The opening of David Barash’s New York Times piece about how parasites can manipulate the behavior of their hosts, whether that host is a bee or a human:

“ZOMBIE bees?

That’s right: zombie bees. First reported in California in 2008, these stranger-than-fiction creatures have spread to North Dakota and, just recently, to my home in Washington State.

Of course, they’re not really zombies, although they act disquietingly like them, showing abnormal behavior like flying at night (almost unheard-of in healthy bees), moving erratically and then dying. These ‘zombees’ are victims of a parasitic fly, Apocephalus borealis. The fly lays eggs within honeybees, inducing their hosts to make a nocturnal ‘flight of the living dead,’ after which the larval flies emerge, having consumed the bee from the inside out.

These events, although bizarre, aren’t all that unusual in the animal world. Many fly and wasp species lay their eggs inside hosts. What is especially interesting, and a bit more unusual, is the way an internal parasite not only feeds on its host, but also frequently alters its behavior, in a way that favors the continued survival and reproduction of the parasite.

Not all internal parasites kill their hosts, of course: pretty much every multicellular animal is home to numerous fellow travelers, each of which has its own agenda, which in some cases involves influencing, or taking control of, part or all of the body in which they temporarily reside.”