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Zebras have their own bug repellent(驱虫剂)?
Eww bugs! They are so annoying! We humans are lucky that we can apply repellents to avoid nasty bites. But what’s an animal to do? They have no choice but to spend their days shooing them off with their tails, unless, of course, they are zebras, who apparently have their own automatic repellent--- their striped skin!
Scientists had originally thought that the reason why the animal had developed the black and white lines was to help protect itself from predators in the African savannah, because the stripes make it difficult to single out one zebra that is traveling with a herd.While that may be true, the theory has never been tested or proven. Now the experts have another---that the stripes have evolved to repel the annoying horse flies that not only feed off their blood, but also, transmit dangerous germs into the bodies of these innocent animals.
The study was performed by a team of Swedish scientists. One of the clues that got them thinking along these lines was the fact that darker horses got bitten more often than light-colored or white ones.
The fact that zebras are born black and only develop strips as they grow older made the scientists theorize that the stripes may be something the animals have developed to make themselves less attractive to flies.
To test if this may be the case, they painted some boards at a horse-infested horse farm in Budapest with patterns of black and white stripes of varying widths and applied a layer of glue on them. What they noticed was that the places where the black and white stripes were at their narrowest (similar to what zebras have) attracted the fewest flies. They achieved similar results when they painted horses with black and white zebra-like stripes.
While the research are not sure why this may be the case, they believe it may be something to do with the way insects operate---horseflies are attracted to horizontally polarized light（偏振光）; since white does not reflect it, white horses are luckier than black ones. But zebras seem to be the luckiest of all. When the researchers measured the polarized light reflected from real zebra skins, they found that it matched light patterns that were the least attractive to horseflies.
While this theory does make logical sense, nobody is 100 percent sure that it is really true, given that it has never been tested on a real zebra. If it is true, it does raise the question of why a horse, a close relative of the zebra has failed to develop stripes. The researchers believe that this could be because there are more horseflies in Africa, where zebras reside, then anywhere else in the world.

Title	Zebras have their own bug repellent?
Reasons for zebras developing their strips	Original belief	With the black and white lines, one zebra is difficult to single out while traveling with a herd, thus ______ it from its enemies.
New theory	Zebras, residing in Africa where there are most horseflies in the world ,have developed strips to avoid being_______ .
A study	Researchers	A team of scientists from _______
________	To test if strips are developed to make zebras less attractive to flies.
Clues	*White or light-colored horses are less _____ to get bitten than dark ones. *Zebras develop strips as they grow older though born black .
Method	*Some boards at a horse farm are painted with patterns of black and white stripes variously ______ , a layer of glue applied on them *Measured the polarized light reflected from real zebra skins
________	*The places where the black and white stripes were similar to the ______zebras have attracted the fewest flies *Strips of zebras matched light patterns that were the least attractive to horseflies
Principle of zebras’ black and white strips repelling the flies	Horizontally polarized light, which white does not reflect, _______ to horseflies.
Conclusion	_______tested on real zebras, the theory isn’t definitely true.

科目 英语   题型 阅读填空   难度 中等

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