The tiger snake (''Notechis scutatus'') is a large and highly venomous snake of southern Australia, including its coastal islands and

Tasmania Tasmania (; palawa kani: ''Lutruwita'') is an island States and territories of Australia, state of Australia. It is located to the south of the Mainland Australia, Australian mainland, and is separated from it by the Bass Strait. The sta ...

. These snakes are often observed and locally well known by their banding, black and yellow like a

tiger The tiger (''Panthera tigris'') is a large Felidae, cat and a member of the genus ''Panthera'' native to Asia. It has a powerful, muscular body with a large head and paws, a long tail and orange fur with black, mostly vertical stripes. It is ...

, although the species can be highly variable in colouration and patterning. All populations are classified within the genus ''Notechis'' (

Elapidae Elapidae (, commonly known as elapids , from , variant of "sea-fish") is a family of snakes characterized by their permanently erect fangs at the front of the mouth. Most elapids are venomous, with the exception of the genus '' Emydocephalus ...

). 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.

Taxonomy

The genus ''Notechis'' is in the

elapid Elapidae (, commonly known as elapids , from , variant of "sea-fish") is a family (biology), family of snakes characterized by their permanently erect fangs at the front of the mouth. Most elapids are venomous, with the exception of the genus ...

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. A 2016 genetic analysis showed that the closest relative of the tiger snakes is the rough-scaled snake (''Tropidechis carinatus''). The two extensively recognized

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

of this genus are ''Notechis scutatus'' (Peters, 1861) and ''Notechis ater'' (Krefft, 1866), which show further variety in their characteristics. Several authors have published revisions or described

subspecies In Taxonomy (biology), biological classification, subspecies (: subspecies) is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (Morphology (biology), morpholog ...

of these species. Others consider the names contained by this taxonomic arrangement to be unwarranted, and describe ''Notechis'' as a

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unisp ...

genus. Various authorities accept some or all the systematics previously applied, but most agree a revision of the genus is needed. 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 Evolution is the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, re ...

larger heads to cope with large prey animals. Young populations have larger heads by

phenotypic plasticity Phenotypic plasticity refers to some of the changes in an organism's behavior, morphology and physiology in response to a unique environment. Fundamental to the way in which organisms cope with environmental variation, phenotypic plasticity encompa ...

, whereas large heads have become genetically assimilated in older populations. ''* Not including the nominate subspecies (typical form).''

Description

''Notechis'' is a genus of large venomous

snake Snakes are elongated limbless reptiles of the suborder Serpentes (). Cladistically squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales much like other members of the group. Many species of snakes have s ...

s in the family

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 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. When threatened, they flatten their bodies and raise their heads above the ground in a classic prestrike stance.

Morphs

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 , with a maximum length of , but has been recorded at . 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. 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.

The western tiger snake head is distinct from its robust body, and grows to 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

, 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 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 in length. Roxby Island specimens are much smaller, averaging 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. They usually mate in spring when it is in the warmer seasons and will give birth to live young in summer.

Habitat

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. Habitat providing an abundance of prey can support large populations. The species' distribution extends from the south of

Western Australia Western Australia (WA) is the westernmost state of Australia. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to the south, the Northern Territory to the north-east, and South Australia to the south-east. Western Aust ...

through to

South Australia South Australia (commonly abbreviated as SA) is a States and territories of Australia, state in the southern central part of Australia. With a total land area of , it is the fourth-largest of Australia's states and territories by area, which in ...

, up through

Victoria Victoria most commonly refers to: * Queen Victoria (1819–1901), Queen of the United Kingdom and Empress of India * Victoria (state), a state of Australia * Victoria, British Columbia, Canada, a provincial capital * Victoria, Seychelles, the capi ...

, and

New South Wales New South Wales (commonly abbreviated as NSW) is a States and territories of Australia, state on the Eastern states of Australia, east coast of :Australia. It borders Queensland to the north, Victoria (state), Victoria to the south, and South ...

. Its common habitat includes the coastal areas of Australia.

Venom

Tiger snakes accounted for 17% of identified snakebite victims in Australia between 2005 and 2015, with four deaths recorded from 119 confirmed envenomations. Tiger snake venoms possess potent

neurotoxin Neurotoxins are toxins that are destructive to nervous tissue, nerve tissue (causing neurotoxicity). Neurotoxins are an extensive class of exogenous chemical neurological insult (medical), insultsSpencer 2000 that can adversely affect function ...

s, coagulants, haemolysins, and

myotoxin Myotoxins are small, basic peptides found in snake venoms (e.g. rattlesnakes) and lizard venoms (e.g. Mexican beaded lizard). This involves a non-enzymatic mechanism that leads to severe muscle necrosis. These peptides act very quickly, causing i ...

s. 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%. Treatment is the same for all Australian

venomous snake ''Venomous snakes'' are species of the suborder Serpentes that are capable of producing venom, which they use for killing prey, for defense, and to assist with digestion of their prey. The venom is typically delivered by injection using hollow ...

s. 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. The venom yield is , while the lethal dose for humans is .

Conservation

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

References

External links

Information on bites from survivaliq.comInformation on the genus from snakeshow.netMainland Tiger Snake - Australian Reptile Park
*Integrated Taxonomic Information System
Notechis
{{Taxonbar, from1=Q1520949, from2=Q169658, from3=Q1496170 Elapidae Reptiles of Western Australia Venomous snakes Reptiles described in 1861 Taxa named by Wilhelm Peters Snakes of Australia Reptiles of Victoria (state)