Charles Kingsley, The boys’ and girls’ book of science, Londres, Strahan & Co., 1881.

Looking down the bottom of the pond we may behold little objects, apparently strips of leaf, dried straws, and shell-covered tubes, moving about with every evidence of life. These quaint things are the larvae of Caddis-flies bearing about their portable homes. In these strange dwellings they remain concealed from view, with the exception of the head and the three first rings of the body, which protrude from the entrance of the cylindrical abode. Réaumur, who devoted much time to the study of the habits of the Caddis-worm, gives the following account of their mode of constructing their cases: –
“The body of these grubs is lodged in a silken tube, the inside of which is smooth and shining. On the exterior of this case are fastened fragments of different materials, serviceable in strengthening it, and necessary to make the garment complete and to give it useful qualities. The elegance of the external form seems to be a matter of small moment to the Caddis-worms: the appearance of some of these tubes is most grotesque, – the outside is often bristling and full of inequalities. Others, again, make themselves garments which have a neater air, the pieces which compose them being symmetrically disposed one upon the other. They change their garments whenever occasion demands it – that is to say, when the tube they occupy becomes too narrow and short, they make themselves one of more suitable size.”
For this work they employ every variety of material, and with the happy faculty of “making the best of everything,” adapt it to their requirements with wonderful ingenuity. Leaves, scraps of withered foliage, stalks of plants, small sticks, slips of straw, roots, tiny pebbles, shells of aquatic molluscs, and grains of sand are all stuck together without the slightest semblance of arrangement. When the little abode is as yet incomplete, should the Caddis-worm alight upon an object likely to add to the solidity of the tube, is appropriated with all speed.
“A Caddis-worm occasionally finds two scraps of the stem of a reed bruised and split lengthways, and if it has as yet only adorned its sheath with small materials, so that it is neither strong enough nor sufficiently large, the Caddis-worm makes a very nice little overcoat with the two slips of reed it has had the good luck to discover, and which it can adjust without much difficulty. It places the tube in the two reed fragments, which it then draws together as closely as possible.” *
Then, again, there are Caddis-worms who decorate the outside of their tubes with the shells of fresh-water mussels and snails; and sometimes with complete disregard of the feelings of the owners, these shells are attached to the sheath while the occupant is still alive, and so firmly are they cemented that no effort of the creatures enables them to remove themselves or to regain their freedom, and in this ignominious manner are they compelled to move about at the will of the insect into whose power they have fallen. Though the Caddis-worm seems so indifferent to the external beauty of its residence, it has sense enough to attend to a far more important particular. It is endowed with a wonderful instinct, which teaches it to avoid making the specific gravity of its dwelling greater than that of the surrounding element, as otherwise the freedom of its movement might be materially hindered. As it is even, it progresses at no great rate in the water.
p. 189-190

V- CAD-BAIT – CADDIS-FLIES

Everyone knows the odd little creatures who are so useful to the anglers, so that a few words will tell the story of their absurdities. If there be anything more comical in nature than the proceedings of a Caddis-worm, I certainly do not know where to find it. They are amusing without being immoral, and this is more than one can say for some other creatures when walking about with whelk-shells on their backs, but one can never help the uncomfortable sensation that they have been burglars and murderers; one has a conscientious objection to laugh at an individual who has obtained a freehold property by eating the original owner. A Caddis-worm does not fall to such a depth of degradation, for he only appropriates the house of the water-snail, and carries its living tenant about with him. This seems to be attended with discomfort to the struggling victim, and I have been often tempted to take the cad from the water and release the unhappy mollusk; upon second thoughts I have decided not to interfere, and as I should probably injure the Caddis-worm more than help the snail, I neglect the opportunity of aiding one animal at the expense of another. These worms, which are commonly called Cad-bait, find themselves inhabitants of the water when they leave the egg, and so far resemble the Dragon and May-fly larvae. But from this point of its life it behaves differently from either of the other water-babies. Without hesitation it sets to work to protect itself from any natural enemies who may be prowling about with good appetites. “Ah,” sighs the poor unprotected larva, “a soft worm like me is just the thing such creatures as trout and perch eat. I will just make myself an unpleasant morsel.” And then she sets to work, and carries out her resolution with such good-will that any creature attempting to eat her would have good courage and better digestion; even then such game would be hardly worth its capture.
Different species of Caddis have different tastes in architecture, and may be known by the materials and fashion of their houses, just as well as the old Greeks and Romans. One species prefer leaves of grass and taking four or five of them, will fasten them together with delicate threads to form a long case open at both ends. Another takes rushes, and unites the pieces with a kind of glue in such a pretty fashion that its house belongs to a very regular order of architecture; another has fine sand curiously packed together; and fourth, old pieces of stick, But those that I know best are utterly unscrupulous, and take sticks, leaves, pebbles, and snails to carry out their defensive works. The ridiculous part of the proceeding is that the occupants of the shells are alive, and have a great wish to move one way, while the Caddis, whose property they are, persistently takes them in an opposite direction. The worms of it is they can never get free, unless it be true that each time the Caddis grows too big for the old case, she makes a new one from fresh materials. This has been proved to be her plan, but not in a way that helps snails much. Caddises who were originally content with homes of leaves and rushes, as they grow older, seize animals and sticks, that they may have stronger defences. The bottom of a clear pond on a fine day, if there are Cad-bait in it, is as much fun as an aquarium at the Crystal Palace. At the bottom of the water are seen little masses resembling wood, pieces of straw, or moving stones: catch some of these in a fine hemp-gauze net, and when you first look at them, you will believe that mud and stones are the only prizes obtained. Hold the net quietly just below the surface of the water, and watch anything that appears like a symmetrical mass. Presently, a little head peeps out at one end of it; not seeing or smelling any danger, six little feet soon follow, and then part of a long thin body. Then the case clears itself of the surrounding mud, because it is fastened to the end of the worm’s body by two hooks, and begins to move solemnly about the net. Shake the net, or drop something into the water, and in a moment the little being draws back into the case, and looks a lifeless object, nor does it again venture forth until fairly sure that peace is restored.
This kind of amusement is harmless enough, if there be no fishermen about, but there is a little chance of the worms again touching the bottom of the pond if any anglers know where they are to be found. A wise old sportsman who thought himself a match in craftiness for any salmon, trout, pike, or perch, in any river within the four seas, wrote a book to inform other fishermen of the wonderful things he discovered. Amongst these is an account of the use of Caddis-worms, which he says are very tempting to fish; if he had not called them pipers, cockspurs, straw-worms, ruffcoats, sand-flies, grannums, cinnamon flies, and silverhorns, his directions would be clearer to the non-fishing part of the community, although I daresay the other part understand him quite well. However it is easy to imagine that the fish are soon caught when they see the tempting worm unprotected by any vegetable or animal abominations in the way of cases, and for this reason Cads are very popular bait for anglers to use.

It may be asked what becomes of the old cases? Now, we are not quite sure about what happens just at this time, but we can guess, because there is a large limestone rock where the Caddises who lived long ago have left their story. Some thousands, possible millions, of years ago, a great deal of water was forced from the country of Auvergne in France. How this happened does not matter to us just now, but it left behind it the sediment or mud which is under all rivers and brooks. This has hardened into a mass of rock called limestone, and when pieces of it are broken away, it is found to contain numbers of these Caddis-worm cases such as we find now. It is so long ago since this rock was under water, that there are no stories written in the world of what happened then, and only these unwritten ones of the Caddis-worm cases help us to guess how things went on. Fancy what clever little atoms they are! All that long time since they knew exactly the best soft of houses to live in, and we have never discovered this important fact for ourselves; even the right way to warm our homes is amongst the mysteries of the future. But if a Caddis were really as intelligent as it ought to be, surely it would have found out something after all these years; but no, it is the most conservative creature, and declines the privilege of letting the old order give place to new, either in its life or its architecture. This, you know, is very provoking, and not at all what Mr. Darwin, Prof. Huxley, and all the sensible part of the world expect. Everything ought to be capable of improvement, even Caddises, and so we must hope they may some day find themselves in circumstances that will cause them to add new conveniences to their house, if they want them. One thing is certain: they helped to make that limestone rock, but only because they could not avoid it; and just the same thing may be said of the old cases of the Caddises now: a really industrious creature is a rock-builder like the corals, but these things leave their cases behind them, and the rock makes itself, which is a very different thing.
One thing Caddises are very careful about: their houses must be fairly easy to carry; to make sure of this they have many contrivances to regulate the weight of them. They manage to adapt themselves to the quality of the element they are in; the same species behaving differently in the same pond when any change occurs in the water. In a “Fairy Tale for a Land Baby” there is a fact which illustrates this, and we may be sure that the author saw it himself, although he did not tell us the reason for it in a fairy tale. Of course we can find a cause now for the curious proceedings he relate:-
“Tom went into a still corner, and watched the Caddises eating dead sticks as greedily as you would plum-pudding, and building houses with silk and glue. Very fanciful ladies they were too: none of them would keep to the same materials even for a day. One would begin with some pebbles, and then she would stick on a piece of green wood, then she found a shell and stuck it on too; and the poor shell was alive and did not like at all being taken to build houses with; but the Caddis did not let him have any voice in the matter, being rude and selfish, as vain people are apt to be; then she stuck on a piece of rotten wood, then a very sweet pink stone, and so on until she was patched all over like an Irishman’s coat. Then she found a straw as long as herself, and said, “ Hurrah! My sister has a tail, and I’ll have one too,” and she stuck it on her back and marched about with it quite proud, though it was very inconvenient indeed. And then tails became all the fashion among the Caddis-worms of that pool, and they all toddled about with long straws sticking out behind, and getting between each other’s legs, and tumbling over eachother, and looking so ridiculous that Tom laughed till he cried.”
Now we can see that this straw was stuck on as a sail to help the Caddis along; something in the water or in the materials was uncomfortable, and by way of making the best of it, the Caddis stuck on a straw. A leaf or a part of a rush is sometimes used instead, but some object of the kind is an absolute necessity, as her home must be light enough to carry about. So much for the home, but now for the food. Truly, I think the word “cad,” as boys commonly use it, to express some mean and grasping companion whose motto is, “ Get what you can, never mind by what means,” must have been taken from these worms. Anything vegetable or animal that comes in their way they will eat with as little scruple as they would take a living snail to put on a roof of their house. They are most certainly “cads,” and I can find no excuse for their selfish conduct; and if the word have not been adapted from them, it might be.

(p. 222-225)