One monarch butterfly flies by. Then another,and another. As they fly the butterflies seem to float on the sky. They make beautiful shadows on the ground below. They seem to be everywhere. In fact, there are so many butterflies that the groups look like beehives in the trees. And when they fly, the sound of 150 million monarchs wings creates a soft sound, as though it is raining. People say Mexico is the only place in the world where you can hear the sound of butterflies wings moving.