- "Poisonous snake" redirects here. For true poisonous snakes, see Rhabdophis.
Venomous snakes use modified saliva, and snake venom, usually delivered through highly specialized teeth, such as (big) hollow fangs, for the purpose of prey immobilization and self-defense. In contrast, nonvenomous species either constrict their prey, or overpower it with their jaws.
Venomous snakes include several families of snakes and do not form a single taxonomic group. This has been interpreted to mean venom in snakes originated more than once as the result of convergent evolution. Evidence has recently been presented for the Toxicofera hypothesis, but venom was present (in small amounts) in the ancestors of all snakes (as well as several lizard families) as 'toxic saliva' and evolved to extremes in those snake families normally classified as venomous by parallel evolution. The Toxicofera hypothesis further implies that 'nonvenomous' snake lineages have either lost the ability to produce venom (but may still have lingering venom pseudogenes), or actually do produce venom in small quantities, likely sufficient enough to help capture small prey but causing no harm to humans when bitten.
Most venomous snakes
The high variability of LD50 tests is a major problem. This includes the age and reliability of the data, the number of species analyzed, and the testing methods and toxicity scale used. While there have been numerous studies on snake venom, potency estimates can vary, creating overlap and greatly complicating the task. Further, LD50 may be measured through intramuscular, intraperitoneal, intravenous or subcutaneous injections on small rodents, although the latter is the most applicable to actual bites. So, considering the toxicity of a species based on LD50 alone may not accurately estimate the danger of the species to humans since the efficiency of venom delivery is not taken into account. Furthermore, results from different tests may cause confusion since different toxicity scales are in use.
Apart from the high variability of toxicity tests, the physiological differences between the animals tested and humans is another major problem in categorizing the most venomous snakes. Mice are the common indicator used to test venom from venomous snakes in LD50 tests, so the LD50 results may not reflect the actual effects on humans due to the physiological differences between mice and humans. Many venomous snakes are specialized predators on mice, and their venom may be adapted specifically to incapacitate mice. While most mammals have a fairly similar physiology, LD50 results may or may not be directly relevant to humans.
If murine LD50 values are considered alone, the Australian Inland Taipan produces drop for drop, the most toxic venom, by far, of any snake in the world. Much more so than even sea snakes.
Toxicity of snake venom is sometimes used to gauge the extent of their danger to humans, but this is inappropriate. A number of other factors are more critical in determining the potential hazard of any given venomous snake to humans, including the distribution and behavior of each species. For example, while the inland taipan is regarded as the world's most venomous snake based on LD50, the so-called Big Four snakes cause far more snakebites because they are much more abundant in highly populated areas. Clinical mortality rate (often estimated by measured toxicity on mice) is another commonly used indicator to determine the danger of any given venomous snake, but important to are its efficiency of venom delivery, its venom yield and its behavior when it encounters humans (as reflected by clinical precedents). Black mamba and coastal taipan bites, when untreated, have a mortality rate of almost 100% due to their willingness of inject fatal amounts of venom in every envenomation. Other species with clinically proven high mortality rates include the common krait at 70-80%  and the inland taipan at 80%,  etc. The timespan between envenomation and death is another measure of how dangerous a given venomous species is to humans; e.g., a black mamba,  inland taipan or coastal taipan  bites are rapidly fatal if untreated.
Examples of LD50 toxicity rankings
|The most venomous land snakes by Ernst and Zug et al. (1996)|
|The most venomous snakes (Australian Venom and Toxins database)|
Venomous snakes are often said to be poisonous, although this is not the correct term since venom and poison are different entities. Poisons are absorbed by the body, such as through skin or the digestive system, while venoms must first be introduced directly into tissues or the bloodstream (envenomated) by mechanical means. It is, for example, harmless to drink snake venom as long as there are no lacerations inside the mouth or digestive tract. The two exceptions are: the Rhabdophis keelback snakes secrete poison from glands they get from the poisonous toads they consume, and similarly, certain garter snakes from Oregon retain toxins in their livers from the newts they eat.
Families of venomous snakes
Over 600 species are known to be venomous—about a quarter of all snake species. The following table lists some major species.
|Atractaspididae (atractaspidids)||Burrowing asps, mole vipers, stiletto snakes|
|Colubridae (colubrids)||Most are harmless, but others have toxic saliva and at least five species, including the boomslang (Dispholidus typus), have caused human fatalities.|
|Elapidae (elapids)||Sea snakes, taipans, brown snakes, mambas, coral snakes, kraits, king cobra, death adders, tiger snakes and cobras|
|Viperidae (viperids)||True vipers, including the Russell's viper, saw-scaled vipers, puff adders and pit vipers, including rattlesnakes, lanceheads and copperheads and cottonmouths.|
- Snake venom
- Big Four (Indian snakes)
- List of venomous animals
- Venomous fish
- Venomous mammals
- Poisonous amphibians
- Toxic birds
- Venomous Snakes. World's Deadliest Snakes – Ranking scale. Reptile Gardens. Retrieved October 18, 2013.
- Walls, Jerry G. . Deadly Snakes: What are the world's most deadly venomous snakes?. Reptiles (magazine). Retrieved November 5, 2013.
- Fry, Bryan Grieg. "Snake LD50 – discussion". Australian Venom & Toxin Database. Retrieved 2009-09-28. "Subcutaneous is the most applicable to actual bites. Only large Bitis or extremely large Bothrops or Crotalus specimens would be able to deliver a bite that is truly intramuscular. IV injections are extremly rare in actual bites."
- Mackessy, Stephen P. (June 2002). "Biochemistry and pharmacology of colubrid snake venoms". Journal of Toxicology: Toxin Reviews 21 (1–2): 43–83. doi:10.1081/TXR-120004741. Retrieved 2009-09-26.
- "What is an LD50 and LC50".
- The Australian venom research unit (August 25, 2007). "Which snakes are the most venomous?". University of Melbourne. Retrieved October 14, 2013.
- Venom Immunochemistry, Pharmacology and Emergency Response (VIPER) Institute. Frequently Asked Questions -What is the most venomous snake?. "Many experts answer that it is the Inland Taipan of Australia, because its drop-by-drop concentration of venom has great potency when measured by its ability to kill rodents" . University of Arizona. Retrieved October 14, 2013.
- Department of Wildlife Ecology and Conservation . Frequently Asked Questions About Venomous Snakes. "A comparative study found that the snake venom that is most toxic to mice (of the species tested) is that of the Inland Taipan (Oxyuranus microlepidotus), found in Australia" . University of Florida. Retrieved November 5, 2013.
- Hodgson WC, Dal Belo CA, Rowan EG (January 14, 2007). The neuromuscular activity of paradoxin: a presynaptic neurotoxin from the venom of the inland taipan (Oxyuranus microlepidotus). "The inland taipan is the world's most venomous snake" . Neuropharmacology (journal). Retrieved October 15, 2013.
- Bell KL, Sutherland SK, Hodgson WC (January 1998). Some pharmacological studies of venom from the inland taipan (Oxyuranus microlepidotus). "The Inland Taipan is believed to have the most toxic venom in the world (Sutherland, 1994)" Toxicon . Retrieved October 15, 2013.
- Cecilie Beatson (November 29, 2011). ANIMAL SPECIES:Inland Taipan "The venom of the Inland Taipan is extremely potent and is rated as the most toxic of all snake venoms in LD50 tests on mice" . Australian Museum. Retrieved October 14, 2013.
- BBC Nature Wildlife. Inland Taipan page. "Australia's inland taipan is considered to be the most venomous snake in the world" . BBC. Retrieved October 15, 2013.
- Steve Irwin presentation. Australia Zoo Tour with Steve Irwin (1m54s) "..the number 1 most venomous snake in the entire world, the fierce snake" Australia Zoo (official Youtube Channel). Retrieved October 14, 2013.
- Dr Cecily Oakley (2011). Interview with Associate Professor Bryan Fry Biochemist and molecular biologist. "...For my PhD, I worked on the inland taipan, which is the world’s most venomous snake..." . Australian Academy of Science. Retrieved October 14, 2013.
- Journal of Herpetology Vol.17 no.1 (1983) Ecology of Highly Venoumous Snakes: the Australian Genus Oxyuranus. "..the number of mouse LD50 doses per bite is much higher for Oxyuranus microlepidotus (218,000 mice)...than for any other snakes, including sea snakes, investigated to date (Broad, Sutherland and Coulter, 1979)." (page 1) University of Sydney. Retrieved November 8, 2013.
- Inland Taipan Venom vs. Sea Snakes Venom (most notable Belcher's sea snake)
- kingsnake.com September Guest Chatter (September 16, 2006).Q&A with Dr. Bryan Grieg Fry, Deputy Director, Australian Venom Research Unit, University of Melbourne. " Q: In retrospect to the LD50 charts, what do you personally feel is the hottest snake, in regards to potency, defensiveness, means of injection, etc.? A: It is the inland taipan (Oxyuranus microlepidotus). Not, as is popularised, any of the sea snakes ". connectedbypets.com. Retrieved October 14, 2013.
- Garden of Eden Exotics (May 2, 2012) Dr. Bryan Grieg Fry - Interview "...The inland taipan (Oxyuranus microlepidotus) is far and away the most toxic, much more so than even sea snakes." . nyexotics.blogspot.com Retrieved October 14, 2013
- Davidson, Terence. "IMMEDIATE FIRST AID - Black Mamba". University of California, San Diego. Retrieved 2010-05-12.
- "IMMEDIATE FIRST AID for bites by Australian taipan or common taipan".
- "University of Adelaide Clinical Toxinology Resources". "Mortality rate:70-80%"
- "University of Adelaide Clinical Toxinology Resources". "Mortality rate:80%"
- Devision of Medical Toxicology. "Summary for Human Bite by Inland Taipan (Oxyuranus microlepidotus)". University of California, San Diego. Retrieved October 19, 2013.
- Zug, George R. (1996). Snakes in Question: The Smithsonian Answer Book. Washington D.C., USA: Smithsonian Institution Scholarly Press. ISBN 1-56098-648-4.
- Dr. Bryan Grieg Fry. "LD50 menu (Archived)".
- Séan Thomas & Eugene Griessel – Dec 1999. "LD50 (Archived)".
- Klauber LM. 1997. Rattlesnakes: Their Habitats, Life Histories, and Influence on Mankind. 2d ed. Berkeley: University of California Press, Berkeley, 1956, 1972. ISBN 0-520-21056-5.