John Henry Comstock & Anna Botsford Comstock, A Manual for the study of Insects, Ithaca New York, The Comstock Publishing Company, 1895, pp. 187-188.
The young naturalist loves to lie face downward on the bank of a brook, and, with shaded eyes, Watch the busy life that goes on there. Among the astonishing things the sees are little bundles of sticks or masses of stones moving about the bottom of a quiet pool as if they were alive; and yet if he takes them out they seem dead enough. But when he pulls them apart he finds that each is a tube lined with silk within which a whitish larva lives. This larva, when it wishes to move, puts out the front part of its body, so that it can creep with its legs over the bottom of the stream, or climb up and down water-plants, dragging its house along after it. When molested it draws back into its tube, and is safe. Larvae of this sort are called Caddice-worms; and the adult insects are know as Caddice-flies.
They are very many species of Caddice-worms ; and each species makes a particular kind of tube. Some Caddice-worms are carpenters, building their houses of straws or sticks. These are usually placed lengthwise the body (Fig. 226) ; but certain species that make their houses chiefly of straws fasten the straws crosswise like the logs of a log-house (Fig. 227). These log-house builders often have the curious habit of decorating their houses by fastening snail-shells to the outside. And strangely enough they do not always take empty shells for this purpose ; we have found shells containing living snails securely fastened to the outside of the house of a Caddice-worm. In this case the snail was afforded comparatively rapid transportation whether it desired it or not. Fortunaley the species that make this style of house live in still water, and may, therefore, be easily kept alive in aquaria.
There are caddice-worm houses closely resembling in plan those just described but differing in appearance being made of bits of moss. Sometimes the houses are built of leaves; these may be fastened so as to form a flat case; or are arranged in three planes, so as to form a tube, a cross-section of which is a triangle.
Other Caddice-worms are masons, building their houses of grains of sand or of small stones. Sometimes these houses are tuby very regular in outline, being composed only of grains of sand fastened together with silk; but certain species of mason Caddice-worms fasten larger stones on each side of this tube of sand (Fig. 228). Some of the species that build tubes of sand make spiral house which very closely resemble in form snail-shells (Fig. 229).
Whether stones or wood are used to build these houses the material, is always fastened together by silk, which the larvae spin from the mouth in the same manner as do caterpillars. In some species the case is composed entirely of silk. Figure 230 represents the form of such a case, which is common in some of our lakes.