Zombies have roamed Earth for at least 48 million years. Zombie ants, that is. Today, Ophiocordyceps fungi are well known for taking over the minds of ants such as the Componotus leonardi worker pictured above. Once infected, an ant wanders away from its colony, bites down on a leaf vein near the forest floor, and dies--creating ideal conditions for the fungal fruiting body that sprouts from its corpse.
For a photo and more about zombie ants, see the story here.