William Houghton, « Caddis-Worms and their Metamorphoses », Londres, Popular Science Review, vol. 7, 1868, p. 288-290.
The insects belongin to the family of Phryganeidae (order Trichopetera of some entomologists) derive their name from the Greek word « a fagot » or « dry stick, » in allusion to the bits of stick of which the larvae very frequently make their habitations. This method of constructing their cases, in which the larvae and nymphae reside appears to have been noticed as early as Aristote, who says : » There is a small worm-like creature called Xylophtorus ; its variegated head extends beyond its case, its feet are the upper extremity, as in other worms ; the rest of the body is contained in a case made of a substance like a spider’s web, around and outside of which are chips of wood, so that the animal walks about with this attached to it. These creatures are attached to their cases as an oyster to its shell ; the whole of the case is joined to the worm, and does not fall out of it, but can be drawn out, as if they grew together. If anyone pulls off the case tha animal dies, and becomes as helpless as a snail without its shell…/…All the larvae of the Phryganeidae are aquatic ; most of them pass this stage of their existence in movable cases of various materials and forms ; but others are enclosed in non-movable cases. The materials out of which the different cases are constructed are bits of stone, sand, wood, grass, leaves, the tenanted and untenanded shells of various fluviatile molluscs. The cases are, for the most part cylindrical, and open at each end. The fragments of stick, small angular pebbles, &c., which the larvae use in the construction of their habitations, are held and cemented by means of a sticky secretion spun from the mouth, as in caterpillar. Of these important organs I will speak by-and-by. Sometimes one meets with cases made of sand, having on either side long slender pieces of stick or rush : the cases are in some instances prettily curved ; these are made of fine sand. Some larvae arrange their materials of stick or straw transversely ; others employ the same materials, but arrange them longitudinally. I am of opinion that, as a rule, each species of Phryganeidae arranges its materials according to a uniform pattern, but that numerous exceptions occur in this particular, depending upon a change of locality. A species for instances, that dwells in the almost still pools under the banks of a rivulet, would form its case of light materials ; but id the same caddis-worm were to be deprived of its house, and placed in the current of a gently running stream, it is very likely that the larva would build a heavier dwelling-house, suitable to the change in its position. Various experiments have been tried on the caddis-worms, with a view to ascertain the materials they would make use of in the construction of their house, and the modes of employing them. In the « Intellectual Observer » (vol. V, p. 307-317), the reader will find a very interesting account, by Miss Smee, of caddis habitations. The author after denuding some worms of their cases, placed in the vessel of water which contained them various materials, such as coloured glass ,cornelian, agate, onyx, brass filings, coralline, tortoishell, which the worms were able to convert to their architectural purposes ; figures of several of these articially constructed cases may be seen in the plate which accompanies Miss Smee’s account.
Some writers have maintained that when the case becomes too small for the larva, it quits it and forms a new one ; but M. Pictet says that it adds fresh materials of an enlarged diameter at the aperture, cutting off a portion of the opposite end. The larvae of the Phryganeidae differ slightly, according to the species to which ; they belong ; in general appearance they are of a cylindrical form, fat and fleshy, a delicate mouthful, no doubt for a hungry fish ; the case they inhabit are a protection to their naked body, and save them from becoming the prey of many fish. A voracious trout, however, does not scruple to swallow house and tenant together. I have frequently found the débris of their habitations in the shape of gravel and bits of wood in the stomachs of trout.