Glenwood G. Clark, Tiny Toilers and their Works, Londres, J. Coker & Co., 1921, pp. 119-125.

An insect submarine

Man is a wonderful creature. Though his body is heavier then air, he can make himself ballons and aeroplanes, and in them soar above the clouds and the highest moutains. He cannot run or walk far without becoming tired, but in his motor-cars and trains he can hurry about over the earth for thousands of miles at a dizzy speed. Not only can he fly in the air and travel over the surface of the earth, but in boats ha has built he can cruise on the warm seas of the tropics or under the frozen oceans of the poles. Though he is a breather of air, without which he canot live, he has learned how to dive beneath the ocean and travel in safety under water. This he can do in his diving-suit and in his submarine. We praise man and his mind that enabled him to build such odd craft, but he was not the first creature to build and navigate underwater boats. Hundreds and hundreds of years before man learned how to construct submarines a little creature, only a few inches long, built and operate them. Despite his wonderful mind man was beaten by an insect, for the first inventor of a real submarine was the larva of the case-making caddis or Limnophilus flavicornis.

The little ship-building insect is found in almost any brook, and a member of his very large family is sometimes discovered in ponds, though the caddis usually prefers running water. When one hunts for this creature and its old boat one must have sharp eyes or one won’t see it, even though it is right under one’s nose. Sometimes when looking into a brook one is surprised to notice a heap of stones or small pebbles moving about over the bottom of the stream. One blinks and rubs one’s eyes. Surely the dancing little waves or the glint of the sun on the water is playing pranks with one’s sight, for pebbles do not move of themselves ! As one looks again, the moving pebbles crawl moved on there is no worm there. It has disappeared inside the moving lump. Thoroughly interested the watcher picks up this mysterious lump and turns it about in his fingers. It is just a lot of tiny shells and small pebbles stuck together. Despite its rough, commonplace appearance that oblong mass in the first submarine ever built, and safe within it is its builder, the caddis-worm. Looking closely, one discovers that these pebbles are glued together. If the investigator prizes them apart with the point of a kniffe he will break into a narrow apartment snugly lined with silk and it he will find a fat white grub with large head and huge jaws. This is the owner and navigator of the submarine. The little boatman has many ennemies in his watery world, and he know a hungry fish or a water-beetle would like to gobble him up if it could get a chance. Then, too, the caddis knows that soon he is going to fall asleep for a long nap, so, to provide himself a snug bedroom, he covers himself with anything he can find to hide and protect his plump white body. The worm is born without any covering, and his first thought is to conceal himself from his ennemies. As he crawls about over the bottom of the brook he finds a bright pebble and immediately fastens it on his back with a drop of liquid glue that quickly hardens. Later on hem ay happen upon an empty snail-shell or a bit of bark, and he adds that to the pebble. In a short while his whole body is covered with a weird case of such odds and ends. If an experimenter pulls the worm out of his houseboat, the creature immediately constructs a second covering as quickly as possible. Some naturalists have got the caddis to make beautiful cases of coloured beads by taking away his natural case and giving him only glass beads to work with. By changing the beads ar intervals the nature-experimenter makes the caddis cover himself with a case of red and blue and green beads arranged in bands or in wonderful variegated patterns. However, though he will use almost any material he can find, the caddis prefers the shells and pebbles found in his native stream.
His rough case of shells and pebbles is both a house and a submarine for the caddis. Outside it is ill-shaped and bumpy, but inside it is a long tube beautifully upholstered with the softest silk spun by the boatman himself. From his front door, which is left open the purpose, the caddis sailor can thrust out his head to watch for food. He can also put out his legs somewhat after the fashion of a tortoise, for his six legs are at one end of his body, close to his head. These legs have little hooks at their ends, and with them the navigator drags himself and his boat along the bottom of the stream as he cruises about in search of food. Then, too, these hooks serve as anchors to hold him in place against the currents and eddies in the brook when he attaches them to an immovable pebble.
But the caddis does not like to remain at the bottom of his brook all the time. He loves to swim about in the water and float lazily in the sun out the surface. His submarine of pebbles and shells is heavier than water and will not float of itself. Before it can float it must be made lighter than the water in which it is placed. Man’s body is heavier than water and will sink in it, but he has made himself water-wings and life-preservers by filling bladders and rubber belts with air. By fastening these to his body man can float safely on the surface. The caddis has discovered the same secret and uses air to transform his case into a submarine.
When the caddis wants to turn his house into an ordinary boat he crawls up a reed or a water-plant until he reaches the surface of the stream and is in the open air. There he draws himself a little way out of his case. A tiny spaces is left at one end of his boat and air rushes into it. Because of his reservoir of air the caddis and his boat scan now float on the surface of the water . His legs are not very good oars, but Mr Caddis can paddle about with his a long as he wishes.
It the small boatman desires to descend under water he has only to creep a little farther back into his case. This crowds out a small bubble of air and the little boat, losing some of its lightness, sinks beneath the surface and hangs midway between it and the bottom. Now, in true submarine fashion, the clever insect takes long cruises in search of food. If he wants to sink all the way to the bottom where he can hide among the stones, the wise navigator forces all the air out of his boat and its immediately sinks.
But the skilful caddis does not always navigate his submarine in safety. Sometimes, when he is floating peacefully along, a huge black water-beeetle, the bold pirate of those seas, spies the queer boat, and, diving after it, makes frantic efforts to break it open and eat the sailor. While the rober is busy tearing at the pebbles and shells of the submarine the cunning caddis crawls hastily out of the open end of it and, escaping beneath the very legs of his enemy, sinks to the bottom of the stream. There he hides and begins the building of another boat.
After many cruises the little navigator begins to feel sleepy. Then he seals uphis front door so that his submarine looks more like a stone thane ver and goes to sleep. When he awakes he swims to the surface, casts off his old skin, and comes out as a caddis-fly, a lovely creature with wings. For the rest of his short life he flies in the air, a submarine-builder transformed into a living aeroplane.