Rat appearances vary from species to species, but most share some characteristics. Like all rodents, rats have two front teeth that grow continuously. These need to be shaped by gnawing, so rats find dense objects that they can chew on to keep their teeth sharp. Rats have furry bodies and little or no hair on their ears, tails and paws. They use their hind legs to stand upright when necessary, either to defend themselves or investigate items out of their range of sight.
The differences in rats manifest themselves in size, shape and color of fur. The two most common rat species, the Norway rat and the roof rat exhibit these differences in a number of ways. Norway rats are larger and thicker than roof rats. They have wider bodies and shorter tails. They are grey brown in color and can swim very well. They tend to dwell near the ground, so their grey brown color blends in with the soil and debris around their habitats.
The roof rat, on the other hand, is dark in color. Roof rats are also called black rats. They have longer, thinner bodies than Norway rats and longer tails, as well. Roof rats can squeeze through very small holes by elongating themselves. Roof rats are excellent climbers and like to make their homes in attics or eaves of roofs. Their dark fur helps them to blend into the darker tree branches.
Other rat species have very distinct traits. Some have thick fur, while the mole rat, for example, has very little fur. Some rats have sharp noses that appear almost pointed, while others are more squared off. Rats and mice share a number of traits, as well, but rats are usually much larger than mice and have larger back feet. A young rat is easily distinguished from a mouse by the size of its back feet.