I'm Creeped Out (But Fascinated)

Image and caption from New York Times: When infected by
thorny-headed worms (the orange spot), gammarids swim
toward light. At the water's surface they become easy prey
for birds, the next creature the worm needs to infect to
complete its life cycle.

From The New York Times on Wednesday (to my attention via MetaFilter):

In the rain forests of Costa Rica lives Anelosimus octavius, a species of spider that sometimes displays a strange and ghoulish habit.

From time to time these spiders abandon their own web and build a radically different one, a home not for the spider but for a parasitic wasp that has been living inside it. Then the spider dies — a zombie architect, its brain hijacked by its parasitic invader — and out of its body crawls the wasp’s larva, which has been growing inside it all this time.

        * * *
[T]he new web is splendidly suited to its wasp invader. Unlike the spider’s normal web, mostly a tangle of threads, this one has a platform topped by a thick sheet that protects it from the rain. The wasp larva crawls to the edge of the platform and spins a cocoon that hangs down through an opening that the spider has kindly provided for the parasite.

To manipulate the spiders, the wasp must have genes that produce proteins that alter spider behavior, and in some species, scientists are now pinpointing this type of gene. ...

The New York Times article is written to draw attention to a new issue of The Journal of Experimental Biology which is dedicated to the subject of neural parasitology. The 18 or so articles at the issue are free. And, as the New York Times note, the issue of parasites (including viruses) taking over their hosts and substnatially altering their behavior is neither new nor rare -- it is a widespread phenomena.

It is also fact that makes arguments about whether "free will" exists or not silly (it's a nonsensical concept).