 The badly injured alien pilot, an Andalite named Prince Elfangor, emerges from the ship and explains to the children that the Earth is being invaded in secret by a race of aliens called the Yeerks, a slug-like parasitic species who infest humans through their ear canals and take complete control of the human's body, turning them into what is called a Controller.The human controllers are still self-aware but the Yeerk in their head has complete control over their body and what they say.Elfangor tells them that more Andalites will not come to Earth for a year or more, and by then, Earth will already be completely taken over.