Pig bugs are caterpillars, which are actually the larval stage of a lepidopteran insect. The pigmy bug is capable of turning into a butterfly, and it goes through four life stages: egg, larva, pupa and adult. In the larval stage, the pigmy bug will continue to eat, its body will gradually grow larger, and it may have a color change that may be caused by the food it eats. When the worm has eaten its fill, it enters the pupal stage, where the pupal shell externalizes to form a protective outer shell, a process we generally refer to as pupation. Inside the chrysalis, the hogweed undergoes a series of changes and reorganization, gradually changing its form to that of a butterfly. Finally, the butterfly will break out of the chrysalis. So, if you have a pigmy bug, when it turns black, it may be entering the chrysalis stage and is about to turn into a butterfly