I’ve just read an article about zombie-ant fungus. As you might guess from the name, it’s a fungus that grows on ants. What’s interesting (and pretty creepy) is that it changes ants’ behavior, making them provide the fungus with favorable conditions before it kills them. From the linked Wikipedia entry:
Infected hosts leave their canopy nests and foraging trails for the forest floor, an area with a temperature and humidity suitable for fungal growth; they then use their mandibles to attach themselves to a major vein on the underside of a leaf, where the host remains after its eventual death. The process, leading up to mortality, takes 4–10 days, and includes a reproductive stage where fruiting bodies grow from the ant’s head, rupturing to release the fungus’s spores.
It was briefly mentioned here on the SDMB a little over two years ago.