No.80 January 2004 Notes from Very venomous but ... the Australia is home to some of the most venomous snakes in the world. Why? Editor It is possible that strong venom may little chance to fight back. There are six main snake families have evolved chiefly as a self-defence in Australia – elapids (venomous strategy. It is interesting to look at the While coastal and inland taipans eat snakes, the largest group), habits of different venomous snakes. only mammals, other venomous colubrids (‘harmless’ snakes) Some, such as the coastal taipan snakes feed largely on reptiles and pythons, blindsnakes, filesnakes (Oxyuranus scutellatus), bite their frogs. Venom acts slowly on these and seasnakes. prey quickly, delivering a large amount ‘cold-blooded’ creatures with slow of venom, and then let go. The strong metabolic rates, so perhaps it needs to Australia is the only continent venom means that the prey doesn’t be especially strong. In addition, as where venomous snakes (70 get far before succumbing so the many prey species develop a degree of percent) outnumber non- snake is able to follow at a safe immunity to snake venom, a form of venomous ones. Despite this, as distance. Taipans eat only mammals – evolutionary arms race may have been the graph on page one illustrates, which are able to bite back, viciously. taking place. very few deaths result from snake This strategy therefore allows the bites. It is estimated that between snake to avoid injury. … not necessarily deadly 50 000 and 60 000 people die of On the other hand, the most Some Australian snakes may be snake bite each year around the particularly venomous, but they are world. By comparison, in venomous snake, the inland taipan (O. microlepidotus), also known as the not the most dangerous for humans, Australia there have been only as the graph below shows. The low 38 deaths from snake bites during small-scaled or fierce snake, tends to live in the burrows of its main prey, the fatality rate, compared with many other the last 23 years – fewer than two parts of the world, is attributed to a year. long-haired rat. Unable to retreat from its prey in this confined space it has a Australia’s sparse population, use of better footwear and better medical Rather than focusing on the greater need to finish it off quickly. Its more risky attack strategy entails treatment, including availability of danger our snakes pose, it is antivenoms. Also, Australian snakes much more interesting to holding its prey with its body and biting repeatedly. However, this snake are shy and comparatively reluctant to concentrate on how fascinating bite, often not injecting venom when these creatures are. can deliver, in one bite, more than 40 000 times the venom needed to kill a they do bite. Indeed, a New South I would like to thank Greg 200g rat and it contains a special Wales study showed that it is humans Watson, Gavin Bedford, Junko component which causes the toxin to who are more aggressive with people Godwin and Brigitta Flick for rapidly invade the body. Its prey has 100 times more likely to attack a snake their help with this issue. than the other way round. 50 45 Contents: 40 Page 1: Very venomous but ... 35 Page 2: Snake venom 30 Page 3: Snake history 25 The next generation 20 Pages 4&5: Scales in the 15 10 savanna 5 Page 6: Questions & answers 0 Facts and stats; Tourist Talk AfricaAus. India Sri Lanka Sth Amer. USA Bush Brian courtesy Graph Page 7: Out and about Page 8: Bookshelf A comparison of annual snakebite fatalities per million people from around the world. To standardise comparisons, published data compiled between 1945-1960 was used. Australia’s current figure is 0.13 per million but during the period used here it was 0.45 per million. Snake venom Venom is modified saliva which is designed, in carnivores, to break down body tissue. If human saliva was injected causes blood pressure to drop and extracts from cobra venom into another human they are used to lower blood pressure in stroke victims. would react as if affected by a toxin – but people are not Fang design considered a venomous Many snakes, such as pythons, have lots of sharp teeth, species. Saliva simply contains but none dedicated to delivering venom. However, various poisonous compounds. groups have evolved pairs of hollow, elongated teeth Sometimes, however, it has been which are connected to venom glands. As the snake bites, modified further and contains components which cause muscles in this gland contract and venom is squeezed paralysis, blood-clotting and other serious symptoms. When through the teeth. an animal has also developed long teeth attached to storage glands, to deliver the venom deep into its victim, the result is Some snakes have fangs in the back of their mouths where potentially fatal. Nonetheless, while venom is often used by a leverage enables the snake to drive the tooth well into the snake to subdue and kill prey, it is also important for starting victim – as long as it has been caught securely. Rear- digestion – useful when a large animal is to be processed in fanged snakes include the brown tree snake, Macleay’s the stomach of a cold-blooded reptile. This could be the water snake and mangrove snakes. These are not primary function of many snake venoms. considered dangerous to humans. Venom is thought to have evolved when snakes began to The more dangerous snakes, from an Australian point of attack and eat the first small, primitive mammals. It has long view, are those with fangs at the front of their mouths. The been thought that this happened several times in different fangs of almost all dangerous Australian snakes are fixed – snake species. However, following analysis of venom from they cannot move – so their length is determined by the snakes all over the world, Dr Bryan Fry*, of the University of need to fit in the mouth. The longest fangs are found in the Melbourne, says evidence indicates that it evolved only once, taipan, with the mulga, western brown, death adder and a few hundred million years ago, in a large swamp monster Collett’s black snake coming close. similar to today’s anacondas. Dr Fry argues that it was the different fang designs which evolved separately, developing Vipers, found outside Australia, have the longest fangs, only when there was something useful – venom – to deliver. hinged to fold back into the mouth. Only one Australian species, the death adder, has fangs which fold back, but On the positive side, there is potential for snake venom to be only to a limited extent. used in drug design, just as the deadly venom from cone shells has been used to create pain killers. Snake venom often *See Bookshelf, p.8, for a link to Dr Fry’s work. Toxicity ratings The toxicity of snake venom is gauged because of their temperament and strike by the amount required to kill 50 percent rate are considered one of the most of a sample of mice. However, this does dangerous snakes. The brown snake Safety first not necessarily relate to the effects in group (several species) is blamed for 22 In Australia, more than 80 percent of humans and different individual humans of the 38 human deaths recorded bites occur when people try to catch vary in susceptibility. When determining between 1980 and 2003. or kill snakes. The golden rule is not how dangerous a snake really is, other to corner or attack a snake. As factors need to be taken into account. The mulga (king brown) snake injects identification is often difficult, people How much venom does the snake inject? more venom in one bite than any other are advised not to handle a snake How long are its fangs? Is the snake snake – but it is of comparatively low even if they believe it is non- likely to attack? How often are people toxicity and few human deaths have venomous. likely to encounter the snake? been blamed on this species. Australia’s venomous snakes are When dealing with a snake bite the relatively shy and reluctant to bite. Bite stats priority is to prevent the poisons from North Queensland has the highest moving from the bite site into the Although the venom of the inland taipan number of reported snake bites in general circulation. is almost four times as toxic as that of its Australia. A report recently released • Do not try to catch a snake, or kill it. cousin, the coastal taipan, when all other from the Cairns Base Hospital** • Do not apply a tourniquet or suck factors are taken into account it is the showed that 264 people were treated at the wound. coastal taipan which tops the list of the hospital for snake bites over a five- • Do not wash the wound. Traces of Australia’s most dangerous snakes. That year period (1 January 1996-31 venom help medical authorities is because the inland taipan lives in a December 2000). Of those bitten, identify the snake. sparsely populated area, is shy and does 61 percent tested positive for venom, • The victim must keep calm and as not have long fangs or deliver a large but only 10 percent showed clinical still as possible. amount of venom. The coastal taipan, symptoms. Antivenom was administered • Wrap the affected limb firmly with however, has long fangs, injects more to 20 patients (7.6 percent). One patient an elastic bandage or clothing, venom, lives in populated areas and is died of a bite from a brown snake.