Extremely difficult to detect

Frederick Howard Shoosmith, Life in the animal world, Londres, Harrap, 1937, p. 115-116.

From such sedentary tube-builders the little caddis-worm of our streams differs in carrying about with it a tubular fortress built of such various materials as small shells, grains sand and gravels, little bits of stick, or leaves, according to the species. The building-material is securely fastened to the outside of a silken tube spun by the larva, and when their occupants are crawling about among water-weeds, some of the leaf-built cases are extremely difficult to detect-an additional measure of protection. Theses tube-builders are herbivores, whereas some species of caddis-worms are carnivorous, spinning silken snares among the weeds in which spider-like they lie in wait for prey. Thus far we have been concerned.