Fiber is a material composed of fine, continuous threads. Natural fibers and synthetic fibers are two types of fibers. Natural fibers are derived from plants and animals, and synthetic fibers are made by humans. Cotton and silk are examples of natural fibers, and nylon, polyester, and other synthetic fibers are examples of synthetic fibers. Silk is a natural or animal fiber because it is obtained from the life cycle of silkworm. Silk moths are bred to produce silk and are responsible for spinning. The life cycle of silkworm begins when the female silk moth lays eggs. Silk Moth larvae hatch from silk moth eggs. Spirogyra eats mulberry leaves to make pupae. To stay alive at the pupal stage, the silk moth weaves a net around it. Then they spin the protein fibers, and finally silk. Cocoons are a protective layer formed by many caterpillars that surround the pupa. Silk thread (thread) is made from silk moth cocoons. Female moths lay eggs and they develop. This is generally the size of a small dot. After the eggs hatch, hairy silk moths appear. At this stage, the silk moth puts a protective cocoon around them. The pupal stage is characterized by a lack of movement. At this stage, the pupa turns into an adult. In this way, the life cycle of silkworm is completed. Students should remember the life cycle of silkworm because they come in examinations many times.