Hollowed-out stems

Ron Wilson, The Urban Dweller’s Wildlife Companion, Poole Dorset, Blandform Press, 1983, p. 108.

Soft-bodies on emergence, many species of caddisfly larvae will find a suitable form of protection by building cases in which to live. The material used for the case varies from species to species. Some make theirs from water weeds, others cement together sand particles or very small stones, and yet others will use the hollowed-out stems of water plants.