The decorations are specific

James L. Gould & Carol Grant Gould, Animal architects : Building and the Evolution of Intelligence, Cambridge Massassuchets, Basic, 2007, p. 36.

Most species of caddisfly larvae build open cocons into which the can retreat. Grasping the cocoon with its tail hooks, the larva puls its home around it by its stubby front legshe caddisfly’s trailer home tapers toward the rear, which is open ; as water flows through, the larva strains it for food, and the current carries away the wastes. As the larva grows it adds new sil kat the opening, decorates it, and often uses its rear hooks to break off a now-unnecessary bit of tube. Many species embed small stones or shells in the silk to privide additional protection or camouflage, and some of their tubes can be quite beautiful. The decorations are specific to each species, and can be used to identity the nondescript larvae.