Eastern Brown Snake

## Description

The eastern brown snake (Pseudonaja textilis ), often referred to as the common brown snake, is a species of highly venomous snake in the family Elapidae. The species is native to eastern and central Australia and southern New Guinea. It was first described by André Marie Constant Duméril, Gabriel Bibron, and Auguste Duméril in 1854. The adult eastern brown snake has a slender build and can grow to 2 m (7 ft) in length. The colour of its surface ranges from pale brown to black, while its underside is pale cream-yellow, often with orange or grey splotches. The eastern brown snake is found in most habitats except dense forests, often in farmland and on the outskirts of urban areas, as such places are populated by its main prey, the house mouse. The species is oviparous. The International Union for Conservation of Nature classifies the snake as a least-concern species, though its status in New Guinea is unclear.

Considered the world's second-most venomous land snake after the inland taipan (*Oxyuranus microlepidotus* ), based on its LD50 value (subcutaneous) in mice, it is responsible for about 60% of human snake-bite deaths in Australia. The main effects of its venom are on the circulatory system—coagulopathy, haemorrhage (bleeding), cardiovascular collapse, and cardiac arrest. One of the main components of the venom is the prothrombinase complex pseutarin-C, which breaks down prothrombin.

## Appearance

The Eastern brown snake is a highly venomous snake native to eastern and central Australia and southern New Guinea. They are variable in color. Their upper parts range from pale to dark brown, or sometimes shades of orange or russet. Eastern brown snakes from Merauke have tan to olive upperparts, while those from eastern Papua New Guinea are very dark grey-brown to blackish. The tongue of these snakes is dark, and the irises are blackish with a paler yellow-brown or orange ring around the pupil. Their chin and underparts are cream or pale yellow, sometimes fading to brown or grey-brown towards the tail. Often, orange, brown, or dark grey blotches occur on the underparts. The ventral scales are often edged with dark brown on their posterior edges.

## Distribution

Eastern brown snakes are found along the east coast of Australia, from Malanda in far north Queensland, along the coasts and inland ranges of Queensland, New South Wales, Victoria, and to the Yorke Peninsula in South Australia. Disjunct populations occur on the Barkly Tableland and the MacDonnell Ranges in the Northern Territory and the far east of the Kimberley in Western Australia, and discontinuously in parts of New Guinea, specifically northern Milne Bay Province and Central Province in Papua New Guinea, and the Merauke region of Papua Province, in the Indonesian part of New Guinea. They are common in southeastern Queensland between Ipswich and Beenleigh. These snakes live in different habitats from dry sclerophyll forests (eucalypt forests) and heaths of coastal ranges, through to savannah woodlands, inner grasslands, and arid scrublands and farmland, as well as drier areas that are intermittently flooded. They are more common in open habitat and also farmland and the outskirts of urban areas. They are not found in rainforests or other wet areas. Because of their mainly rodent diet, they can often be found near houses and farms. Such areas also provide shelter in the form of rubbish and another cover; the snakes use sheets of corrugated iron or buildings as hiding spots, as well as large rocks, burrows, and cracks in the ground.

## Behavior

Eastern brown snakes generally solitary, with females and younger males avoiding adult males. They are active during the day, though they may retire in the heat of hot days to come out again in the late afternoon. Eastern brown snakes hunt by sight more than other snakes, and a foraging snake raises its head like a periscope every so often to survey the landscape for prey. These snakes generally find their food source in their refuges rather than chasing fleeing prey. Adults generally hunt during the day, while juveniles sometimes hunt at night. Eastern brown snakes rarely eat during winter, and females rarely eat while pregnant with eggs. These snakes are most active in spring, the males venturing out earlier in the season than females, and are sometimes active on warm winter days. The occasional nocturnal activity has been reported. At night, they retire to a crack in the soil or burrow that has been used by a House mouse. During winter, they hibernate, emerging on warm days to sunbathe. Many people mistake defensive displays of these snakes for aggression. When confronted, Eastern brown snakes react with one of two neck displays. During a partial display, the snake raises the front part of its body horizontally just off the ground, flattening its neck and sometimes opening its mouth. In a full display, the snake rises up vertically high off the ground, coiling its neck into an S shape, and opening its mouth. The snake can strike more accurately from a full display and more likely to deliver an envenomed bite.

## Venom

The eastern brown snake is considered the second-most venomous terrestrial snake in the world, behind only the inland taipan (Oxyuranus microlepidotus ) of central east Australia. Responsible for more deaths from snakebite in Australia than any other species, it is the most commonly encountered dangerous snake in Adelaide, and is also found in Melbourne, Canberra, Sydney, and Brisbane. As a genus, brown snakes were responsible for 41% of identified snakebite victims in Australia between 2005 and 2015, and for 15 of the 19 deaths during this period. Within the genus, the eastern brown snake is the species most commonly implicated. It is classified as a snake of medical importance by the World Health Organization.

Clinically, the venom of the eastern brown snake causes venom-induced consumption coagulopathy; a third of cases develop serious systemic envenoming including hypotension and collapse, thrombotic microangiopathy, severe haemorrhage, and cardiac arrest. Other common systemic symptoms include nausea and vomiting, diaphoresis (sweating), and abdominal pain. Acute kidney injury and seizures can also occur. Onset of symptoms can be rapid, with a headache developing in 15 minutes and clotting abnormalities within 30 minutes; collapse has been recorded as occurring as little as two minutes after being bitten. Death is due to cardiovascular causes such as cardiac arrest or intracranial haemorrhage. Often, little local reaction occurs at the site of the bite. The classical appearance is of two fangmarks around 1 cm apart. Neurotoxicity is rare and generally mild, and myotoxicity (rhabdomyolysis) has not been reported.

The eastern brown snake yields an average of under 5 mg of venom per milking, less than other dangerous Australian snakes. The volume of venom produced is largely dependent on the size of the snake, with larger snakes producing more venom; Queensland eastern brown snakes produced over triple the average amount of venom (11 mg vs 3 mg) than those from South Australia. Worrell reported a milking of 41.4 mg from a relatively large 2.1-m (6.9-ft) specimen. The venom has a murine median lethal dose (LD50) has been measured at 41 μg/kg—when using 0.1% bovine serum albumin in saline rather than saline alone—to 53 μg/kg when administered subcutaneously. While the lethal dose for humans is just 3 mg. The composition of venom of captive snakes did not differ from that of wild snakes.

The eastern brown snake's venom contains coagulation factors VF5a and VF10, which together form the prothrombinase complex pseutarin-C. This cleaves prothrombin at two sites, converting it to thrombin. Pseutarin-C is a procoagulant in the laboratory, but ultimately an anticoagulant in snakebite victims, as the prothrombin is used up and coagulopathy and spontaneous bleeding set in. Another agent, textilinin, is a Kunitz-like serine protease inhibitor that selectively and reversibly inhibits plasmin. A 2006 study comparing the venom components of eastern brown snakes from Queensland with those from South Australia found that the former had a stronger procoagulant effect and greater antiplasmin activity of textilinin.

The venom also contains pre- and postsynaptic neurotoxins; textilotoxin is a presynaptic neurotoxin, at one stage considered the most potent recovered from any land snake. Making up 3% of the crude venom by weight, it is composed of six subunits. Existing in two forms, the venom weighs 83,770 ± 22 daltons (TxI) and about 87,000 daltons (TxII), respectively. Textilotoxin is a type of phospholipase A2, a group of enzymes with diverse effects that are commonly found in snake venoms. At least two further phospholipase A2 enzymes have been found in eastern brown snake venom. Two postsynaptic neurotoxins have been labelled pseudonajatoxin a and pseudonajatoxin b. These are three-finger toxins, a superfamily of proteins found in the venom of many elapid snakes and responsible for neurotoxic effects. Another three-finger toxin was identified in eastern brown snake venom in 2015. Professor Bart Currie coined the term ‘brown snake paradox' in 2000 to query why neurotoxic effects were rare or mild despite the presence of textilotoxin in eastern brown snake venom. This is thought to be due to the low concentration of the toxin in the venom, which is injected in only small amounts compared with other snake species.

Analysis of venom in 2016 found—unlike most other snake species—that the venom of juvenile eastern brown snakes differed from that of adults; prothrombinases (found in adults) were absent and the venom did not affect clotting times. Snakes found with a similar profile generally preyed upon dormant animals such as skinks.

The eastern brown snake is the second-most commonly reported species responsible for envenoming of dogs in New South Wales. Dogs and cats are much more likely than people to have neurotoxic symptoms such as weakness or paralysis. One dog bitten suffered a massive haemorrhage of the respiratory tract requiring euthanasia. The venom is uniformly toxic to warm-blooded vertebrates, yet reptile species differ markedly in their susceptibility.

## Diet

Eastern brown snakes are carnivores. Their diet is made up almost wholly of vertebrates, with mammals predominating - particularly the introduced House mouse. Mammals as large as feral rabbits have been eaten. Small birds, eggs, and even other snakes are also consumed.

## Reproduction

Eastern brown snakes are polygynous which means that one males mates with several females. They generally mate from early October onwards - during the Southern Hemisphere spring. These snakes are oviparous meaning that they lay eggs. During the mating season, males engage in ritual combat with other males for access to females. The appearance of two males wrestling has been likened to a pleated rope. The most dominant male will mate with females in the area. The females produce a clutch of 10 to 35 eggs, with the eggs typically weighing 8.0 g (0.28 oz) each. The eggs are laid in a sheltered spot, such as a burrow or hollow inside a tree stump or rotting log. Multiple females may even use the same location, such as a rabbit warren. Ambient temperature influences the rate at which eggs develop; eggs incubated at 25 °C (77 °F) hatch after 95 days, while those at 30 °C (86 °F) hatch after 36 days. Snakelets are born fully developed. They are independent at hatching and can reach reproductive maturity by 31 months of age.

## Population

### Population threats

There are no major threats facing Eastern brown snakes at present.

### Population number

According to IUCN, the Eastern brown snake is locally common and widespread throughout its range but no overall population estimate is available. Currently, this species is classified as Least Concern (LC) on the IUCN Red List and its numbers today are stable.

## Fun Facts for Kids

The Eastern brown snake is considered the second-most venomous terrestrial snake in the world, behind only the Inland taipan of central east Australia. It is responsible for about 60% of snake-bite deaths in Australia.

Eastern brown snakes are not only very aggressive, but they are also very fast. Australian naturalist David Fleay reported that these snakes could outpace a person running at full speed.

Eastern brown snakes are available in Australia via breeding in captivity. They are regarded as challenging to keep, and due to the snakes' speed and toxicity, suitable for only experienced snake keepers.