Commercially reared silkworm pupae are killed by dipping them in boiling water before the adult moths emerge, or by piercing them with a needle, allowing the whole cocoon to be unraveled as one continuous thread. As the process of harvesting the silk from the cocoon kills the larvae, silk has been criticized in the by animal rights activists, especially since artificial silks are available.
Silk is a natural protein fiber, some forms of which can be woven into textiles. Silk is one of the strongest natural fibers but loses up to 20% of its strength when wet. The best-known type of silk is obtained from cocoons made by the larvae of the mulberry silkworm which is reared in captivity.