There are many examples of parasites hijacking their hosts' bodies and altering their behavior in alarming and grotesque ways. An article at The Scientist describes four of these parasite-host relationships and discusses how scientists are starting to figure out how some parasites become mind control experts. You can read about these disgusting stories and more (WARNING: probably not for the squeamish):The Jewel Wasp and the Cockroach - The female jewel wasp guides the cockroach to its nest, where she lays an egg on the roach and then seals the nursery. Her larva will feed on the cockroach and then pupate in its abdomen, emerging as an adult one month later.Toxoplasma and the Rat -  A rat eats cat feces that contain Toxoplasma eggs, which initiate behavioral changes in the rat that cause it to be attracted to the scent of cat urine. Instead of hiding, the rat becomes easy prey for a hungry cat - and Toxoplasma ends up in the cat's gut again, restarting the cycle.Acanthocephalans and the Gammarid - Small crustaceans called gammarids can be infected by eating acanthocephalan eggs, which results in a suite of behavioral changes that make the crustacean more likely to be eaten by a duck or other host. The worms grow and mate inside the duck's gut, and their eggs are expelled in feces to be eaten by the next unsuspecting gammarid.The Hairworm and the Cricket - Aquatic hairworm larvae find their way into aquatic mosquito larvae. The mosquitoes metamorphose into their adult, flying form. If an infected mosquito is eaten by a cricket or other terrestrial insect, the ingested hairworms take over the host's body, eventually causing it to jump into a body of water - where the hairworms make their exit and complete their life cycle.Parasites: the more you know, the more freaked out you'll be.