James Chester Bradley & E. L. Palmer, Insect Life: a manual for the use of scouts in fulfilling the requirements for the insect life merit badge and for all students of insect life, New-York, The Boy Scouts of America, 1925, p. 12-13.
No, they are not walking-sticks, nor swimming-stiks either. In fact they are not exactly sticks at all, and if you watch carefully you will see the head and legs of a sort of caterpillar sticking out of each, and it is these legs that are doing the crawling. Fish out one of the sticks and pull on the creature by his head and legs, and as soon as you can make him let go with a sort of hook that he has at his tail to hold on with, you can drag him right out, and you will see that the stick is just a hollow case that he is living in. In fact, he is a caddis-worm, and he built that case, bit by bit, by fastening twigs or bits of bark, or weeds, or something else together with silk, and it is his house, and he not only lives in it and builds it biger as he grows, but he carries it around with him wherever he goes.
There are many kinds of caddis-worm cases, each made by a particular kind of caddis-worm. Sticks, pieces of leaf, pebbles, sand grains and shells are the things mostly used in building their cases. The sticks or pieces of leaf may be laid on lengthwise, or in regular spirals, or cross-wise, like a stick chimney. Some kinds build little spiral case of sand grains that lok like snail-shells. Others build fixed tubes among stones in swift currents, with the open end facing the current. Leading to this opening they spin fine-meshed funnels, nets of silk. Then they lie waiting in their case, jaws ready to seize whatever bit of food chance and the current bring into their trap!