Inland Taipan

## Description

The inland taipan (Oxyuranus microlepidotus ), also commonly known as the western taipan, the small-scaled snake or the fierce snake, is a species of extremely venomous snake in the family Elapidae. The species is endemic to semi-arid regions of central east Australia. Aboriginal Australians living in those regions named the snake dandarabilla. It was first described by Frederick McCoy in 1879 and then by William John Macleay in 1882, but for the next 90 years it was a mystery to the scientific community; no further specimens were found, and virtually nothing was added to the knowledge of this species until its rediscovery in 1972.

Based on the median lethal dose value in mice, the venom of the inland taipan is by far the most toxic of any snake – much more so than even that of sea snakes – and it has the most toxic venom of any reptile when tested on human heart cell culture. The inland taipan is a specialist hunter of mammals, so its venom is specially adapted to kill warm-blooded species. It is estimated that one bite possesses enough lethality to kill at least 100 fully grown humans. It is an extremely fast and agile snake that can strike instantly with extreme accuracy, often striking multiple times in the same attack, and it envenomates in almost every case.

Although the most venomous and a capable striker, in contrast to the coastal taipan which many experts cite as an extremely dangerous snake due to its behavior when it encounters humans, the inland taipan is usually a quite shy and reclusive snake, with a placid disposition, and prefers to escape from trouble. However, it will defend itself and strike if provoked, mishandled, or prevented from escaping. Because it lives in such remote locations, the inland taipan seldom comes in contact with people; therefore it is not considered the deadliest snake in the world overall, especially in terms of disposition and human deaths per year. The word "fierce" from its alternative name describes its venom, not its temperament.

## Appearance

The Inland taipan is an extremely venomous snake native to central east Australia. This snake is dark tan in color, ranging from a rich, dark hue to a brownish light-green, depending on the season. Its back, sides, and tail may be different shades of brown and grey, with many scales having a wide blackish edge. These dark-marked scales occur in diagonal rows so that the marks align to form broken chevrons of variable length that are inclined backward and downward. The lowermost lateral scales often have an anterior yellow edge. The dorsal scales are smooth and without keels. The round-snouted head and neck are usually noticeably darker than the body (glossy black in winter, dark brown in summer), the darker color allowing the snake to heat itself while exposing only a smaller portion of the body at the burrow entrance. The eye is of average size with a blackish-brown iris and without a noticeable colored rim around the pupil.

## Distribution

Inland taipans occur in the semi-arid regions where Queensland and South Australia borders converge. In Queensland, they have been observed in Channel Country region (e.g., Diamantina National Park, Durrie Station, Morney Plains Station and Astrebla Downs National Park) and in South Australia, these snakes have been observed in the Marree-Innamincka NRM District (e.g., Goyder Lagoon Tirari Desert, Sturt Stony Desert, Coongie Lakes, Innamincka Regional Reserve, and Oodnadatta). An isolated population also occurs near Coober Pedy, South Australia. Inland taipans inhabit the black soil plains or floodplains, and gibber plains.

## Behavior

Inland taipans are solitary and diurnal creatures. They are most active in the early morning, spending their time basking in the sun and foraging. The rest part of the day they spend in shelters. In cooler days they may also be seen in the afternoon. Inland taipans adapt to their environment by changing the color of the skin during seasonal changes. They tend to become lighter during summer and darker during the winter. This seasonal color change serves the purpose of thermoregulation, allowing the snake to absorb more light in the colder months. Although extremely venomous and capable strikers, Inland taipans are usually quite shy and reclusive snakes and prefer to escape from trouble. However, they will defend themselves and strike if provoked, mishandled, or prevented from escaping. Because they live in such remote locations, Inland taipans seldom come in contact with people.

## Venom

The average quantity of venom delivered by this species is 44 mg and the maximum dose recorded is 110 mg, compared to the Indian cobra (Naja naja ) 169 mg/max 610 mg, and the North American eastern diamondback rattlesnake (Crotalus adamanteus ) 410 mg/max 848 mg etc.

The median lethal dose (LD50), subcutaneous (the most applicable to actual bites) for mice is 0.025 mg/kg (0.01 mg/kg subcutaneous, in bovine serum albumin). Compared to the beaked sea snake (Enhydrina schistosa ) 0.164 mg/kg, Indian cobra 0.565 mg/kg, North American eastern diamondback rattlesnake 11.4 mg/kg, etc., the inland taipan has a smaller venom yield than its cousin the coastal taipan yet its venom is almost four times as toxic. One bite's worth of venom is enough to kill 100 fully grown men.

Intravenous, intraperitoneal and intramuscular LD50 for the inland taipan venom have not been tested.

Belcher's sea snake (Hydrophis belcheri ), which many times is mistakenly called the hook-nosed sea snake (Enhydrina schistosa ), has been erroneously popularized as the most venomous snake in the world, due to Ernst and Zug's published book Snakes in Question: The Smithsonian Answer Book from 1996. Bryan Grieg Fry, a prominent venom expert, has clarified the error: "The hook-nosed myth was due to a fundamental error in a book called Snakes in Question. In there, all the toxicity testing results were lumped in together, regardless of the mode of testing (e.g. subcutaneous vs. intramuscular vs intravenous vs intraperitoneal). As the mode can influence the relative number, venoms can only be compared within a mode. Otherwise, it's apples and rocks." Belcher's sea snake's actual LD50 (recorded only intramuscularly) is 0.24 mg/kg and 0.155 mg/kg, less lethal than other sea snakes such as the olive sea snake (Aipysurus laevis ) 0.09 mg/kg and the most toxic intramuscularly, recorded of the sea snakes – the black-banded robust sea snake (Hydrophis melanosoma ) 0.082 mg/kg. The black-banded robust sea snake has also been tested subcutaneously registering at 0.111 mg/kg, which is in line with the coastal taipan and thus more than four times less toxic than the inland taipan's venom. In the LD50 subcutaneous test, it is actually Dubois' sea snake (Aipysurus duboisii ) which has the most toxic venom of any of the sea snakes tested, registering at 0.044 mg/kg. This is still nearly half as lethal as the inland taipan's venom.

The biological properties and toxicity of a baby inland taipan's venom are not significantly different or weaker than that of an adult's.

The inland taipan's venom consists of:

* Neurotoxins: Presynaptic neurotoxins; paradoxin (PDX), and postsynaptic neurotoxins; Oxylepitoxin-1, alpha-oxytoxin 1, alpha-scutoxin 1 – affecting the nervous system.
* Hemotoxins ( procoagulants) – affecting the blood
* Myotoxins – affecting the muscles
* Possibly nephrotoxins – affecting the kidneys
* Possibly haemorrhagins – affecting the blood vessels ( endothelium)
* Hyaluronidase enzyme – increases the rate of absorption of venom

Paradoxin (PDX) appears to be one of the most potent, if not the most potent, beta-neurotoxin yet discovered. Beta-neurotoxins keep nerve endings from liberating the neurotransmitter acetylcholine.

According to researcher Ronelle Welton of James Cook University, the majority of components in the venom have not been characterized and little molecular research has been undertaken on taipan (*Oxyuranus* ) species at large. As of 2005, the amino acid sequences of only seven proteins from inland taipan have been submitted to SWISS-PROT databases.

## Diet

Inland taipans are carnivores. They consume only mammals, mostly rodents, such as the long-haired rat, the plains rat, and the introduced house mouse.

## Reproduction

The reproduction rate of Inland taipans depends in part on their diet: if there is not enough food, then these snakes will reproduce less. Females lay between 12-24 eggs in abandoned animal burrows and deep crevices. The eggs hatch two months later. In captivity, males reach reproductive maturity at 16 months of age and females become reproductively mature when they are 28 months old.

## Population

### Population threats

Main threats to Inland taipans include habitat loss and degradation. These snakes also suffer from the loss of their main food source, rodents. This happens mainly because of predation by non-native predators including cats and foxes.

### Population number

The IUCN Red List and other sources don’t provide the number of the Inland taipan total population size. Currently, this species is classified as Least Concern (LC) on the IUCN Red List.

## Fun Facts for Kids

Aboriginal Australians living in regions of central east Australia named Inland taipans Dandarabilla.

Unlike most snakes, the Inland taipan is a specialist hunter of mammals so its venom is specially adapted to kill warm-blooded species. It is estimated that one bite possesses enough lethality to kill at least 100 fully grown men, and, depending on the nature of the bite, it has the potential to kill someone in as little as 30-45 minutes if left untreated.

The Inland taipan is an extremely fast and agile snake that can strike instantly with extreme accuracy, often striking multiple times in the same attack.

The word "fierce" from the alternative name of the Inland taipan describes its venom, not its temperament.