Edith Holden, Natures Notes of the Country Diary of an Edwardian Lady, New York, Harper & Row, 1984
Now, the caddis grub has a hard head and thorax, but the rest of its body is soft and vulnerable. So, in order to protect itself, the grub makes an admirable little container, picking up pieces of sticks and leaves, grains of sand, fragments of freshwater shells, fastening them together by means of a fine silk thread which is also used to line the case. With its head sticking out freely, the grub holds the case on by dint of claws at the base of its abdomen. In clear water you can occasionally see caddis cases jerking here and there over the bottom as the grub goes about its minute affairs.