“Why are they always adding to the length of their cases?” asked Tom.
“Because they are always growing,” said Frank.
“That is the reason,” said Uncle George; “and they grow so fast that they have actually to work hard at building.
“Observe those that make their cases out of tiny shells and stones. They have made free use of the coloured beads and small pieces of coal which we put in.”
“How do they manage to stick these things together?” asked Tom.
“A caddis worm is a busy creature,” his uncle replied. “He does two things besides eating and growing. With those strong pincers, which you see at his head, he saws off pieces of weed.
“Near his mouth he has got a kind of loom for spinning silk. These pieces are stuck together with silk, which is a gluey substance when it first comes from the creature’s body.
“Why does he have to make a house for himself, and carry it about with him?” said Frank.
In answer to this, his uncle took out a few of the active caddis worms, and placed them in a saucer with water. He held one up.
“You see,” he said, “his case is open at both ends. Now, if I tried to get him out from the front, I should never manage it. This is the way to get him out.”
As he spoke, Uncle George pushed the head of a pin into the tail end of the case, and the creature scrambled out at once.
“It is too bad turning you out of your cosy room, Mr Caddis,” Uncle George observed; “but you’ll go back again as soon as you get the chance, won’t you? I want my nephews to understand why you work so very hard.
“Now, Frank, you can answer your own question, I think—‘Why does the caddis worm build a house?’”
“Quite right. But why is he forced to protect his body?”
“Right again, Frank. If trout could speak, they might tell you that the sweetest morsel in the stream is the caddis worm. Now, take your lens, please, and tell me something about him.”
“His body is divided into rings, and there are the same number of them as we found in the caterpillar.”
“Very good, Frank. Now give Tom a chance.”
“His head and the first three divisions of his body are hard cased. They are black and yellow in colour.”
“He has six legs,” said Frank, “and they are attached to the first three divisions of his body.”
“What about the last division of his body?” Uncle George asked.