James G. Needham & J. T. Lloyd, The Life of Inland Waters ; An Elementary Text Book of Fresh-Water Biology for Students, Ithaca (New York) Comstock, 1937, p. 199, 215-216
The larva of Limnophilus ives in the case shown in figure 105. This is a dwelling composed of flat plant fragments placed edgewise and attached to the outside of a thin silken tube. The larva, living in this tube, clambers about over the vegetation, jerkily dragging its cumbrous case along, foaging here and there where softened plant tissues offer, and when disturbed, quickly retreating inside. It frequently makes additions to the front of its case, and casts off fragments from the rear ; so it increases the diameter to accommodate its own growth.
The larvae of the caddis-flies mostly live in portable cases, which they drag about with them as they crawl or climb ; but a few having cases of lighter construction, swim freely about in them. Such is Triaenodes, whose spirally wound case made from bits of slender stems is shown in the accompanying figure.
The cases are wonderful in their diversity of form, of materials and of construction. They are usually cylindric tubes, open at both ends, but they may be sharply quadrangular or triangular in cross section, and the tube may be curved or even coiled into a close spiral.
Almost any solid materials that may be available in the water in pieces of suitable size may be used in their case building : sticks, pebbles, sand-grains and shells are the staple materials. Sticks may be placed parallel and lengthwise, either irregularly, or in a continuous spiral. They may be placed crosswise with ends overlapping like the elements of a stick chimney, making thick walls and rather cumbrous cases. However built, the cases is always lined with the secretion from the silk glands of the larva. This substance is indeed the basis of all case construction. The larva builds by adding pieces one by one at the end of the tube, bedding each one in this secretion, which herdens on contact with the water and holds fast. Small snails and mussel shells aresometimes added to the exterior with striking ornamental effect, and sometimes these are added while the protesting molluscs are yet living in them.