毛毛虫变成蝴蝶的过程称为"蛹-->幼虫-->成虫"的变态发育过程。在这个过程中，毛毛虫会经历幼虫期和蛹期两个阶段，最终变成蝴蝶。
英文表达为:
"The caterpillar turns into a butterfly."
"The metamorphosis of a caterpillar into a butterfly."
例句:
"The butterfly is a beautiful creature, but most people don't reapze that it starts off as a small, unremarkable caterpillar."
"The metamorphosis of a caterpillar into a butterfly is one of the most remarkable transformations in nature."
中文翻译:
"蝴蝶是一种美丽的生物，但大多数人并不知道它最初是一只小小的、不起眼的毛毛虫。"
"毛毛虫变成蝴蝶是自然界中最令人惊奇的变化之一。"