Cotton, flax, hemp, jute, and sisal are the chief plant fibers. Wool, the principal animal fiber, comes mainly from sheep but also from such animals as goats and members of the camel family. Silk fibers are obtained from the cocoons of silkworms. Farms in japan and China raise most of the world's silkworms. The development of nylon and other manufactured fibers during the 20th century has reduced the demand for natural fibers in some countries.