The variations in this butterfly are shown by the differences in the marking of both surfaces of the wings. These markings may run from a faint blackish border along the extreme margin and a few faint dots upon the under surface, to a wide black margin around the wings and a deep abundant spotting of the under surface. The markings of the various forms are so uniform that the varieties are easily distinguished. It is beyond the scope of this book to attempt to differentiate all these varieties but any reader interested will find an admirable summary of the conditions illustrated by an excellent plate in Comstock's "How to Know the Butterflies." The species as a whole may be known from the fact that the upper surface is blue, the lower surface ash-gray, more or less spotted with dark brown, and the wings are without tails. (_See plate, page 256._) _The Strange Structures of the Larvae_ A remarkable variation of the adults is sufficient to give this species a special interest, but the larvae also have a unique attraction for the naturalist. The mother butterflies lay their eggs upon the flower buds of various plants, especially those which have clustered racemes of blossoms. These eggs hatch into minute slug-like larvae which feed upon the buds, commonly burrowing through the calyx lobes and devouring the undeveloped stamens and pistils inside. They finally change to chrysalids, which are more or less securely attached to a central flower stalk, from which in due time the butterflies emerge. So far there is nothing remarkable about this story of the life of the Spring Azure, but that is yet to come. These little caterpillars are subject to attack by tiny parasitic flies which lay eggs in their bodies. Each egg hatches into a still more tiny maggot that lives at the expense of the tissues of the caterpillar and finally kills it. When one of these little caterpillars has its head buried in the round ball of a flower bud, about half of its body is exposed defenseless, so that the little fly that lights upon it to lay her egg cannot even be dislodged by the head of the caterpillar, as is often the case with other species. There is a very curious provision for defense, however. If you look carefully through a lens at the hind part of the body you will find a little opening on the back of the seventh abdominal ring. This opening leads to a sort of tiny pocket, a pocket which the caterpillar can turn inside out when it so desires. Now the curious thing about it is that the caterpillar, while this pocket is concealed in its body, is able to secrete in it a drop of liquid which we presume to be sweet to the taste. When the little pocket is partly filled with this drop of liquid the caterpillar turns it inside out in such a way that the liquid drop remains in position on top of the protruded pocket.