Cordyceps are a group of parasitic fungi containing over 400 described species. Their hosts are usually insects but they can also infect other fungi, are considered to have medicinal properties in China and Tibet.
Fungi of the genus Ophiocordyceps (so called zombie ant fungi)
Ophoiocordyceps need ants to complete their life cycle. When an ant comes across fungal spores while foraging, the fungus infects the insect and quickly spreads throughout its body.
The microorganism is some how able to recognize the brains of different ant species, and releases its mind-controlling chemical cocktail only when in its preferred host.