新概念英语第四册 Lesson1 Lesson 2 Spare that spider讲义

Why,you may wonder,should spiders be our friends?Because they destroy so many insects,and insects include some of the greatest enemies of the human race.Insects would make it impossible for us to live in the world;they would devour all our crops and kill our flocks and herds,if it were not for the protection we get from insect-eating animals.We owe a lot to the birds and beasts who eat insects but all of them put together kill only a fraction of the number destroyed by spiders.Moreover, unlike some of the other insect eaters,spiders never do the least harm to us or our belongings. Spiders are not insects,as many people think,nor even nearly related to them.One can tell the difference almost at a glance, for a spider always has eight legs and an insect never more than six. How many spiders are engaged in this work on our behalf?One authority on spiders made a census of the spiders in a grass field in the south of England,and he estimated that there were more than 2,250,000 in one acre;that is something like 6 million spiders of different kinds on a football pitch.Spiders are busy for at least half the year in killing insects.It is impossible to make more than the wildest guess at how many they kill,but they are hungry creatures,not content with only three meals a day.It has been estimated that the weight of all the insects destroyed by spiders in Britain in one year would be greater than the total weight of all the human beings in the country.(by T.H. GILLESPLE from The Listener) New Words and expressions beast/bi:st/n.野兽 acre/'ek本n,英亩 census/'sams/n,统计数字 content/'kam,tamt/adj.满足的 Notes on the text 1.you may wonder是这个疑问句的插入语。 2.if it were not for the protection we get from inscet-eating animals这是一个非真实条件状语从句，were表示虚拟语气。 3.almost at a glance几呼一眼（就能看出）。不要伤害蜘蛛你可能会觉 得奇怪，蜘蛛怎么会是我们的朋友呢？因为它们能消灭那么多的昆虫，其 中包括一些人类的大敌，要不是人类受一些食虫动物的保护，昆虫就会使 我们无法在地球上生活下去，昆虫会吞食我们的全部庄稼，杀死我们的成 群的牛羊。我们要十分感谢那些吃昆虫的鸟和兽，然而把它们所杀死的昆 虫全部加在一起也只相当干蜘蛛所消灭的一小部分。此外，蜘蛛不同于其 他食虫动物，它们丝毫不危害我们和我们的财物。许多人认为蜘蛛是昆虫 但它们不是昆虫，甚至