The skin of snakes is covered in scales. Like human fingernails and rhinoceros horns, these scales are made of a strong protein called keratin. Contrary to popular belief, the snake's skin itself is not made of scales, but lies under the scales. Snakes use their scales for a number of different functions.
The scales on some reptiles assist the reptile with movement. In the case of snakes, the snake's belly scales are able to grab onto tiny imperfections on surfaces and create friction to propel the snake forward.
The thick, prickly scales on a reptile can help protect it from predators. They can make it difficult for predators to bite or attack the reptile, as well as cause injury to the predator.
In the case of other reptiles, the color of the scales can provide a defense against attack. One example of this is the non-venomous milk snake, whose black and red ringed pattern resembles that of the highly venomous coral snake.
Reptiles living in the desert have evolved special adaptations that allow them to thrive in the hot and dry climate. The scales of many desert reptile species allow them to retain moisture by preventing the evaporation of water through the skin. This allows the animal to become dehydrated less frequently and require smaller amounts of water to survive.
The scales of many reptile species are either plainly or elaborately colored to assist with camouflage. This includes certain species of leaf-tail geckos, who can completely blend in to surrounding tree trunks and branches in their natural environment.
Chameleons also have an additional advantage, and can change the color of their scales at will. In the wild, the chameleon will use this ability for camouflage or to absorb sunlight by darkening parts of its body.
Not all reptile scales are merely plates that coat the reptile's skin, and some have other interesting uses.
When rattlesnakes shed their skin, a portion of the scales remains behind at the end of the tail. This creates a hollowed-out area full of dead scales, which the rattlesnake vibrates to create its famous rattling noise. This allows the rattlesnake to warn predators to stay away.
Another example of modified reptile scales are the ones on the underside of the feet of many gecko species. These modified scales resemble hairs and are called "lamellae". These lamellae allow the gecko species to grip onto tiny imperfections on surfaces, giving them the appearance that they are "sticking" to the surface. This allows various gecko species such as the day gecko or crested gecko to climb smooth surfaces like glass with ease.