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Venomous snake

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For the video game character, seeVenom Snake.
The lateral view of aking cobra's skull showing fangs

Venomous snakesarespeciesof thesuborderSerpentesthat are capable of producingvenom,which they use for killing prey, for defense, and to assist with digestion of their prey. The venom is typically delivered by injection using hollow or groovedfangs,although some venomous snakes lack well-developed fangs. Common venomous snakes include thefamiliesElapidae,Viperidae,Atractaspididae,and some of theColubridae.The toxicity of venom is mainly indicated by murineLD50,while multiple factors are considered to judge the potential danger to humans. Other important factors for risk assessment include the likelihood that a snake will bite, the quantity of venom delivered with the bite, the efficiency of the delivery mechanism, and the location of a bite on the body of the victim. Snake venom may have bothneurotoxicandhemotoxicproperties. There are about 600 venomous snake species in the world.

Evolution

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Main article:Evolution of snake venom

The evolutionary history of venomous snakes can be traced back to as far as 28 million years ago.[1]Snake venomis modifiedsalivaused forpreyimmobilization and self-defense and is usually delivered through highly specialized teeth, hollow fangs, directly into the bloodstream or tissue of the target. Evidence has recently been presented for theToxicoferahypothesis, that venom was present (in small amounts) in the ancestors of all snakes (as well as severallizardfamilies) as "toxic saliva" and evolved to extremes in those snake families normally classified as venomous byparallel evolution.The Toxicofera hypothesis further implies[according to whom?]that "nonvenomous" snake lineages have either lost the ability to produce venom (but may still have lingering venompseudogenes), or actually do produce venom in small quantities, likely sufficient[according to whom?]to help capture small prey but causing no harm to humans when bitten.

Taxonomy

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There is not a single or specialtaxonomicgroup for venomous snakes. Venom is known in several families. This has been interpreted[by whom?]to mean venom in snakes originated more than once as the result ofconvergent evolution.Around a quarter of all snake species are identified as being venomous.

Family Description
Atractaspididae(atractaspidids) Purple-glossed snakes,centipede eaters,burrowing asps,Revoil's short snake,Chilorhinophis,Hypoptophis,Homoroselaps,Macrelaps,Micrelaps,and more.
Colubridae(colubrids) Most are harmless, but others have potent venom and at least five species, including theboomslang,have caused human fatalities.
Elapidae(elapids) Sea snakes,taipans,brown snakes,coral snakes,kraits,death adders,tiger snakes,mambas,king cobras,cobrasand more.
Viperidae(viperids) True vipers,including theRussell's viper,saw-scaled vipers,puff addersandpit vipers,includingrattlesnakes,lanceheadsandcopperheads and cottonmouths.

Terminology

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Venomous snakes are often said to bepoisonous,but poison and venom are not the same thing. Poisons must be ingested, inhaled or absorbed, while venom must be injected into the body by mechanical means. While unusual, there are a few species of snake that are actually poisonous.Keelback snakesare both venomous and poisonous – their poisons are stored in nuchal glands and are acquired by sequestering toxins frompoisonous toadsthe snakes eat.[2]Similarly, certaingarter snakesfromOregoncan retain toxins in their livers from ingestingrough-skinned newts.[3]

Danger

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The world's most venomous snake, based onLD50,is theinland taipanof Australia.

Toxicity issues

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Venom toxicities are compared by looking at themedian lethal dose(usually usingrodentsas test animals and termed the murine LD50), which is the dose of venom per unit body mass that kills half of the test animals that receive it. The result obtained depends on which of the four delivery sites is used for the injection:subcutis(SC),vein(IV),muscleorperitoneum(IP). Smaller murine LD50values indicate venoms that are more toxic, and there have been numerous studies on snake venom with a variability of potency estimates.[4]SC LD50is considered[by whom?]the most applicable to actual bites as only vipers with large fangs (such as large specimens from the generaBitis,Bothrops,Crotalus,orDaboia) are capable of a truly intramuscular bite, snakebites rarely cause IVenvenomation,and IP envenomation is even rarer. Measurements of LD50using dry venom mixed with 0.1%bovine serum albumininsalineare more consistent than the results obtained using saline alone. As an example, the venom of theeastern brown snakehas a murine LD50(SC) of41 μg/kgwhen measured in 0.1% bovine serum albumin in saline; when saline alone is used, the value is53 μg/kg.[5]

Belcher's sea snake,which sometimes is mistakenly called thehook-nosed sea snake,has been erroneously popularized[according to whom?]as the most venomous snake in the world, due to the first edition of Ernst and Zug's book,Snakes in Question: The Smithsonian Answer Book,published in 1996. Prominent venom expert Associate Professor Bryan Grieg Fry has clarified the error: "The hook nosed myth was due to a fundamental error in a book calledSnakes in Question.In there, all the toxicity testing results were lumped in together, regardless of the mode of testing (e.g., subcutaneous vs. intramuscular vs. intravenous vs. intraperitoneal). As the mode can influence the relative number, venoms can only be compared within a mode. Otherwise, it's apples and rocks. "[6]Belcher's sea snake's actual LD50(IM) is 0.24 mg/kg[7]and 0.155 mg/kg.[8]Studies on mice[9][10][11]and humancardiac cellculture[6][12][13]show that venom of theinland taipanis the most toxic among all snakes.

Most venomous snakes of the world[5][8][14]
Snake Region subcutaneous injectionLD50 intravenous injectionLD50
0.1%bovine serum albumininsaline in saline
Inland taipan Australia 0.01 mg/kg 0.025 mg/kg N/A
Dubois' sea snake Coral Sea,Arafura Sea,Timor Sea,Tar River, andIndian Ocean N/A 0.044 mg/kg N/A
Eastern brown snake Australia, Papua New Guinea, Indonesia 0.041 mg/kg 0.053 mg/kg 0.01 mg/kg
Yellow-bellied sea snake Tropical oceanic waters N/A 0.067 mg/kg N/A
Peron's sea snake Gulf of Siam,Taiwan Strait,Coral Sea Islands,and other places N/A 0.079 mg/kg N/A
Coastal taipan Australia 0.064 mg/kg 0.105 mg/kg 0.013 mg/kg
Many-banded krait Mainland China, Taiwan, Vietnam, Laos, Burma N/A 0.108 mg/kg 0.061 mg/kg
Black-banded sea krait eastern coast of theMalay Peninsulaand Brunei, and in Halmahera, Indonesia N/A 0.111 mg/kg N/A
Black tiger snake Australia 0.099 mg/kg 0.131 mg/kg N/A
Mainland tiger snake Australia 0.118 mg/kg 0.118 mg/kg 0.014 mg/kg
Western Australian Tiger snake Australia 0.124 mg/kg 0.194 mg/kg N/A
Beaked sea snake TropicalIndo-Pacific 0.164 mg/kg 0.1125 mg/kg N/A

Other factors

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Common krait(Bungarus caeruleus)
Russell's viper(Daboia russelii)
Indian cobra(Naja naja)
Saw-scaled viper(Echis carinatus)
TheBig Foursnakes responsible for most fatal bites on theIndian Subcontinent

The toxicity of snake venom, based on laboratory tests conducted on mice, is sometimes used to gauge the extent of danger to humans, but this is not enough. Many venomous snakes are specialized predators whose venom may be adapted specifically to incapacitate their preferred prey.[15]A number of other factors are also critical in determining the potential hazard of any given venomous snake to humans, including their distribution and behavior.[16][17]For example, while the inland taipan is regarded as the world's most venomous snake based on LD50tests on mice, it is a shy species and rarely strikes, and has not caused any known human fatalities. On the other hand, India'sBig Four(Indian cobra,common krait,Russell's viper, and saw-scaled viper), while less venomous than the inland taipan, are found in closer proximity to human settlements and are more confrontational, thus leading to more deaths from snakebite. In addition, some species, such as theblack mambaandcoastal taipan,occasionally show some aggression, generally when alarmed or in self-defence, and then may deliver fatal doses of venom, resulting in high human mortality rates.[18][19]

See also

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References

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  1. ^McCartney, JA; Stevens, NJ; O'Connor, PM (March 20, 2014), "Oldest fossil evidence of modern African venomous snakes found in Tanzania",PLOS ONE,9(3): e90415,doi:10.1371/journal.pone.0090415,PMC3960104,PMID24646522
  2. ^Klauber LM. (1997).Rattlesnakes: Their Habitats, Life Histories, and Influence on Mankind(2 ed.). Berkeley:University of California Press,Berkeley, 1956, 1972.ISBN978-0-520-21056-1.
  3. ^Williams, Becky L.; Brodie, Edmund D. Jr.; Brodie III, Edmund D. (2004). "A resistant predator and its toxic prey: persistence of newt toxin leads to poisonous (not venomous) snakes".Journal of Chemical Ecology.30(10): 1901–1919.Bibcode:2004JCEco..30.1901W.doi:10.1023/B:JOEC.0000045585.77875.09.PMID15609827.S2CID14274035.
  4. ^Mackessy, Stephen P. (June 2002)."Biochemistry and pharmacology of colubrid snake venoms"(PDF).Journal of Toxicology: Toxin Reviews.21(1–2): 43–83.CiteSeerX10.1.1.596.5081.doi:10.1081/TXR-120004741.S2CID86568032.Archived fromthe original(PDF)on 2010-06-02.Retrieved2009-09-26.
  5. ^abBroad, A. J.;Sutherland, S. K.;Coulter, A. R. (1979)."The lethality in mice of dangerous Australian and other snake venom"(PDF).Toxicon.17(6): 661–664.doi:10.1016/0041-0101(79)90245-9.PMID524395.
  6. ^abFry, BryanArchived2014-04-19 at theWayback Machine(February 08, 2005)Most VenomousArchived2014-10-17 at theWayback Machine,"Q;I was wondering what snakes venom is the most potent to humans A:Drop for drop it is the inland taipan (Oxyuranus microlepidotus), which has a venom more toxic than any other land snake or even the sea snakes. "venomdoc Forums, Retrieved April 17, 2014
  7. ^Tamiya, N.; Puffer, H. (1974). "Lethality of sea snake venoms".Toxicon.12(1): 85–87.doi:10.1016/0041-0101(74)90104-4.PMID4818649.
  8. ^abFry, B. G. (February 24, 2012)."Snakes Venom LD50– List of the Available Data and Sorted by Route of Injection ".venomdoc.Archived fromthe originalon April 13, 2012.RetrievedOctober 14,2013.
  9. ^*"Which snakes are the most venomous?".Australian Venom Research Unit,University of Melbourne.August 25, 2007. Archived fromthe originalon June 26, 2014.RetrievedOctober 14,2013.
  10. ^
  11. ^Inland Taipan Venom vs. Sea Snakes Venom (most notableBelcher's sea snake)
  12. ^Seymour, Jamie."World's Worst Venom".National Geographic Channel.RetrievedApril 17,2014.(starting at 44 min 33 s): "Among the reptiles tested, the most toxic venom belongs to inland taipan, killing over 60% of heart cells in the first 10 minutes
  13. ^Seymour, Jamie."Venom Deathmatch".National Geographic Channel.Archived fromthe originalon February 10, 2011.RetrievedApril 17,2014.(starting at 1 min 49 s): "They have the most toxic venom towards humans then any other snake in the world
  14. ^"Facts and Figures: World's Most Venomous Snakes".Australian Venom Research Unit,University of Melbourne.January 11, 2014. Archived fromthe originalon October 11, 2014.RetrievedJuly 14,2014.
  15. ^"What is an LD50 and LC50".2018-12-31.
  16. ^"Most venomous snakes".Reptile Gardens.Archived fromthe originalon May 8, 2017.RetrievedOctober 13,2014.
  17. ^Walls, Jerry G."Deadly Snakes: What are the world's most deadly venomous snakes?".Reptiles.RetrievedNovember 5,2013.
  18. ^Davidson, Terence."Immediate First Aid – Black Mamba".University of California, San Diego. Archived fromthe originalon 2023-07-25.Retrieved2010-05-12.
  19. ^"Immediate First Aid for bites by Australian taipan or common taipan".
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Wikivoyage has a travel guide forVenomous snakes.
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