Forster Robson, Pond and Stream Life, Londres, Holden & Hardingham, 1916, p.73-74.
All anglers are familiar with the Caddis-worms; it is eagerly sought for as a bait for trout. If you look carefully on the stones in the bed of a stream you will find now and then little cylinders which move occasionally. On taking up one of these you will find the cylinder composed of little particles of stone, or bark, according to the character of the bottom of the stream. These particles are cemented together, and form a sheath containing the larva of caddis Fly. All sorts of materials are used for the sheath, the main objects being to deceive its ennemies by ressemblance to inanimate objects.