Tiger snake

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Not to be confused with the tiger rattlesnake.
For the African snake, see Telescopus semiannulatus.

Tiger snake
Notechis scutatus
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Suborder: Serpentes
Family: Elapidae
Genus: Notechis
Boulenger, 1896[3]
Species:
N. scutatus
Binomial name
Notechis scutatus
Peters, 1861[2]

The tiger snake (Notechis scutatus) is a large and highly venomous snake of southern Australia, including its coastal islands and Tasmania. These snakes are often observed and locally well known by their banding, black and yellow like a tiger, although the species can be highly variable in colouration and patterning. All populations are classified within the genus Notechis (Elapidae). Their diverse characteristics have been classified either as distinct species or by subspecies and regional variation.

While tiger snakes are usually ground-dwelling, they are able to swim as well as climb into trees and buildings.[4][5]

Taxonomy

The genus Notechis is in the elapid family, venomous snakes with fixed front fangs. The classification of this genus is given as a single and highly variable species, Notechis scutatus, or a second species Notechis ater, and by an arrangement of subspecies or regional morphs.[5]

A 2016 genetic analysis showed that the closest relative of the tiger snakes is the rough-scaled snake (Tropidechis carinatus).[6]

The two extensively recognized species of this genus are Notechis scutatus (Peters, 1861) and Notechis ater (Krefft, 1866), which show further variety in their characteristics.[3] Several authors have published revisions or described subspecies of these species.[7] Others consider the names contained by this taxonomic arrangement to be unwarranted, and describe Notechis as a monotypic genus.[8] Various authorities accept some or all the systematics previously applied, but most agree a revision of the genus is needed.[7] Names for these subdivisions include the western types, appended to both species names as occidentalis (Glauert 1948) The island groups have also been described as subspecies: Chappell Island tiger snake as N. ater serventyi (Warrell, 1963), King Island and Tasmanian tiger snakes subspecies as N. ater humphreysi, (Warrell, 1963) and the Peninsula tiger snake as N. ater niger (Kinghorn 1921).

Island populations of N. scutatus have evolved larger heads to cope with large prey animals. Young populations have larger heads by phenotypic plasticity, whereas large heads have become genetically assimilated in older populations.[9]

Species Authority Subsp.* Common name Geographic range
N. ater Krefft, 1866 3 Black tiger snake Australia (Western Australia, South Australia, Tasmania)
N. scutatus Peters, 1861 1 Mainland tiger snake Australia (New South Wales, Queensland, South Australia, Victoria, Western Australia)

* Not including the nominate subspecies (typical form).

Description

Mainland tiger snake, Banyule Flats Reserve, Melbourne, Victoria, in threat pose with body flattened and head raised

Notechis is a genus of large venomous snakes in the family Elapidae restricted to subtropical and temperate regions of Australia. Tiger snakes are a large group of distinct populations, which may be isolated or overlapping, with extreme variance in size and colour. Individuals also show seasonal variation in colour. The total length is typically about 1.2 metres (3 ft 11 in)[10] The patterning is darker bands, strongly contrasting or indistinct, which are pale to very dark in colour. Colouration is olive, yellow, orange-brown, or jet-black, and the underside of the snake is light yellow or orange. Tiger snakes use venom to kill prey, and may also bite an aggressor; they are potentially fatal to humans. Tolerant of low temperatures, the snake may be active on warmer nights.[8] When threatened, they flatten their bodies and raise their heads above the ground in a classic prestrike stance.

Morphs

Tasmanian Tiger Snake (Notechis ater)

The widely dispersed populations (sometimes referred as polymorphs) show some conformity in their descriptions, but these characters may be shared by separate or adjacent groups. Tiger snakes are also identified by the region or island in which the forms occur, which is prefixed to a common name.

The common tiger snake has a flat, blunt head, slightly distinct from a robust body. Its body is capable of being flattened along its entire length when the snake is agitated or basking. Its average length is 0.9 m (2 ft 11 in), with a maximum length of 1.2 m (3 ft 11 in), but has been recorded at 2 m (6 ft 7 in). Highly variable in colour, its base colours are brown, grey olive, or green with lighter crossbands usually of creamy yellow. Occasionally, unbanded specimens are found.[11] Scales appear like overlapping shields, especially around the neck. Ventral scales number 140 to 190, subcaudals 35 to 65, mid-body in 17 or 19 rows and the anal scale is single.

Western tiger snake near a farm dam in Mount Barker, Western Australia

The western tiger snake head is distinct from its robust body, and grows to 2 m (6 ft 7 in) in length. Dorsally, it is steel-blue to black in color with bright yellow bands; unbanded specimens occur. The ventral surface is yellow, tending black towards the tail. Midbody scales are in 17 or 19 rows, ventrals number 140 to 165, subcaudals 36 to 51 (single) and the anal scale is single (rarely divided).

The Chappell Island tiger snake has a blunt head distinct from a robust body. The giant of the tiger snakes species, it averages 1.9 m (over 6 ft) in length. Dorsally, its colour is olive-brown to almost black, sometimes with lighter crossbands. The ventral surface is usually lighter in colour. Juveniles are banded. Mid-body scales are in 17 rows; ventrals number 160 to 171, subcaudals 47 to 52 (single), and the anal scale is single. These snakes are quite docile.

The King Island and Tasmanian tiger snakes each have a blunt head distinct from a robust body. Younger snakes may be slimmer and similar to other tiger snakes, eventually growing up to 1.5 m (4 ft 11 in) in length. Dorsally, they may be jet black, jet black with lighter crossbands, grey with black flecks forming faint bands, or an unbanded grey or brown. The ventral surface is usually a lighter colour. Midbody scales are in 19, 17 or sometimes 15 rows, ventrals number 161 to 174, subcaudals 48 to 52 (single) and the anal scale is single. Tasmanian tiger snakes tend to be quiet snakes, probably due to the lower temperature ranges they inhabit.

The Peninsula tiger snake has a blunt head distinct from a robust body; it averages 1.1 m (3 ft 7 in) in length. Roxby Island specimens are much smaller, averaging 0.86 m (2 ft 10 in) in length. Dorsally, it is generally jet black, sometimes with white or cream markings around the lips and chin. On Kangaroo Island, specimens are highly variable in colour, often exhibiting banding and uniform brown colours. The ventral surface is dark grey to black, with some specimens on Kangaroo Island even possessing red bellies. The ventral surface becomes much lighter prior to shedding. Juveniles nearly always have banding. Midbody scales are in 17, 18, 19 and rarely 21 rows, ventrals number 160 to 184, subcaudals 45 to 54 (single) and the anal scale is single.

The subspecies Notechis ater ater, found away from mainland Australia, is typically uniformly black.

As with most snakes, the colours vary widely between individuals and are an unreliable means of identifying subspecies. Accurate identification is best performed with a venom test kit or scale count.

Reproduction

Tiger snakes give birth to 20 to 30 live young; an exceptional record was made of 64 from an eastern female.[8] They usually mate in spring when it is in the warmer seasons and will give birth to live young in summer.

Habitat

King Island tiger snake, with barely visible banding, near Petrified Forest on King Island, Australia

Tiger snakes are usually found in coastal regions, where they favour wetlands, creeks, dams, and other habitat around watercourses, or at shelter near permanent sources of water in pastoral areas.[5] Habitat providing an abundance of prey can support large populations. The species' distribution extends from the south of Western Australia through to South Australia, Tasmania, up through Victoria, and New South Wales. Its common habitat includes the coastal areas of Australia.

Venom

Dangerous snake poster published by Museums Victoria in 1877

Tiger snakes accounted for 17% of identified snakebite victims in Australia between 2005 and 2015, with four deaths recorded from 119 confirmed envenomations.[12]

Tiger snake venoms possess potent neurotoxins, coagulants, haemolysins, and myotoxins. Symptoms of a bite include localized pain in the foot and neck region, tingling, numbness, and sweating, followed by a fairly rapid onset of breathing difficulties and paralysis. In a study, the mortality rate from untreated bites is reported to be between 40% and 60%.[13][14]

Treatment is the same for all Australian venomous snakes. The pressure immobilization method is used to inhibit the flow of venom through the lymphatic system. Broad, thick bandages are applied over the bite, then down and back along the limb to the armpit or groin. The affected limb is then immobilized with a splint. Identification of the venom is possible if traces are left near the wound. Identifying the snake is not necessary if bitten in Tasmania, because the same antivenom is used to treat all Tasmanian snakes' bites. The availability of antivenom has greatly reduced the incidence of fatal tiger snake bites. Among the number of deaths caused by snakebite in Australia, those from tiger snakes are exceeded only by the brown snake.[15] The venom yield is 35–65 milligrams (0.54–1.00 gr), while the lethal dose for humans is 3 milligrams (0.046 gr).[16]

Conservation

They are protected species in most Australian states, and to kill or injure one incurs a fine up to A$7,500, as well as a jail sentence of 18 months in some states.[17] It is also illegal to export a native Australian snake.

References

  1. ^ Michael, D.; Clemann, N.; Robertson, P. (2018). "Notechis scutatus". IUCN Red List of Threatened Species. 2018: e.T169687A83767147. doi:10.2305/IUCN.UK.2018-1.RLTS.T169687A83767147.en. Retrieved November 19, 2021.
  2. ^ Species Notechis scutatus at The Reptile Database
  3. ^ a b "Notechis". Integrated Taxonomic Information System. Retrieved March 23, 2008.
  4. ^ Our Wildlife Fact Sheet - Tiger Snake (PDF), Victoria State Government, Australia, 2017
  5. ^ a b c Beatson, Cecilie (November 19, 2020). "Tiger Snake". Factsheet. Australian Museum. Retrieved January 29, 2022.
  6. ^ Figueroa, A.; McKelvy, A. D.; Grismer, L. L.; Bell, C. D.; Lailvaux, S. P. (2016). "A species-level phylogeny of extant snakes with description of a new colubrid subfamily and genus". PLOS ONE. 11 (9): e0161070. Bibcode:2016PLoSO..1161070F. doi:10.1371/journal.pone.0161070. PMC 5014348. PMID 27603205.
  7. ^ a b Genus Notechis at The Reptile Database
  8. ^ a b c Browne-Cooper R, Bush B, Maryan B, Robinson D (2007). Reptiles and Frogs in the Bush: Southwestern Australia. University of Western Australia Press. pp. 254, 255. ISBN 978-1-920694-74-6.
  9. ^ Aubret F, Shine R (2009). "Genetic assimilation and the postcolonisation erosion of phenotypic plasticity in island Tiger snakes" (PDF). Current Biology. 19 (22): 1932–1936. Bibcode:2009CBio...19.1932A. doi:10.1016/j.cub.2009.09.061. PMID 19879141. S2CID 205091.
  10. ^ Cogger, Harold (2014). Reptiles andAmphibians of Australia. CSIRO. p. 905. ISBN 9780643100350.
  11. ^ Video of dark unbanded Tiger Snake
  12. ^ Johnston, Christopher I.; Ryan, Nicole M; Page, Colin B; Buckley, Nicholas A; Brown, Simon GA; O'Leary, Margaret A; Isbister, Geoffrey K (2017). "The Australian Snakebite Project, 2005–2015 (ASP-20)" (PDF). Medical Journal of Australia. 207 (3): 119–25. doi:10.5694/mja17.00094. hdl:1959.13/1354903. PMID 28764620. S2CID 19567016. Archived from the original (PDF) on October 6, 2017. Retrieved October 6, 2017.
  13. ^ University of Adelaide Clinical Toxinology Resource
  14. ^ Brent W. Burkhart; Phillips Donovan (2005). "Critical Care Toxicology: Diagnosis and Management of the Critically Poisoned Patient". Toxicological Diagnosis and Management of Envenomated Patients. Mosby.
  15. ^ Chris Thompson; Struan Sutherland (November 2003). "Australian Snake Bites". Envenomation in Australia. University of Sydney. Archived from the original on February 15, 2008. Retrieved March 3, 2008.
  16. ^ Mercurio (August 30, 2016). Understanding Toxicology. Jones & Bartlett Publishers. ISBN 978-0-7637-7116-4.
  17. ^ "National Parks and wildlife Act (SA)" (PDF). Parliament of SA. 2009. Retrieved April 23, 2009.[dead link‍]

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