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Giant Snakes and Their Evolution,
 Reticulated Python, Python reticulatus, Anaconda, Eunectes murinus


At a field study site in northern Borneo, it was necessary to wade through a deep pool in a rainforest stream. I had to maneuver between huge boulders in neck deep water to exit. The forest completely covered the stream, so it was always very dark, with the only light coming from our headlamps. We were in search of frogs, lizards, and snakes, and the best time to find them was at night. Every time I waded through that pool, I didn't worry about king cobras, sun bears, or elephants, despite their living in the study site.

What really increased my anxiety level was the thought of reticulated pythons, Broghammerus reticulatus (formerly Python reticulatus). A large python lying in ambush along the stream, between those boulders would be formidable and invisible, especially in the dark.

Python reticulatus, Reticulated Python
Python reticulatus, Reticulated Python


Retics are the longest documented snakes. Colossus, a reticulated python that lived in the Pittsburg Zoo in the late 1940's to the late 1950's was measured at 28.5 feet. The Anaconda (Eunectes murinus) of South America is a much heavier snake, but the longest documented specimen is about 26 feet. Many of the exaggerated lengths for these snakes are based upon tall tails, hearsay, or measured skins. It is impossible to skin a snake without stretching the skin by at least 20%. Thus, a 30 foot snake skin probably came from a snake that was 24 feet long (or less). Two other species of snakes regularly exceed 20 feet (6.1 m) in length, the Asian Rock Python (Python molurus) and the African Rock Python (Python sebae). An Australian-New Guinea species that may exceed 20 feet is Kinghorn's Scrub Python (Liasis kinghorni).
I find big snakes of interest not just because of their imposing size, but because giant snakes have evolved multiple times. Anacondas are in the family Boidae which bear live young, lack parental care for the young after birth, share common skeletal features, and a common ancestry. Boid snakes include the boa constrictor, tree boas, rainbow boas, and some lesser known smaller species. Pythons lay eggs but share common skeletal features and a common ancestry. Female pythons care for their eggs, which includes controlling egg temperature. For many years, boas and pythons were believed to be each others closest relatives. We now know this isn't true, so they're currently placed in separate families.

Anaconda, Eunectes murinus
Anaconda, Eunectes murinus
Additionally, the African-Asian giant Rock Pythons are not closely related to the Reticulated Python, or its Australian-New Guinea relatives. Therefore, gigantism (defined as snakes capable of growing to 20 feet or 6.1 m) has evolved at least three times in living snakes: once in boids, the anaconda; once in the African-Asian Rock Pythons (these are sister species); and at least once in the Reticulated-Australian-New Guinea pythons. There is also fossil evidence of snakes that rivaled the largest living snakes. Understanding the factors that lead to gigantism can improve our understanding of the mechanisms of evolution.

Python sebae, African Rock Python
Python sebae, African Rock Python
Reticulated Pythons have been known to kill and ingest humans. Bob Henderson (Milwaukee Public Museum) and I analyzed the giant snake literature from the last 400 years and summarized it in Tales of Giant Snakes. We found sufficient evidence to suggest that all four of the giant species are dangerous to humans, but reticulated pythons may be particularly dangerous. In part, the danger is because they live close to large human populations, even today.





In Southeast Asia, Reticulated Pythons and Asian Rock Pythons are human commensals, meaning they benefit by living in human modified environments while humans are largely unaffected. Retics can be found in urban Bangkok as well as other cities within its distribution, and Asian Rock Pythons are relatively common in rice paddies and other agro-ecosystems. Thanks to human activity, rats, chickens, dogs, and cats are abundant, and these big snakes take advantage of the readily available warm blooded prey.

Reticulated Python, Broghammerus reticulates
Reticulated Python, Broghammerus reticulates
Australian herpetologist Rick Shine and colleagues studied the reticulated python on the Indonesian island of Sumatra by hanging out at reptile skin dealers. Hunters sold reticulated pythons to the skin dealers where they were skinned and butchered. This was an opportunity to collect a huge amount of biological information. One finding was startling; the biggest Retics came from areas that were disturbed by humans. Habitats that had a dependable food supply of rats and chickens produced the biggest snakes. They examined more than 1000 snakes. The largest male was 4.5 meters and the largest female was about 6.1 meters.

Python molurus, Asian Rock Python, in water
Python molurus, Asian Rock Python, in water

Python molurus, Asian Rock Python, in cage
Python molurus, Asian Rock Python, in cage
Despite my 50 days of field work in Borneo, I never saw a wild python. During more recent work in Thailand, I have seen a few Asian Rock Pythons, frequently in agricultural environments, and a single Reticulated Python from a more pristine habitat. They may be giants, but they are cryptic and overlooking their presence is highly probable.


John C. Murphy / CritterZone.com

Literature Cited
Isabell, L. A. 2006. Snakes as agents of evolutionary change in primate brains. Journal of Human Evolution 51:1-35.
Murphy, J. C. and R. W. Henderson. 1997. Tales of Giant Snakes, A Historical Natural History of Anacondas and Pythons Malabar: Krieger Publishing. 219 page.
Shine, R., P. S. Harlow, J. S. Keogh, and Boeadi. 1998. The influence of sex and body size on food habits of a giant tropical snake, Python reticulatus. Functional Ecology 12:248-258.

John C. Murphy is a Research Associate at the Division of Amphibians and Reptiles, Department of Zoology, Field Museum of Natural History, Chicago
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