Left: Chrysalis of a painted lady butterfly, showing breathing tubes (blue) and guts (red), at day 1 (left), day 13 (centre) and day 16 (right). Credit: Lowe et al. 2013. Interface.
The transformation from caterpillar to butterfly is one of the most exquisite in the natural world. Within the chrysalis, an inching, cylindrical eating machine remakes itself into a beautiful flying creature that drinks through a straw.
This strategy—known as holometaboly, or complete metamorphosis—partitions youngsters and adults into completely different worlds, so that neither competes with the other. It’s such a successful way of life that it’s used by the majority of insects (and therefore, the majority of all animals). Butterflies, ants, beetles and flies all radically remodel their bodies within a pupa as they develop from larvae to adults.
For the rest of the story: http://phenomena.nationalgeographic.com/2013/05/14/3-d-scans-caterpillars-transforming-butterflies-metamorphosis/