Red-bellied black snake

Venomous snake native to eastern Australia
the snake native to Australia

The red bellied black snake (Pseudechis porphyriacus) is a species of venomous snake in the family Elapidae, indigenous to Australia. Originally described by George Shaw in 1794 as a species new to science, it is one of eastern Australia's most commonly encountered snakes. Averaging around in length, it has glossy black upperparts, bright red or orange flanks, and a pink or dull red belly. It is not aggressive and generally retreats from human encounters, but can attack if provoked. Although its venom can cause significant illness, no deaths have been recorded from its bite, which is less venomous than other Australian elapid snakes. The venom contains neurotoxins, myotoxins, and coagulants and has haemolytic properties. Victims can also lose their sense of smell. Common in woodlands, forests, swamplands, along river banks and waterways the red bellied black snake often ventures into nearby urban areas. It forages in bodies of shallow water, commonly with tangles of water plants and logs, where it hunts its main prey item, frogs, as well as fish, reptiles, and small mammals. The snake is a least concern species according to the IUCN, but its numbers are thought to be declining due to habitat fragmentation and decline of frog populations.

The red bellied black snake was first described and named by English naturalist George Shaw in Zoology of New Holland (1794) as Coluber porphyriacus. The species name is derived from the Greek porphyrous, which can mean "dark purple", "red purple" or "beauteous". It was the first Australian elapid snake described. The syntype is presumed lost. His countryman René Lesson described it as Acanthophis tortor in 1826. German biologist Hermann Schlegel felt it was allied with cobras and called it Naja porphyrica in 1837. The genus Pseudechis was created for this species by German biologist Johann Georg Wagler in 1830; several more species have been added to the genus subsequently. The name is derived from the Greek words pseudēs "false", and echis "viper". Snake expert Eric Worrell, in 1961, analysed the skulls of the genus and found that of the red bellied black snake to be the most divergent. Its position as an early offshoot from the rest of the genus has been confirmed genetically in 2017. In addition to red bellied black snake, the species has been called common black snake, redbelly, and RBBS. It was known as djirrabidi to the Eora and Darug inhabitants of the Sydney basin.

The red bellied black snake has a glossy black top body with a light grey snout and brown mouth, and a completely black tail. It lacks a well defined neck; its head merges seamlessly into the body. The red bellied black snake can have a strong smell, which some field experts have used to find the snakes in the wild. Like all elapid snakes, it is proteroglyphous (front fanged). Juveniles are similar to the eastern small eyed snake (Cryptophis nigrescens), with which they can be easily confused, although the latter species lacks the red flanks. Other similar species include the blue bellied black snake (Pseudechis guttatus) and copperheads of the genus Austrelaps. This error was recognised as such by Australian zoologist Gerard Krefft in his 1869 work Snakes of Australia.

The number and arrangement of scales on a snake's body are a key element of identification to species level. The red bellied black snake has 17 rows of dorsal scales at midbody, 180 to 215 ventral scales, 48 to 60 subcaudal scales (the anterior—and sometimes all—subcaudals are undivided), and a divided anal scale. There are two anterior and two posterior temporal scales, and the rostral shield is roughly square shaped.

The red bellied black snake is native to the east coast of Australia, where it is one of the most commonly encountered snakes.

Red bellied black snakes can hide in many places in their habitat, including logs, old mammal burrows, and grass tussocks. They can flee into water and hide there; one was reported as staying submerged for 23 minutes. When swimming, they may hold their full head or the nostrils above the water's surface. At times, they may float without moving on the water surface, thus looking like a stick. Within their habitat, red bellied black snakes appear to have ranges or territories with which they are familiar and generally remain within. A 1987 field study in three New South Wales localities found that these areas vary widely, from in size. Groups of up to six hibernating red bellied black snakes have been recorded from under concrete slabs around Mount Druitt and Rooty Hill in western Sydney. Males are more active in the Southern Hemisphere spring (early October to November) as they roam looking for mates; one reportedly travelled in a day. In summer, both sexes are less active generally. The male seeks out a female and rubs his chin on her body, and may twitch, hiss, and rarely bite as he becomes aroused. The female indicates readiness to mate by straightening out and allowing their bodies to align. Pregnancy takes place any time from early spring to late summer. Females become much less active and band together in small groups in late pregnancy. They share the same retreat and bask in the sun together. The red bellied black snake is ovoviviparous; that is, it gives birth to live young in individual membranous sacs, Young snakes almost triple their length and increase their weight 18 fold in their first year of life, and are sexually mature when they reach SVL (snoutvent length) of for males or for females. Females can breed at around 31 months of age, while males can slightly earlier. Red bellied black snakes can live up to 25 years.

Early settlers feared the red bellied black snake, though it turned out to be much less dangerous than many other species. The murine median lethal dose (LD50) is 2.52 mg/kg when administered subcutaneously. A red bellied black snake yields an average of 37 mg of venom when milked, with the maximum recorded being 94 mg. It accounted for 16% of identified snakebite victims in Australia between 2005 and 2015, with no deaths recorded. Its venom contains neurotoxins, myotoxins, and coagulants and also has haemolytic properties. Bites from red bellied black snakes can be very painful—needing analgesia—and result in local swelling, prolonged bleeding, and even local necrosis, particularly if the bite is on a finger. Severe local reactions may require surgical debridement or even amputation. Symptoms of systemic envenomation—including nausea, vomiting, headache, abdominal pain, diarrhoea, or excessive sweating—were thought to be rare, but a 2010 review found they occurred in most bite victims. Most people also go on to develop an anticoagulant coagulopathy in a few hours. This is characterised by a raised activated partial thromboplastin time (aPTT), and subsides over 24 hours. It resolves quickly with antivenom. A few people go on to develop a myotoxicity and associated generalised muscle pain and occasionally weakness, which may last up to 7 days. Patients may suffer a loss of sense of smell (anosmia); this is unrelated to the severity of the envenoming and can be temporary or permanent. Although the venom contains the three finger toxin α elapitoxin Ppr1, which acts as a neurotoxin in laboratory experiments, neurotoxic symptoms are generally absent in clinical cases. A biologically active agent—pseudexin—was isolated from red bellied black snake venom in 1981. Making up 25% of the venom, it is a single polypeptide chain with a molecular weight around 16.5 kilodaltons. In 1989, it was found to be composed of three phospholipase A2 isoenzymes. If antivenom is indicated, red bellied black snake bites are generally treated with tiger snake antivenom. While black snake antivenom can be used, tiger snake antivenom can be used at a lower volume and is a cheaper treatment. In 2006, a 12 year old golden retriever suffered rhabdomyolysis and acute kidney injury secondary to a red bellied black snake bite. Laboratory testing has found that cats are relatively resistant to the venom, with a lethal dose as high as 7 mg/kg.

The red bellied black snake is considered to be a least concern species according to the International Union for Conservation of Nature. the red bellied black snake adapts readily to captivity and lives on a supply of mice, though it can also survive on fish fillets, chicken, and dog food.