Eastern brown snake
Eastern brown snake | |
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Eastern brown snake, NSW, Australia | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Reptilia |
Order: | Squamata |
Suborder: | Serpentes |
Family: | Elapidae |
Genus: | Pseudonaja |
Species: | P. textilis
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Binomial name | |
Pseudonaja textilis | |
Range of eastern brown snake (in green) | |
Synonyms[2][3] | |
List
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The eastern brown snake (Pseudonaja textilis), often referred to as the common brown snake, is a
It is considered the world's second-most venomous land snake after the
Taxonomy
The brown snakes were moved from Diemenia/Demansia to Pseudonaja by Australian naturalist Eric Worrell in 1961 on the basis of skull morphology,[16] and upheld by American herpetologist Samuel Booker McDowell in 1967 on the basis of the muscles of the venom glands. This classification has been followed by subsequent authors.[15] In 2002, Australian herpetologist Richard W. Wells split the genus Pseudonaja, placing the eastern brown snake in the new genus Euprepiosoma,[17] though this has not been recognised by other authors,[2] and Wells has been strongly criticised for a lack of rigour in his research.[18]
Within the genus Pseudonaja, the eastern brown snake has the largest diploid number of chromosomes at 38; those of the other species range from 30 to 36.[19] A 2008 study of mitochondrial DNA across its range showed three broad lineages - a southeastern clade from South Australia, Victoria, and southeastern and coastal New South Wales; a northeastern clade from northern and western New South Wales and Queensland; and a central (and presumably northern) Australian clade from the Northern Territory. The central Australian clade had colonised the region around Merauke in southern West Papua, and the northeastern clade had colonised Milne Bay, Oro, and Central Provinces in eastern Papua New Guinea in the Pleistocene via landbridges between Australia and New Guinea.[20]
P. textilis is
The species is commonly called the eastern brown snake or common brown snake. It was known as marragawan to the
Description
The eastern brown snake is of slender to average build with no demarcation between its head and neck.[25] Its snout appears rounded when viewed from above.[19] Most specimens have a total length (including tail) up to 1.5 m (4.9 ft),[26] with some large individuals reaching 2 m (6.6 ft).[27] The maximum recorded total length for the species is 2.4 m (7.9 ft).[26] Evidence indicates that snakes from the northern populations tend to be larger than those from southern populations.[25] The adult eastern brown snake is variable in colour.[27] Its upper parts range from pale to dark brown,[19] or sometimes shades of orange or russet,[27] with the pigment more richly coloured in the posterior part of the dorsal scales.[19] Eastern brown snakes from Merauke have tan to olive upper parts, while those from eastern Papua New Guinea are very dark grey-brown to blackish.[20]
The eastern brown snake's fangs are small compared to those of other Australian venomous snakes, averaging 2.8 mm (0.11 in) in length or up to 4 mm (0.16 in) in larger specimens, and are 11 mm (0.43 in) apart.[28] The tongue is dark.[29] The iris is blackish with a paler yellow-brown or orange ring around the pupil. The snake's chin and under parts are cream or pale yellow, sometimes fading to brown or grey-brown towards the tail.[19] Often, orange, brown, or dark grey blotches occur on the under parts, more prominent anteriorly. The ventral scales are often edged with dark brown on their posterior edges.[19]
Juveniles can vary in markings, but generally have a black head, with a lighter brown snout and band behind, and a black nuchal band. Their bodies can be uniform brown, or have many black bands, or a reticulated pattern, with all darker markings fading with age.[27] Snake clutches in colder areas tend have a higher proportion of young snakes with banded markings on their bodies.[30]
Its yellowish under parts serve to distinguish it from the
Scalation
The number and arrangement of scales on a snake's body are a key element of identification to species level.
Distribution and habitat
The eastern brown snake is found along the east coast of Australia, from
The eastern brown snake occupies a varied range of
In December 2023 an eastern brown snake interrupted play at the Brisbane International tennis tournament. Play was paused for 40 minutes, while the animal was removed by a professional snake catcher.[36]
Behaviour
The eastern brown snake is generally solitary, with females and younger males avoiding adult males.[37] It is active during the day, though it may retire in the heat of hot days to come out again in the late afternoon. It is most active in spring, the males venturing out earlier in the season than females, and is sometimes active on warm winter days. Individuals have been recorded basking on days with temperatures as low as 14 °C (57 °F).[25] Occasional nocturnal activity has been reported.[38] At night, it retires to a crack in the soil or burrow that has been used by a house mouse, or (less commonly) skink, rat, or rabbit. Snakes may use the refuge for a few days before moving on, and may remain above ground during hot summer nights. During winter, they hibernate, emerging on warm days to sunbathe. Fieldwork in the Murrumbidgee Irrigation Area found that snakes spent on average 140 days in a burrow over winter, and that most males had entered hibernation by the beginning of May (autumn) while females did not begin till mid-May; the males mostly became active in the first week of September (spring), while the females not until the end of the month.[37] The concrete slabs of houses have been used by eastern brown snakes hibernating in winter, with 13 recorded coiled up together under a 5 m × 3 m (16 ft × 10 ft) slab of a demolished house between Mount Druitt and Rooty Hill in western Sydney, and another 17 (in groups of one to four) under smaller slabs within 20 m (66 ft) in late autumn 1972. Groups of up to six hibernating eastern brown snakes have been recorded from under other slabs in the area.[39] In July 1991 in Melton, six eastern brown snakes were uncovered in a nest in long grass.[40]
Eastern brown snakes are very fast-moving; Australian naturalist David Fleay reported that the snake could outpace a person running at full speed.[41] Many people mistake defensive displays for aggression.[42] When confronted, the eastern brown snake reacts with one of two neck displays. During a partial display, the snake raises the front part of its body horizontally just off the ground, flattening its neck and sometimes opening its mouth. In a full display, the snake rises up vertically high off the ground,[43] coiling its neck into an S shape, and opening its mouth.[41] The snake is able to strike more accurately from a full display and more likely to deliver an envenomed bite.[44] Due to the snake's height off the ground in full display, the resulting bites are often on the victim's upper thigh.[26]
A field study in farmland around Leeton that monitored 455 encounters between eastern brown snakes and people found that the snake withdrew around half the time and tried to hide for almost all remaining encounters. In only 12 encounters did the snake advance. They noted that snakes were more likely to notice dark clothing and move away early, reducing the chance of a close encounter. Close encounters were more likely if a person were walking slowly, but a snake was less likely to be aggressive in this situation. Encountering male snakes on windy days with cloud cover heightened risk, as the snake was less likely to see persons until they were close, hence more likely to be startled. Similarly, walking in undisturbed areas on cool days in September and October (early spring) risked running into courting male snakes that would not notice people until close, as they were preoccupied with mating.[45]
Reproduction
Eastern brown snakes generally mate from early October onwards—during the Southern Hemisphere spring; they are
Feeding
The eastern brown snake appears to hunt by sight more than other snakes, and a foraging snake raises its head like a periscope every so often to survey the landscape for prey.[41] It generally finds its prey in their refuges rather than chasing them while they flee.[49] The adult is generally diurnal, while juveniles sometimes hunt at night.[50] The eastern brown snake rarely eats during winter, and females rarely eat while pregnant with eggs.[51] The eastern brown snake has been observed coiling around and constricting prey to immobilise and subdue it,[52] adopting a strategy of envenomating and grappling their prey.[49] Herpetologists Richard Shine and Terry Schwaner proposed that it might be resorting to constriction when attacking skinks, as it might facilitate piercing the skink's thick scales with its small fangs.[53]
The eastern brown snake's diet is made up almost wholly of vertebrates, with mammals predominating—particularly the introduced house mouse. Mammals as large as feral rabbits have been eaten. Small
Venom
The eastern brown snake is considered the
Clinically, the venom of the eastern brown snake causes
The eastern brown snake yields an average of under 5 mg of venom per milking, less than other dangerous Australian snakes.
The eastern brown snake's venom contains coagulation factors VF5a and
The venom also contains pre- and postsynaptic
Analysis of venom in 2016 found—unlike most other snake species—that the venom of juvenile eastern brown snakes differed from that of adults; prothrombinases (found in adults) were absent and the venom did not affect clotting times. Snakes found with a similar profile generally preyed upon dormant animals such as skinks.[49]
The eastern brown snake is the second-most commonly reported species responsible for envenoming of dogs in New South Wales.[80] Dogs and cats are much more likely than people to have neurotoxic symptoms such as weakness or paralysis. One dog bitten suffered a massive haemorrhage of the respiratory tract requiring euthanasia.[81] The venom is uniformly toxic to warm-blooded vertebrates, yet reptile species differ markedly in their susceptibility.[51]
Treatment
Standard first-aid treatment for any suspected bite from a venomous snake is for a pressure bandage to be applied to the bite site. The victims should move as little as possible, and to be conveyed to a hospital or clinic, where they should be monitored for at least 24 hours. Tetanus toxoid is given, though the mainstay of treatment is the administration of the appropriate antivenom.[82] Brown snake antivenom has been available since 1956. Before this, tiger snake antivenom was used, though it was of negligible benefit in brown snake envenoming.[62] The antivenom had been difficult to research and manufacture as the species was hard to catch, and the amount of venom it produced was generally insufficient for horse immunisation, though these challenges were eventually overcome.[83] Dogs and cats can be treated with a caprylic acid-fractionated, bivalent, whole IgG, equine antivenom.[81]
Captivity
Eastern brown snakes are readily available in Australia via breeding in captivity. They are regarded as challenging to keep, and due to the snakes' speed and toxicity, suitable for only experienced snake keepers.[48]
Notes
- ^ Although many Australian snakes are highly venomous, the number of deaths from snakebite in Australia is minuscule when compared to India or Africa. Hence, the labelling of some Australian species as "most dangerous" has been challenged.[4]
- ^ A divided scale is one split down the midline into two scales.[33]
- ^ Snakes of medical importance include those with highly dangerous venom resulting in high rates of morbidity and mortality, or those that are common agents in snakebite.[61]
- ^ This was based on murine LD50 results rather than neurotoxic effects on skeletal muscle.[75]
References
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Cited texts
- ISBN 978-0-949324-68-9.
- Mirtschin, Peter; Rasmussen, Arne; Weinstein, Scott (2017). Australia's Dangerous Snakes: Identification, Biology and Envenoming. Clayton South, Victoria: Csiro Publishing. ISBN 978-0-643-10674-1.
- Sutherland, Struan K.; Tibballs, James (2001) [1983]. Australian Animal Toxins (2nd ed.). South Melbourne, Victoria: Oxford University Press. ISBN 978-0-19-550643-3.
Further reading
- Wilson, Steve; Swan, Gerry (2013). A Complete Guide to Reptiles of Australia, Fourth Edition. Sydney: New Holland Publishers. 522 pp. ISBN 978-1921517280.
External links