Peggy MacNamara, Architecture by Birds and Insects, a Natural Art, Chicago, The University of Chicago Press, 2008, p. 14.

After the larvae hatch they begin to build small homes while they mature to adults. They first surround themselves with silk from their salivary glands. They keep their abdomen safe Inside the tubes and use their legs and mouth parts to gather material, cut it, and attach it to their casings. If they live in a moving streams, they will need materials from their environment heavy enough to weigh down their homes, like stones or shells, where as if they live in stagnant water, lighter materials are more suitable. As the larvae grow they continually strengthen and enlarge these tubes with vegetation, sand, shells, or snails. Different species create different designs with different materials. These tiny architectural masterpieces provide perfect camouflage.