One of the outstanding problems now involving North American Trichoptera is that about 80% of the species are still totally unknown in the immature stages. As in many other insect groups, most initial work has been concerned with species differentiation, classification and distribution, and has dealt largely with adults. There are now about 1000 species of caddisflies known from Canada and the United States, but larvae, the best known of the immature stages, have been described for only about 190 of them. Lack of information concerning larvae is especially conspicnous in the Limnephilidae, our largest family, where this stage is known in only about one-half of the genera. Although inadequate knowledge about the immature stages of insects is not uncommon there are, for the study of Trichoptera, several reasons why much could be gained by overcoming it.