Tiger snake

Identification

The tiger snake is a robust, muscular snake whose colour varies greatly between and within populations^1,2. The best-known form is dark olive-brown to blackish with off-white to yellowish crossbands of varying width, but some individuals have no bands and range from yellowish-brown or sandy grey to jet black^1,2. The belly is usually pale yellow, white or grey, and the broad, blunt head is only slightly wider than the neck^1,2. When threatened it can flatten its neck and forebody, showing black skin between the large, smooth, semi-glossy scales^1,3. Mainland adults average about 1.2 m long and can reach 2.1 m, while island populations range from about 1 m on Roxby Island to 2.4 m on Chappell Island in Bass Strait¹. Males grow larger than females^1,2.

Distribution

Tiger snakes are found only in Australia, in two separate regions: the south-east, including Tasmania and the Bass Strait islands, and the far south-west^1,3. They also live on many offshore islands, from Carnac and Garden islands off Western Australia to Kangaroo Island and the islands of Bass Strait¹. Their patchy range is the result of a drying climate and of rising seas that cut islands off from the mainland in the past 6,000–10,000 years¹. The black tiger snake, once called Notechis ater, was merged into N. scutatus in 2005, and the island and regional forms are now treated as variants of one highly variable species^1,3.

Habitat

Tiger snakes are often found near water, such as creeks, dams, drains, lagoons, wetlands and swamps¹. They also live on grazing land and in other heavily changed areas where there is water and cover, and in Tasmania they occur in most habitats, from dry rocky areas to wet marshes^1,2. They shelter under fallen timber, in thick matted vegetation and in old animal burrows¹. They range from sea level to over 1,000 m in Tasmania¹.

Behaviour

Tiger snakes are mostly active by day but will forage on warm evenings¹. They are good climbers, recorded up to 10 m above the ground, and can stay underwater for at least 9 minutes¹. In cool weather they retreat to burrows, under boulders or into dead trees, sometimes 1.2 m underground, and up to 26 young snakes have been found sharing one winter shelter^1,2. They are normally timid and usually retreat when a person approaches². If threatened, a tiger snake flattens its neck, raises its head and may make a mock strike with an explosive hiss, and like most snakes it will not bite unless provoked².

Diet

Tiger snakes have a broad diet of frogs and tadpoles, fish, lizards, birds and mammals, and they also eat carrion¹. They often raid birds’ nests and readily enter the burrows of mice, rats and rabbits². Prey is quickly subdued by the venom, sometimes with the help of constriction^1,2. On Chappell Island, where they feed on muttonbird chicks, tiger snakes grow up to 2.4 m long, while on Roxby Island, with no nesting seabirds, they reach only about 1 m¹.

Reproduction

Tiger snakes give birth to live young^1,3. At the start of the breeding season males fight, each trying to press down the other’s head, and in Tasmania mating can last up to seven hours^1,2. In south-western Australia, litters of 10 to 64 young are born between late summer and mid-autumn, and a litter of 126 young has been recorded^1,2. The newborn snakes are 21.5–27 cm long and receive no parental care, and females breed at most every second year².

Venom and medical significance

The World Health Organization places the tiger snake in its highest category of medical importance in Australia⁶. Its venom mainly affects the nerves and blood clotting, and it can also break down muscle, which can lead to kidney failure^1,2. In 56 confirmed tiger snake envenomings, nearly all patients lost the ability to clot their blood normally, 17 developed paralysis, 11 had muscle damage and three developed kidney failure⁴. From 2005 to 2015, tiger snakes caused 17% of confirmed envenomings recorded by the Australian Snakebite Project and four of the 23 deaths⁵. Tiger snake antivenom is used to treat these bites, and one vial appears to bind all the venom in the blood⁴. Anyone bitten should go to hospital immediately.

Conservation

The tiger snake is listed as Least Concern on the IUCN Red List, based on an assessment published in 2018⁷. Some isolated populations have been listed as vulnerable, including the Flinders Ranges population and the Chappell Island population in Tasmania¹. Some island populations could decline if muttonbird colonies are disturbed². Tiger snakes are legally protected in Tasmania and New South Wales, but many are still killed deliberately or on roads^1,2,8.

Similar species

Large banded tiger snakes are fairly distinctive, but they can be confused with banded eastern brown snakes (Pseudonaja textilis), which have a divided anal scale and paired scales under the tail, whereas a tiger snake’s are single^1,10. Unbanded tiger snakes can resemble copperheads (Austrelaps) and black snakes (Pseudechis), and in Tasmania tiger snakes and copperheads overlap in size, habitat and behaviour^1,2. On Kangaroo Island some tiger snakes have reddish bellies and have been mistaken for red-bellied black snakes (Pseudechis porphyriacus)¹. Young tiger snakes can look like rough-scaled snakes (Tropidechis carinatus) or Stephens’ banded snakes (Hoplocephalus stephensii)¹. These differences are not a safe basis for handling any snake. Keep your distance from every snake you cannot identify.

In captivity

The tiger snake is dangerously venomous and is not suitable as a pet. In New South Wales, all native reptiles are protected, and keeping venomous species requires an advanced reptile keeper licence and references confirming experience in handling them^8,9.