When the larva has eaten enough it will will form a chrysalis (Butterflies do not spin cocoons, moths do.) The larva usually moves to the underside of a leaf. To form a cocoon it spins a silk-like thread around itself. A chrysalis is formed by hardening bodily secretions. A larva completely covered by a cocoon or chrysalis is called a pupa. Inside its protective shell the larva will transform into a butterfly (or moth), a process known as metamorphosis.