Snakes are carnivorous reptiles. They are distinguished from lizards by their lack of eyelids and external ears. They are known as 'squamates' and are covered in overlapping scales. There are over 2,900 species of snake.
Snakes are thought to have evolved from lizards during the mid-Cretaceous period about 112 million years ago. Most species do not have venom. Those that do use it to kill their prey which are usually small mammals such as mice.