If you gently pull a caddis-worm

Alice GrayThe Adventure Book of Insects, New York, Capitol Publishing, 1957, p. 34.

The case from which caddis-flies (adult of the caddis-« worm ») take their name, is a little portable house made by the larva. It has a silk lining, but the outside is covered with sticks or pebbles neatly fitted together. If you gently pull a caddis-worm out of its case and put it in a dish of water with building materials, it will make a new house while you watch.