Oh, so many choices! But the nuances of evolution blow my mind.
A fungus that attacks a certain species of ant, altering the ant’s behavior so that it leaves its natural environment and seeks out an environment that benefits the fungus.
A parasite that affects mice, attracting them to the smell of cat urine (cats being the next carriers).
A snail that eats infected cow feces, that then coughs up infected slime that is eaten by an ant, that then paradoxically climbs a blade of grass, which is then eaten by a cow, starting the multistage life cycle all over again.
Amazing.
Edit: Oh, drat, I belatedly read the details. I am awed and frightened by the power of tornados, especially those that are a mile wide – how is that even possible?