Theodore Wood, Our insect allies, Londres, Society for Promoting Christian Knowledge, General Literature Committee, 1884, p. 130-132.
The larvae are very remarkable objects, long and slender, with no apparent means of escape from their ennemies. They are not gifted with the power of swimming, and, were it not for a very curious instinct, would speedily be exterminated by their manifold foes.
This instinct lies in the construction of a cylindrical case sufficiently large to enclose the whole of the body, which is formed by the insect from materials of almost every kind, – stones, sand, shells, leaves and various other objects being generally utilised for this purpose, – firmly fastened together by means of a glutinous secretion not affected by the action of water. In these the larvae dwell retaining their position by means of two forked appendages to the tail, and withdrawing even their heads under cover at the first sign of danger. In most of the species of caddis-fly these cases are freely movable, and are carried about at the will of the larva, whose six legs, small though they are, are yet sufficient for the limited amount of locomotion required by the insect. In one or two however, they are firmly fastened to the lower surfaces of stones or similar objects, the anal claspers being placed at the end of long footstalks, in order to enable the insect to protrude its body to some little distance from its habitation when searching for food.
If a few of these larvae be taken home and carefully expelled from their habitation, they will at once set to work to repair damages with any small substances which may be supplied to them. They can thus be forced to construct freh cases of beads, coloured sand, and similar objects, the effect produced being sometimes very curious and pretty.