Hanry Patrick White, The Continuing conurbation : change and development in Great Manchester, Aldershot, Gower, 1980, p.185.

This case building caddis larva normaly collect particles of sand and then fastens them together with silk and builds them into a conical tube in which the larva lives. This species also uses sand grains to make a fly-sheet- like covering to the larval shelter to give it extra protection against its ennemies. In the Salford canal, lack of sand grains forced the insects to make their cases of particles of coal, which in spite of their low specific gravity compared with that of silica proved a satisfactory alternative building material.