Of all the insects that interest boys and girls, moths and butterflies seem to hold the first place. I find, however, that young people are not always able to distinguish these insects one from another, and do not know very much of the strange lives they lead. Perhaps you may have found out a few facts about them in books, but this is not _knowing_. To know, one must see some of the wonderful things that they do. When you have watched the whole life-story of a moth or butterfly, you will have a far greater interest in these animals than their handsome wings and graceful flight have ever given you. The most important thing to remember in the study of moths and butterflies is that they appear in four different forms during their lives. These forms are: _The egg._ _The larva._ _The pupa._ _The adult._ THE EGGS. The eggs are laid singly or in clusters. They are usually found on the plant which is the favorite food of the young. Look for the shining masses of the eggs of the tent-caterpillar on apple and wild cherry trees; also for the yellow eggs of potato beetles on potato leaves. THE LARVA. The larva or "worm" hatches from the egg. During this period in its history the insect _eats_ and _grows_. If you doubt that they have good appetites, undertake to feed a few healthy caterpillars this spring. If you doubt that they are particular as to the kind of food they have, find out for yourselves whether the apple tree "worm" will eat milk-weed leaves or whether the milk-weed caterpillar will eat leaves taken from an apple tree. One of the most interesting things to notice in the study of larvæ or caterpillars is that they occasionally appear in bright new coats, and we find the old ones have been cast aside. It is necessity, not pride, that leads them to do this. You see, an insect's skeleton is on the outside of its body; and if it could not be shed once in a while how would there be room for the little creature to grow? [Illustration: _Fig. 346. Chrys'-a-lids of the mourning-cloak butterfly._] THE PUPA. [Illustration: _Fig. 347. Cocoon of the cecropia moth. It is often attached to the twig of a fruit tree._] Of all the forms in which moths and butterflies appear, the pupa is the strangest. Although we speak of this period in the life of the insect as one of rest or sleep, it is the time when the most wonderful changes take place in its body. The queer little objects that you see illustrated in Fig. 346 are the pupæ of the mourning-cloak butterfly. When the caterpillars were about to shed their coats for the last time, they hung themselves head downward from a twig by means of a silk button which they had spun. Then they cast off their skins, leaving the chrysalids or naked pupæ hanging; protected from birds by their spiny form and protected from many enemies, even from young naturalists, by their wood-brown color which so closely resembles the support from which they are suspended.