In all cases the caterpillar feeds on the plant on which he is hatched from the egg. When he is ready to come out of the egg all he has to do is to bite a hole in his shell and crawl forth. Then, at once, he begins to eat. He may begin at the tip of the leaf, and eat up to the mid-vein on both sides. He is careful not to bite the mid-vein. When he has had a full meal, he goes and lies along the mid-vein to rest. Then, when rested, he eats again. Many do this, but not all. When one leaf is finished, he takes the next one on the twig. After the first leaf he is not so careful to begin at the tip. He just bites out pieces anywhere, but he does not bite the big vein. Perhaps it is too hard. Perhaps he knows he must have it for a roadway. Do you remember what you read in the First Nature Reader about the spider, which has in her body little knobs for spinning silk?[22] The caterpillar has a silk-spinner. It is in the underside of his head. It is a little tube in the shape of a cone. Did you ever notice the queer way a caterpillar has of wagging his head from side to side? He acts as if in great pain. But he is not in pain. He is only laying down a silk web with that motion. It is by means of this silk that the caterpillar makes his home. Let us look at him while he works. He fastens his line to the edge of a leaf. Then he carries it to the other edge, or to the next leaf. Then another line, and so on. Each line is a little shorter than the one before. This bends the leaf. At last it is bent into a tube, or box, or several leaves are bound into a bower. The caterpillar bites a notch, or line, in the tip of the leaf to make it bend over for a roof. Is not that cunning? Think how strange it is, that a tiny thing, just out of the egg, away up alone on a tree, should know how to build this pretty house! The caterpillar of the swallow-tail chooses a leaf for a home, weaves a silk carpet over it, and lies along the mid-vein. What do you think he does on rainy days, when the water begins to take his bent leaf for a spout or gutter? He builds a second floor of silk, a little higher up, between the edges of the leaf. That makes a nice, dry, silk hammock. There he lies, while the water ripples along the mid-vein below him. I suppose the sound of the water sings him to sleep. A caterpillar which makes a bag of a nettle leaf, for a nest, lies in it so snug that he is too lazy to go out for food. So he eats up his roof for his dinner! Another caterpillar draws a leaf together into a pretty little pocket. He weaves silk over it, outside and in, and then,--he eats up this dear little home, and has to make another! These caterpillars make their homes for summer. There are some which need winter homes. The caterpillar of the Viceroy butterfly is only half-grown when winter comes. He lives in a willow-tree. He makes his warm winter house of a willow leaf.