Peter Farb, The story of Butterflies and others insects, Ill. Kazue Mizamura, New York, Harvey House, 1959, p. 76.
If you turn over rocks and stones along the shore line, you will usually find insects under them that construct their own portable homes. They are the larvae of the Caddis-fly, an insect closely related to butterflies and moths, but whose young have taken to strange ways. They use their silk to tie together pebbles, bits of sand, tiny twigs, anything from the bottom of a pond. In some Western states they even use gold nuggets ! They carry these trailers around with them as they search for food.