A white and a blue caddis larva

Maxwell Knight, Instruction to young naturalist, n° 1, British, Amphibians, Reptiles and Pond Dwellers, Londres, Museum Press, 1956, pp. 122-113.

The larvae of the two divisions of caddis flies are also different in that those from ponds make protective cases of different kinds in which the larva lives, while those from streams in the main do not use cases at all. The illustration privided here will show quite plainty the diversity in shape and construction of the cases made by different species of caddis fly, some of them being quite simple, such as the hollow stem of some water plant: while others are highly complicated, being composed of tiny bits of stick, small stones, or grains of sand. Many a young naturalist, before he becomes an experienced pond hunter, has been surprised on looking at a mass of debris brought up from the bottom by his net, to see what looks like a little plie of sticks or stones crawling about in the mud. This, of course, will be a caddis larva walking about taking its house with it. The softer parts of the larva remain in the tube, while the front part containing the legs and head can be moved forward in order to enable the creature to crawl along.
The construction of the case is very marvellous; for the innermost part of it is composed of silk, and the decorative protection is fastened to the outside of this silken cylinder. The type of case constructed by the larva has some relations to the species of caddis fly, and many species have their own particular sort of dwelling.
If several caddis larvae are captured it is possible to carry out an experiment by which you will be enabled to watch the construction of one of these cases The larva and its case should be taken gently out of the water and then, with a stem of grass be taken gently out of the water and then, with a stem of grass or a very fine twig, you should very carefully poke the rear end of the case which will often lead to the actual larva coming out of the case. If this can de done with two or three specimens, and they are then transferred to a dish of water in which you have previously placed some very small coloured beads, you will find that in time the little larva will construct a new house for itself, using the beads for the purpose. The result is not only most interesring, but very pretty into the bargain. I have often done this, using different coloured beads for individual larvae. When they have constructed their cases they can de put into a miniature aquarium together with some water plants and the effect will be very quaint, as you might be able to see a red, a white and a blue caddis larva crawling about the bottom of their tank. In conducting these experiments you must be careful only to provide beads for the case-building ; for it you have sticks, stones, leaves and so on in your tank, the larva will probably choose these instead of your beads. After the case has been made, of course, it does not matter ; and you can make your tank as natural as you please.