Jean-Henri Fabre, Insect adventures, (Retold for Young People by Louise Seymour Hasbrouck), Ill. Elias Goldberg, New York, Dodd, Mead and Company, 1917, p. 31- 36.
(The caddis-worm is the grub of the caddis-fly, which is like a small moth and is often seen flitting over our streams and ponds. There are about one hundred and fifty species of this fly in America.)
Whom shall I lodge in my glass trough, kept permanently wholesome by the action of the water weeds? I shall keep Caddis-worms, insects wich clothe themselves with little sticks and other materials. They are among the most ingenious of the self-clothng insects.
The particular species of Caddis-worm I have chosen is found in muddy-bottomed, stagnant pools crammed with small reeds. It is the little grub that carries through the still waters a bundle of tiny fragments fallen from the reeds. Its sheath, a traveling house, is an elaborate piece of work, made of many different materials.
The young worms, the beginners, start with a sort of deep basket in wicker-work, made of small, stiff roots, long steeped and peeled under water. The grub that has made a find of these fibers saws them with its jaws and cuts them into little straight sticks, which it fixes one by one to the edge of its basket, always crosswise. This pile of spikes is a fine protection, but hard to steer through the tangle of water-plants. Sooner or later the worm forsakes it, and builds with round bits of wood, browned by the water, often as wide as a thick straw and a finger’s breadth long, more or less-taking them as chance supplies them.
It does not always use wood however . If there are plenty of small, dead Pond-snails in the pond, all of the same size, the Caddis-worm make a splendid patchwork scabbard ; with a cluster of slender roots, reduced by rotting to their stiff, straight, woody axis, it manufactures pretty specimens of wicker-work like baskets. With grains of rice, which I gave the grubs in my glass pond as an experiment, they buil themselves magnificent towers of ivory. Next to the sheaths of snail-shells, this was the prettiest thing I ever saw the Caddis-worm make.
The pirates’ attack
What is the use of these houses which the Cadis-worms carry about with them ? I catch a glimpse of the reason for making them. My glass pond was at first occupied by a dozen Water-beetles, whose diving performances are so curious to watch. One day, meaning no harmand for want of a better place to put them. I fling among them a couple of handfuls of Caddis-worms. Blunderer that I am, what have I done ! The pirate Water-beetles, hiding in the rugged corners of the rockwork, at once perceive the windfall. They rise to the surface with great strokes of their oras ; they hasten and fling themselves upon the crowd of carpenter Caddis-worms. Each Beetle grabs as sheath by the middle and tries to rip it open by tearing off shells and sticks. While this is going on, the Caddis-worm, close-pressed, appears at the mouth of the sheath, slips out, and quickly escapes unde the eyes of the Water-beetle, who appears to notice nothing.
The brutal ripper of sheaths does not see the little worm, like a white sausage, that slips between his legs, passes under his fangs, and madly flees. He continues to tear away the outer case and to tug at the silken lining. When the breach is made, he is quite crestfallen at not finding what he expected.
Poor fool ! Your victim went out under your nose and you never saw it. The worm has sunk to the bottom and taken refuge in the mysteries of the rock-work. If things were happening in a larger, outdoor pond, it is clear that, with their clever way of removing themselves, most of the worms would escape scotfree. Fleeing to a distance and recovering from the sharp alarm, they would build themselves a nex scabbard, and all would be over until the next attack, which would be foiled all over again by the very same trick !
An insect submarine
Caddis-worm are able to remain on the level of the water indefinitely with no other support than their house ; they can rest in unsinkable flotillas and can even shift their place by working the ruddler.
How do they do it ? Do their sticks make a sort of raft ? Can the shells contain a few bubbles of air and serve as floats ? Let us see.
I remove a number of Caddis-worms from their sheaths and put the sheaths in the water. Not one of them floats, neither those made of shells nor those of woody materials. The Worm also, when removed from its tube, is unable to float.
This is how the Worm manages. When at rest, at the bottom of the pond, it fills the whole of the tube of its sheath. When it wishes to reach the top of the pond, it climbs up the reeds, dragging its house of sticks with it ; the nit sticks the front of its body out of the sheath, leaving a vacant space in the rear, like the vacuum in a pump when one draws ou the piston. This promptly fills with air, enabling the Worm to float, sheath and all, just as the air in a life-preserver holds a person up in the water. The Caddis-worm does not need to cling to the grasses any longer. It can move about on the surface of the pond, in the glad sunlight.
To be sure, it is not very talented as a boatman. But it can turn round, tack about and shift its place slightly by using the front part of its body, which isout of the tube, as a rudder and paddle ; and that is all it wishes to do. When it has had enough of the sun, and thinks it time to return to the quiet of the mud-bed at the bottom, it draws itself back into its sheath, expelling the air, and at once begins to sink.
We have our submarines-the Caddis-worms have theirs. They can come out of the water, they can dip down and even stop at mid-depth by releasing gradually the surplus air. And this apparatus, so perfectly balanced, so skillful, requires no knowledge on the part of its maker. It comes into being of itself, in accordance with the plans of the universal harmony of things.