Are enclosed in artificial cases

Louis Rhead, American trout stream insects, New-York, Fredericka Stokes, 1916, p. 10.

Duns all bredd in the water from creepers that are enclosed in artificial cases, ingeniously fashioned around them for self-preservation. Trout consume these creepers while in their cases at the bottom, also while they are rising from the mud to the surface, which they do twice a year.