Imagine a creature that wants to be eaten. The Schistocephalus tapeworm has to be,in order to continue its impressively complex life cycle.In each different stage,it must adapt itself to its host in order to survive and reproduce. First the larvae are eaten by a copepod,a kind of rudder-footed crustacean,which in turn is eaten by a three-spined stickleback,a fish which later winds up in the belly of a bird. Parasites may have an unsavory reputation,but they are in fact among nature's great success stories. A report by Anne Hoffmann.