Venomous snakes are species of the suborder Snake that are capable of producing Snake 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 , 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 , 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. There are about 600 venomous snake species in the world.
Evolution
The evolutionary history of venomous snakes can be traced back to as far as 28 million years ago.
is 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, that 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
), or actually do produce venom in small quantities, likely sufficient to help capture small prey but causing no harm to humans when bitten.
Taxonomy
There is not a single or special taxonomic group for venomous snakes. Venom is known in several 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) | Amblyodipsas, Aparallactus, Atractaspididae, Brachyophis, Chilorhinophis, Hypoptophis, Homoroselaps, Macrelaps, Micrelaps, and more. |
| Colubridae (colubrids) | Most are harmless, but others have potent venom and at least five species, including the boomslang, have caused human fatalities. |
| Elapidae (elapids) | , Oxyuranus, Pseudonaja, Coral snake, Bungarus, Acanthophis, Notechis, Dendroaspis, king cobras, Naja and more. |
| Viperidae (viperids) | Viperinae, including the Daboia, Echis, Bitis and Crotalinae, including Crotalus, Bothrops and Agkistrodon. |
Terminology
Venomous snakes are often said to be
Poison, 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.
Rhabdophis 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
from
Oregon can retain toxins in their livers from ingesting rough-skinned newts.
Danger
Toxicity issues
Venom toxicities are compared by looking at the median lethal dose (usually using
as test animals and termed the murine LD
50), 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), muscle or peritoneum (IP). Smaller murine LD
50 values indicate venoms that are more toxic, and there have been numerous studies on snake venom with a variability of potency estimates.
SC LD
50 is considered the most applicable to actual bites as only vipers with large fangs (such as large specimens from the genera
Bitis,
Bothrops,
Crotalus, or
Daboia) are capable of a truly intramuscular bite, snakebites rarely cause IV
envenomation, and IP envenomation is even rarer. Measurements of LD
50 using dry venom mixed with 0.1% bovine serum albumin in saline are more consistent than the results obtained using saline alone. As an example, the venom of the eastern brown snake has a murine LD
50 (SC) of when measured in 0.1% bovine serum albumin in saline; when saline alone is used, the value is .
Belcher's sea snake, which sometimes is mistakenly called the hook-nosed sea snake, 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 (IM) is 0.24 mg/kg][ Studies on mice][*
][
LISTS . Nine of the World's Deadliest Snakes. "#1: The snake with the world's deadliest venom - Oxyuranus microlepidotus" . Encyclopædia Britannica. Retrieved November 5, 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.
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.
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.][Inland Taipan Venom vs. Sea Snakes Venom (most notable Belcher's sea snake)
Oakley, Cecily (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.
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. Though many (Oxyuranus microlepidotus) do -have- lots of venom stored. They are actually not as brutal as other snakes.
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] and human cardiac cell cell culture[ Fry, Bryan (February 08, 2005) Most Venomous ,"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.com Forums, Retrieved April 17, 2014]
+ Most venomous snakes of the world |
|
|
| N/A |
| N/A |
| 0.01 mg/kg |
| N/A |
| N/A |
| 0.013 mg/kg |
| 0.061 mg/kg |
| N/A |
| N/A |
| 0.014 mg/kg |
| N/A |
| N/A |
Other factors
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.
See also
External links
