Bill posted Weirdest Parasite Ever today...thanks a lot, Bill. Of course I had to read the page that he linked (yes it was stomach churning but it was also really interesting) and this particular genius of adaptability caught my eye.
The life cycle of the lancet fluke (Dicrocoelium dendriticum) goes as follows: adults inhabit cows or other grazers, releasing eggs that are spread in manure. When swallowed by scavenging snails, the eggs hatch and the parasites are eventually coughed up by the snail in balls of slime, which are then consumed by ants. Late in the evening as the temperature drops, infected ants experience an uncontrollable urge to wander from their colony, climb a blade of grass and attach to the tip by their jaws. The ants will remain in this position until accidentally eaten by a large, grazing mammal...beginning the cycle again.
The image belongs to these folks.