Twenty-four genera representing ten families of case-building caddis larvae were tested for their capacity to recognize and re-enter their cases following eviction from them. Glossosomatidae entered cases readily only under conditions of turbulence, which was the only condition under which they tended to remain in their cases. A small sample of Hydroptilidae showed excellent case recognition. In eight families of tube-case builders, some degree of recognition was present in all, but only the Phryganeidae consistently showed good recognition and rapid entry. Entry by backing occurred in two genera of different families. It is suggested that case recognition is a primitive trait which has been reduced or lost in several species. The trait is probably unnecessary in these species because the larvae rarely leave their cases.