Arthur Smith, Insect Life, Harmondsworth, Middlesex,  Puffin Pictures Books, 1950, p.11.

The young caddis-flies are known as caddis-worms and are to be found in fresh water. Seen for the first time through the running water of a stream they appear as strange little bundles of objects, moving along the bottom as though gently rocked by the flow of the stream. If one is taken out and put in a jar of water for closer examination, we shall presently see the front part of a larva thrust out from one end of the bundle and the larva dragging it along as it walks.