W. G. Bainbridge, The Fly-Fisher’s Guide to Aquatic Flies and Their Imitations, Londres, A. & C. Black, 1936, pp. 16-18. 

…make cases of sand, gravel, plant stems and pieces of stick cemented together by means of the secretion of the salivary glands. Other species are free and make no cases, crawling about amongst the stones in search of food, only covering themselves with gravel and slime when about to pupate.

The larva of the case-making Caddis begins to construct its case soon after it emerges from the egg, choosing the materials nearest to hand, and anchoring itself to the end of the case by two hooks. As the insect grows it adds to the length of the case. In moving about from place to place, it protrudes its head and fore-legs and drag itself slowly along in search of food.

The shape and construction of the case is a guide to the species to which the larva belongs, and here is an opportunity for the serious-minded angler to take up the study of Caddis cases- a subject in need of investigation.

As many of the Caddis larvae live in standing water, it is an easy matter to bring a few home in damp moss. Place them in a flat glass basin half full of water, with a few sprigs of water plant, and watch them develop.

An interesting experiment may be tried. Collect a few small Caddis grubs, from standing water preferred ; if they have built cases, get them to quit by inserting a stiff grass stem in the hinder end of the case work the stem gently round and the insect will creep out of its case. Place in a dish of water in which is a quantity of tiny coloured glass beads. The insect will begin to construct its case from these,- a very pretty effect will be produced.