E. O. Essig, Insects of Western North America, New York, The MacMillan Company, 1926, pp. 172-173.

The larvae are the most interesting and are know as case worms, caddis worms or to many country boys as fish baits. They inhabit the bottoms of ponds, lakes, creeks, and rivers, and are caterpillar-like in form with a soft cylindrical body with chitinized head, thorax, and strong, well-developped legs. The most important thing about these ugly creatures is the manner in which they protect their tender bodies from the cunning trout and other fish which are exceedingly fond of them. This is accomplished by spinning a silken tube to fit the body, closing the posterior end, and camouflaging and protecting the exterior by webbing together and incorporating small pebbles, shells, sticks, and other objects common to the botom which they frequent (Fig. 92). Some species construct very simple cases on the sides of stones, others make very elaborate ones from small shells, sticks, and so size. Those building the movable cases attach themselves by means of two posterior proleg-like organs at the closed end and allow only the armored head, thorax, and legs to protrude when feeding or dragging their abode about, and withdraw entirely into the same at will. Thus it is that one often sees small bits of sticks and peculiar forms of pebbles, leaves, and other shapeless objects moving about on the bottoms of stream in a show jerky fashion, and then suddenly disappear altogether with the current.