Do you know why different animals or pests have their special colors? Colors in them seem to be mainly used to protect themselves. Some birds like eating locusts  , but birds cannot easily catch them. Why? It is because locusts change their colors with the change of the colors of crops. When crops are green, locusts look green. But as the harvest time comes, locusts change into the same brown color as crops have. Some other pests whose colors are different form 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 animals' life, you'll find the main use of colors is to protect themselves. Bears, lions and other animals move quietly through forests. They cannot be easily seen by hunters because their colors are much like the trees. Colors are useful not only on the land, but also in the sea. A kind of fish in the sea can give out a kind of black liquid   when the fish face danger. The liquid spreads over quickly, so they cannot be found by their enemies and can quickly swim away. That is why they live safely though they are not strong at all. Those pests with different colors from plants have to   _   to keep out of danger.
change their colors hide in the day time and appear at night move quietly hide at night and appear in the day time