There's a fungus that turns ants into "zombies"

The fungus Ophiocordyceps unilateralis infects ants in the rainforest, taking control of their bodies and eventually killing them. But before it does, the fungus causes the ant to climb to a high location and bite onto a leaf, creating a perfect environment for the fungus to produce spores. This fungus has a 99% success rate in infecting ants, and its unique life cycle has been extensively studied by scientists.

(verified by various scientific studies, including a 2009 paper published in the journal Science)