The caterpillars' job is to eat and eat. Lots of host plants are needed to meet their demands. As they grow the caterpillars shed their skin. The caterpillars are camouflaged for defense. Each shedding produces a new instar, of which there are five or six before pupating into a pupa. Each instar may be a different color.  Before the caterpillar begins to pupate it first creates a silken pad from which it attaches itself to a twig or leaf while it develops into a butterfly.