Eastern brown snake

Eastern brown snake
Eastern brown snake, Tamban Forest near Kempsey, New South Wales
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Suborder: Serpentes
Family: Elapidae
Genus: Pseudonaja
Species: P. textilis
Binomial name
Pseudonaja textilis
(Duméril, Bibron & Duméril, 1854)

The eastern brown snake (Pseudonaja textilis), often referred to as the common brown snake, is a species of genus Pseudonaja. This snake is considered the second most venomous land snake based on its LD50 value (SC) in mice.[1][2] It is native to Australia, New Guinea and Indonesia.[3]

Contents

Description

Adult eastern brown snakes are highly variable in colour. Whilst usually a uniform shade of brown, they can have various patterns including speckles and bands, and range from a very pale fawn colour through to black, including orange, silver, yellow and grey. Juveniles can be banded and have a black head, with a lighter band behind, a black nape, and numerous red-brown spots on the belly.

This species has an average length of 1.5–1.8 m and it is rarely larger than 2 m. Large eastern brown snakes are often confused with "king brown" snakes (Pseudechis australis), whose habitat they share in many areas.

Scalation

They have 17 rows of mid-body scales, a divided anal scale and 45–75 divided subcaudal scales.

Distribution and habitat

The eastern brown snake is found all the way along the East coast of Australia, from the tip of Cape York, along the coasts and inland ranges of Queensland, New South Wales, Victoria and South Australia. They are also found in arid areas of the Northern Territory, the far east of the Kimberley in Western Australia[4] and discontinuously in parts of New Guinea, specifically northern Milne Bay Province and Central Province in Papua New Guinea, and the Merauke region of Papua Province, in the Indonesian part of New Guinea. Because their mainly rodent diet, they can often be found near houses and farms.

The snake occupies a varied range of habitats from wet to dry sclerophyll forests (Eucalypt forests) and heaths of coastal ranges, through to savannah woodlands, inner grasslands and arid scrublands. It is not found in rainforests or other wet areas.

Behaviour

The eastern brown snake is diurnal (meaning it is active during the day). It is notorious for its speed and aggression throughout its habitats.[5] When highly agitated, they hold their necks high, appearing in an upright S-shape. The snake usually seeks to flee when confronted, though it can be highly aggressive if provoked.[5][3] This species is attracted to rural and farming areas, probably due to the large numbers of associated rodents. Such areas also normally provide shelter in the form of rubbish and other cover.

Diet

Being an opportunistic feeder, the eastern brown snake will consume almost any vertebrate animal, including frogs, lizards, birds, rodents or other snakes.

Venom

The eastern brown snake is considered to be the second most venomous terrestrial snake.[1][2] The venom with the LD50 values of 0.0365 mg/kg[1][2]—0.053 mg/kg[3] SC consists mostly of neurotoxins (pre-&post-synaptic neurotoxins)[3] and blood coagulants.[6] These snakes kept at venom supply laboratories yield an average of 2—10 mg [3] of venom per milking. As with most venomous snakes, the volume of venom produced is largely dependent on the size of the snake. Worrell (1963) reported a milking of 41.4 mg from a relatively large (2.1 m) specimen. This record is atypical, as on average the eastern brown snake yields a low volume of venom which is reported as not more than 10 mg.[7][3]

Clinically, the venom of the eastern brown snake is known to cause diarrhea, dizziness, collapse or convulsions, renal failure, paralysis and cardiac arrest.[3] Without medical treatment, bites can be fatal.[8] As this species tends to initiate their defence with non-fatal bites, the untreated mortality rate in most snakebite cases reported is 10—20% which is not very high.[3]

Neurotoxins

The neurotoxin of the eastern brown snake is textilotoxin (a presynaptic neurotoxin). It is a potent neurotoxin and represent 3% of the crude venom by weight. Southcott and Coulter (1979), reported that textilotoxin acted on the prejunctional terminal by selectively blocking the release of acetycholine after the appearance of the action potential. This blockage had no effect on the resting membrane potential of the muscle cells, nor was the nerve conduction altered. Sutherland (1983), reported,"that textilotoxin had direct presynaptic actions and no appreciable effect on muscle or acetylcholine receptors. The presynaptic blockade was due to the phosphoilpase, a component of the textilotoxin acting on the axolemma.

Hamilton et al. (1980), showed that the crude venom produced "coated omega figures" in the axolemma of the rat nerve terminals. Those figures are probably due to the action of the textilotoxin.

Barnett et al. (1980), isolated a postsynaptic neurotoxin called pseudonajatoxin A. It has 117 amino acid residues and a molecular weight of 12,280. It causes irreversible blockade by firm binding to the acetylcholine receptors.[7]

Coagulants

Kellaway (1933), stated that P. textilis venom possessed a strong, highly diffusible coagulation factor. Denson (1969), concluded that the coagulation factor was a complete prothrombin activator. Masci et al. (1988) found the prothrombin activator to be a major component of the venom with a high molecular weight of larger than 200,000. They found it was related antigenically to the prothrombin activator of O. scutellatus venom, able to activate citrated blood plasma, wartrin plasma, factor V and factor X deficient plasmas and will hydrolyse peptide p-nitroanilide substrale S-222.Ca++ and phospholipids have little effect on it. It was shown by Doery and Pearson (1961), that P. textilis venom was low in direct haemolytic properties and phospholipase. A.Kaire (1964), reported it had the least amount of heat stable anticoagulant than in most other Australian snakes.[7]

Some snake bite cases

It is reported that at 8:45 am on February 4, 1981, an experienced herpetologist was cleaning the cage of a female eastern brown snake which had laid a clutch of 33 eggs on December 8, 1980. The snake suddenly bit the herpetologist's right thumb in a single fast strike. Two fangs marks were clearly visible 30 minutes later. The right arm was ensheathed in a self-applied compression bandage consisting of two rubber Esmarch's bandages, and the victim was transported to the hospital by ambulance. One hour after the release of the compression bandage, one ampule (50 ml) of CSL brown snake anti-venom mixed with 50 ml of dextrose saline was adminsitered intravenously. The herpetologist recovered and returned to work within six days.[7]

A 16-year-old boy from Sydney died on 13 January 2007 after being bitten on the hand in a reserve at Whalan.[9]

9-year-old girl Milena Swilks from Rocky River, south of Armidale in rural New South Wales, died on 8 March 2007 after being bitten on the foot while picking corn. She collapsed and was taken to hospital unconscious, with the cause not known until after her death two hours later.[10]

Reproduction

Eastern brown snakes mate during spring; they are oviparous. Males engage in 'ritual combat' with other males for control of territory. The most dominant male will mate with females in the area. The females produce a clutch of 10–40 eggs in late spring or early summer. They do not guard the nest after the eggs are laid — the juvenile snakes are totally independent of the mother.

Gallery

References

  1. ^ a b c "LD50". http://www.seanthomas.net/oldsite/ld50tot.html. 
  2. ^ a b c "LD50 menu". http://www.kingsnake.com/toxinology/LD50/LD50men.html. 
  3. ^ a b c d e f g h "Clinical Toxinology Resources-Pseudonaja textilis". http://toxinology.com/fusebox.cfm?fuseaction=main.snakes.display&id=SN0041. 
  4. ^ Shea, G.M. (2006). "Three Western Australian snake venoms on blood coagulation of the dog, cat, horse and wallaby". Australian Veterinary Journal. 63 (10): 352. doi:10.1111/j.1751-0813.1986.tb02893.x. PMID 3800793. 
  5. ^ a b Mark O'Shea. Venomou snakes of the world (2011). ISBN 9780691150239. http://www.amazon.com/Venomous-Snakes-World-Mark-OShea/dp/0691150230/ref=sr_1_1?ie=UTF8&qid=1321001317&sr=8-1. 
  6. ^ "CSL Antivenom Handbook – Brown Snake Antivenom". http://www.toxinology.com/generic_static_files/cslavh_antivenom_brown.html. Retrieved 2008-01-24. 
  7. ^ a b c d Venom and toxins research group. Snake of medical importance: Venomous snakes (Australia); Snakebite cases of the Common brown snake. Singapore. ISBN 9971622173. 
  8. ^ Brent W. Burkhart; Phillips Donovan (2005). Critical Care Toxicology: Diagnosis and Management of the Critically Poisoned Patient. Mosby. ISBN 0815143877. http://books.google.com/books?id=WuA4LsWXXWEC. 
  9. ^ "Snakebite teenager dies in hospital". Melbourne: The Age. 2007-01-15. http://www.theage.com.au/articles/2007/01/14/1168709615872.html. 
  10. ^ Williams, Samantha (2007-03-12). "Girl dies of snake bite". Herald Sun. http://www.news.com.au/heraldsun/story/0,21985,21363822-661,00.html. 

Further reading


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