Larry Solomon & Eric Leiser, The Caddis and the Angler, Harrisburg, Pennsylvanie, Stackpole Books, 1977, p. 23.

The caddis larva is a worker. The caddis is also an architect. Most of use are familiar with the casemaker, those families (not all) of caddis flies that build protective cases, which are commonly found under rocks. Cases can be made of bits of twigs and vegetation such as in the genus Brachycentrus, which are know for their chimney type of structures; or they may be made entirely of pebbles ; or a combination of pebbles and twigs or stray objects found on the stream bottom. All the larvae emit a gelatinous substance from their salivary glands which is used to glue the pieces of their case togethe, in addition to attaching the case to a rock or other submerged object. Each family has its own style of architecture and preference  of material used. The casemaker groups begin work immediately after entering the larval stage. The case whatever its architectural style, becomes the home of the larva until it is for pupation.