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Updated: May 21, 2025
A hard winter doubtless commits sad havoc among the caddis and larvae at the bottom of the river; the trout, not being able to get much fly, are then compelled to fall back on the crustaceans. The food in these limestone rivers is so plentiful that the fish are able to pick and choose from a very varied bill of fare. This is the reason they are so difficult to catch.
When the time comes to return to the quiet of the mud bed at the bottom, the animal, having had enough of the sun, draws itself wholly into its sheath again and, with a piston stroke, expels the air from the back room. The normal density is restored and it sinks slowly to the bottom. We see, therefore, that the caddis worm has not to trouble about hydrostatics when building its scabbard.
That is enough: the secret is out. When cased in wood or in shells, the caddis worms, which are always heavier than water, are able to keep on the surface by means of a temporary air balloon which decreases the density of the whole structure. This apparatus works in the simplest manner. Consider the rear of the sheath.
Obviously, my denuded caddis worms cannot start their work with bricks of this kind. Where would they fix their first layer? They must have a foundation, quick and easy to build. This is once more supplied by a temporary cylinder of watercress roots. On this support follow the grains of rice, which, grouped one atop the other, straight or slanting, end by giving a magnificent turret of ivory.
I am ready to see its origin in the persecutions of the Dytiscus and other pirates. Necessity is the mother of industry. Certain caddis worms, of the Sericostoma and Leptocerus species, clothe themselves in grains of sand and do not leave the bed of the stream.
The fairies had washed him, you see, in the swift river, so thoroughly, that not only his dirt, but his whole husk and shell had been washed quite off him, and the pretty little real Tom was washed out of the inside of it, and swam away, as a caddis does when its case of stones and silk is bored through, and away it goes on its back, paddling to the shore, there to split its skin, and fly away as a caperer, on four fawn-coloured wings, with long legs and horns.
Caddis had previously stood eminent as an iceberg of the Lakelands' party. Mr. Inchling and Mr. Caddis were introduced. The former in Commerce, the latter in Politics, their sustaining boast was, the being our stable Englishmen; and at once, with cousinly minds, they fell to chatting upon the nothings agreeably and seriously.
The result of three or four similar operations is to surround the Caddis worm with a conical bag, whose wide mouth is scalloped with pointed and very irregular notches. The work of the nippers continues; fresh pieces are fixed, from one to another, inside the funnel, not far from the edge, so that the bag lengthens, tapers and ends by wrapping the animal in a light and floating drapery.
The regularity of the method produces the regularity of the work; but it is essential, of course, that the materials should lend themselves to precise coordination. In its natural pond, the caddis worm does not often have at its disposal the picked joists which I give it in the tumbler. It comes across something of everything; and that something of everything it employs as it finds it.
Here the fundamental characters of the larva are those of the Corydalus and Sialis and Panorpa, types of closely allied groups. The features that remind us of caterpillars are superadded, evidently the result of the peculiar tube-inhabiting habits of the young Caddis fly. In like manner the caterpillar-form is probably the result of the leaf-eating life of a primitive Leptiform larva.
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