Sunday, August 19, 2007
Venom ER (animal planet.co.uk)
Snakes have symbolised all that is bad on this planet of ours since the dawn of humanity – they’re the original bête noir. These reptiles slither and slide, hide in holes and peer out with glassy, unblinking eyes. Then there’s the forked tongues flicking between a pair of sharp fangs.
But is this a good enough reason for our primeval fear and loathing? The experts don’t think so.
But the facts remain: venomous snakes are amongst the deadliest animals on earth. They can strike without warning – some with bites so noxious they dissolve human skin on contact. They kill over 100,000 people worldwide each year - more than are killed from all other animal attacks combined.
…And still the experts tell us we’re over reacting. How can this be?
Well for starters, the majority of snakes catch their prey and suffocate it by means of constriction. Out of approximately 2500 species of snake, less than a quarter are actually venomous.
Mike Cardwell is a Deputy Chief Sheriff who works closely with the Loma Linda’s Venom ER. He’s conducted a long term study of over 1,200 Mojave rattlesnakes - arguably, one of the world’s most infamous reptile families. Their fearsome reputation for aggression, he says is misplaced. Rattlesnakes have relatively weak venom when compared to the world's other vipers and cobras.
“These snakes never show any aggression to us. They usually sit still; they occasionally rattle or crawl away, and sometimes they come over and sniff our equipment or sniff our feet without showing any aggression.”
Rattlesnakes strike fast but don’t have more than a metre range. Outside their striking distance, we’re quite safe.
According to the University of Florida, 7000 venomous snake bites are reported annually in the United States. Out of those unfortunates, just 2 in every thousand prove to be fatal – more Americans die being struck by lightning. In fact, it’s estimated that as many as half the attacks are ‘dry bites’ – where no venom is transmitted.
Less than one percent of properly-treated snake bites in developed countries actually results in death.
Scientists believe that snakes produce venom with a voluntary action. So strikes against humans – which, they say, are too large to be legitimate prey - are likely to be a defensive reaction. It’s a warning an intimidating and superior threat to back off.
Cardwell agrees. He can’t imagine why anything that’s that close to the ground would pick a fight with another animal over 5 feet tall.
Snakes in the deserts of South Western America are essentially ambush specialists. They prey on lizards and small mammals that burrow into the sandy desert to escape from the heat of the sun.
All snakes have very strong saliva – this common trait allows them to swallow their prey whole and digest it chemically as it passes through their limbless bodies. But venomous snakes have another trick up their sleeves – or more accurately, their fangs.
A dedicated supply of proteins and enzymes is efficiently injected using their needle-like teeth, right into the bloodstream of their prey. The venom destroys tissue to kill the prey and starts the digestion before their quarry hits the ground. In fact, death doesn’t come immediately.
The snake’s victim will try to make its escape once it has been bitten - its progress hampered, however, by the debilitating and ultimately fatal dose of poison.
The snake simply follows the powerful scent of its own saliva. It finally catches its prey, devouring it whole without suffering any injuries that other predators frequently face from a meal that puts up too much of a fight.
What’s your Poison?
Snake venoms can be roughly divided into three types: hemotoxic and neurotoxic, and haemolytic. They are classified essentially by their effects on the victim’s body.
• Haemotoxins - breaks down vessels, and causes bleeding into internal body cavities.
• Neurotoxins - act on the nervous system; primarily effecting muscle reactions, digestion, sight, and breathing.
• Haemolysins – dissolve red blood cells and prevent their ability to clot.
However, venom is more complex than scientists had first imagined. Some snakes have a cocktail of two or more of these deadly ingredients.
It was initially thought that only a special group of Mojave rattlesnakes had neurotoxin venom. But then a different species presented itself to Venom ER with the same symptoms.
At first, the experts didn’t know whether the snakes were interbreeding or evolving. Though scientists haven’t mapped snake venom perfectly, they now believe venom properties are flexible – they can change daily; as a snake gets older; even depending on its last meal.
And so, the mysterious serpent saga continues…
Posted by Anju Devanur at 4:53 AM