A fungus found in tropical forests, Ophiocordyceps unilateralis, (save that for your next game of Scattergories) uses a mind controlling chemical concoction to control the brains of ants.
Once an ant is infected with the fungus, the cells of the fungus multiply and start working with each other. They build short tubes as a way to communicate and exchange nutrients. They also begin to invade the ants muscles, but leave the brain untouched:
Together, these brainless cells can commandeer the brain of a much larger creature…
Over the course of a week, it compels the ant to leave the safety of its nest and ascend a nearby plant stem. It stops the ant at a height of 25 centimeters—a zone with precisely the right temperature and humidity for the fungus to grow…
It effectively cuts the ant’s limbs off from its brain and inserts itself in place, releasing chemicals that force the muscles there to contract. If this is right, then the ant ends its life as a prisoner in its own body.
The fungus forces the ant to lock its little ant legs around a leaf, and “eventually, it sends a long stalk through the ant’s head, growing into a bulbous capsule full of spores.” This is a pretty gruesome thing to do to an ant, even if you are a bug hater like me.