Do you know why different animals or pests have their special colours? Colours 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 colours together with the change of the colours of crops. When crops are green, locusts look green. But as the harvest time comes, locusts change to the same brown colour as crops have. Some other pests with different colours from plants are easily found and eaten by others. So they have to hide themselves and appear only at night.
If you study the animal life, you'll find the main use of colouring is to protect themselves. Bears, lions and other animals move quietly through forests. They cannot be easily seen by hunters. This is because they have the colours 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 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 why they can live safely though they aren't strong at all.
