The mystery

W.G. S., « The beech »,  vol. XXV, n° 1279, The Builder, 10 août 1867, p. 584. 

Several very pretty agarics grow upon and are peculiar to beech-nuts in a stream apparently endowed with life and moving to and fro. The mystery was explained by finding that a colony of caddis-worms had secured the old shells for habitations ; and were going hither and thither in search of prey with their houses on their backs.