They weigh almost nothing.Yet they are1 than steel.In fact，some spiders' webs are among the world's strongest materials， 2 they can be pulled longer than elastic（橡皮筋）.They can also be any 3 .Spider webs are amazing.
A spider has hundreds of small openings in its body.Silk comes out of these openings as a liquid（液体），and，as it reaches the air，it becomes tread﹣like.These 4 threads（线）come together to form a single thread.
The spider can make many different kinds of thread.The tread can be thick or thin，wet or dry，or sticky.Each kind has a different 5 .Some webs create an egg box.Others6 hiding places.The most common purpose of a spider web，however，is to catch food.
There are many7 the spider uses its web to catch food.For example some spiders produce a single thread.An inset then sits on it8 realizing what it is doing，and becomes9 .Slowly，the spider moves towards the insect.10 ，it covers its food in silk.
Some spiders use a different kind of11 ，They make webs that cheat insects.An insect sees the web and thinks it's a flower.It then12 the web.The spider can feel even the smallest movement of the web，and rushes at the inset13 it can get away.
Spider webs are so 14 that engineers have been studying them for years.They want to learn why they are so strong and elastic.However，for the moment，spiders are keeping their15 .Although they have made great progress in science and technology，humans till haven't been able to copy natural webs.
