Ampulex compressa is a wasp that has evolved to tackle roaches, insert a stinger into their brains and disable their escape reflexes. This lets the wasp use the roach's antennae to steer the roach to its lair, where it can lay its egg in it.
…
From the outside, the effect is surreal. The wasp does not paralyze the cockroach. In fact, the roach is able to lift up its front legs again and walk. But now it cannot move of its own accord.
…
The larva grows inside the roach, devouring the organs of its host, for about eight days. It is then ready to weave itself a cocoon–which it makes within the roach as well

So if you ever see me looking vacant, then I die four weeks later and cockroaches come out of my head, you know why.

Source [Via: BoingBoing]