Thomas Rymer Jones, The Natural History of Animals, vol. II, Londres, John van Voorst, 1852, p. 205- 210.
In their larva condition, they are aquatic grubs, inhabiting factitious tubes, constructed of various materials, under which aspect they are called « caddis worms » », « cadbait », « stick-baits » &. …/….
../.. The hinder portion of the body of the caddis-worm being extremely soft, it has been instructed by Nature to clothe itself in a suit of armour of unique construction. To the under-lip of the grub is attached a spinnaret, similar in every respect to that with which so many caterpillars are furnished; from this it can produce a silken thread ; and thus provided with no other tools than its feeble legs, it sets about the formation of its ingeniously-constructed residence, employing such materials as are adapted to the particular necessities of the species to which it belongs. Several kinds of these curious portable house are figured in an interesting little volume, published in the Library of Entertaining Knowledge, together with some good observations relative to the manner of the fabrication, * of wich substance is as follows.
Among the materials used these singular grubs may be mentionned, sand skilfully joined together, and strongly cemented. When leaves are employed, they are glued together longitudanally, (fig. 59h) with their ends pointed backwards, so as to form an imbricated cylinder, the leaves in front overlapping those behind, like the tiles of a house. Another species employ pieces of reeds or of grass, straw, wood (59 ef), &., cut into convenaient lengths , carefully joining and cementing each piece to its fellows as the work proceeds; and, moreover, the tenement is not unfrequently finished by adding a broad piece, longer than the rest, to shade the door-way over head of the occupant, so that hem ay not be seen from above. A still more laborious fabric is constructed by others, which weave together the leaves of aquatic plants into a roundish ball, and, in the interior of this, form a cell for their abode. A fourth kind of these ingenious architects make choice of the tiny shells of frehs-water mollusca, with which it constructs a moveable grotto (fig. 59 g); and as these little shells are for the most part inhabited, the poor animals contained in them are unceremoniously dragged about at the mercy of the tyrant whose prisonners they have become. These grotto-building grubs are by no means uncommon in ponds; and in chalk districts, such as the country about Woolwich and Gravesand, they are very abundant.
One of the most surprising instances of their skill occurs in those structures, in the building of which small stones are employed as the principal material. The problem is, to make a tube, about the width of his hollow of a wheat-straw or a crow-quill, the cavity of which shall be throughout smooth and uniform. Now the materials being small stones full of angles and irregularities, the difficulty of accomplishing this will appear to be considerable, if not insurmountable ; yet the little architects, by patiently examining the stones, and turning them round on every side, never fail to succeed in their undertaking. This, however, is only part of the task, which is complicated with another condition, namely, that the under surface shall be flat and smooth, without any projecting angles, which might impede its progress when dragged along the bottom of the rivulet which these stone-builders generally frequent. The selection of the stones as materials for building, may indeed be account for from the circumstance that this species inhabits running streams, where, but for the weight of its house, it would to a certainty be swept away by the current. In order to guard against such an accident, it is probable that the caddis makes use of larger stones than it would otherwise want; and doubtless from the same reason, cases are frequently met with which, being composed of very small stones and sand, have a large stone added to them when nearly finished, by way of ballast. Or
the reverse of this is sometimes seen, when the materials rmployed, having been found to possess too great specific gravity, a bit of light wood or a straw is addes, to render the edifice more buoyant.
We have repeatedly, says Mr. Renie, the writer of the above remarks, tried experiments with the inhabitants of these aquatic tents, to ascertain their mode of building, by depriving them of their houses and furnishing them with materials for constructing new ones, so as to be enabled to watch their proceedings, from their laying the first stone or shell of their structure. They work at the commencement in a very clumsy manner attaching a great number of chips to whatever materials may be within their reach, by means of loose threads of silk : and many of these they never use at all in the construction of their residence. They act, indeed, much like an unskiful workman trying his hand before committing himself upon an intended work of difficult execution. Their main execution is, however, to have abundance of materials within reach ; for after their dwelling is fairly begun, they do not again protrude more than half of their body in quest of substances wherewith to build ; and even when they have dragged a stone, a shell, or a chip of reed within building reach, they have often to reject it as unfit fior their purpose.
Some species, instead of constructing moveable houses, fasten their cases firmly to the surface of large stones, and consequently have to quit their retreats whenever they go in search of food. These, however, have their bodies covered with a firmer integument than the residents in locomotive habitations, and consequently are better adapted to such a kind of life.
In the construction of their cases, whether the materials employed be simply bound together with silken filaments, or, as some writers assert, also united by means of a peculiar cement, the conecting substance, which is necessarily at first produced in a fluid state, must have the property of hardening under water- a circumstance by no means to be overlooked by those who would appreciate the difficulties that have to be surmounted in the formation of these remarkable defences.
*Insect Architecture, p. 185.