The life-story of a generation of these butterflies is much like that of the other Yellows. The eggs are laid, one in a place, on the leaflets of various species of wild senna (_Cassia_) and soon hatch into cylindrical caterpillars that devour the tender leaflets. In a few weeks the caterpillars mature and change to curious and characteristic chrysalids. The head projects in the shape of a cone and the back is so concave as to give the side view of the chrysalis a very striking appearance. Like so many of the Yellows this butterfly is sun-loving and social in its habits. Great numbers flock together, their large size and bright coloring rendering them very conspicuous. They often alight on the ground to sip moisture when they have been likened to beds of yellow crocuses. They also fly long distances in flocks that attract much attention. It is likely that the northward distribution takes place in summer through such migrating hosts. _Other Sulphur Butterflies_ The Large Orange Sulphur is a closely related butterfly of about the same size, in which the coloring is uniformly orange-yellow instead of lemon-yellow. It also belongs to the tropics, occurring in our extreme Southern states and ranging occasionally as far north as Nebraska. The Red-barred Sulphur is another splendid butterfly, somewhat larger than the Brimstone, which is easily distinguished by the broad reddish bar across the upper surface of the front wings. It is tropical but migrates rarely even as far north as Indiana, Illinois, and Wisconsin. =The Dog's-head Butterfly= _Meganostoma caesonia_ The Dog's-head butterfly furnishes one of the most remarkable examples of accidental resemblance in wing markings that can be found in the whole order of scale-winged insects. It is comparable with the skull and crossbones on the back of the death's-head moth. In the butterfly the middle of the front wings has a broad band of yellow against a black margin on each side and the yellow outlines make an excellent silhouette of the profile of a poodle with a large black eye-spot in exactly the proper place. The females are less brightly colored than the males but they still show the dog's-head silhouette. This is a southern species, which occasionally strays as far north as New York City, New Hampshire, Wisconsin, and Iowa. The larvae feed on species of Amorpha and are believed to be three-brooded in southern regions where the butterfly occurs.