How does a caterpillar spin a cocoon?

Caterpillars are the larvae of certain butterflies or moths. Caterpillars undergo several changes before they become butterflies or moths. This is called metamorphosis. The first stage is the cocoon which is spun with threads of sticky fluid that flows from an opening in the lower lip. The fluid hardens in the air and becomes like natural silk. The caterpillar then becomes enclosed in the silk.