Silk is a natural protein fiber produced by the silkworm (the larva of the domesticated silkworm, Bombyx mori). Silk production is a complex process involving many stages. Female silkworms lay eggs, which hatch into larvae. The larvae then feed on mulberry leaves, which provide the necessary nutrients for their cocoons to grow. Silkworms spin their cocoons using a gland, which produces a liquid silk fiber. The fiber hardens on contact with air, forming a continuous thread. The pods are collected and usually boiled or steamed, a process that kills the silkworms and relaxes the silk fibers. The next step is to unravel the silk fibers from the cocoons. The threads are then cleaned and turned into thread, which can be used to weave cloth.