Posted by Alan Bellows on September 27th,
2005 at 11:27 am
There is no small number of unsettling parasites crawling, flying,
and swimming about the Earth, the lucky ones hitching rides on
hapless host organisms. And while many parasites are harmless, or
even beneficial in their way, others can wreak havoc with their
hosts' existence. The worst of these offenders can actually force
their host to do their will.
A tiny barnacle called Sacculina is one such parasite. Upon finding
a host crab, a female Sacculina will crawl over the crab's surface
until she finds a chink in the armor: a joint. She then ejects her
protective shell, reducing herself to a gelatinous blob, and
invades.
Inside the host, the parasite grows long, root-like tendrils
throughout the crab's body, eventually emerging as a bump on the
its underside. During this process she renders the crab infertile,
and creates a small opening in the crab's back that will allow a
male Sacculina to make residence there. Soon the crab is filled
with millions of Sacculina eggs and larvae, and like a zombie, the
crab cares for these eggs and larvae as though they were its own,
losing all interest in mating. When a male crab is infected, the
parasite alters its physiology and behavior to be female, to better
care for the Sacculina's young.
The parasite basically rewires the crab for its own ends, and the
crab becomes a helpless vehicle, expending its energy caring for
the young organisms that will move on to inflict themselves upon
other crabs.
http://www.damninteresting.com/?p=53
Wow talk about attack of the zombies......crabs 
