One of the privileges of being Australian is getting to share this wide brown land of ours with some of the world's most painful and poisonous creatures. Of the planet's top ten most deadly snakes, Australia has the lot. Our spiders out-perform the best biters from anywhere around the globe and, when it comes to causing pain, even the cute platypus produces one of the most excruciating venoms known.

So what is it that encourages such brutish behaviour in Australian animals? Humans aren't to blame - archaeologists insist the Australian bush was teeming with vicious creatures long before convicts and public floggings made it onto the continent. And even before Aborigines set foot on our antipodean shores, Aussie animals were a bad bunch.

Dr Tim Flannery, a mammologist and bush wildlife expert from the Australian Museum, thinks the testiness of our creatures has something to do with the harshness of the Australian countryside - in a tough country, only the meanest and leanest survive.

Here we take a look at Australia's big three poisonous animals and exactly how their toxins cause us so much grief. We have chosen the most poisonous snake, the inland taipan, the most lethal spider, the funnel web, and the much under-recognised platypus, whose bashful personality hides a set of poisonous spurs that cause the most exquisite, excruciating pain.

Taipan

The coastal taipan (Oxyuranus scutellatus) has earned a reputation as the country's most feared snake because it sports the biggest fangs, one of the most lethal venoms and a rather aggressive nature - an unsettling combination if you find yourself in the parts of north Queensland and the Northern Territory which it calls home. Yet its cousin, the inland taipan (Oxyuranus microlepidotus) is actually more deadly and, drop-for-drop, produces the most lethal poison of any snake in the world. Mercifully, O. microlepidotus only lives in the arid deserts of central eastern Australia and no human death has been reported from its bite.

Those unlucky enough to have a taipan sink its 12 millimetre fangs into their skin are injected with an extremely nasty chemical cocktail. Unlike most snakes, the taipan is a specialist mammal hunter so its poison is specially adapted to knock out warm-blooded furry creatures like ourselves.

In a single strike, a taipan can inject 60mg of venom - enough to quickly paralyse a small marsupial but also more than enough to wipe out several human adults. Dr Julian White, a snake venom expert from the Women and Children's Hospital in Adelaide, says the venom does the damage in two different ways:

The most deadly component is a neurotoxin that immobilises by paralysis. It essentially scrambles the body's communication lines - the nerves that carry electrical signals around the body. The taipan neurotoxin acts at the point where nerves join to muscles, called the neuro-muscular junction. The toxin binds to the ends of the nerves, blocking electrical activity and shutting down communication between the brain and muscles.

As the poison spreads the victim experiences headache, nausea, vomiting, pain in the belly and dizziness. Blurred vision follows, sometimes accompanied by convulsions and, in severe cases, coma.

As if this were not bad enough, the neurotoxin (like many other snake venoms) is also a myotoxin, meaning it eats away at muscle tissue. The urine of a bite victim often turns reddish-brown as their muscles dissolve and are passed through the kidneys. In fact, the kidneys are often badly damaged by filtering so much tissue debris out of the blood and kidney failure is a common complication in serious snake-bites and a frequent cause of death.

Internal bleeding is the other major complication of taipan bites. The snake's second main toxin is a procoagulant which prevents blood-clotting by removing the body's supply of its natural blood clotting agent, fibrinogen. This causes persistent bleeding from the bite site and can lead to more serious - sometimes fatal - internal haemorrhaging, especially in the brain.

This is all bad news for the victim but good news for the snake, which simply has to wait for its prey to stop shaking before devouring it at leisure. Thankfully, the snake rarely attacks anything as big as a human except in self-defence - so at the risk of stating the obvious, faced with a taipan the best action is to let it go about its snake business undisturbed.

For information on treating snake bites see the web page at the SA Women and Children's Hospital or the University of Queensland for venom and antivenom information.

Funnel web

Along with the red-back and its mythical toilet-seat antics, the funnel web spider holds a special place in the Australian psyche. But what most people think of as "the funnel web" is actually a collection of about 35 different species of spiders, most of which are dangerous. The one that gets most publicity is the Sydney funnel web (Atrax robustus), the species responsible for Australia's 13 recorded funnel web fatalities.

The males are the deadly ones and Jamie Fletcher, who studies funnel web toxins at the University of Sydney, says the venom is packed with at least 40 different toxic proteins (called peptides). Only one of them is dangerous to humans as far as anyone can tell, but it's more than effective enough on its own.

Called robustoxin, the peptide is another neurotoxin that disrupts nerve signals. However, it works in the opposite way to the taipan venom. Instead of shutting-down nerve signalling, it switches it all on at once causing massive electrical over-load in the body's nervous system. The protein attaches itself to nerve synapses and prevents them from switching off - salivary glands, tear ducts and sweat glands all start running uncontrollably, muscles begin to spasm, blood pressure climbs as blood vessels contract and then falls to dangerously low levels. Ultimately, most funnel web fatalities occur from either cardiac arrest or a condition known as pulmonary oedema, where the capillaries around the lungs begin to leak and the patient effectively drowns. Death can come as quickly as two hours after a bite.

People and other primates are exquisitely sensitive to funnel web venom but, intriguingly, other mammals such as mice, rabbits, guineapigs, dogs and cats are relatively immune and often survive 100 times the human lethal dosage. For years scientists wondered whether funnel webs had some special grudge against people. But recently it was discovered the toxin is equally lethal to insects - the spiders' main prey. Dr Graham Nicholson, a funnel web expert from the University of Technology in Sydney, puts our unusual sensitivity to the toxin down to "simple bad luck". He says there's no question humans and funnel webs evolved independently and our susceptibility probably has something to do with the wiring of our highly-evolved primate brains - one of the down-sides to being smart.

Cashing-in on the funnel web's expertise in insect control, Jamie Fletcher and his group at Sydney University are analysing funnel web venom for compounds that could be used as commercial insecticides. To test the potency of the different venom components the researchers inject them into cockroaches - "If they flip over and die, we know it works," he explained.

Platypus

For a shy little animal, the platypus (Ornithorhynchus anatinus) can cause a lot of grief. Tucked away on the back legs of mature males are a pair of short spurs each hooked-up to a venom gland that makes a viciously painful toxin.

Platypus spurrings of people are rare, but the select group who have survived the trauma (often fishermen trying to free irate monotremes from their nets) report pain strong enough to induce vomiting which can persist for days, weeks or even months. The pain is resistant to morphine and other pain-killing drugs and anaesthesia of the main nerve from the spur site is often the only way to relieve the patient's suffering.

A witness to one of the first recorded platypus spurrings made these observations:

"... the pain was intense and almost paralysing. But for the administration of small doses of brandy, he would have fainted on the spot: as it was, it was half and hour before he could stand without support: by that time the arm was swollen to the shoulder, and quite useless, and the pain in the hand very severe." - W.W. Spicer (1876)

Professor Philip Kuchel, from Sydney University, says there are at least 25 components in the platypus venom, including a protein that lowers blood pressure causing shock, digestive enzymes called hyaluronidases and peptidases that dissolve body tissue helping the poison to spread, and a protein that increases blood-flow to the spur site causing severe swelling. The slight acidity of the venom adds further sting.

But the special ingredient in platypus venom that accounts for its outstanding pain-inducing qualities is thought to act directly on nerve cells that register pain, called nocioceptors. Greg de Plater, who discovered the compound recently at the John Curtin School of Medical Research in Canberra, says it works a bit like capsacin (the active ingredient in chillies that makes them taste hot) by stimulating electrical activity in the pain cells.

Why this placid animal swims around with such a nasty toxin hidden in its back legs is still something of a mystery - the platypus doesn't use its spurs to catch or kill prey as far as anyone can tell. Cliff Gallagher, an emeritus professor studying the platypus at Sydney's Taronga Zoo, says the toxin is most often used in deadly skirmishes between rival males to stake out territory and also as an "excruciatingly painful" defence mechanism.

Study on the toxin is continuing and, ultimately, Greg de Plater hopes an understanding of how the different components of the platypus venom work could lead to new treatments for chronic pain sufferers.