Anonyme, « Entomology », The Young Lady’s, Book, a Manual of Elegant Recreations, Exercises, and Pursuits, Londres, Vizetelly, Branston & Co., 1829, p. 164-165.
If you be desirous of examining the insects to which I am alluding, you have only to place yourself by the side of a clear and shallow pool of water, and you cannot fail to observe, at the bottom, litte oblong, moveable masses, resembling pieces of straw, wood, or even stone: these are the larvae in question, well know to fishermen by the title of Caddis-worms; and which if you take them out of the water, you will observe to inhabit cases of a very singular conformation. Of the larva itself, which somewhat resembles in the Caterpillars of many Lepidoptera, nothing is to be seen but the head and six legs, by means of which it moves itself in the water, and drags after it the case, in which the rest of the body is enclosed, and into which, on any alarm, it wholly retires. The construction of these habitations is very various. Some select four or five pieces of the leaves of grass, which they glue together into a shapely plygonal case; others employ portions of the stems of rushes, placed side by side, so as to form an elegant fluted cylinder; some arrange round them pieces of leaves, like a spirally-rolled ribbon; others inclose themselves in a mass of the leaves of any aquatic plants, united without regularity; and others, agin, form their abode of minute pieces of wood, either fresh or decayed. One, like the Sabella, forms a horn-shaped case, composed of grains of sand, so equal in size, and so nicely and regularly gummed together, – the sides, throughout, being of the thickness of one grain only,- that the first time I viewed it, I could scarcely persuade myself it could be the work of an insect. The case of P. Cimaculata, which is less artificially ci-onstructed, of a mixture of mud and sand, is pyriform, and has its end curiously stopped by a plate, formed of grains of sand, with a central aperture. Other species construct houses,which may be called alive, forming them of the shells of various aquatic snails, of different kinds and sizes, even while inhabited ; all of which are immoveably fixed to it, and dragged about at its pleasure,- a covering as singular as that of a savage, who instead of clothing himself with squirrel’s skins, should sew together, into a coat, the animals themselves. ( Vide Figs. 75,76,77,78, and 79).
Under these circumstances our Caddis-worms evince their proficiency in hydrostatics ; selecting the most suitable substances ; and if the cell be too heavy, gluing tightly a bit of leaf or straw ; or, if too light, a shell, or piece of gravel. It is from this necessity of regulating the specific gravity, that to the cases, formed with the greatest regularity, we often see attached a seemingly superfluous piece of wood, leaf, or the like.