Raymond Lee Ditmars, Strange Animals I have know, New York, Blue Ribbon Books, 1931, p. 360.

Tortoises are, of course, very fortunate, but other creatures are undaunted in their labours to build their own travelling shelters. The grub of the caddice-fly makes a little cylinder of silk and plasters it with coarse sand grain on the outside to render it inconspicuous. It keps part of the bag over its back, carrying the protective covering wherever it goes.