To protect that abdomen

Charles Paul May, A Book of Insects, Ill. John Crosby, New York, Saint Martin’s Press, 1972, p. 105-106.

A thick, dark skin covers its head and thorax, but its abdomen looks soft and white. It sets about building a case to protect that abdomen. Depending on its species, a caddisworm uses sand, bits of leaves, twigs, or other material for its «  houses ».

It glues the pieces together with stickly silk from organs in its mouth until it has a solid tube in which to live.

When in danger, a larva pulls its head and thorax into its case. Danger comes mainly from fish, tough water bugs, and muskrats. Its ennemies must break the case, for the larva holds itself in by hooks on the end of its abdomen.

Some caddisworms feed on small, soft plants. Other catch tiny larvae and other living creatures to eat.