Do you know why different animals or pests(害虫) have their special colors? Colors in them seem to be mainly used to    1   themselves.
Some birds like eating locusts(蝗虫), but birds cannot    2  catch them. Why? It is because locusts change their   3   with the change of the colors of crops. When crops are green, locusts look    4 . But as the harvest time comes, locusts change into the same brown color    5  crops have. Some other pests whose colors are   6   plants are easily found and eaten by   7  . So they have to hide themselves for lives and appear only   8  .
If you    9 animals’ life, you’ll find the main use of colors is to protect    10  . Bears, lions and other animals  11  quietly through forests. They cannot be easily seen by hunters   12  their colors are much like the trees.
Colors are useful not only on the land, but also in the   13 . A kind of fish can   14  a kind of black liquid(液体) when they face danger. The liquid spreads over quickly, so they cannot be found by their enemies and can quickly swim away. That is   15  they can live safely though they are not strong at all. So colors are really useful to animals.

Do you know why different animals or pests (昆虫) have their special colors? Colors in them seem to be used mainly to protect themselves.
　　Some birds like eating locusts (蝗虫), but birds cannot easily catch them. Why? It is because locusts change their colors together with the change of the colors of crops(庄稼). When crops are green, locusts look green. But as the harvest time comes, locusts change to the same brown color as crops have. Some other pests with different colors from plants are easily found and eaten by others. So they have to hide themselves for lives and appear only at night.
If you study the animal life, you’ll find the main use of coloring is to protect themselves. Bears, lions and other animals move quietly through forests. They cannot be easily seen by hunters (猎人). This is because they have the colors much like the trees.
Have you ever noticed an even stranger act? A kind of fish in the sea can send out a kind of very black liquid (液体)when it faces danger. While the liquid spreads over (散开), its enemies (敌人)cannot find it. And it immediately swims away. So it has lived up to now though it is not strong at all.
【小题1】From the passage we learn that locusts________.