Are butterflies really two animals in one?

Insect have exoskeleton so they can't grow like ducks or bats. They have to make a series of metamorphosis to grow. Usually the form for change from one stage to the next step, because they are adapted to different lifestyle. See: http://en.wikipedia.org/wiki/Metamorphosis#Insect_metamorpho...

Butterflies are one of the most well known and extremes cases of changes. The caterpillar shape is adapted to eat a lot and be camouflaged, the butterfly shape is adapted to travel and mate. (Both shapes share the same general blueprint. For example, if you see a caterpillar carefully, it has only 6 small real legs in the front, and some prolegs in the back.)