Eastern brown snake

The eastern brown snake (Pseudonaja textilis), often referred to as the common brown snake, is a species of venomous elapid snake of the genus Pseudonaja. This snake is considered the world's second most venomous land snake based on its LD₅₀ value (SC) in mice.^[2][3] It is native to Australia, Papua New Guinea, and Indonesia.^[4]

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 total length (including tail) of 1.1–1.8 m (3.6–5.9 ft). The maximum recorded size for the species is 2.4 m (7.9 ft), although any specimen of greater than 2 m (6.6 ft) in total length would be considered exceptionally large.^[5] 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 dorsal scales at midbody, a divided anal scale, and 45–75 divided subcaudal scales.

Geographic range

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,^[6] 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.

Habitat

The snake occupies a varied range of habitats from dry sclerophyll forests (Eucalypt forests) and heaths of coastal ranges, through to savannah woodlands, inner grasslands and arid scrublands and farmland. It is not found in rainforests or other wet areas, nor is it found in very dry deserts with little or no cover. Because of their mainly rodent diet, they can often be found near houses and farms.

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.^[7] 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 defensive if provoked.^[7][4] 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

The main component of their diet is rodents, particularly introduced house mice. Frogs, small birds, eggs, and even other snakes are also consumed.

Venom

The eastern brown snake is considered to be the second most venomous terrestrial snake.^[2][3] The venom has a SC LD₅₀ range of 36.5^[2][3] —53^[4] μg/kg and consists mostly of neurotoxins (pre- & post-synaptic neurotoxins)^[4] and blood coagulants.^[8] These snakes kept at venom supply laboratories yield an average of 2—10 mg^[4] of venom per milking. Engelmann and Obst (1981) give a venom yield of 2 mg (dry weight).^[9] 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 metres (6.9 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,^[10][4] averaging only 2 mg (dry weight).^[9]

Clinically, the venom of the eastern brown snake is known to cause diarrhea, dizziness, collapse or convulsions, renal failure, paralysis and cardiac arrest.^[4] Without medical treatment, bites can be fatal.^[11] 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.^[4]

Neurotoxins

The neurotoxin of the eastern brown snake is textilotoxin, a presynaptic neurotoxin. It is a potent neurotoxin and represents 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 acetylcholine. 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 phospholipase, 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.^[10]

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 substrate S-2222.Ca++ and phospholipids have little effect on it. Doery and Pearson (1961) showed that P. textilis venom was low in direct haemolytic properties and phospholipase. Kaire (1964), reported it had the least amount of heat stable anticoagulant than in most other Australian snakes.^[10]

Treatment

Treatment for eastern brown snake bites is the same as for all venomous Australian snakes. According to the Australian Venom Research Unit, the pressure immobilization technique should always be used.^[12] The bite itself should not be washed, as residual venom can be used to identify the snake, and therefore allow the selection of the appropriate antivenom. Broad bandages should be applied from below the bite site all the way up the affected limb. The bandages must not inhibit the circulation of blood, and as such a tourniquet should never be used. The limb should then be immobilized with a splint. If the bite is on the trunk of the body, pressure bandages should still be applied, however chest movement must not be restricted.

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

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  Close up of the eastern brown snake (in Victoria).

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  Juvenile eastern brown snake on Narrabeen Sandstone at Resolute Beach, Pittwater, New South Wales.

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  Juvenile eastern brown snake on the main street at Nerrigundah, Australia.

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  Eastern brown snake photographed at Brookfield Queensland, Australia.

References

Further reading

• Boulenger GA. 1896. Catalogue of the Snakes in the British Museum (Natural History). Volume III., Containing the Colubridæ (Opisthoglyphæ and Proteroglyphæ), ... London: Trustees of the British Museum (Natural History). (Taylor and Francis, printers). xiv + 727 pp. + Plates I-XXV. (Dieminia textilis, pp. 325–326).

• Cogger H. 2014. Reptiles & Amphibians of Australia, Seventh Edition. Collingwood, Victoria, Australia: CSIRO Publishing. 1,064 pp. ISBN 978-0643100350. (Pseudonaja textilis, p. 928).

• Duméril A-M-C, Bibron G, Duméril A[-H-A]. 1854. Erpétologie générale ou histoire naturelle complète des reptiles. Tome septième. Deuxième partie. Comprenant l'histoire des serpents venimeux. Paris: Roret. xii + pp. 781–1536. (Furina textilis, new species, pp. 1242–1243).

External links

Wikimedia Commons has media related to Brown Snake.

• Video: Eastern or Common Brown Snake
• Animal Planet
• The Australian Reptile Park
• Australia Zoo