Do you know why different animals or insects have their special colors? Colors are used mainly to protect themselves.
    Why can't some birds easily catch locusts（蝗虫）? It is because locusts change their colors together with the change of the colors of crops. When crops are green, locusts look green. But as autumn comes, locusts change to the same brown color as crops have. Some other insects with different colors from plants are easily found and eaten by others. So they have to hide themselves for lives in the day 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 can't be easily seen by hunters. This is because they have the colors much like the trees.
    Have you ever noticed an even more strange thing? A kind of fish in the sea can send out black liquid when it faces danger. While the liquid spreads over, its enemies can't find it. And it quickly swims away. So it has lived up to now though it is not strong at all.