Zombie-ant fungus (Ophiocordyceps unilateralis) is a pathogenic fungi that enters the body of an ant and begins to consume the non-vital soft tissues. It then spreads and produces compounds that affects the ant’s brain, changing it’s behavior. It causes the ant to climb up the stem of a plant then lock it’s mandibles using ‘abnormal force’ to secure itself to the plant.
The fungus then kills the ant but continues to grow and sprout mycelia out of the ant to anchor it to the plant substrate. Finally, the fungus consumes the ant’s brain, ruptures it’s head and releases it’s spores.
This behavior has been going on for 48 million years!
I am not making this up. I first read about this many years ago, I believe it was in Discover magazine. You can find all the details here at wikipedia.
Also, apparently, there is a parasite that fights the zombie-ant fungus saving some ants. Read about it here.
Image by pennstatelive on flickr – Some Rights Reserved