James G. Needham, About Ourselves, Man’s Development and Behaviour from the Zoological Viewpoint, Ill. William D. Sargent, Londres, Georges Allen & Unwin, 1951, p .95
Caddisworms are caterpillar-like aquatic larvae that live in all fresh waters. They construct tubular cases in which to dwell-portable cases, made of sticks and sand grains fastened together and lined with silk. Any one may see these on looking closely into the bed of a clear brook. At first he will see what appear to be cylindric clusters of dead sticks and pebbles moving jerkily about over the bottom ; then on looking closer he will see a head and legs reaching forward from the front end of a cylinder, instantly disappearing within it on the slightest disturbance. Hooked claws on the feet take hold of the stream bed, and drag-hooks on the tail end of the worm clutch the silken lining of the case and drag it along. Thus the caddisworm always carries its house on its backl. It travels by thrusting the legs out at the front door and pulling the case along.
The case itself is most ingeniously constructed. Whatever the materials (and thse vary with the species and with the stuffs available) they are fashioned into a neat cylindric tube a little longer than the body of the worm. There is great variety in the decoration of the exterior but the inner wall is alwayus smoothly lined with silk.