Fred Smith (Edit), The World of Animal Life, Londres, Blackie, 1910, p. 370-371.
Now these grubs are somewhat like the hermit crab. The front part of their body is encased in a coat of shelly armour, while the hinder part is soft and quite unprotected. The little creatures seem quite aware of this, and also of the fact that number of hungry foes are always on the watch to devour them. So they set to work to protect themselves from assault.
This they do by making a little « case » in which to live. The material of which it is constructed varies greatly. Some caddis grubs simply fasten two dead leaves together and live between them. Some make a case of little stones, or grains of sand ; others will have nothing but grass blades, or bits of reed, which they carefully cut up into suitable lengths. Others, again prefer the shells of minute water snails, and do not seem to care in the least whether their inmates are alive or not ; so that, when the case is finished, one sometimes sees the inhabitants of the shells pulling in one direction, while the caddis grub bis dragging them in another !