My fascination with parasites has been long standing – With his husky, very colonial accent, David Attenborough had a wonderfully understated way of showing how incredible the interplay between parasite and the preyed upon actually is.

Carl Zimmer recently wrote a wonderful piece on the Ampulex compressa wasp that essentially turns cockroaches into ‘zombies’ and then into a living food repository for it’s young.

Now a few more articles have come to my attention today on “Damn Interesting”:

The Sacculina barnacle infects crabs:

“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.

nside 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.”

The Cymothoa exigua parasite kills (and replaces) the tongue of the Spotted Rose Snapper Fish:

“The Spotted Rose Snapper Fish, which lives off the coast of California, is plagued by what must be one of the most disturbing parasites in all of nature. The crustacean parasite, called Cymothoa exigua, enters the fish’s mouth and leeches blood from the fish’s tongue until the muscle atrophies and dies. The parasite then attaches itself to the withered tongue-stump, and acts as a working replacement for the organ, spending the rest of its life living off bits of food that enter the fish’s mouth.

The Cymothoa exigua is the only parasite known to effectively replace a body organ.”

A species of wasp removes the free will of the Costa Rican Plesiometa argyra orb spider and before it kills it gets the spider to build it a protective shelter:

“On the night before the parasites kill their host, events take a bizarre turn. Through some unknown mechanism, the larvae compel their host spider to build a web that is very different from that it has always constructed before. Instead of a flat, round web, the spider builds a stout, reinforced platform which is much smaller. Once the new web is complete, the larvae kill their host, and cocoon themselves on the structure. It is ideal for the task, being resistant to wind and rain, and safe from the ants that inhabit the forest floor.”

The most disturbing quality of these articles is the ability for certain parasites to essentially alter the minds of their hosts, to turn on or off certain instinctual drives and motivations. Carl Zimmer also wrote about a common organism known as Toxoplasma gondii – transmitted to people through cats. 50 million Americans are aparently infected with it and there is a strong possibility that it may be linked to schizophrenia in humans. In rats, Toxoplasma apparently removes a rat’s fear for cats meaning that more of these infected rats will be eaten thus allowing better transmission of the parasite.

“The scientists speculated that Toxoplasma was secreted some substance that was altering the patterns of brain activity in the rats. This manipulation likely evolved through natural selection, since parasites that were more likely to end up in cats would leave more offspring.”

The question begs asking: How much of the personalties of host animals (including humans) is controlled by these creepy unseen back-seat drivers?