A nice reference on this subject (in addition to the ever-helpful Schmidt and
Roberts) is "Parasites that change the behavior of their host" by Janice Moore
in Scientific American, 250(5), pp. 108-115, 1984. Dr. Moore (at Colorado
State) has some some elegant work on this general theme over the years.
Another Scientific American reference: "Living Together", by John Rennie,
January 1992, pp. 122-133. It's a bit broader in scope than Dr. Moore's paper,
but it still addresses your question. (It also describes the life cycle of
Dr. Bob Garrison