A member of the reptile family which usually has limbs, although there are some burrowing lizards, such as the Slow-worm, which lost its limbs during the course of evolution. Britain has three native lizards - the Slow-worm, the Common Lizard and the Sand Lizard.
Reptiles may lay eggs or give birth to live young, depending on how they have evolved to cope with the British climate. Egg-layers such as the Grass Snake and Sand Lizard choose a warm place for their eggs (rotting vegetation or sandy banks respectively). Unlike birds’ eggs, reptile eggs do not need turning (indeed it is harmful), so the females can leave their clutch and resume their normal lives. Those which carry their young inside them until they are born, like the Adder or Slow-worm, have to bask out through the summer develop their young, acting as mobile incubators.
Egg-layers have one advantage - the females do not have to bask out for long periods and therefore expose themselves to predation when they are heavy with young. On the other hand, they risk losing their whole clutch if the summer is too cool to allow the embryos to develop or if the laying site is disturbed.
Reptile bodies are covered by small horny plates made of keratin under the skin instead of fur or feathers and these protect them from injury. Snakes even have a special protective transparent scale over each eye, called a spectacle.
In most reptiles the body scales overlap for protection and some have keeled scales. Here each scale has a raised line along its centre like a small fold which helps the reptile to move faster. In many reptiles the belly scales are much wider than those on the upper part of the body. Snakes may use these large overlapping belly scales to grip the ground as they slip over it. The scales are dry and snakes do not feel slimy!
Reptile shed their skins frequently as they grow (scientifically ecdysis). As the old skin prepares to be shed, oil builds up between the old and new layers, making the reptile look dull in colour, and in snakes this creates a film over the eyes, interfering with their vision and making them vulnerable to predation. The animal may also become lethargic and remain in the same area. When it is ready to slough the reptile rubs its jaws on a log or stone to loosen the skin, which then peels off, inside out. These cast skins are sometimes found in the grass.
Play detective. Find out which animal shed the skin you have found. A long thin slough with small dorsal scales and broad belly scales will belong to a snake. Hold the skin up to the light. You may be able to see the animal’s body pattern and discover which species you have found. Look for vertical bars along the sides for a Grass Snake or a broad zigzag across the back for an Adder. An unmarked slough with tiny, uniform scales all the way round comes from a Slow-worm. Snake sloughs are usually whole but lizard sloughs are often found in fragments. In Common Lizards you can sometimes find the whole slough in several pieces over a small area, including complete sloughs of the feet, rather like a transparent glove.
Reptiles raise their body temperatures by lying out in a warm place, called basking. They seek out a sunny spot and lie there until their bodies have warmed up enough for them to search for prey. This process is called thermoregulation. If they cannot get warm enough, they cannot digest food so they will not hunt. Some lizards and snakes can flatten themselves to expose more of their skin surface to the sun, heating up more quickly. Such cold-blooded animals are known as ecototherms; warm-blooded animals like mammals are endotherms.
Many animals cannot remain active in cold northern countries when night temperatures are close to freezing and daytime temperatures are still low. They cope with this by seeking a sheltered place in which to spend the winter in a state of torpor. Their body temperatures fall, they breathe slowly and they stop moving. This is not sleep but a different state which allows their bodies to ‘shut down’ and not waste energy until it becomes warm enough to resume active life.
Reptiles and amphibians sense hibernation is close when night temperatures start to fall, days get shorter and the sun starts to lose its warmth. They may stay in hibernation for up to six months in an English winter, less if it the autumn and spring are mild. Some hibernate together in a group: adult Slow-worms may gather at the bottom of an old mammal burrow with the young at the top, so that if there are heavy frosts which reach their shelter, the young may die of cold. However, the adults should survive to breed again and replace them. Workmen have dug up football-sized groups under old walls. Many of the Slow-worms will have returned to the same hibernation spot year after year.
Adders also hibernate communally – often with Common Lizards, which seem to sense that they are safe from being eaten because the Adder cannot feed before hibernation. Food would rot in its stomach if it did so and it would not survive the winter.
Lizards drop their tails (scientifically autotomy) to distract predators while they escape from danger. Lizard tails are made in a special way which allows the individual vertebrae and the muscles surrounding them to break apart with little loss of blood or damage to the lizard. The vertebra breaks along a fracture plane through the middle of the bone, not between the bones, when the lizard contracts its muscles. This allows the tail to drop off, jerking and twitching for several minutes, with little loss of blood or damage to its owner. If the lizard escapes, it will grow a new smaller tail, but with cartilage instead of bone inside. The tail skin will also be a different colour from the rest of the lizard.
Reptiles often use their tongues to find prey, flicking them in and out to pick up scent particles in the air. These particles are then carried back on to the tongue to a special nerve centre in the roof of the reptile’s mouth, called the Jacobson’s organ, which analyses the scent. Snakes usually have long, black, forked tongues while lizards have short, blunt, greyish tongues with a notch in the tip.