They eat the larvæ of the May flies when they can find them and no doubt they build these strong cases about themselves to prevent the May fly larvæ from returning the compliment.
Frank has found some empty cases, yes, and some that are closed at both ends.
Now, let us look at this one closed at both ends. What do you suppose is in it?
We will open just one of these closed cases.
There! It is a pupa! Yes, Nell, a very pretty doll is this.
It has a thorax, you see, and an abdomen. Its long antennæ lie close to its body as do its little wing pads.
Yes, the caddice larva grows and moults in the usual way. It keeps adding to its house as it grows longer. Finally, it closes the end of its little tube and lies quite still.
You know what happens next. Its wormlike form divides into thorax and abdomen. Legs and wings appear, attached to the thorax. In short, it is no longer a wormlike creature.
Finally, it comes forth from its case. It never goes into it again.