What are the caddis-worms

William Rhind, A Catechism of Zoology or Natural History of the Animal Kingdom, Edimbourg, 1831, p. 67. 

Q. What are the caddis-worms .

A. The genus phryganea, or caddis-worms, in the larva state, live in the water, generally in running streams, and construct curious habitations, by attaching to their bodies, by means of a gluey substances, small stones, shells, and pieces of straws and rushes. Thus defend from their ennemies, they crawl about at the bottom of the streams, and, by throwing off or adding additional stones and shells, they can render themselves heavier or lighter in the water at pleasure.