Venomous snakes are species of the suborder Serpentes that are capable of producing venom, 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 grooved fangs, although some venomous snakes lack well-developed fangs. Common venomous snakes include the families Elapidae, Viperidae, Atractaspididae, and some of the Colubridae. The toxicity of venom is mainly indicated by murine LD50, 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 both neurotoxic and hemotoxic properties.
The evolutionary history of venomous snakes can be traced back to as far as 25 million years ago. Snake venom is actually modified saliva used for prey immobilization 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 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 to help capture small prey but causing no harm to humans when bitten.
There is not a single or special taxonomic group for venomous snakes that comprise species from different families. This has been interpreted to mean venom in snakes originated more than once as the result of convergent evolution. Around a quarter of all snake species are identified as being venomous.
|Atractaspididae (atractaspidids)||Burrowing asps, mole vipers, stiletto snakes|
|Colubridae (colubrids)||Most are harmless, but others have potent venom and at least five species, including the boomslang (Dispholidus typus), have caused human fatalities.|
|Elapidae (elapids)||Sea snakes, taipans, brown snakes, coral snakes, kraits, death adders, tiger snakes, mambas, king cobra 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.|
Venomous snakes are often said to be poisonous, 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 which are actually poisonous. Rhabdophis keelback snakes are both venomous and poisonous – their poisons are stored in nuchal glands and are acquired by sequestering toxins from poisonous toads the snakes eat. Similarly, certain garter snakes from Oregon can retain toxins in their livers from ingesting rough-skinned newts.
LD50, mostly on rodents, is a common indicator of snakes' toxicity with a smaller resultant value indicating a higher level of toxicity. There have been numerous studies on snake venom with a variability of potency estimates. There are four methods in which the LD50 test is conducted, which are injections to subcutis (SC), vein (IV), muscle (IM or IC), and peritoneum (IP). The former (SC) is most applicable to actual bites as only vipers with large fangs, such as large Bitis, Bothrops, Crotalus, or Daboia specimens, would be able to deliver a bite that is truly intramuscular, and snakebites rarely cause IV envenomation. Testing using dry venom mixed with 0.1% bovine serum albumin in saline, gives more consistent results than just saline alone.
Belcher's sea snake (Hydrophis belcheri), which many times is mistakenly called the hook-nosed sea snake (Enhydrina schistosa), has been erroneously popularized 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 called Snakes 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." Belcher's sea snake's actual LD50 (recorded only intramuscularly) is 0.24 mg/kg and 0.155 mg/kg,. Studies on mice and human cardiac cell culture show that venom of the inland taipan, drop by drop, is the most toxic among all snakes.
|Snake||Region||subcutaneous injection LD50 0.1% bovine serum albumin in Saline||subcutaneous injection LD50 Saline||intravenous injection LD50|
|Inland taipan||Australia||0.01 mg/kg||0.025 mg/kg||N/A|
|Dubois' sea snake||Coral Sea, Arafura Sea, Timor Sea, Tar River, and Indian 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, Strait of Taiwan, 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 the Malay Peninsula and 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||Tropical Indo-Pacific||0.164 mg/kg||0.1125 mg/kg||N/A|
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. 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. For example, while the inland taipan is regarded as the world's most venomous snake based on LD50 tests on mice, it is a shy species and rarely strikes, and has not caused any known human fatalities. On the other hand, India's Big 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 the black mamba and coastal 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.
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- 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.
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The inland taipan is the world's most venomous snake
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The Inland Taipan is believed to have the most toxic venom in the world (Sutherland, 1994)
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- 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
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