Harold Bastin, Freaks and marvels of insect life, Londres, Hutchinson, 1954, pp. 104-105.
The most noteworthy aquatic case-makers are the numerous species of caddis-worms, of which almost any pond or stream will provide examples. Their cases or sheaths are familiar objects to the keeper of an aquarium, but comparatively few know what the creature inside really look like, because it objects strongly to vacate its portable house, and all attempts to persuade it to do so by the front door prove futile. But insert gently a fine grass-stem through the rear opening and the owner of the castle shuffles hastily into view. Thus seen the larva is more like a caterpillar than a grub; but its six thoracis legs are very long, and it has no pro-legs on the abdominal segments. A pair of strong hooks at its tail-end fixes it to its case. Noticeable also are tufts of soft white filaments along the side and back, thses being the tracheal gills by means of which oxygen is extracted from the water.
Naked caddis-worms dropped into an aquarium and supplied with building material soon start work on homes for themselves, and if hard pressed will utilize almost any objects of suitable size that may be given them- beads, small pieces of coloured glass, china or metal, to say nothing of scraps of cloth, fragments of paper and vegetable debris. But in normal circumstances each species evinces a characteristic conservatism and builds only with materials that its ancestors have used, following also a time-honoured plan. Thus, while some of the cases are of tiny stones, or of mixed stones and shells of molluscs (sometimes still tenanted by their owners !), others are formed of pieces of leaf or grass, eihter arranged lengthwise or obliquely. Then there are flattish productions made by fixing several largish fragments of leaf together, and others, again of cylindrical form laboriously constructed of sand grains, with the invariable addition of a trailing bit of twig or reed-this, probably as Réaumur suggested for the purpose of adjusting the specific gravity of the case to that of the water in which it is immersed. In this way the transportation of the case, already nearly floating, is rendered easy, and the larva clambers nimbly among the stems of plants, and over stones, oblivious to the fact that it is dragging a loas which, in the air, would prove all too heavy for its utmost exertion. Those species whose cases are made wholly of heavy materials, such as gravel, never leave the bottom of their stream or pond. Perhaps the most wonderful of all these caddis-worm’s cases are those which consist of innumerable sand grains pieced together to form an elegant, curved tube not unlike the elephant’s tusk shell of the sea-shore.
The cement used by caddis-worms for fixing together their building materials is a secretion of the salivary glands indistinguishable in essence from the silk spun by caterpillars ans similary issues in a viscid state from a « spinneret » situated just behind the mouth.