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Venomous snakes are species of suborder Serpentes that are capable of producing venom which is used primarily for immobilizing prey and defense mostly via mechanical injection by fangs. Common venomous snakes include Families Elapidae, Viperidae, Atractaspididae and some of Colubridae. The toxicity of them is mainly indicated by murine LD50, while multifarious factors are considered to judge their potential danger to humans.
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 enough to help capture small prey but causing no harm to humans when bitten.
There is no a single or special taxonomic group for venomous snakes which 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, 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.
LD50, mostly on rodents, is a common indicator of snakes' toxicity whose level is higher with a smaller resultant value. 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 or Crotalus 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.
|Snake||Region||SC (0.1% bovine serum albumin in Saline)||SC (Saline alone)||IV|
|Inland taipan||Australia||0.01 mg/kg||0.025 mg/kg||N/A|
|Dubois' seasnake||Coral Sea, Arafura Sea, Timor Sea 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|
|Black Mamba||Sub-Saharan Africa||0.05 mg/kg||0.12 mg/kg - 0.32 mg/kg||N/A|
|Coastal Taipan||Australia, Papua New Guinea||0.064 mg/kg||0.099 mg/kg||0.013 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|
|Black Tiger snake||Australia||0.099 mg/kg||0.131 mg/kg||N/A|
|Many-banded krait||Mainland China, Taiwan, Vietnam, Laos, Burma||0.09 mg/kg||0.108 mg/kg||0.113 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|
|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|
Toxicity of snake venom is sometimes used to gauge the extent of their danger to humans, but this is inappropriate. Many venomous snakes are specialized predators of rodents whose venom may be adapted specifically to incapacitate mice. A number of other factors are more critical in determining the potential hazard of any given venomous snake to humans, including the distribution and the behavior of them. For example, while the inland taipan is regarded as the world's most venomous snake based on LD50, the "Big Four" snakes cause far more snakebites due to their proximity to populous areas. Clinical mortality rates, reflected by medical precedents, are another commonly used indicator to determine the danger of any given venomous snake, as determined by the efficiency of their venom delivery, venom yield and the behavior in response to humans. The black mamba and coastal taipan, for instance, can cause a 100% untreated mortality rate as tending to deliver bites with a fatal quantity of venom in every case.
The inland taipan is the world's most venomous snake
The Inland Taipan is believed to have the most toxic venom in the world (Sutherland, 1994)