happen thousands of feet above ground. Only recently

　　have scientists developed technologies that can detect such little creatures at such great heights.

　　To their surprise，though，the insects weren't passive travelers on the winds.In autumn，for example，most light winds blew from the east，but the insects somehow sought out ones that carried

　　them south and they positioned themselves to navigate directly to their winter homes.Even in the spring，when most winds flowed northward，the insects didn't always go with the flow.If breezes weren't blowing in the exact direction they wanted to go，the insects changed their body positions to compensate.Many migrating birds do the same thing.

　　The study also found，butterflies and moths actively flew within the air streams that pushed them along.By adding flight speeds to wind speeds，the scientists calculated that butterflies and moths can travel as fast as 100 kilometers an hour.The findings may have real­world applications.

　　With climate warming，migrating insects are growing in number.Knowing how and when these pests move could help when farmers decide when to spray their crops.

　　【语篇解读】 随着它们的迁徙，蝴蝶和飞蛾在飞行中会选择风向，并且如果它们走错了方向，它们会改变身体的位置。

　　68．What's the main idea of the text?

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