Sunday, December 19, 1999
SNAKES are the most notorious poisoners of the animal world. Their fame in this regard has been the major cause of the needless persecution and destruction of countless millions of harmless reptiles. Since some are dangerous for humans in the real sense, all snakes are feared. However, the fact is only 15 per cent of the living species are poisonous. If we go by numbers, only 400 species out of 2,300 are venomous. We usually do not take the trouble of finding out whether the particular snake is poisonous or not and kill it on sighting it.
The most simple way of spotting a venomous species is to observe the shape of the head. If it is unusually wide, it is almost certainly a highly poisonous one, but this does not mean that it should be killed. Snakes are very timid and elusive creatures. They themselves avoid the company of human beings or other animals. They strike only when hungry or threatened. If they are given the chance to escape they will prefer to flee rather than face the adversary.
Poisonous snakes have unusually wide heads because the poison is stored in enlarged and modified salivary glands. These glands are connected to long, pointed, hollow teeth that act as hypodermic needles, injecting the lethal liquid into the victims flesh. In the most advanced types, these fangs are hinged. When the snakes mouth is shut they lie flat, but when the jaws are opened wide to strike, the two upper teeth that supply the venom are pivoted down through about 90 degrees, so that they are at right angles to the top of the head. This means that when the jaws gape fully open, the sharp fangs are aimed directly forward. At this moment the snake strikes, flinging its neck towards its victim at the astonishing speed of 8 feet per second.
The actual distance covered will probably be no more than 2 feet, so it is necessary to respond in less than a quarter of a second in order to avoid being struck.
As the teeth sink into the flesh, the pressure of this action squeezes venom out of the glands and down the hollow tubes of the paired fangs. It spreads quickly once inside the victim and is soon circulated in the bloodstream.
If we see typical snakebites, we will find that snakes stab their victims rather than biting. They do not grab, but merely hit with an open mouth. The reason is that the snake must do its best to protect its precious fangs. If it bit its victim and then hung on tight, the ensuing struggle while the injected individual died would probably damage the long, delicate teeth, ripping them from their sockets.
So the snake makes its deft, rapid lunge and then immediately withdraws to await results. The poison works so quickly that the victim rapidly succumbs and the snake to make its move. The primary function of snake venom is, of course, to quieten prey before swallowing it. Its use in self-defence is entirely secondary and only employed as a last resort.
All snakes prefer to retreat from predators as quickly as possible, but if cornered, they will then use their bite as an ultimate weapon. While defending itself from the predator or stabbing a prey it sometimes happens that fangs become dislodged by the ferocity of the strike. When this happens a new fang quickly grows to replace the lost one. At any moment there are about six fangs in reserve on each side of the mouth, at various stages of development. When an active fang is lost, the next most mature will take its place and grow very quickly so that it is ready for use.
Usually, many of the big vipers have fangs about an inch long , but gaboon viper from Africa has the most impressive of them all, measuring about two inches in length, these penetrate well into the deeper tissues where there is a rich supply of blood vessels to carry the poison away.
Snake venom is a yellowish, cloudy liquid which contains neurotoxins (nerve-poisons) and haemotoxins (blood poisons). In some snakes like cobras, mambas and sea-snakes venom contains nerve-poison pre-dominantly whereas in vipers and rattlesnakes blood-poisons are more active. In case where neurotixin is injected, there is a creeping paralysis accompanied by nausea and vomiting, leading to convulsions and the cessation of breathing. When the venom containing haemotoxins is injected, it causes massive swelling around the bitten part with the flesh turning blue, green, purple or black, with livid blotches and blisters. This gradually spreads throughout most of the body, affecting the heart and eventually stopping its action.
The body of the adult human, however, can often withstand this chemical onslaught and ultimately recover fully. It has been estimated that, of the thousand people bitten by rattlesnakes annually in the U.S. only about 30 die. This puts the chances of survival at about 33 to 1, and some experts believe this should be even higher as much as 50 to 1. An attempt at a global survey carried out in the 1950s gave a total world figure of 30,000 deaths annually from all forms of snakebites.
In the world of serpents
perhaps the most remarkable is spitting cobra of Africa.
They have evolved the ability to rear up and squeeze
their poison glands so forcibly that the venom inside
them is propelled towards their enemy as a jet or spray
of droplets. They are capable of aiming accurately enough
to splash a mans face from a distance of 6 ft. If
the venom strikes his eyes it can temporarily blind him
and possibly even permanently damage his sight. The pain
is severe and no predator would risk a second close
encounter with this snake.
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