Vernon Lyman Kellogg, American insects, Ill. Wellman Mary, New York, H. Holt & Co, 1905, pp. 240-241.
These case are familiar objects in most clear streams and ponds. Figures 331 and 332 show several kinds. These is great variety in the material uses and in the size and shape of the cases, each kind of caddis-worm having a particular and constant style of house-building. Grains of sand may be fastened together to form tiny, smooth-walled, symmetrical cornucopia, or smal stones to form larger, rough-walled, irregular cylinders.
Small bits of twigs or pine-neddles may be used ; and these chips may be laid longitudinally or transversely and with projecting ends. Small snail-shells or bits of leaves and grass may serve for building materials. One kind of caddis-worm makes a small, coiled case which so much resembles a snail-shell that it has actually been described as a shell by conchologists. Some cases in California streams gleam and sparkle in the water like gold ; bits of mica and iron pyrites were mixed with other bits of mineral picked up from the stream-bed to form these brilliant house. An English student removed a caddis-worm from its case, and provided it only small pieces of clear mica, hoping it would build a case of transparent walls. This it really did, and inside its glass house the behaviour of the caddis-worm at home was observed. While most of the cases are free and care carried about by the worm in its rambling, some are fastened to the boulders or rock banks or bed of the Stream.