All over the world, unlikely pairs of plants and animals work together. Under the sea, the stinging anemone protects the boxer crab in exchange for food. In the desert, the woodpecker shelters inside a tall saguaro cactus and then distributes its seeds so more will grow. Near the water, the mighty hippopotamus stays pest-free because of the hungry egret that rides comfortably on its back. Even humans have to do our part--we depend on Earth for our survival, so we must do our best to protect our amazing planet.