Water bear, also called the tardigrade, is a microscopic animal known for its ability to survive extreme conditions. It has a segmented, tubelike body, with eight legs that usually end in claws. Adults typically range from about 1/250 to 1/50 inch (0.1 to 0.5 millimeter) long. There are more than 1,000 known species (kinds), but scientists think thousands of other species have yet to be discovered.
Water bears live in moist environments around the world. They are often found in pools or thin films of water. Many live on land in moss, lichens, soil, or other moist environments. Other water bear species live in fresh water or the oceans. Many kinds of water bears appear slow and clumsy when crawling. Their movements somewhat resemble those of a bear, which helped to inspire their name. Most water bears feed on algae, bacteria, or plant cells. Some species feed on small animals, including rotifers, roundworms, and even other water bears. Water bears are eaten by a wide variety of animals.
Scientists have found water bears living in extreme habitats, including in Antarctica and in hot springs. Water bears even survived a scientific experiment that exposed them to outer space. Many species of water bears are especially resistant to dehydration. To avoid drying out, they can curl up into a ball and enter an inactive state. Water bears in this state are known as tuns. Tuns can survive for many years. When tuns are exposed to water again, the water bears can become active within minutes.
A water bear must molt as it grows. To molt, the animal grows a new cuticle (skin) and sheds the old one. Water bears reproduce by laying eggs. They can live for about 3 months to 2 1/2 years.
