The inland taipan (Oxyuranus microlepidotus), also commonly known as the western taipan, small-scaled snake, or fierce snake, is a species of extremely venomous snake in the family Elapidae. It is endemic to semiarid regions of central‑eastern Australia. Aboriginal Australians living in areas where Karnic languages are spoken refer to this species as dandarabilla.

The species was formally described by Frederick McCoy in 1879 and William John Macleay in 1882, but for almost 90 years it remained poorly known to science: no additional specimens were collected and virtually nothing was added to knowledge of its biology until the species was rediscovered in 1972.

Based on the median lethal dose (LD<sub>50</sub>) of its venom in laboratory mice, the inland taipan is widely regarded as the most venomous snake in the world; its venom is substantially more toxic, drop for drop, than that of any tested sea snake. It is also considered to possess the most toxic venom of any reptile when tested on human heart cell cultures. The inland taipan is a specialised predator of mammals, and its venom is particularly adapted to killing warm-blooded prey. A single bite has been estimated to contain sufficient venom to kill more than 100 adult humans.

Despite this extreme potency, the inland taipan is usually shy and reclusive, with a generally placid disposition, and it rarely comes into contact with people because it inhabits remote areas. By contrast, the coastal taipan (Oxyuranus scutellatus) is often considered the more dangerous species in practice, largely because of its behaviour when it encounters humans and its proximity to populated coastal regions. The word "fierce" in one of the inland taipan's common names refers to the strength of its venom rather than its temperament.

Taxonomy

Among the Aboriginal people from the area now known as Goyder Lagoon in north‑eastern South Australia, the inland taipan was traditionally known as dandarabilla.

The current binomial name of the inland taipan has therefore been Oxyuranus microlepidotus since the early 1980s. The specific epithet microlepidotus is from Latin and means "small‑scaled", referring to the small body scales, and is the origin of the common name "small‑scaled snake".

Once Covacevich et al. (1981) had shown that the fierce snake (formerly Parademansia microlepidota) belonged to the genus Oxyuranus, the name "taipan" (derived from the Aboriginal term dhayban) was retained for O. scutellatus, which became known as the coastal taipan (or "eastern taipan"), while O. microlepidotus came to be widely referred to as the "inland taipan" (also "western taipan").

In Queensland the species has been recorded from the Channel Country bioregion, including Diamantina National Park, Durrie Station, Morney Plains Station and Astrebla Downs National Park. In South Australia it has been observed in the Marree–Innamincka NRM district, including Goyder Lagoon, the Tirari Desert, Sturt Stony Desert, Coongie Lakes, Innamincka Regional Reserve and near Oodnadatta. An isolated population is also known from near Coober Pedy, South Australia.

Two historical records exist from further south‑east, at the junction of the Murray and Darling Rivers in north‑western Victoria (1879) and near Bourke, New South Wales (1882), but the species has not been recorded from either state since the late 19th century. The species was assessed for the IUCN Red List for the first time in July 2017, and in 2018 it was listed as Least Concern. The assessment notes that the species is widespread within its range and is not thought to be in overall decline, although the potential impacts of threats require further investigation and may be locally significant.

South Australia: listed as "Least Concern" within the Outback region.

New South Wales: listed as presumed Extinct on the basis that it has not been recorded in suitable habitat despite targeted surveys conducted over an appropriate timeframe for the species’ life cycle.

Victoria: listed as Regionally Extinct, meaning that exhaustive surveys in all suitable habitats within Victoria have failed to locate the species, even though it still occurs elsewhere within its global range. The Australian Museum likewise lists the inland taipan as "presumed extinct" in Victoria. the Australian Reptile Park, Billabong Sanctuary, Lone Pine Koala Sanctuary and Shoalhaven Zoo.

Outside Australia, inland taipans are kept in several North American zoos, including Reptile Gardens in South Dakota, Kentucky Reptile Zoo and Animal World & Snake Farm Zoo in Texas.

In Europe the species is held at the Stockholm Skansen Zoo and Gothenburg Universeum in Sweden, at Moscow Zoo in Russia, and at the London Zoo in the United Kingdom. Various smaller facilities and private collections in continental Europe also maintain the species.

In Asia inland taipans are held at Singapore Zoo, where they have been the subject of detailed veterinary case reports.

Private ownership law

In the Australian state of New South Wales, private ownership of an inland taipan is legal only for keepers who hold the highest class of venomous reptile licence, reflecting the very high risk associated with the species.

Description

thumb|200px|right|Brown‑coloured (winter) thumb|200px|right|Olive‑coloured (summer)

The inland taipan is typically dark tan in overall colour, varying from a rich, dark brown to a brownish light green depending on season. The back, flanks and tail may show various shades of brown and grey. Many dorsal scales have broad blackish margins which, because the scales are arranged in diagonal rows, align to form broken chevron‑like markings that slope backwards and downwards. The lowermost lateral scales frequently have a yellowish anterior edge. The dorsal scales are smooth and lack keels.

The rounded snout, head and neck are usually noticeably darker than the body – glossy black in winter and dark brown in summer. This darker pigmentation is thought to assist thermoregulation by allowing the snake to absorb heat while exposing only a small portion of the body at the entrance of a burrow. The eyes are of moderate size with dark brown to blackish irises and without a distinct pale ring around the pupil.

The species has 23 rows of dorsal scales at mid‑body, 55–70 divided subcaudal scales, and a single anal scale. The average total length is about , although larger individuals can attain . The fangs measure approximately 3.5–6.2 mm, somewhat shorter than those of the coastal taipan. particularly rodents such as the long-haired rat (Rattus villosissimus), plains rat (Pseudomys australis), the introduced house mouse (Mus musculus), and various dasyurid marsupials. In captivity the species will also take day‑old chicks.

Natural threats

The inland taipan has few natural predators as an adult, but juveniles are vulnerable. The mulga snake (Pseudechis australis) is resistant to the venom of many Australian snakes and has been documented preying on young inland taipans. The large monitor lizard perentie (Varanus giganteus) shares much of the inland taipan's habitat and, once large enough, readily preys on venomous snakes, including taipans.

Interaction with humans

Many experienced reptile keepers consider the inland taipan to be comparatively placid to handle, at least in controlled conditions, Nevertheless, a safe distance must always be maintained because any bite is a medical emergency.

When threatened the inland taipan will usually attempt escape, but if it is cornered, provoked, mishandled or prevented from fleeing, it will adopt a characteristic threat posture in which the anterior body is raised in a tight, low S‑shaped curve with the head oriented towards the source of danger. If the warning is ignored it may strike with great speed and precision, and it envenoms in the vast majority of bites.

Clinical toxicologist, venom researcher and herpetologist Scott A. Weinstein and colleagues have noted that only a small number of inland taipan bites have been documented in the medical literature. In an analysis published in Toxicon they reported 11 well‑documented cases of envenoming, only two of which were inflicted by wild snakes. They emphasised that, when indicated, early administration of adequate antivenom, combined with rapid pressure‑immobilisation first aid and efficient retrieval of victims from remote locations (preferably by well‑equipped aircraft), is central to achieving favourable outcomes.

Snakebite victims

Most confirmed inland taipan bites have involved herpetologists, professional snake handlers, venom extractors or zoo keepers. Since the introduction of specific taipan antivenom, no deaths have been conclusively attributed to inland taipan bites, although recovery can be prolonged and complications may be severe.

A notable early case of survival without antivenom was recorded in 1967. On 15 September a tour guide was bitten while attempting to capture a snake for a tour group in the Channel Country. He was transported to Broken Hill Hospital and subsequently to Queen Elizabeth Hospital in Adelaide. Because he reported a severe allergy to horse serum and believed he had been bitten by a brown snake, antivenom was not administered. He was hospitalised for four weeks with a clinical picture likened to severe myasthenia gravis. The snake itself was initially identified by Eric Worrell as a coastal taipan, but following the species’ rediscovery it was recognised as an inland taipan.

In September 2012 a teenage boy in Kurri Kurri, New South Wales, more than from the species’ natural range, was bitten on the finger by an inland taipan being kept illegally in captivity. The victim applied a compression bandage promptly and was treated with polyvalent antivenom at the local hospital, surviving without major sequelae.

In December 2013 reptile handler Scott Grant was bitten while demonstrating an inland taipan at a public event in Portland, Victoria. He applied a bandage and sought urgent medical care. He experienced convulsions and was airlifted in a serious condition to Royal Melbourne Hospital, where he was stabilised and ultimately recovered. Only a small amount of venom appears to have been injected, and some of his early symptoms were attributed to an allergic reaction, likely related to his history of multiple previous snake bites.

Weinstein et al. (2017) described a case in which a field herpetologist was bitten while attempting to photograph an approximately inland taipan in remote outback South Australia. The victim developed drowsiness, blurred vision progressing to ptosis, followed by dysphagia and dysarthria. He received one vial of polyvalent antivenom followed by two vials of monovalent taipan antivenom, required intubation and three days of intensive care, and experienced a unilateral ophthalmoplegia that persisted for about one week before resolving.

Venom

The average venom yield per bite of an adult inland taipan has been estimated at about 44 mg, with a recorded maximum of 110 mg. For comparison, typical yields for the Indian cobra (Naja naja) are around 169 mg (maximum 610 mg), and for the North American eastern diamondback rattlesnake (Crotalus adamanteus) about 410 mg (maximum 848 mg).

The median lethal dose (LD<sub>50</sub>) of inland taipan venom in mice, administered subcutaneously – the route most relevant to typical snake bites – is approximately 0.025 mg/kg, This is markedly lower (i.e. more toxic) than values reported for many other dangerously venomous snakes, including the beaked sea snake (Enhydrina schistosa; 0.164 mg/kg), Indian cobra (0.565 mg/kg) and eastern diamondback rattlesnake (11.4 mg/kg). A single bite is estimated to contain enough venom to kill at least 100 adult humans.

Intravenous, intraperitoneal and intramuscular LD<sub>50</sub> values for inland taipan venom have not been systematically determined in the published literature.

For many years Belcher's sea snake (Hydrophis belcheri) was popularly but erroneously described as the most venomous snake, largely because toxicity data from different modes of administration were conflated in a widely read book, Snakes in Question: The Smithsonian Answer Book (1996). Venom researcher Bryan Grieg Fry has pointed out that LD<sub>50</sub> values can only be meaningfully compared when determined using the same route of administration; otherwise comparisons are invalid. Belcher's sea snake venom, tested intramuscularly, has reported LD<sub>50</sub> values of 0.24 mg/kg and 0.155 mg/kg,

The venom of the inland taipan contains a complex mixture of toxins, including: alpha-oxytoxin 1 and alpha-scutoxin 1,

Hemotoxins with strong procoagulant activity, affecting blood clotting;

Myotoxins that damage muscle tissue;

possibly nephrotoxins, affecting the kidneys;

possibly haemorrhagins, which damage the vascular endothelium;

the enzyme hyaluronidase, which facilitates rapid spread of venom through tissues.

severe envenoming is likely after a significant bite;

the rate of systemic envenoming is estimated at more than 80%;

the untreated case fatality rate is also thought to exceed 80%. Early local symptoms include pain at the bite site, often followed by nonspecific systemic features such as headache, nausea, vomiting, abdominal pain, diarrhoea, dizziness, collapse or convulsions. Major complications then develop, including progressive neurotoxicity, coagulopathy, muscle breakdown and renal impairment, which without treatment can culminate in death. Clinically, patients often develop a descending flaccid paralysis: early ptosis is followed by facial weakness (dysarthria), bulbar involvement, dyspnoea and ultimately respiratory paralysis and peripheral weakness. Once advanced general or respiratory paralysis has developed it may be difficult to reverse even with large doses of antivenom; prolonged intubation and mechanical ventilation—sometimes for a week or more—may be required. Early recognition of neurotoxic signs and prompt administration of adequate antivenom are therefore critical.

Common proximate causes of death in untreated or inadequately treated bites include: is also effective against inland taipan venom, although some evidence suggests that it may be somewhat less effective in inland taipan cases than in bites from coastal taipans, possibly because of differences in venom composition.

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 (Taylor and Francis, printers). xiv + 727 pp. + Plates I–XXV. (Pseudechis microlepidotus and P. ferox, p. 332).
  • McCoy F (1879). Natural History of Victoria. Prodromus of the Zoology of Victoria; or, Figures and Descriptions of the Living Species of All Classes of the Victorian Indigenous Animals. Decade III. London: G. Robertson (J. Ferres, government printer, Melbourne). 50 pp. + Plates 21–30. (Diemenia microlepidota, new species, pp. 12–13 + Plate 23, figures 2–3).
  • a new window International Programme on Chemical Safety, Oxyuranus microlepidotus: extended review
  • a new window James Cook University, Proteomic and genomic characterisation of venom proteins from Oxyuranus species (extended review)
  • a new window Australian Reptile Park, fierce snake fact file
  • a new window Australia Zoo, fierce snake fact file
  • (ContentMint; source: a new window Absolutely Wild Visuals stock footage library)