Water Bears: Tardigrada

Although many species of water bears are slow and lumbering like bears, species that prey on other microscopic animals are fairly quick and can move faster than the human eye can follow.

Water bears can survive extreme conditions for months, even years, by shutting down all life processes, a phenomenon known as cryptobiosis (KRIP-toe-bye-OH-sihs). Cryptobiosis is triggered mainly by lack of water, or dehydration (dih-high-DRAY-shun), and very low temperatures. Water bears in cryptobiosis as a result of dehydration are said to be in the tun (tuhn) stage.

Most water bears require males and females to reproduce. Some males place sperm directly into special sperm-storing organs on the female's body. Some females have special structures that are inserted into the male, allowing them to grab sperm inside the male's body. A few species are parthenogenic (PAR-thih-no-JEH-nik) and capable of producing young without mating. In some species, individuals have reproductive organs of both males and females. Most water bears are thought to lay eggs. Young water bears resemble the adults, but may have fewer claws and other structures.