The largest living snakes in the world, measured either by length or by weight, are various members of the Boidae and Pythonidae families. They include anacondas, pythons and boa constrictors, which are all non-venomous constrictors. The longest venomous snake, with a length up to , is the king cobra, while contesters for the heaviest title include the Gaboon viper and the Eastern diamondback rattlesnake. All of these three species reach a maximum mass in the range of . The largest known snake overall is the extinct Titanoboa.
There are fourteen or fifteen living snake species that have a maximum mass of at least , as shown in the table below. These include all species that reach a length of at least . There are also two other species that reach nearly this length the Oenpelli python (binomial name Nyctophilopython oenpelliensis, Simalia oenpelliensis or Morelia oenpelliensis), and the olive python (Liasis olivaceus). The information available about these two species is rather limited. The Oenpelli python, in particular, has been called the rarest python in the world.
There is considerable variation in the maximum reported size of these species, and most measurements are not verifiable, so the sizes listed should not be considered definitive. In general, the reported lengths are likely to be somewhat overestimated. In spite of what has been, for many years, a standing offer of a large financial reward (initially $1,000 offered by U.S. President Theodore Roosevelt in the early 1900s,Gordon, David George, "The Search for the $50,000 Snake". MSN Encarta. Archived 31 October 2009. later raised to $5,000, then $15,000 in 1978 and $50,000 in 1980) for a live, healthy snake over long by the New York Zoological Society (later renamed as the Wildlife Conservation Society), no attempt to claim the reward has ever been made.
Although it is generally accepted that the reticulated python is the world's longest snake, most length estimates longer than have been called into question. It has been suggested that confident length records for the largest snakes must be established from a dead body soon after death, or alternatively from a heavily sedated snake, using a steel tape and in the presence of witnesses, and must be published (and preferably recorded on video). At least one reticulated python was measured under full anesthesia at , and somewhat less reliable scientific reports up to have appeared.
Although weight is easier to measure reliably than length (e.g., by simply measuring the weight of a container with and without the snake inside it and subtracting one measurement from the other), a significant factor in the weight of a snake is whether it has been kept in captivity and provided an unusual abundance of food in conditions that also cause reduced levels of activity. Moreover, the weight of wild specimens is often reduced as a symptom of parasite infestations that are eliminated by veterinary care in captivity. Thus, the largest weights measured for captive specimens often greatly exceed the largest weights observed in the wild for the same species. This phenomenon may particularly affect the weight measurements for anaconda species that are especially difficult to keep in captivity due to their semi-aquatic nature, resulting in other species having larger weights measured in captivity. In particular, the green anaconda (Eunectes murinus) is an especially massive snake if only observations in the wild are considered.
Largest serpent species in the world Rank Common name Scientific name Family Mass Image Length Range map1Green anaconda (a.k.a. giant anaconda)Eunectes murinusBoidaeMay exceed , measurement validity questionable, unverified but plausible weight for wild-caught specimen in Acre, Brazil, see section on remarkable individual specimens to , not firmly verified, specimen kept at Reptilarium du Larzac in Sainte-Eulalie-de-Cernon, France , reliable, maximum among 780 specimens caught over a seven-year period 1992–98Average among 45 specimens (1992–98)Generally considered the heaviest in the wild (exceeded by P.bivittatus and M. reticulatus in captivity) Some specimens may be of a distinct "northern green anaconda" species. May exceed , not firmly verified, reliable for specimen listed by Rivas et al., somewhat reliable ., somewhat reliable, reliable, maximum among 780 specimens caught over a seven-year period 1992–98Average among 45 specimens (1992–98)Minimum adult length
Some specimens may be of a distinct "northern green anaconda" species. 2Burmese pythonPython bivittatus(now recognized as distinct from P. molurus)Pythonidae, reliable, for "Baby" in 1998 (in captivity), reliable, for the heaviest specimen found in the wild, reliable, for the biggest male in the wild, reliable, for the longest specimen found in the wild 10 July 2023 Minimum adult length 3Reticulated pythonMalayopython reticulatusPythonidaeUp to , somewhat reliable, somewhat reliable, for "Medusa" in 2011About , somewhat reliable, for "Twinkie" in 2014, somewhat reliable, for "Fluffy" in 2010, reasonably reliable, for "Colossus" in 1954 (with an empty stomach), somewhat reliable, for "Samantha" in 2002, somewhat reliable, for "Super Snake" in 2021, reliable, wild specimen in 1999 (after not eating for nearly 3 months), not firmly verified, somewhat reliable, for "Samantha" in 2002, somewhat reliable, for "Medusa" in 2011, somewhat reliable, for "Fluffy" in 2010, somewhat reliable, for "Twinkie" in 2014, somewhat reliable, for "Super Snake" in 2021, reliable, wild specimen in 1999, reasonably reliable, for "Colossus" in 1963 (skeletal length)Specimens longer than are rare Minimum adult length Generally considered the world's longest4Central African rock pythonPython sebae(now recognized as distinct from P. natalensis)PythonidaeUp to , not firmly verified, reliableMurphy, J. C., & Henderson, R. W. (1997). Tales of giant snakes: a historical natural history of anacondas and pythons. Florida: Krieger Publishing Company.Bodson, L. (2003). A Python (" Python sebae" Gmelin) for the King: The Third Century BC Herpetological Expedition to Aithiopia (Diodorus of Sicily 3.36–37). Museum Helveticum, 60(1), 22-38.Up to , not firmly verified, reliableW. R. Branch, W. D. Haacke: A Fatal Attack on a Young Boy by an African Rock Python Python sebae. Journal of Herpetology Vol.14, No.3, 1980, pp. 305–307.Minimum adult length Range shown as green region5Southern African rock pythonPython natalensis(now recognized as distinct from P. sebae)Pythonidae, somewhat reliable, for the largest specimen, reliableOf 75 specimens measured in South Africa, the longest female weighed .G. J. Alexander: Thermal Biology of the Southern African Python (Python natalensis): Does temperature limit its distribution? In: R. W. Henderson, R. Powell (Hrsg.): Biology of the Boas and Pythons. Eagle Mountain Publishing Company, Eagle Mountain 2007, , pp. 51–75. not firmly verified, reliableOf 75 specimens measured in South Africa, the longest female was long.Specimens longer than are rare.F. W. FitzSimons: Pythons and their ways. George G. Harrap & Co. Ltd, London 1930, pp. 12, 17, 23, 32, 34, 39, 41, 67.Typically p. Spawls, K Howell, R Drewes, J Ashe: A Field Guide to the Reptiles of East Africa. Academic Press, London 2002, , pp. 305–310.Range shown as orange region6Indian pythonPython molurus(now recognized as distinct from P. bivittatus)Pythonidae, not firmly verified, reliable., not firmly verified, reliable7Australian scrub pythonSimalia kinghorni(now recognized as distinct from S. amethistina)Pythonidae, reliable, reliable Some reports up to or exceeding , not firmly verified, not firmly verifiedIn excess of , reliableTypically Minimum adult length Little information about size is availableRange shown as dark green region8Amethystine pythonSimalia amethistina(recently recognized as distinct from S. kinghorni)PythonidaeAble to reach , and probably largerLittle information about size is availableAble to reach , reliableLittle information about size is availableRange shown as dark orange and bright orange regions9Yellow anacondaEunectes notaeusBoidaeThey commonly weigh , though large specimens can weigh or even more.Mendez, M; Waller, T; Micucci, P; Alvarenga, E; Morales, JC (2007). "Genetic population structure of the yellow anaconda (Eunectes notaeus) in Northern Argentina: management implications". In Robert W. Henderson and Robert Powell. Biology of the Boas and Pythons (PDF). Eagle Mountain Publishing. pp. 405–415. ., reasonably reliableTypically maximum among 86 specimens in a field studySouth America10Red tailed boaBoa constrictorBoidaeMore than Boa Constrictor Fact Sheet – Woodland Park Zoo Seattle WA. Zoo.org. Retrieved on 22 August 2012.Possibly up to Wagner, D. "Boas". Barron's. A much larger report was debunked11Cuban boaChilabothrus anguliferBoidaeMaximum , reliable, reliable, for the largest specimen Up to 12 Beni anacondaEunectes beniensis(now recognized as distinct from E. murinus and E. notaeus)BoidaeLargest specimen , relatively reliableTypically up to , relatively reliableLittle information about size is available (known from only six specimens as of 2009)13Dark-spotted anacondaEunectes deschauenseei(sometimes confused with E. notaeus)Boidae, relatively reliable14Papuan pythonApodora papuanaPythonidaeAverage reported as Little information about size is availableOne reasonably reliable report of Average reported as Often reaches Most specimens Little information about size is available
By families Boas (Boidae) The most massive living member of this highly diverse reptilian order is the green anaconda (Eunectes murinus) of the neotropical riverways. These may exceed and , although such reports are not fully verified. Rumors of larger anacondas also persist.Green Anacondas, Green Anaconda Pictures, Green Anaconda Facts. Animals.nationalgeographic.com
Pythons (Pythonidae) The reticulated python (Python reticulatus) of Southeast Asia is longer but more slender than the green anaconda, and has been reported to measure as much as in length and to weigh up to .
Typical snakes (Colubridae) Among the colubrids, the most diverse snake family, the largest snakes may be the keeled rat snake (Ptyas carinata) at up to . The genus Drymarchon also contains some of the largest colubrids such as the eastern indigo snake (Drymarchon couperi) and the indigo snake (Drymarchon corais) which can both reach lengths of almost .Lee, Julian C. 2000. A Field Guide to the Amphibians and Reptiles of the Maya World: the lowlands of Mexico, Northern Guatemala, and Belize. p. 286-287. 402 pp. (paper). The former may grow to weights of or greater.Godwin, James C. Eastern Indigo Snake Fact Sheet. alaparc.org Another large species in this family is the false water cobra (Hydrodynastes gigas) reaching a length of , and a mass of ,Loughman, Z. J. (2020). Utilization of Natural History Information in Evidence based Herpetoculture: A Proposed Protocol and Case Study with Hydrodynastes gigas (False Water Cobra). Animals, 10(11), 2021.Martinelli, I. M. (2011). 290 290 NATURAL HISTORY NOTES. Herpetological Review, 42, 2. one of the largest venomous snakes in South America. The tiger rat snake (Spilotes pullatus), also living in South America, can reach a length of . The yellow-bellied puffing snake (Pseustes sulphureus) can exceed a length of .