Why, you may wonder, should spiders be our friends? Because they destroy so many insects, and insects __1__ some of the greatest enemies of the human race. Insects would make __2__ impossible for us to live in the world. They would devour (eat up quickly) all our crops and kill our flocks and herds, were it not __3__ the protection we get from insect-eating animals. We __4__ a lot to the birds and beasts who eat insects but all of them __5__ together kill only a fraction of the __6__ destroyed by spiders. __7__ , unlike some of the insect eaters, spiders never do the least __8__ to us or our belongings.

　　Spiders are not insects, __9__ many people think, __10__ even nearly related to them. One can tell the __11__ almost at a glance, __12__ a spider always has eight legs but an insect never more than six.

　　How many spiders are __13__ in this work on our __14__ ? One authority __15__ spiders made a __16__ 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 __17__ like 6000 000 spiders of different kinds on a football field. Spiders are busy for at least half the year in killing insects. It is __18__ to make more than the __19__ guess at how many they kill, but they are hungry creature, not __20__ with only three meals a day.