George Philip Rigney Pulman,  The Vade Mecum of Fly-Fishing for Trout, Londres, Longman, Brown, Green and Longmans, 1851, p. 47-48.

When seen at the bottom of the water theses cases appear like short bits of stick, but they will be found, on examination, to be regularity and beautiful constructed of various materials- some of minute portions of the leaves and other parts of aquatic plants ; others of pieces of reed, grass, and the like ; and many of fine gravel, sand, and even little shell fish- each species selecting its peculiar materials, which are neatly and strongly cemented together with a kind of glue, which the larvar produce, and which completely resists the action of water. The cases are lined inside with a kind of silk, which the insect spins from its mouth in the same manner that caterillar do. The cases of most species being specifically lighter than water, the larvae swim with facility, and thus have a greater range for their food than species which inhabit cases composed of denser materials.