For Halloween, Scientific American featured parasites that "control" their hosts. This picture shows a wasp "enslaving" a cockroach.
In a well-documented example of external parasite control, an emerald cockroach wasp (Ampulex compressa) enslaves a much larger cockroach (Periplaneta americana). The wasp injects a neurotoxin into the cockroach's brain. This toxin kills off the roach's ability to control its own movement but doesn't paralyze it entirely. The wasp is then able to grasp the roach's antenna and lead it into a nest before laying an egg in the live cockroach's body.
Permanently incapacitated, the cockroach is unable to escape and is eaten from the inside by the growing wasp larva.