened due to the invasive species. 

“Survival of the Fittest” Argument Rebuffed

Some counter that survival-of-the-fittest dictates the pythons should spread, as they are simply more powerful predators than their prey. They argue there’s nothing fundamentally wrong with this scenario as it simply represents natural selection playing course. But this argument makes little sense as it runs counter to how ecosystems function. 

Burmese pythons in their native habitat in Southeast Asia do not cause a 90+% decline in the population of their prey. And neither do large carnivorous snakes like anacondas in the Amazon. Populations of predator and prey evolve together over time and live in balance. Prey develop natural instinctive defenses from these predators. The animals of the Everglades have no natural instinctive defense from these large snakes. 

It’s worth noting a further element of tragic irony in this story. While the pythons are spreading like rabbits throughout south Florida, they are endangered in their native habitat of Southeast Asia. Back home, they are hunted for their skins and captured alive for sale abroad as pets. 

How did they get here?

Between 1996 and 2006, roughly 99,000 pythons were imported into the United States as pets. 

It’s believed the pythons began breeding in the wild as a result of two primary causes: irresponsible pet owners releasing them and the animals escaping their loosely-kept cages as a result of hurricane or stormy weather. 

As for the former, these snakes grow to an average of 12 feet. Pet owners likely grew uncomfortable with the health risk and financial burden of securing and feeding a 12-foot snake in their home. After not wanting to deal with these challenges, many released them into the wild.

As for the latter, in 1992, Florida’s Hurricane Andrew was responsible for destroying a python breeding facility. In the late 90’s and early 2000’s, other less severe storms likely enabled snakes in loosely secured cages to escape during stormy weather. 

Here’s a brief timeline of how the population began to spiral out of control: 

  • 2000: A breeding population was confirmed in the Everglades. 
  • 2001-2005: 201 pythons observed or killed in the Everglades. 
  • 2006-2007: 418 pythons seen or killed in the Everglades. 
  • 2009: 5,000 – 180,000 estimated by South Florida Water Management District.

It’s difficult to know exact population numbers over the last decade as these animals are difficult to spot. The above numbers are based on sightings and killings of pythons. The bottom line is that from early 2000 to the present, the population of breeding pythons in the Everglades spiraled to well over 30,000. 

More on the Python’s Biology

The severity of this proliferation is better understood after learning about certain aspects of this snake’s biology. 

For starters, the Burmese python routinely lives 25 years or more. Astonishingly, the record lifespan for a python in captivity is 47 years!

Females typically lay one clutch of eggs per year, usually in the spring. Each clutch contains somewhere between 12 and 36 eggs. But much larger numbers have been recorded. This August 15 report from the New York Times included finding a 17-foot python with 87 eggs. 

These key aspects of the python’s reproductive behavior, combined with the prey’s lack of natural defenses, have led to a perfect storm of ecological collapse for the land-dwelling mammals. 

A Brief Thought Experiment

Consider a brief thought experiment where we entertain the consequences of some conservative numbers. Let’s assume there are presently 30,000 pythons in the wild, the lowest number from scientists. Assume a third are female for a total of 10,000. Assume half are large enough to be actively breeding in the wild. And finally, let’s assume the average clutch is 12, the lowest number. So we have 5,000 female pythons producing 12 eggs per year. The result is 60,000 new young per year. Assume half that number of young survives and we are left with 30,000 new pythons being added to the habitat per year. In conclusion, by conservative estimates, without even considering compounding, Florida will be adding 30,000 new Pythons per year. Assuming 30,000 now live in the wild, that is doubling the first year and 50% growth in year two. Again, these are conservative numbers that ignore compound growth.

If 30,000+ pythons are presently causing 90+% declines in the population of native mammalian life, then this level of growth appears completely unsustainable. Food sources will simply run out. Native species will go extinct.

As for what happens next, I’m not a formally-trained biologist, but I gather one of two things will inevitably happen: either the population will stabilize due to starvation and cannibalism; or worse, the snakes will continue to spread geographically in search of new sources of food.

Some Good News: Pythons Can’t Survive the Winter

I was thrilled to learn some apparent good news in this otherwise awful story. The consensus among herpetologists appears that the python cannot survive through a winter beyond south Florida. 

An initial USGS study by Reed Rodda in 2008 claimed the pythons could expand as far north as the southern third of the United States. But that study appears to be an outlier. 

Consensus among snake biologists is that Burmese pythons are unable to withstand a winter beyond south Florida.  An experimental closure in South Carolina kept a number of pythons over winter. All of the animals died, as they could not properly acclimate to the change in climate. When it gets cold, these pythons simply die. The study did note, however, that the pythons could survive extended periods of temperatures lower than southern Florida. 

Python's inability to survive winter, however, may very well be the only good news with regards to their ability to spread throughout the region.

Research in an early 2012 issue of the Journal of Experimental Marine Biology and Ecology report concluded that pythons are able to tolerate salt water and can therefore travel through marine and estuarine environments like bays or inlets. The open seas are also a possibility. Prior to the report, it was hoped that the pythons would die in saltwater and would therefore be primarily limited to the freshwater of the Everglades. 

The snakes can therefore travel along the southeastern coastline and would only be limited by climate restrictions. Worse still, many climate biologists and snake herpetologists claim this climatic range is quite suitable habitat and very similar to that of Southeast Asia. 

Burmese Pythons and the American Alligator

One animal in the Everglades appears able to pose a threat to an adult python. In a battle between the Burmese Python and an American Alligator, who wins? The answer: it depends. Both animals have been found to prey on one another. A large alligator can kill and eat a medium-sized python. And the opposite holds true for a large python.

To be fair, newly hatched juvenile pythons are vulnerable to predation by birds and other animals; but that doesn’t say much as the young of any species are always vulnerable. 

Back to the alligator-python battle. How is it decided? The battle is often decided by two main factors: the respective size of each animal and the caliber of the first strike. If the alligator secures a swift bite at the python’s head, the snake’s neck will snap and it dies instantly. The python, on the other hand, aims to wrap itself around the alligator, as it would any other prey. After securing a full wrap, it suffocates the animal and then eats it whole. For a successful alligator hunt, size is key for the snake. The larger the python, the greater its chance of successfully wrapping itself around the alligator. Pythons are not venomous and must wrap around their prey to secure a kill. Naturally, small and medium-sized alligators are more vulnerable.  

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Some sensational pictures have showed up online of battles between the python and the alligator: alligator eating python, python eating alligator.

There’s even a grotesque story of a python’s stomach exploding after attempting to consume an alligator too large to digest. Its body rejected the meal outright and the snake died a gruesome death. For any remaining survival-of-the-fittest arguers out there - no, ecosystems are not supposed to function in which a predator’s remaining food source causes its stomach to explode. 

If there’s any silver lining here, however small, some predation of the python is good and healthy. 

Size becomes a key-determining factor of survival between what will inevitably be the two significant remaining animals. Over time, as evolution runs its course, natural selection would favor increasingly large alligators and pythons. 

Yes, what was previously a balanced and varied ecosystem of rabbits, foxes, bobcats, deer and opossums in the Everglades is now becoming a battle between larger-and-larger pythons and alligators.

People & Pythons 

But this natural selection is unlikely to take shape. Burmese pythons and American alligators will not battle over the course of millions of years for the same reason this highly imbalanced ecosystem arose in the first place: human intervention. 

The python problem will get so bad that humans will have to take comprehensive and aggressive action to curtail the population.  

Families living in rural areas have reason to worry. As food sources run out, the snakes will grow increasingly desperate in search of a new meal. If a snake is willing to attack a large alligator, household pets are unquestionably vulnerable to attack. Dogs and cats must be properly confined in rural areas to stay safe. 

The snakes do not typically pose a threat to adults and tend to be wary of approaching people. Although, when food sources run out, the animals could become desperate and children might be vulnerable. 

In the summer of 2009, a 12-foot Burmese python inside a central Florida home escaped from its enclosure and killed a 2-year-old girl. The girl was strangled in her crib. Apparently, the snake’s tank was only fitted with a light quilt for a lid. The snake had not been fed for a month and was severely underweight. The girl’s parents were each sentenced to 12 years in prison on charges of third-degree murder, manslaughter and child neglect. It was a tragic event for the local community and the story made national headlines. 

Media Coverage

An aspect of this story that gets under my skin is the media coverage. 

Media coverage of this story typically runs as follows: background on how the python problem originated; acknowledgement of the pythons causing widespread native species collapse; some more scientific observations about the pythons; Florida’s attempt to respond to the crisis; acknowledgement of the situation being dire and uncontrollable; end of story. 

This coverage fails to meaningfully tackle what I view as the obvious and serious bigger questions: what happens when these animals inevitably begin surrounding rural communities? How will children and household pets be protected? How many native species of animals will have to collapse before more comprehensive, aggressive action will be taken? What specific tactics will be taken by Florida to prevent the python from spreading throughout the coastline of the southeast United States? 

In fairness, this problem is enormously challenging. And there are no easy answers. But doesn’t meaningful progress begin around a discussion of the right questions?

Florida’s lackadaisical attitude now speaks to their attitude in mid-2000 when the problem had a better chance of being resolved. It’s difficult to know exactly how many pythons were in the wild then, but likely no more than 5,000.  Aggressive, comprehensive action at that time could have prevented their spread or even potentially killed them all.   

Yes, hindsight is 20-20. But at the same time, I would be willing to wager that any educated scientist could have predicted in 2005 that 5,000 pythons breeding in the wild in the Everglades would lead to ecological collapse. 

Florida’s Solution Now: “Controlling the Snakes”

In February of 2012, the Florida Fish and Wildlife Conservation Commission initiated a 30-day hunt to raise public awareness on this issue. Around 1,600 people from 38 states participated in the hunt. 68 pythons were killed. 68. Assuming 30,000 are in the wild, the low end of figures, 68 represents .2% of the python population. The primary reason for this low number is that the snakes are notoriously difficult to locate. 

The most recent hunt, as part of Florida's 2016 Python Challenge, took place this past January. 106 pythons were captured this past year. This represents an improvement from 2013 but hardly puts a dent in the total number in the wild. Cooler temperatures have forced snakes into open spaces and assists hunters in finding them. In addition, hunters are improving their hunting skills. 

Florida appears to have fully resigned itself to containing the snakes as the solution. This hunt represents one of the first steps in the process. And the hunt also was meant as a way of doing some introductory research on where the snakes are located. 

The Nature Conservancy also launched a Python Patrol program in 2008 where citizens are trained to alert authorities of snake sightings. As part of the program, wildlife officials then move forward with capturing the snakes. The program was effective in the Florida Keys and then was expanded mainland to the Everglades with support from the National Park Service and the Florida Fish and Wildlife Conservation Commission. In total, 200 python capture responders are trained. 

This python patrol program is unquestionably a step in the right direction. At the same time, the program is at least 5 years too late. And it’s doubtful the program is being administered with the scope and urgency this problem demands. 

Preventing the spread of these animals is an enormously challenging undertaking. I have no idea how it can be done. These animals are excellent swimmers and travel extensively through marsh, swamps and river valleys. They also travel by land and are great climbers with prehensile tails. 

Worse still, a fundamental flaw exists with Florida’s proposed attempt at containment. Reducing the population of pythons decreases the competition for remaining food resources. As a result, the pythons that do remain become healthier, stronger and more fertile. And in the end, the population continues to grow at high rates. Yep, decreasing the population in the short-term will actually cause it to spike in the long-term. 

More questions remain: Is Florida going to dam every lake and stream to prevent their movement? Florida certainly won’t erect a wall along its border with Georgia and Alabama, but what about the coastal regions? How do you possibly prevent the spread of these animals along the coast? 

The brutal reality is that preventing the spread of these animals appears impossible. Deciding to address this problem through this approach is tacit resignation. Resignation that these pythons will inevitably decimate all of the native wildlife in the Everglades and every new ecosystem they encounter. Those rural communities where the pythons spread will face an alarming public health debacle. 

Florida’s attempt at containment strikes me as a way to save face publicly.  It’s a way for them to look like they are taking action and doing something to address the problem. But privately, they probably know their steps towards containment will have no chance at solving the python’s devastating impact on every ecosystem they encounter. 

In the end, the spread of these animals depends on two primary factors: Florida’s relative success at containment and the snake’s ability to adapt to changing climates. I wish I were writing a script for a movie, but unfortunately this blog represents reality. 

Removing all of the Pythons?

Florida authorities are operating under the assumption that the problem is so bad that it is fundamentally unsolvable. The only solution here is containing the population and preventing their spread. 

I would challenge that assumption. As per the above arguments, containing the snake population is an extraordinarily difficult undertaking. It might be impossible. To my knowledge, Florida has not created any effective model, or even offered a hypothetical scenario, in which the movement of these animals can be effectively controlled. Even deeper, containment is fundamentally flawed since a slight decrease in the population will only cause it to spike in the long-term.

The only way to truly solve the problem is to remove every last python from this ecosystem. Due to the obvious security risks and financial costs of transporting thousands of large carnivorous snakes halfway across the planet, removal naturally means killing every last snake. It's worth quickly noting the snakes themselves did nothing wrong here; when they are hungry, they eat. This problem is entirely human-generated. 

No reliable alternatives exist besides removal. And the urgency here just grows over time. As the snakes spread along the southeastern coast, I suspect this problem will expand beyond Florida in no time.

Florida authorities should get creative in thinking through possible solutions. Think outside the box. If we can put a man on the moon, surely we can use technology towards achieving meaningful gains at wiping out breeding reptiles.

Put together a team of top snake biologists, ecological scientists and extermination experts. Entertain ways to attract the animals through crafting the right smell. Discover their favorite foods and recreate this scent on a large scale. Attract males through recreating the scent of a breeding female. See if a similar tactic might work for what drives female attraction. Experiment with ways of making the animals infertile. Killing off the females would prevent new young from being introduced and inevitably lead to population collapse (albeit 25+ years down the line).

A reasonable counterargument might be as follows: if you don't believe the snakes could be contained, how could they possibly all be killed. And I would fully acknowledge that both goals would be extraordinarily hard to accomplish. But, at the same time, I think gearing energy, money and resources towards removal, as opposed to containment, makes infinitely more sense. As per the above arguments, containment is both fundamentally flawed and impossible to achieve. 

But a goal of removal relies on different tactics with an alternate set of questions: How do we attract the animals to specific locations (where they are then swiftly killed)? How do we attract females? How can we make the animals infertile? Do females tend to congregate or breed in specific locations? Energy, resources and money geared towards these questions will be the most effective approach at restoring what remains of the Everglades. 

I’m fully aware that killing off the entire breeding population would be a monumentally challenging undertaking. It’s quite possible this problem has spiraled completely out of control. But on behalf of all the people who will inevitably be living near these animals and all of the native species devastated, we should at least try. They deserve a shot. 

Moreover, I even think introducing a predator to control the pythons shoul be on the table for debate. With 30,000+ pythons in Florida, one could beg the question - At what point is a species no longer invasive? That is a fascinating question. 

In Conclusion

It's a tragic situation for all the native wildlife defenseless from these invasive animals - bobcat, deer, opossum, raccoon, rabbit and fox. When these animals run out, it seems any remaining animals would be vulnerable as the pythons basically eat anything. Had authorities been more thoughtful and proactive about managing this crisis, we may very well have a balanced ecosystem in the Everglades. 

My point isn't a sentimental one in favor of one specific animal over another; I have nothing against the pythons. It's simply an appreciation for ecological balance, sustainability and life. The situation now is completely imbalanced and unsustainable. It's truly tragic to see the devastating consequences humanity can have on an ecosystem because of some people's misguided desire to own as a "pet" a 12-foot wild snake. 

In January of 2012, the federal government announced a ban on the import of the Burmese pythons, South African python, North African python, and yellow anaconda. Interior Secretary Ken Salazar acknowledges the severity of the crisis when he uses the word "forever" to describe how long the ban would last. 

Apparently, the law was held up in bureaucracy for nearly two years by the reptile industry. Furthermore, environmentalists were pushing for 9 species of non-native snakes to be included in the legislation but only 4 were listed. 

Good. Thank you, government. Obviously, this ban represents progress and is a good thing.  

At the same time, the ban is monumentally overdue, at least 7 years too late. With populations of many native mammals down 90+% and the most conservative estimate pinning 30,000 pythons breeding in the wild, the damage is done and irreversible. While good and necessary, this ban is a bit like administering a vaccine to a patient that died years ago. Perhaps, we will learn faster next time. 

I suspect things will get so bad that Florida will ultimately decide that complete removal of the invasive species is the only solution. Given the devastating species collapse that has already taken place, I hate to consider what more tragic events would have to occur for Florida to reach this conclusion.