Friday Cat-erpillar Blogging: Living With Cocoonase

Silkworm Cocoon, Post-Adult Emergence
Photo: jneal

Silkworm larvae spin a very tight cocoon, a protective case where pupation occurs. The adult moth emerges inside the cocoon and must then escape. How?

Butterflies and moths have long coiled sucking mouthparts, unsuitable for making an exit hole in the cocoon. What other options are available? Enzymes! The cocoon of the silk moth is made of silk which is a protein. Proteins can be digested by proteases that hydrolyze the bonds between amino acids that comprise the silk protein polymer. Silk moths produce proteases called cocoonases that can digest a hole in the cocoon. Cocoonase is produced by the labial gland with a duct opening in the front of the head. Cocoons is secreted onto the silk directly in front of the head and digests a hole in the cocoon large enough for the moth to exit. Once formed, the moth crawls forward to exit the cocoon through the hole.