Burmese python

• 1. Introduction

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  The Burmese python, Python bivittatus, is a snake that can grow longer than a car is wide and heavier than a grown man. In July 2023, hunters in Big Cypress National Preserve in South Florida caught one that set the record for the species: 5.79 m long. Its home is not Florida at all. The species belongs to Southeast Asia, where its numbers have fallen and it is now rated Vulnerable. Yet thousands of miles away it has become one of the most closely studied invaders in North America. Until 2009, scientists treated it as a mere subspecies of the Indian python. How did one animal come to be both threatened and a threat? What does its body do when it swallows something nearly its own size? And why does a pet with a reputation for gentleness end up loose in a swamp?

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• 2. Built for Size

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  A dark body with brown blotches edged in black down the back is the signature look of this non-venomous snake. In the wild, adults typically reach about 5 m, and claims of more than 7 m have never been confirmed. Females and males differ less in length than in bulk. Captive measurements show a female of 3.47 m weighing 29 kg, while one of 5 m weighed 75 kg. Males are far lighter at similar lengths. A 3.05 m male weighed 18.5 kg. The heaviest snake ever recorded at the time of her death was a Burmese named Baby, at 182.8 kg. Her length was measured at 5.74 m around 1999. Not every Burmese python is a giant. Dwarf forms live on Java, Bali and Sulawesi, where the average on Bali is only 2 m. Wild adults overall average 3.7 m. The smallest adults measure 2.35 m. Those island populations raise a question about range, and the range is wide.

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• 3. Water and Grassland

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  From eastern India and southeastern Nepal to Hong Kong and the Indonesian island of Sumbawa, the Burmese python occupies a wide stretch of Asia. In southern China it is found in Fujian, Jiangxi, Guangdong, Hainan, Guangxi and Yunnan. It has even been reported on Kinmen. Wherever it lives, it needs a permanent source of water. It is an excellent swimmer and can stay submerged for around 30 minutes, though it spends most of its time on land. Grasslands, marshes, swamps, rocky foothills, woodlands, river valleys and jungles with open clearings all suit it. It also climbs well, using a prehensile tail. Young snakes are equally at home on the ground and in trees. As they gain girth, they stay mostly on the ground. Most of their time is spent hidden in the underbrush, and they are mainly nocturnal.

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• 4. The Slow Meal

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  A Burmese python may go as long as 18 months without eating. Typically it feeds every month or two. It is a sit-and-wait predator. It lies nearly motionless until prey comes close, strikes, grabs with sharp teeth, and kills by constriction. Birds and mammals make up most of its diet, with some amphibians and reptiles. Then it swallows the animal whole, which makes its body a favorite subject for physiologists. During fasting, the costly digestive tissues shrink. Stomach volume and acidity drop, and the intestines lose mass. Eating reverses all of this. The intestines swell rapidly, stomach acid production starts up, and the heart's ventricle gains 40% in mass. Oxygen consumption climbs to between 17 and 40 times the resting rate, depending on meal size. With no chewing to break the prey down, acid has to do the work, turning the meal into a semi-liquid. The cost peaks in the first few days, so the snake draws on stored energy. From swallowing to defecation, the process takes 8-14 days. Rats and mice near homes draw these snakes toward people, and they will also take poultry, which is why farmers treat them as pests.

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• 5. Eggs and Clones

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  In March or April, a female Burmese python lays a clutch of 12-36 eggs. Pairs are rare outside mating, since these snakes are solitary. The mother then coils around the eggs and twitches her muscles. That raises the temperature around them by several degrees. When the young cut their way out with an egg tooth, maternal care ends. Hatchlings often stay inside the shell until their first shedding of skin, and only then go hunting. In cooler northern parts of the range, adults may brumate for some months in a hollow tree, a riverbank hole or under rocks. Brumation differs biologically from hibernation, because it also prepares the reproductive organs of both sexes for the breeding season. A stranger reproductive route exists in captivity. Females can reproduce without a male. The offspring are clones of their mother, produced through a modified form of meiosis, a process called parthenogenesis.

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• 6. Florida's Invader

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  Between 1996 and 2006, more than 90,000 Burmese pythons were imported into the United States for the pet trade. Many ended up in the Florida Everglades. Hurricane Andrew in 1992 is held responsible for destroying a python-breeding facility and zoo, and the escaped snakes spread into the Everglades. A 2018 genetic study found that the Florida population is made up of hybrids between the Burmese and Indian pythons. The snakes had reached northern Florida and the coastal Panhandle by 2007. The Department of the Interior banned imports in January 2012. As of 2024, estimates of the Everglades population ran anywhere from 30,000 to 300,000 snakes. The wide gap shows how hard a hidden, camouflaged animal is to count. The mammal losses are easier to measure.

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• 7. What the Everglades Lost

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  A 2012 report on areas where the snakes are well established recorded that raccoon sightings were down by 99.3%, opossums by 98.9% and white-tailed deer by 94.1%. Foxes and rabbits had vanished from some places. Road surveys between 2003 and 2011 showed an 87.3% decline in bobcats. Efforts to reintroduce rabbits mostly failed, and 77% of the deaths were from python predation. Experiments have shown that the snakes reduce marsh rabbit numbers, which suggests they cause many of the observed declines. Birds suffer too. By 2011, researchers had identified up to 25 species from nine avian orders in the remains inside 85 pythons in Everglades National Park. The wood stork, now federally endangered, is of particular concern. The already-rare Florida panther and coyotes may also be at risk. Large pythons have been known to attack and eat alligators and adult deer. Florida pythons feed year-round, unlike their native counterparts, which fast through seasons when prey is scarce. Even so, the winter holds one weakness.

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• 8. Cold, Parasites and Hunters

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  Winter freezes in Florida have killed up to 90% of the pythons in some cases. Genomic data suggests natural selection is favoring greater cold tolerance among the survivors. The snakes also carried a parasite from Asia, Raillietiella orientalis, a pentastome. Other Florida reptiles have been infested, and the parasite appears to have become endemic. Humans have tried many tactics. Researchers found the pythons prefer broad-leafed and low-flooded habitats, as well as elevated sites good for nesting. Edge habitats serve them for warmth, nesting and hunting. A 2017 study even detected the snakes by screening the blood in mosquitoes, which feed on them in southern Florida. Public hunts add pressure. The first Florida Python Challenge, in 2013, lasted a month and removed 68 pythons. It is now an annual ten-day event. The 2023 edition saw 1,050 participants remove 209 pythons. Individual captures have grown dramatic. A Burmese caught in December 2021 weighed 215 lbs, measured 18 ft and held a record 122 developing eggs.

  Attractive coloring and a calm temperament make Burmese pythons popular pets. Breeders have developed the white amelanistic morph with butterscotch yellow and burnt orange patterns, the most widely available type. Others include labyrinth, granite and caramel forms. The leucistic Burmese, bright white with blue eyes, was reproduced in captivity as the homozygous form only in 2008/2009. But the gentle reputation hides power. A python can exceed 2.1 m in a year if power fed, reaches adult size by age four and may live beyond 20 years. Handlers are advised to have up to one person per meter of snake. Because owners struggle with size and food costs, some release their pets. Florida restricts keeping them, with penalties of more than seven years in prison or a $500,000 fine. In Asia the picture is reversed. The species is on CITES Appendix II and has been Vulnerable on the IUCN Red List since 2012, after an estimated decline of at least 30% in the first decade of this century from habitat loss and over-harvesting. It is common only in Hong Kong and Thailand, where it is protected.

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