Speaking of the screwfly, remember the big push to eradicate the screwfly back in the 60s or 70s? This fly lays its eggs on an open sore, the maggots hatch and go through a series of instars, pupate and become flies. The flesh is further damaged by this activity, making more open sores for more flies. Screwfly larvae can devour an infested animal in a matter of days. They also infest babies eyes, so there was a huge effort to control them. This is a fascinating story about using pheromones to exterminate a species.
Ok, since you asked… The screwfly gets its name by its mating habits. When screwflies mate, they line up head-to-tail. The female emits a pheromone that triggers the male to turn around – hence screwfly – and then they mate. To control screwflies, entomologists came up with a chemical that interfered with the female’s chemical message. Instead of turning around, the male happily mated with her head. Problem solved!
This sort of thing was the basis of an interesting sci-fi story by Racoona Sheldon called “The Screwfly Solution.” In this story, aliens who wanted to colonize the Earth sprayed a pheromone blocker that brought out the aggressive component of male sexual desire and suppressed the sexual component. All of the women were killed, of course. Too bad it didn’t turn the women into human Preying Mantises instead.
Here’s a fun parasite: the Guinea worm. These 3-foot-long parasites have been with us for so long that some Egyptian mummies have them. They feed only upon humans. One can only conclude that Adam was created infested.
You get guinea worms by drinking contaminated water. The worms then chew their way out and orient themselves so that their genitals dangle outside the flesh, usually the flesh of the foot, but they can really show up in any part of the body. The lesion burns like mad, so sufferers douse it with cold water to ease the pain. In the parts of the world where the Guinea worm is found, the sufferers recontaminate the water supply.
So now you have a three-foot long worm embedded in your body. 
The locals used to burn the exposed parts with cigarettes to try to kill the worm. Unfortunately, this often resulted in infection or even a massive allergic reaction when the three-foot long worm died. The worms are more safely removed by wrapping the exposed parts around a small stick then slowly drawing the worm out over days or weeks. The symbol the Rod of Asclepius may represent this procedure.
The caduceus with its two snakes is similar to the Rod of Asclepius, but is probably a symbol of wisdom rather than of medicine in particular.
The snake is a symbol of wisdom in
cultures where knowledge is encouraged. In cultures where Blind Faith is enforced, the snake is Evil Incarnate. Serpent Knowledge is the source of Original Sin, and it is knowledge that brings about the Fall. In this mythology, our progenitor Adam is infested with guinea worms. They can’t possibly have evolved into human parasites from something else, right?
Damn, there I go spouting heresy again. Burn the witch!
An apple a day keeps the doctor away!
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http://wrongquestions.blogspot.com/2006/12/screwfly-solution-by-james-tiptree-jr.html Interesting analysis of the story.
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