Snakes are reptiles. There are more than 2900 species in the world. Lizards, alligators, and turtles are also reptiles. Snakes are cold-blooded creatures. That means that their internal temperature adjusts to the climate they are in. They lie in the sun to raise their temperature. If they are too hot, they can lower their temperature by going into the shade. Snakes which live in cold climates hibernate in the winter to avoid the cold temperatures.

Snakes live everywhere. They live in deserts, ponds, rivers, forests, oceans, streams and lakes. They live on the ground and in trees. They cannot live anywhere the ground stays frozen all year long, so there are no snakes in Antarctica or above the Arctic Circle. Ireland and New Zealand have no snakes.

A snake's body is covered with scales. These are waterproof and help the snake to move over rough ground or branches because they give them a grip on what they need to move from. Scales are made of layers of cells. The outer layer is made up of dead cells, while the layers underneath are alive. A few times each year, a snake will shed the outer dead layer of cells, and the new ones underneath become the outer layer. When a snake is ready to shed its skin, it will rub up against something rough, tear the layer off from around its mouth and slide out.

Snakes are vertebrates. That means that they have backbones. A snake's vertebrae are attached to ribs. They are so flexible because they have two hundred to four hundred vertebrae and an equal number of ribs. Human beings have only thirty-three vertebrae and twenty-four ribs. This help protects the inner organs, like in humans.

A snake's throat is very long and takes up one-third of its body. Its stomach can stretch to fit just about anything it can swallow. A snake's two lungs are very long. It has kidneys and intestines also. The end of its body has an opening for the snake to get rid of waste. The tail beyond is more bone.

Snakes have four ways of moving using their muscles and scales. The serpentine method is what snakes normally use for movement. They slither forward in a wavy motion. In the concertina method, the snake pushes the front of its body forward and then drags them back part up to meet it. It is good for small areas. Sidewinding is used on a slippery surface. A snake throws its head forward. The rest of its body follows. In the rectilinear method, the snake moves forward in a straight line. Some of the scales grip the ground while others push forward.

Snake jaws are not like those of a human. They are not connected at the back of their mouths. They can open much wider than the mouths of humans. While they are putting some huge prey into their mouths, a small tube at the bottom of their mouth comes out to help them breathe.

Only poisonous snakes have fangs, although all snakes have teeth. These fangs are long sharp teeth connected to sacs behind the snake's eyes. These sacs contain venom, a poisonous liquid. As soon as a snake bites, the venom is released. It will paralyze or kill its prey. If a fang is lost, another will grow. Sometimes a snake will hold onto the prey until it dies and then eats it. Sometimes it will let the prey go and follow it until it dies and then eats it.

In some countries, people catch poisonous snakes and get the venom out of them to be used to make an anti-venom medicine to help those who get snake bites. Snakes can keep on producing more venom. Sea snakes are the most poisonous snakes. Adders, Cottonmouths, Cobras, Rattlesnakes, and Copperheads are also poisonous.