Look, something had to inspire those "Alien" movies.
By one estimate, somewhere around40 percentof all known animal species areparasitic. From 30-foot (9-meter)fish tapewormstoOrthione griffenis, a "cough drop-sized" crustacean thatdrinks shrimp bloodto survive, planet Earth is crawling with parasites.
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Many of them have evolved to find very specific hosts. TakeStrigiphilus garylarsoni, a "chewing louse" named after cartoonist Gary Larson (you may remember him as the creator of "The Far Side"). It spends its entire life cycle on the skin of anunsuspecting owl, where the stowaway feeds on feathers and other organic materials. Besides owls, no other animals are known to harbor this particular kind of louse.
但有时,一个主机是不够的。有时,the only way for a parasite to reproduce and complete its own life cycle is by passing throughmultiple carriers.
Such is the case forLeucochloridiumworms, biological oddities that have been accused of turning snails into "zombies."
This behavior is said to be part of an elaborate scheme that also involves hungry birds and their poop. Supposedly, if things go according to plan — for the worms — those poor old snails get their eyes pecked out.
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