英语听力文摘 English Digest 536、缓慢的生存！！

搜索关注在线英语听力室公众号：tingroom，领取免费英语资料大礼包。

 

　　Silkworms have been bred over thousands of years to behave quite unlike their caterpillar² cousins in the wild. That’s because people purposely breed silkworms to fit this job description:

 

　　WANTED–Superlative silk producers. Benefits include housing, unlimited³ food and protection from all predators⁴. Wanderlust greatly discouraged. No opportunity for travel.

 

　　Obviously, what makes a good silk producer in captivity⁵ is very different from what helps a caterpillar survive in the wild. Commercial silkworms are dynamos at silk production, and compared to their wild relatives, rather sluggish about everything else.

 

　　Outdoors, you’ve probably seen caterpillars⁶ crawling to find food or hide from birds, but commercial silkworm caterpillars hardly move. For silk production, they’re kept on open trays because they’re content to stay put, as long as they have a steady supply of mulberry leaves. Even when they reach the moth⁷ stage, commercial silkworms are surprisingly immobile. Wild moths⁸ fly to evade⁹ predators and to lay their eggs in different areas. However, commercial silkworm moths haven’t needed to do these things for thousands of years. They’ve completely lost the ability to fly, even though they still have wings!

 

　　Here’s another difference. In the wild, moths are often very particular about where they’ll lay eggs. This ensures that baby caterpillars can chomp¹⁰ their favorite leaves as soon as they hatch. Commercial silkworm moths have lost that instinct too. They’ll even lay eggs on a sheet of paper, where it’s easy for humans to keep track of them.

分享到：