Norman Wymer, In nature’s workshop, Londres, Harrap, 1948, pp. 69-76.
« Ah, there’s one….. No….no, it isn’t – it’s a bit of soil, or leaf or something… Wait a minute, though- it’s moving! Yes, by Jove, it is! Just what I was looking for ! See that little oblong thing right at the bottom of the pond? » I pointed with a stick. It is always a little difficult pointing out anything small when it is right under water, and it was some time before either of them could find it.
« Surely that isn’t anything? » Michael commented. « It’s just a bit of mud, isn’t it? »
«It looks to me more like a mess than anything else. » Tom can be very damping when he likes.
« Look again, then, but this time look with your eyes open! Can’t you see those funny little things sticking out at one end? Lo know! Quick! It’s moving. »
« Ah, yes! Whatever is it? » They both seemed to see it at once.
« That’s a caddis-worm moving about in the quaint little portable house he has build himself. Those little thing sticking out are his head and legs. »
Naturally, the boys were anxious to know how he built this strange house, but before telling them I explained that the caddis-worm is not really a worm at all, but the grub, or larva, of a caddis-fly – just as the Caterpillar we talked about the other day was the larva of a moth.
I told them that caddis-worms could be found in most shallow streams or pools and that they were used a great deal by anglers as bait for catching trout…/…; It is not long before they are searching round for suitable material with witch to build their homes, and are off to the bottom to start work.
There are about a hundred and fifty to two hundred different kinds of caddis-fly in the British Isles, and they make their homes with a wide variety of materials.
« The homes they build and the materials they use depend on two things » I said. « They depend, first on the type of caddis-worm, and, secondly, on where they are living. You see, the little creatures have to make use of whatever materials are available in their particular water. But they have to be guided, too, by the nature of the water itself-whether it is still, like this pond, or whether there is a current. »
« What is this one made of? » asked Tom.
« Yes, and how is it made? » went on Michael.
« This one? Well, this is a comparatively simple affair. The water here is so still that the caddis-worm has had no great problems to overcome. He has simply spun himself a little tube of silk and fastened bits and pieces of grass and twig- anything he has had handly- to it as he has gone along. It serves his purpose very well, and that is all that matters. »
« I suppose he makes his home for the same reason as the caterpillar-to protect himself? » asked Michael.
« Yes. Do you know, you would be surprised at the number of creatures that lives in even the smallest pool of water. They seem to come from nowhere, and so many of them are out to eat each other that they have to be very much on their guard. The caddis-worms is not abble to move very quickly, and so has to take sperial care. He is really in rather a difficult position. You see, although the front part of his body, containing his head and legs, is quite hard and horny, the rest of it is extremely soft and délicate. So he always tries to be certain that this end, at any rate, is covered, even though his head and legs may sometimes be exposed. And, do you know, he even keeps Inside his home while he is actually building it? »
« Very I should imagine, but the caddis-worm seems to be able to manage it. What he does is this. Immediately he has chosen his building material he takes a number of pieces and quickly spins them together with his silk to form a small circle- a very narrow circle, mind you-and into this he wriggles his back portion. As soon as he is safely settled in position he clings on the silk lining of his case by means of little horns right at the end of his body. But his head and legs are still exposed thus leaving him quite fre to continue his building activities. And so he quickly goes on spinning yet more silk and adding yet more bits and pieces, until, at last, his home is of the right length. »
Yet it is not really as simple as it sounds. I went on to explain. Many of the homes built by the caddis-worm are remarkable clever. While some of these insects will collect blades of grass and weave them together into a smoothish circular wall, others prefer to use little bits of haïr and fibre as well, so as to make them rather more bristly. Others again, choose to cut out fragments of leaf or twig and fix them in as they go, while some actually collect small particles of sand and introduce them into their silk in such a way that their finished houses are really quite solid affairs.
« But the two homes that I think are the most interesting are both made chiefly by caddis-worms living in streams, » I went on. « You see, there they have a very real problem: they have to guard against the danger of being swept away by the strong current. They have to look for a heavier type of building material, ans so choose little stones, which they carefully piece together like a human bricklayer-except, of course, that they use silk instead of cement. But what do you think the others go for? Small shells. Shells in which water-snails or other such creatures are still living. Think of that! They simply fasten them together with silk as before and then get in between them. It doesn’t seem to worry them a bit, even if the snails are still there. »
« Goodness! »
« Gosh! »
The boys were too surprised to say more. But I thought I would puzzle them a bit further by asking them a question.
« Can you see any disadvantage in home like these? » I asked. Neither of them could and, indeed, I didn’t really expect them to be abble to. So I went on to explain.
« You remember how the Caterpillar walks about in her suit of clothes? » I asked.
« yes, rather! »
« Well, the caddis-worm wants to do just the same. Now can you see it? »
« Well…oh, I don’t know. » Michael hesitated. « I was wondering whether the case might not to be too heavy to move… I mean, the caddis-worm is very tiny, isn’t he, Dad? »
« Bravo! Quite right. Cases like these would be too heavy in the ordinary way. So what do you think the clever little creature does? Why, he takes two longis pieces of stick and fixes them on to each side of his home. As he is in the water the sticks have the effect of lightening the case without, on the other hand, making it so light that it floats away. Clever, isn’t it? »
« Insects really do seem to think of everything, don’t they, Dad? »
« It is amazing, isn’t it? You know, it would take a human being a long time to find out a thing like that if he wasn’t taught the secret. Yess this little creepy-crawly comes along and, almost as soon as he is born, gets straight down to work without anyone to tell him what to do. »
« I see that this case is narrower at one end than the other. Do all caddis-worms make their homes the same shape? » Michael asked.
« What I want to know is why it is nerrower one end » Tom went on.
« Two good questions, boys. No, the homes are not always the same shape, but you will usually find that they are inclined to be narrower one end. The reason for this is simply that, unlike the caterpillar, the caddis-worm is not able to unpick his home and let in a new bit, when he grown. On the other hand, he does not want to be continually making new homes. So he carefully chooses a design that will overcome these problems.
« You see, the tail-end of the insects is narrower than the head-end. As he grows, then, he simply moves forward a little in his case and adds a piece more on to the wider end, cutting away, at the same time, a little from the back-»
« Well, at that rate, » Michael broke in, « the part that once formed the front end will later become the back. »
« That’s it. This idea makes his home both longer and wider. He merely cuts away the back because naturally, he doesn’t want to have to drag about a longer home than is absolutely necessary. »
« I suppose he moves along with him because as I told you, he is clinging on to the silk lining with the little horns at the back of his body. »
But, lest the boys should imagine that the caddis-worm simply wandered round eating, I told them how the time would come when, like the caterpillar, he would decide to go into a chrysalis, preparatory to becoming a fully develpoed caddis-fly…/…
I was just wondering how to get the boys away from the pond now that I had finished telling them about the caddis-worms- it was getting late and I thought it time to be going- when I hit upon a bright idea.
« Run and ask Aunt Edith if she can let you have a jam-jar, »I said, turning to Michael.
« A jam-jar ? What for, Dad? »
« We’ll take this caddis-worm home in the jar. Then, when get back, we’ll carefully take him out of his home and place him in water with a fex bits of stick and stone and odds and ends. In that way you will both be able to watch him make a new case for himself. »
« Oh, yes. Gosh, what fun! »
So Michael and Tom went bouding off to ask Aunt Edith for a jam-jar. And when we has safely placed the little caddis-worm- still in his house- in the jar I thought they seemed almost rude in their hurry to get back home again. But Aunt Edith understood. She knew what all their excitement was about, and she was delighted to see their pleasure. You see, she’s a nature-lover herself.