Sound Familiar?

A parasitic wasp called Glyptapantes plants its larvae inside a caterpillar.

The wasp larvae make the caterpillar their bodyguard. As the larvae emerge from the caterpillar and attach themselves to a nearby plant, the caterpillar watches over the larvae and attacks anything that tries to get near them.

Scientists studying this arrangement have found that one or two larvae stay behind in the caterpillar. It's possible that the stragglers secrete some kind of chemical to control the mind of the poor caterpillar, which is already partially eaten.

More parasites at this link:
http://discovermagazine.com/photos/04-zombie-animals-and-the-parasites-that-control-them