Why snakes and lizards bask in the sun.

Although reptiles such as snakes and lizards are usually described as cold-blooded,they spend much of their lives with their bodies nearly as warm as in a warm-blooded animal. What they lack is a means of producing and maintaining their own body heat. To reach a body temperature at which muscles, senses and digestion are fully active (about 77-90f and 25-32c), they have to rely on outside heat-either conducted from their surroundings or, more often, direct from the sun`s rays. In Britain, reptiles are dormant in winter because they cannot reach their working temperatures. In spring they emerge on sunny days, but the sunshine is so weak they need to bask almost all of the time.  As the sun gets stronger, basking time is shorter-mainly early and late in the day- and there is time for hunting and breeding. By midsummer basking is hardly necessary, but as autumn comes the need increases, and finally the animals are forced into hibernation. Reptile species that bear live young can usually survive in cooler climates than those that lay eggs, by basking during pregnancy, they can get enough heat to ensure faster development of the young but warmth cannot ensured for the eggs. This is one reason why the adder and the common lizard, which bear live young, can live further north than the grass snake and sand lizard, which lay eggs.