Magel C. Wilder, Field Zoology, Providence, RI, Roger Williams Naturalist,  Roger Williams Park Museum, 1929, p. 3.

One day the class studied caddis worms, those little creatures which live nearly all of their lives in water until at last they emerge as the adult caddis-flies to spend the remainder of the existence in a different element of air. Like Diogenes, they carry their shelter with them wherever they go. The various kinds of caddis-worms can be identified by the type of house they build. Sometimes it is made of tiny sand-grains, sometimes of bits of leaves and stalks of plants, giving a «  log-cabin » effect and occasionally one is found with tiny snails shells glued into it. According to the species, too, these cases vary in shape-some are cylindrical, some horn-shaped, while some are so coiled that one must look twice to see whether it is a caddis or one of the shells of the little spirally coiled snails.

There is one adventurous caddis-worm which dispenses with all semblance of a  protective case and goes out without armor to catch what he can. His name is Hydropsyche and he can be found on spillways or on rocks where there is a steady stream of water flowing.