Why do caterpillars eat leaves, then go into a chrysalis, then grow wings and then become a butterfly?
That’s a very good question, but one that is complicated to answer. All of these things–caterpillars eating leaves, the formation of the chrysalis and the emergence of the winged adult butterfly–have evolved over millions of years because those characteristics made the individuals that have them very successful.
Take eating leaves, for example. Leaves are not particularly nutritious if that’s all you eat. They are tough, they contain very little protein and they sometimes contain nasty chemicals. However, the first insects that were able to survive off a diet of just leaves had this food almost entirely to themselves, and they became quite successful. Over millions of years, they evolved into the hundreds of thousands of species of butterflies, moths and beetles that we know today.
The butterfly and moth life cycle–egg, caterpillar, pupa (chrysalis), winged adult–is also a strategy that is very successful. Caterpillars concentrate on feeding and growing. The simple caterpillar shape (sort of pool-noodle shaped) is the most efficient shape for growing fast and molting several times to get bigger. The winged adult is the most efficient form for finding a mate and, for the females, for searching for host plants to lay eggs on. These things together make the Lepidoptera (butterflies and moths) hugely successful, and have led to the amazing diversity of species that we see today. – Dr. Naomi Cappuccino