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Myth-Buster – Will Non-Native Burmese Pythons Spread Beyond Southern Florida?

Burmese Python in the EvergladesThis is the first in a new series of what I’ll call “Myth-Buster Articles”, which will focus on beliefs or practices that have aroused debate in the herpetological community.  After reviewing the available research and my own and others experiences, I will attempt to sort fact from fiction.  Today I’ll highlight the recent studies that have sought to determine if introduced Burmese Pythons, Python molurus bivittatus (a.k.a. P. b. bivittatus) may eventually spread north and west from their current strongholds in South Florida.  Links to the articles mentioned are included below.

Studies comparing the climate in the USA with that in the Burmese Python’s native range (South and Southeast Asia), including one by the US Geological Survey, have predicted that the huge snakes may eventually range north to Delaware and southern Maryland  and west to California.  In all, 32 states were said to provide possible habitat.

Central Florida Study

A study of pythons housed outdoors in north-central Florida(Biological Invasions, 12: 3649-3652) concluded that Burmese Pythons would not likely become established outside of South Florida.

In this study, the snakes had access to heated shelters, but most individuals remained outside despite a severe cold snap (10 days of sub-freezing temperatures).  Seven of the nine snakes in the study died, and researchers concluded that the snakes were unable to respond appropriately to the threat of cold weather.  Two individuals did utilize shelters and survived.  It is important to note, however, that, in addition to heated shelters, the study snakes had been well fed and cared for by professionals prior to winter’s onset; such would not be the case for free-living individuals.

Green AnoleWeather differences between north and south Floridalimit native species as well.  For example, Green Anoles, Anolis carolinensis, living inSouth Florida cannot tolerate winters in the north.

South Carolina Study

As in the Florida study, most of the Burmese Pythons held outdoors inSouth Carolinatried to bask despite potentially lethal temperatures.  Several utilized shelters, but none survived the winter.

City University of New York Study

The CUNY study used a climate-comparison approach.  An earlier USGS climate study utilized two variables (average temperature and rainfall) and concluded that Burmese Pythons could expand their range.  However, after taking 19 climatic variables into account, CUNY researchers found that the snakes would not likely spread beyond the Everglades and extreme South Florida.

Interestingly, the study authors also predicted that global warming would cause the python’s current range to shrink, not expand.

Personal Observations

During a cold spell in the winter of 2009, a colleague of mine found 14 Burmese Pythons that had been killed, apparently while attempting to bask, along a single stretch of road near Florida City.

Cold Weather in South Asia

Burmese Python in the Everglades with AlligatorBurmese Pythons occupying high elevations in their natural range do experience sub-freezing temperatures, at which time they become dormant.  So why have those introduced to the USA not adapted?

I believe that the answer may lie in the origin of those animals in the pet trade (the source of theUSA’s introduced population).  If the pet trade animals originated in warmer parts of the natural range, they may not be genetically programmed to survive cold winters (see Green Anole note, above).

Researchers in the North Florida study also speculated that the introduced pythons likely originated from a very small number of founders (parents/ancestors).  They may, therefore, possess a limited ability to change their behavior in order to cope with cold weather.

African Rock Pythons

Studies have not yet been carried out on these massive invaders, which so far “seem” restricted to a relatively small area in southern Florida.  Please see this article to learn more about what is being done to track their movements and population growth.



Further Reading

Text of FloridaStudy

Snakes and Cold

CUNY Study

Cold Snap Decimates Florida’s Introduced Reptiles



  1. avatar

    Re: personal observations… killed by cold or traffic? Thanks.

    • avatar

      Hello Mark, Frank Indiviglio here.

      Thanks; it appeared that they were sluggish and that most were killed by traffic. Some drivers had apparently driven back and forth over the animals several times.

      Best regards, Frank Indiviglio.

  2. avatar

    I have saw one study they made on Nat geo if i remember correctly.. they sure are very resilient creatures

    • avatar

      Hello Mike Frank Indiviglio here.

      Thanks for your note; here in the US it’s hard to avoid TV shows dealing with pythons in Florida! Nat Geo sponsored films usually good, as are BBC’s, but many are not at all factual and overly-dramatic.

      Best regards, Frank Indiviglio.

  3. avatar

    Hey Frank, thanks for this article, I sat on the early planning committees in Florida, and I can say without doubt our general concensus was an extended cold period (like in 2009-2010 would kill off many of the burms. Of greater concern, and one that is not so media friendly as the big scary python that can constrict you is the monitor population. Monitor lizards are much more elusive, cold resilient, and voracious predators feeding on a large variety of prey.. Hopefully one day we will put as much time and energy in invasive monitors in South Florida as the burm… thanks for the article.

    • avatar

      Hello Tom, Frank Indiviglio here.

      Thanks for your interest in my article. I agree re the monitors and plan an article shortly; from what I’ve seen, they can probably travel farther and faster than pythons, and can “figure out” more ways to cause trouble and avoid capture.

      I’ll check your site as well; I did some work in Tortuguero with CCC and WCS years ago, hope to go back.

      Good luck, enjoy and please keep me posted.

      Best regards, Frank Indiviglio.

  4. avatar

    We are just now constructing a breeding center a ways south of Tortuguero. Beautiful area, look me up if you come down, we go out in a park called Hitoy Cerere all the time, lots of eyelashes, corals, galliwasps, and other wildlife.

    • avatar

      Hello Tom, Frank Indiviglio here.

      Thanks, I sure will. Sounds like a great project….good luck and enjoy; please keep me posted when you have a chance,

      Best regards, Frank Indiviglio.

  5. avatar

    Hello Frank,
    Very amusing that the USGS survey look at only average temperatures and rainfall. Afterall-it is the extremes which determine organism survival and ability to expand range, not the averages.

    ~Joseph See

    • avatar

      Hello Joseph, Frank Indiviglio here.

      Nice to hear form you; I hope all is well.

      I agree…that study was odd in general, and not on par with others I’ve seen from the USGS; most herpetologists discount it.

      Best regards, Frank Indiviglio.

  6. avatar

    I just want to say thank you for posting this. I’ve been working on fighting the bans and I’ve been looking for sources since it looks like Virginia is up next on the list that HSUS wants to hit. As long as it’s ok with you I’d like to use this article as a source.
    Might I ask if you think that HSUS had something to do with the USGS study being so faulted?

    • avatar

      Hello Brittany

      Thanks for your interest and kind words. I’m okay in principle with your using the article, but would like to see the context…how and where it will be used, beforehand, thanks. Here is a bit more info on the South Carolina study that was mentioned.

      I do not know what if any involvement HSUS has had with the process, but as far as I know USGS does not generally consult such groups.

      In Virginia and points north, proposed laws will likely be based more on the danger factor than possible establishment of feral populations, so the USGS and related studies may not be a factor.

      Please let me know if you need any further information.

      Best regards, Frank Indiviglio.

About Frank Indiviglio

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Being born with a deep interest in animals might seem unfortunate for a native Bronxite , but my family encouraged my interest and the menagerie that sprung from it. Jobs with pet stores and importers had me caring for a fantastic assortment of reptiles and amphibians. After a detour as a lawyer, I was hired as a Bronx Zoo animal keeper and was soon caring for gharials, goliath frogs, king cobras and everything in-between. Research has taken me in pursuit of anacondas, Orinoco crocodiles and other animals in locales ranging from Venezuela’s llanos to Tortuguero’s beaches. Now, after 20+ years with the Bronx Zoo, I am a consultant for several zoos and museums. I have spent time in Japan, and often exchange ideas with zoologists there. I have written books on salamanders, geckos and other “herps”, discussed reptile-keeping on television and presented papers at conferences. A Master’s Degree in biology has led to teaching opportunities. My work puts me in contact with thousands of hobbyists keeping an array of pets. Without fail, I have learned much from them and hope, dear readers, that you will be generous in sharing your thoughts on this blog and web site. For a complete biography of my experience click here.
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