From Wikipedia, the free encyclopedia
A venomous snake is a snake that uses modified saliva, snake venom, usually delivered through highly specialized teeth such as hollow fangs, for the purpose of prey immobilization and self-defense. In contrast, non-venomous species either constrict their prey, or simply 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 that venom in snakes originated more than once as the result of convergent evolution. Evidence has recently been presented for the Toxicofera hypothesis however; venom was present (in small amounts) in the ancestor 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 'non venomous' 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 assist in small prey capture, but cause no harm to humans if bitten.
Venomous snakes are often said to be poisonous, although this is not the correct term, as venoms and poisons are different. Poisons can be absorbed by the body, such as through the skin or digestive system, while venoms must first be introduced directly into tissues or the blood stream (envenomated) through mechanical means. It is, for example, therefore harmless to drink snake venom as long as there are no lacerations inside the mouth or digestive tract. There are however two exceptions: the Rhabdophis snakes (keelback snales) secrete poison from glands that it gets from the poisonous toads that it preys on; similarly certain garter snakes from Oregon retain toxins in their liver from the newts they eat.
Many other snakes, such as boas and pythons may not be venomous, but their bites should be attended to medically. Their teeth may be long and sharp, capable of inflicting lacerations, with bites often introducing mouth bacteria and shed teeth into the wound.
Most venomous snakes
Lists or rankings of the world's "most venomous snakes" or "most dangerous snakes" are tentative and differ greatly due to numerous factors, including the recentness and reliability of the data, the number of species analyzed, and the testing methods used. In terms of human fatalities, the most venomous species may not always be the most dangerous; for example, while the Russell's viper has a significantly weaker venom than the inland taipan, it is responsible for far more deaths due to its aggressiveness.
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, although the latter is the most applicable to actual bites. It should also be considered that mice, the most commonly used animals in determining LD50, may react to some snake venoms differently than humans do. Thus, it remains difficult to compile such lists.
- World's Most Venomous Snakes, Australian Venom Research Unit
- World's Most Venomous Snakes, Australian Venom & Toxin Database
Families of venomous snakes
Over 600 species are known to be venomous—about a quarter of all snake species. The following groups of snakes can be aggressive and inflict dangerous, even potentially lethal bites:
|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)||Cobras, coral snakes, kraits, mambas, sea snakes, sea kraits and Australian elapids.|
|Viperidae (viperids)||True vipers and pit vipers, including rattlesnakes.|
- ^ Klauber LM. 1997. Rattlesnakes: Their Habitats, Life Histories, and Influence on Mankind. Second Edition. First published in 1956, 1972. University of California Press, Berkeley. ISBN 0-520-21056-5.
- ^ a b Fry, Bryan Grieg. "Snake LD50 - discussion". Australian Venom & Toxin Database. http://www.kingsnake.com/toxinology/LD50/LD50men.html. Retrieved 2009-09-28. "Subcutaneous is the most applicable to actual bites. Only large Bitis or extremely large Bothrops or Crotalus specimens wouls be able to deliver a bite that is truly intramuscular. IV injections are extremly rare in actual bites."
- ^ Chippaux, J.P. (1998). "Snake-bites: appraisal of the global situation". Bulletin of the World Health Organization 76 (5): 515–24. http://www.kingsnake.com/aho/pdf/menu6/chippaux1998.pdf. Retrieved 2009-07-03.
- ^ 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. http://www.unco.edu/nhs/biology/faculty_staff/mackessy/colubrid.pdf. Retrieved 2009-09-26.
- ^ "Venom variability". Women's & Children's Hospital - Clinical Toxinology Resources. University of Adelaide. http://www.toxinology.com/fusebox.cfm?staticaction=snakes/ns-venom02.htm. Retrieved 28 September 2009. "The rough scaled snake, Tropidechis carinatus has a much less potent venom than the tiger snake, Notechis scutatus, on LD50 testing in mice. Yet clinically, the two venoms are virtually identical in the type and severity of effects on envenomed humans."
- For goodness snakes Treating and Preventing Venomous Bites.
- Venomous Snakes Pictures, videos and description of the most venomous snakes in the world.
- Venomous snakes and outdoor workers Bite-prevention and treatment information for outdoor workers.