Minecraft wiki entry for Savanna, associated text: Horses, donkeys, and llamas spawn in savannas. This does make it the only biome where both horses and llamas can spawn together. As the savanna has an arid climate, it never rains here, and thus lightning can never naturally strike; however, overcast skies (and daytime hostile mobs spawning in the case of thunderstorms) still apply. Grass and leaves in the savanna take on a dull, olive-green color, giving an illusion of dryness.