A well-established population of Burmese pythons resides in the Everglades of southern Florida. Prompted in part by a report that identified much of southern USA as suitable habitat for expansion or establishment of the Burmese python, we examined the plausibility of this snake to survive winters at sites north of the Everglades. We integrated daily low and high temperatures recorded from October to February from 2005-2011 at Homestead, Orlando and Gainesville, Florida; and Aiken, South Carolina, with minimum temperatures projected for python digestion (16 °C), activity (5 °C) and survival (0 °C). Mean low and high temperatures decreased northward from Homestead to Aiken and the number of days of freezing temperatures increased northward. Digestion was impaired or inhibited for 2 months in the Everglades and up to at least 5 months in Aiken, and activity was increasingly limited northward during these months. Reports of overwinter survivorship document that a single bout of low and freezing temperatures results in python death. The capacity for Burmese pythons to successfully overwinter in more temperate regions of the USA is seemingly prohibited because they lack the behaviors to seek refuge from, and the physiology to tolerate, cold temperatures. As tropical Southeast Asia is the source of the Everglades Burmese pythons, we predict it is unlikely that they will be able to successfully expand to or colonize more temperate areas of Florida and adjoining states due to their lack of behavioral and physiological traits to seek refuge from cold temperatures.

Here we review research over the past quarter century regarding the systematics and taxonomy of an ancient, popular and economically valuable group of snakes referred to as pythons (Serpentes, Pythonidae). All recent phylogenetic studies recognize the pythons as monophyletic; however, the phylogenetic relationships at supraspecific levels are conflicting, and many of the relationships recovered are paraphyletic. We identify several taxonomic changes as necessary to clarify supraspecific relationships and which resolve the issue of paraphyly recovered in several studies. Overall, our review of the phylogenetic systematics of pythons points to considerable incongruence among recovered relationships. Instances of paraphyly emerge, low node support is detected, and terminal taxa are unstable across phylogenetic hypotheses. We thus recognize that pythonid gene trees have been unable, for various reasons, to reveal the true species tree. This occurrence is not unexpected and can arise from incomplete taxon sampling, long-branch attraction and repulsion, homoplasy, ancestral polymorphism, and, more notably, the anomaly zone. These phenomena ultimately yield incomplete lineage sorting, or the failure of lineages to coalesce over evolutionary time. We discuss future directions to resolve these troubling issues. Without resolution, adaptive hypotheses about pythons will be limited, including hypotheses of geographic origin. Analyses that recover the clade Python as sister to the Indo-Australian clade are interpreted to support a Laurasian origin of Pythonidae. In contrast, a Gondwanan origin is supported when the Indo-Australian clade is recovered as basal to the Python clade. We describe the morphology of two recently proposed genera. Finally, we designate and describe the neotype for Morelia azurea and offer a list of the currently accepted python species and their taxonomy.