Do you know why different animals or pests (昆虫) have their special colors?Colors in them seem to be

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.
1、Why do different animals or pests have their special colors?
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2、How do locusts protect themselves?___________________________________________________
3、What does that kind of fish in the sea do with the danger it faces?___________________________________________________