Eastern brown snake
|Eastern brown snake|
Eastern brown snake
| Pseudonaja textilis|
(Duméril, Bibron and Duméril, 1854)
The Eastern brown snake (Pseudonaja textilis), also known as the common brown snake is a species of highly venomous snake that's found in both Australia and New Guinea. It is often cited as the worlds second most venomous land snake with a murine subcutaneous LD50 of 0.0365 mg/kg. This species is responsible for the most snakebite incidents and fatalities in Australia. The eastern brown snake is responsible for perhaps 60% of deaths caused by snakebite in Australia.
The eastern brown snake was described by French zoologists Auguste Duméril, André Marie Constant Duméril, and Gabriel Bibron in 1854. The word "pseudo" is derived from Greek and means "false", while the word "naja" is a Latinisation of the Sanskrit word nāgá (नाग) meaning "cobra" or "serpent". The word "textilis" is derived from the medieval Latin word "textus" and means "woven fabric" or "cloth".
This is a medium to large in length, slender to moderately robust bodied snake with a medium length tail.The head is indistinct from the neck with a prominent canthus rostralis. The eyes are medium in size with round pupils. Dorsal scales are smooth. The average length of this species is around 1.2 m (3.94 ft) to 1.4 m (4.59 ft) in length, but they may grow to a maximum length of approximately 2.5 m (8.2 ft). The longest recorded specimen of this species is 2.4 m (7.87 ft). The colouration and pattern on this species is highly variable. They are usually uniform in colour and colours range from pale tan through orange, russet, dark brown and almost black, sometimes with cross-body banding. However, they are often uniform in colour. The belly or ventral scales are usually cream, yellow or orange with scattered orange or grey blotches. Hatchling and juveniles particularly vary in colour, the young eastern brown snakes frequently have dark heads or neck bands, or they may be completely banded along the body length. Juveniles usually have an orange band across a black patch on top of its head. By three years of age, the bands disappear, and the uniform adult colouration takes over.
Midbody scales 17 rows, 185 - 235 ventral scales, divided anal scale, 45 - 75 divided sub-caudal scales.
Distribution and habitat
This species is found throughout the eastern half of Australia, its distribution becoming patchier as one moves westwards. To date only one specimen has been recorded from Western Australia. That specimen was caught in the South-east Kimberley, at Gordon Downs (Storr, Smith and Johnstone, 1986). The eastern brown snake is also found on the island of New Guinea. Its distribution in New Guinea is poorly understood, and the origin of the New Guinea populations and its timing have been the subject of much speculation. Phylogenetic analysis of mitochondrial DNA sequences from three New Guinea populations of the eastern brown snake indicates that New Guinea was colonised from two independent eastern and western migration routes most likely in the Pleistocene. One dispersal event from northern Queensland led to the populations in eastern New Guinea (Milne Bay, Oro and Central Provinces, Papua New Guinea), whereas another, from Arnhem Land to central southern New Guinea, led to the populations from the Merauke area, Indonesian Papua. The results are consistent with the effects of Pleistocene sea level changes on the physical geography of Australasia, and are thus suggestive of a natural rather than anthropogenic origin of the New Guinea populations.
The eastern brown snake is found in a diverse range of habitats from wet and dry sclerophyll forests (Eucalypt forests) and heaths of the coast and ranges, through savanna woodlands to arid inland shrublands and grasslands. Particularly common in pasture and cropping regions of the eastern half of mainland Australia. Also found in urban and semi-urban areas, where it comes in direct contact with humans. Also found in open, wet country, especially near water courses; sometimes swampland or in sandy or rocky areas.
Behaviour and ecology
Behaviour and habits
The eastern brown snake is a diurnal and terrestrial snake with nocturnal tendencies in hotter weather. It is a swift moving snake with a more aggressive disposition than other species of the genus. If approached it will attempt to escape. If cornered it will hiss loudly, flatten the neck for a short period, then raise the forebody into an upright double S position and face the threat. Provocation or any approach too close will result in a rapid and snap like bite. Takes shelter in or under logs, abandoned animal burrows, deep soil cracks, under building materials and often found in and around farm sheds (particularly hay sheds and grain silos which tend to attract mice).
Being an opportunistic feeder, the eastern brown snake will consume almost any vertebrate animal, including frogs, lizards (particularly skinks, agamids and geckos), birds, rodents or other snakes.
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.
The eastern brown snake is considered to be the second most venomous terrestrial snake. The venom has a subcutaneous LD50 range of 36.5 —53 μg/kg (0.0365 - 0.053 mg/kg) and consists mostly of neurotoxins (pre- & post-synaptic neurotoxins) and blood coagulants. These snakes kept at venom supply laboratories yield an average of 2—10 mg of venom per milking. Engelmann and Obst (1981) give a venom yield of 2 mg (dry weight). 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 (6.89 ft) specimen. This record is atypical, as the eastern brown snake yields a low volume of venom which is reported as not more than 10 mg, averaging only 2 mg (dry weight).
Clinically, the venom of the eastern brown snake is known to cause diarrhea, dizziness, collapse or convulsions, renal failure, paralysis and cardiac arrest. Without medical treatment, bites can be fatal. 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.
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 high molecular weight of 12,280, meaning it is slow to act. It causes irreversible blockade by firm binding to the acetylcholine receptors.
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 coastal taipan 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 eastern brown snake 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.
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 administered intravenously. The herpetologist recovered and returned to work within six days.
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.
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