Ray Palmer, Marvels of Pond Life, Londres, Thornton Butterworth Limited, 1927, pp. 129-130.
The larva of Caddis Flies will some of the first objects the collector of pond life wil meet with, and are well know to anglers who use them as bait. Most species construct portable cases, which they drag or carry about with them, only the head and thorax with its six legs protruding from the case. As soon as the larvae are hatched they set to work to construct cases of all sorts of materials, fastened together with threads of silk. This power of spinning silk seems yet another link with the Lepidoptera.
The form and materials of the case vary with the specie, but also, depend somewhat on local conditions (plate XIV, 4). Some, which are very abundant in ponds or slow streams with sandy bottoms, are simply tubes formed of particles of sand. These are always larges tat the head end and taper considerably behind ; their shape is usually somewhat curved. The larva is frequently adding to the head end of its case as it grows , and the back part becomes too narrow to accomodate its body. The body of the larva does not completely fill the case, and leaves sufficient room for it actually to reverse its position Inside. This it does periodically, and cuts off the tail end of the case as it becomes too long.
Other species use pieces of stick and dead leaves, reed stems and parts of dead water plants. Many of these attach long straight pieces of stems to their cases, which give them a very curious appearance. Some small species use green leaves, being particulary fond to the Ivy-leaved Duckweed ; while others, which live in ponds overhung by trees, make large flattened cases with the dead leaves which fall into the water. (This latter method is adopted by Glyphotoelius pellucidus, the specie shown on Plate I.) Some members of the genus Limnophilus make prickly-looking cases with bits of stick or vegetable fibres, which they cut into short lengths and place transversely. A number of species use small stones while others condine their attention to the shells of small water snails and are by no means particular to use empty ones ; in fact, living snails may frequently be found in the shells composing the cases, and may continue to live for a time, but must ultimately die of starvation.