Snakes are a successful group of reptiles with over 3000 species found world-wide and on every continent but Antarctica. Only about 300 of these snakes are poisonous to humans. Even in Australia, one is much more likely to die in a road accident than from a poisonous snake bite.
Snakes are long, thin animals with no eyelids on their eyes, no external ear openings and of course, no legs. Their tail looks long but this is an illusion. The tail is the part past the cloaca or vent and this is often much shorter than the elongated body. Other general snake characteristics are tough scales and forked tongues that can flick in and out to taste and smell the air.
All snakes are predators and eat their prey whole. Small snakes may catch insects, frogs and small lizards while the biggest snakes, like the South American anaconda or the southeast Asian python, can take much larger birds and mammals and occasionally even humans. Poisonous snakes do not consider humans as food, but just as threats. The best way to avoid getting bitten is to not hassle snakes and to give them a wide berth.
There are eighteen families of snakes. The largest family, with about three quarters of all species, is the Colubridae. Colubrids are, for the most part, non-poisonous. They lack a left lung, have no hip bones at all and have large, symmetrical scales on their heads. The milk snake is an example of a colubrid as are corn snakes, rat snakes, hognoses and racers. The most well-known poisonous colubrid is the African boomslang. This is a green arboreal snake with rear fangs that normally preys on birds and lizards but occasionally bites and even kills a human.
Most poisonous snakes belong to one of two families: the elapidae and the viperidae. Elapids are circumtropical in distribution and include the Asian and African cobras, African mambas and American coral snakes. All the poisonous snakes of Australia, including the brown, the tiger and the taipan, are elapids. The vipers are short, thick bodied snakes like rattlers with wide heads and heavily ridged scales. Their fangs are long and hollow and can be folded back in the mouth when not needed.
The other poisonous snakes are the sea snakes, family Hydrophiidae and the sea kraits, Laticaudidae. These interesting animals are adapted for marine life, with valvular nostrils and a vertically compressed, paddle-shaped tail for swimming.
Sea snakes bear live young that can immediately swim away when born. They have lungs and must surface regularly to breathe but because they are cold-blooded, can stay underwater for long periods. They are closely allied to elapids and although they have small fangs, they make up for this with highly toxic venom. Sea snakes feed on a variety of fish and fish eggs. Sea kraits are characterised by smooth scales and bodies with numerous black cross bands. These snakes are partly terrestrial and will come ashore to lay their eggs. They can also be found in rocky crevices on sea shores or in mangrove swamps.
The largest family of non-poisonous snakes is the Boidae, which contains all the major constrictors. Boas and pythons are bulky, slow moving snakes that feed mostly on birds and mammals, with some taking reptiles. Pythons and boas coil around their prey and then slowly tighten until it suffocates. They must then swallow the prey whole and this involves dislocating the jaws and moving them around the prey until it can be swallowed. Most boids lay eggs, which they coil around to protect until they hatch.
The family Typhlophidae is a group of small, secretive burrowing blind snakes. These snakes occur in tropical regions around the world and are characterised by vestigial eyes and shovel-shaped snouts for digging. They mainly feed on insects like ants and termites and their larvae.
There are many other types of snakes in the world. Most are found in rainforests or desert regions. Some are arboreal while others are terrestrial. They are successful in most habitats except excessively cold ones because they are cold blooded and become sluggish or die if it gets too cold.
Some snakes, like garter snakes, can cope with cold winters by burrowing and going dormant until the weather warms up again. Wherever they live, snakes move remarkably well without legs. They have very flexible backbones which allow a wavy movement. They push themselves along with the help of rib muscles and their scales help by gripping the surface. This allows arboreal snakes to climb vertically up trees.
Snakes basically have four types of movement: wriggling side to side in an S shaped movement; crawling caterpillar-like; a concertina movement which involves pulling one half of the body forward and then the other half; and sidewinding, where the snake throws the middle part of its body forwards, while keeping the head and tail on the ground.
Snakes are diverse, successful and interesting. They have turned leglessness into an art form. They are important components of many ecosystems and habitats and vital parts of the food chain. They may seem frightening and strange but they deserve to be respected and conserved.
For more information:
http://www.reptileknowledge.com/ has good information about snakes and other reptiles.