Snakes and snakebites
Source: Herald
Date: 11 August 2007
Author: Timothy Stamps
I have noticed, going round Zimbabwe, two popular, but, I'm afraid, false beliefs. One is that all snakes are dangerous, and therefore should be killed on sight, and the other is that being bitten by a snake needs anti-serum and a tourniquet. Neither, of course, is remotely true. Snakes, in fact, do a lot of good, helping keep down other vermin, especially rats who are more harmful to man by eating grain and spreading disease such as plague and louse infestation. The commonest enemies of snakes in Zimbabwe are, in reality, other snakes, closely followed by motor vehicles!
Pythons are eaten by larger carnivores, such as lions or leopards, but more frequently by crocodiles. Interestingly, the male snake has two genital organs, but it only uses one to fertilise the female, and a female snake can preserve, in her body, viable sperm for up to five years. So much for the "new" invention of artificial insemination. Sometimes the female loses interest, and if the penis is barbed, can drag the hapless male after her, with his penis very firmly fixed inside the, usually larger, female. Sometimes, two males catch up with one female at the same time, and then she watches while they do a trial of strength -- the combat dance in which the two male snakes rear up and twist round each other -- the weaker one giving in and running (or writhing) off.Most of the snakes found here are ovo-viparous, meaning that they give birth to live young inside an egg or membrane, from which the baby snake liberates itself using a specially designed conical egg tooth on the snout. The eggs are retained in the female snake's body and laid just before birth. Snakes mostly lay eggs then leave, but some snakes stay near their eggs until they hatch. Whilst the python (Shato, iNhlatu) actually coils round her eggs to ensure that they incubate at the right temperature, a few of our snakes develop a placenta, and therefore can be termed viviparous.
Most daytime and burrowing snakes have a round pupil, whist nocturnal snakes a vertical slit, like a cat, which enlarges in dim light. Generally speaking most snakes have poor vision, but any slight movement is immediately noticed. Tree snakes, as you would expect, have the best eyesight, and the boomslang (Danhamakatu, iNdlondlo) and the vine snake have specially shaped pupils -- described as key-hole or pear-shaped -- pupils to make their vision sharper.
The teeth are needle pointed and curve backward. There are six rows attached to a very specialised skull. Poisonous snakes have unique teeth, or fangs with which to inject poison. The fangs of a Gaboon viper, and there are two Gaboon vipers in the Mutare museum, are up to 25mm long! The poison glands are modified salivary glands, which are under the voluntary control of the snake itself.
Not always do venomous snakes use their poison, and, when they do they can control the amount of poison. The victim is stabbed, rather than bitten, because of a complex movement of the specialised bones of the mouth. Snakes regularly replace their lost (or resorbed) teeth in rotation, so they don't need a dentist, like humans do, and they can't be made permanently harmless by removing the fangs because new fangs will grow in a couple of days. Each species has its own type of skull, peculiarly adapted to its way of life. Yet all snakes look superficially similar.
All snakes have poor hearing. There is no external ear. Perhaps that's why the serpent in the Garden of Eden asked the woman, Eve, to confirm what God had really said. Doubt entered the human mind and the rest, as they say, is history. But snakes do have a very acute sense of vibration, transmitted through the lower jaw, to alert ground snakes of approaching prey, or danger. The tongue is long, forked, and is used to detect smell, and explores the surroundings or examines the food. That's why the tongue is very active, and makes up for both the lack of a nose and the absence of hands. On the other hand, the tongue isn't used for drinking as we do.
The snake only uses its right lung for actual breathing, the other being either extremely reduced or acting as an air reserve in the form of a thin, plastic bag. This bag is also used, especially by the puff adder, to inflate the girth of a snake when threatened. The active lung can extend over two-thirds the length of the snake, and there are also, in some snakes, tracheal, or windpipe lungs. When the snake swallows a large object, such as a dead rat, the trachea, covered by a flap called the glottis, may be extended out of the mouth of the snake in order that it can continue breathing whilst digesting the prey.
In Zimbabwe there are about 74 different types of snake. They are "ectothermic" - they have to keep their body temperature within a range by changing their place in the environment. That's why bites from puff adders (Chiva, iBululu, or Piri) are common, because they frequently occupy paths to warm their bodies, and, being slow and camouflaged, they'd rather defend themselves than run away, like lizards and other cold-blooded animals do. That, incidentally, is why they are so often run over by cars and trucks, too.
To be continued Dr T J Stamps is the Health Advisor in The Office of The President and Cabinet.