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Parasitic Wasp Reprograms Its Host Spider
Dan writes: "The New York Times has an article about a bizarre Costa Rican spider parasite. This tiny wasp larva forces its host, an orb spider, to do its bidding before killing it. Instead of building a normal round web, the spider spends its last night stringing together a frame. The larva then kills the spider and uses the frame to support its cocoon. The scientist who discovered the behavior still doesn't know how the parasite does it." Since this is an older article, there's probably some more recent information available about this critter.
Some time ago, I saw an interesting documentary on TV about snail parasites (IIRC, the parasite was some kind of worm). The snail gets infected by eating the parasite's eggs which stick to edible plants. The eggs hatch inside the snail, and the parasitic larvae move to the snail's antennae where they start to grow. When they are mature, they somehow modify their hosts' behaviour - normally, the snail would hide from predators during the day. But now it exposes itself to birds, which mistake the swollen, bloated, parasite-containing snail antennae for yummy insects, rip them off and eat them. The snail doesn't survive this for long...
Inside the bird, the parasite lays its eggs and dies. The eggs get spread with the bird droppings, which hopefully fall on snail-edible plants, etc...
Cthulhu fhtagn!
One interesting example of host behavioral modification is in the single-celled protozoan Toxoplasma gondii.
This organism has two different hosts in it's life cycle, cats and rats. An infected cat will shed parasites in its feces which are then picked up by rats. The parasites take up residence in the rat until it is eaten by a cat, completing the life cycle.
The parasite takes up residence in various tissues of the rat, including the brain. Interestingly enough, infected rats show behavioral modifications. They become less cautious and more "curious", and may lose their normal aversion to the scent of cat urine -- thus making them easier prey.
Toxoplasma gondii also frequently infects humans, with some estimates suggesting up to half of the population having been exposed. It is dangerous to human fetuses and individuals with deficient immune systems (such as those with AIDS), but healthly carriers are usually asymptomatic.
It is uncertain whether or not the organism produces behavioral changes in humans, but there have been some suggestions that it might. Toxoplasma gondii link.
Philosophy aside, this could have some real applications. By manipulating basic, instinctual behavior of animals with a chemical application, you could all sorts of things.
For example, in California we have a well known problem with fruit fly infestations. There are two basic ways to deal with them: poison the buggers en masse, or sterilize a batch of males with radiation and release them (apparently, the females will mate only once, so they hook up with the guys shooting blanks and never reproduce - thus eliminating two of the creatures for the price of one). If a chemical could be developed that causes male fruit flies to somehow interrupt their mating behavior (say, do the courtship dance but never consumate the deed) you've essentially combined both techniques. Instead of releasing a few thousand sterile males (an expensive process), you wind up esentially sterilizing any male you expose - potentially many millions.
I just hope Madison Avenue never finds the equivilent formula for human buying behavior. (*GRIN*)
"Prepare for the worst - hope for the best."
Interestingingly, there is a a parasite that sort-of does reorder the host's DNA. There is a wasp that lays its eggs tobacco hornworm. It also injects a virus into the hornworm to disable the hornworm's immune cells, and mess up some other biological systems. Here is a link the researcher, but I couldn't find a link to an article explaining exactly what happens.