Butterflies breed from the marriage between a male butterfly with a female butterfly. From the marriage, the female butterfly will produce eggs. From the egg to the caterpillar, from the caterpillar to the cocoon, from a cocoon to a young butterfly, after which an adult butterfly. This can be called perfect metamorphosis. If you want to clear again (with pictures) can be searched on the internet. I hope this helps.
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From @endang76