新概念4-2
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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 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 insect never more than six.
How many spiders are engaged in this work no our behalf? One authority on spiders made a census of the spiders in 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 6,000,000 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.
Q:How much of each year do spiders spend killing insects?
A:At least half of year.
spare that spider
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