If you'd like to read more about parasites that are capable of changing host behavior than Carl Zimmer's book, Parasite Rex, contains several chapters devoted to them. Zimmer is an excellent writer and this book is a very entertaining read. You can also check out his science blog, The Loom, where he frequently talks about parasites.
Imagine a world where parasites control the minds of their hosts, sending them to their destruction.
Imagine a world where parasites are masters of chemical warfare and camouflage, able to cloak themselves with their hosts' own molecules.
Imagine a world where parasites steer the course of evolution, where the majority of species are parasites.
Welcome to earth.