Here we see the final life stages of several Painted Lady (Vanessa cardui) Butterflies. Once the caterpillar matures, it spins a silk pad on a twig or other substrate, then suspends itself upside-down, by attaching a special part of its body part at the tail-end called a "cremaster" to the pad. The cremester sticks to the pad much like the hooks and loops of Velcro.
In about 24 hours, the caterpillar sheds its final skin to complete the pupation process. Inside the pupa, the caterpillar has essentially liquified itself into a soup of cells. During the next 12-14 days, metamorphosis takes place as the cells are "re-arranged" and transformed into the adult insect. For most of this process, there is no visible change on the outside, but as the final few days approach, the developing adult butterfly can be seen through the semi-transparent pupal case. The butterfly's wing colors and pattern can be seen to darken. Finally, the fully developed adult separates from the pupal shell about an hour before it emerges, a process called "eclosion".
Once the adult emerges, it takes only a few minutes to expand its wings by pumping a body fluid into the wing vein structure. After a couple of hours, the fluid dries and hardens inside the veins, leaving the wings rigid enough propel it in flight.