Theses circumstances

William Sweetland Dallas, Elements of Entomology: an outline of the Natural History and Classification of British Insects, Londres, John Van Voorst, 1857, p. 216-217.

But the most singular thing connected with these larvae is the faculty which they possess of forming a portable habitation for the protection of their soft bodies, which they appear very justly to suppose would constitute too temting morsels for the voracious fishes, their cohabitants of the water, if left freely exposed to view. These consist of tube composed of various extraneous materials, such as fragments of leaves, straws, small sticks, sand and stones ; and some species even make use of the shells of the small freshwater mollusca in the construction of their domicile, without paying much attention to the feeling of the rightful owners of the dwelling thus appropriated * The building materials are united into a tube of the required form by means of delicate silken threads, which the larva spins from a spinneret situated beneath the labium, and, according to M. Pictet of Geneva, the creature increase the size of its habitation by the addition of materials at the mouth, at the same time cutting off a portion of the opposite end. The tube are open at both ends to allow of the free passage of water, which is absolutelt necessary to enable this fluid to come in contact with the gills, as without this, respiration could not be affected. To retain them firmly in their tubes, the larvae are provided with a pair of jointed, hook-like appendages at the extremety of the body, which are assisted in most instances by three fleshy tubercles on the first segment of the abdomen.
From the mouth or anterior opening of this curious habitation the larva protrudes its head and the first three segments of its body bearing the legs, and as the case is generally composed of materials which are scarcely, if at all, heavier than water, it has little difficulty under theses circumstances inkeping its house over its tail at all events, wherever it goes.

*A few foreigh species make a spiral case like a small shell.