G.R. Knap, Pond Life, Exeter, Wheaton, 1962.

The Caddis-fly larva quickly seks to protect itself. It does this by forming a strong, tube-like case around itself, made out of either vegetation or materials from the bed of the pond or streams. The case, when made, usually matches the surroundings, and gives good camouflage. The material selected for the case are stuck together with fine silk threads, spun from glands near the mouth. The Inside of the case is lined with silk, and the larva holds itself in the case by means of two tiny hooks in its rear segment. Attached to the other segments are minute gills which take in oxygen from the water.