You may ask, how does a caterpillar become a Moth or a Butterfly?
The answer to that can actually get quite complicated but basically what happens is this. When the caterpillar has eaten enough it turns into a pupa, more about this later on because it is different for different groups of Lepidoptera. To do this it stops eating and finds somewhere safe, here it becomes very still (pupa never eat and seldomly move at all) it then moults its skin the same as it does when it is growing only instead of another larval skin it secretes a pupal skin, (inside its old larval skin) that is much thicker and stronger. Generally this pupa then breaks out of the old larval skin, though in many moths the pupa remains inside the old larval skin, you can often find the remains of the caterpillar skin around the tail of a Butterfly pupa. All that is fairly straight forward, where it gets tricky is how the caterpillar inside its new pupal case changes itself into a Butterfly or Moth. The first thing that happens is that a lot of the caterpillars old body dies. It is attacked by the same sort of juices the caterpillar used in its earlier life to digest its food, it would not be far wrong to say the caterpillar digests itself from the inside out, this process is called ‘histolysis'. Not all the tissue is destroyed however some of the insects old tissue passes on to its new self, the amount that does this varies between different insects, and is not very much in the Lepidoptera. There is one particular sort of tissue left, in a number of places in the insects body are collections of special formative cells, which have played no part in the insects larval life, and have stayed hidden or protected during this partial death, each of these groups of cells is called an ‘imaginal bud' or a ‘histoblast'. The job of these histoblasts is to supervise the building of a new body out of the soup that the insects digestive juices have made of the old larval body. This they do using the same biochemical processes that all insects use to turn their food into part of their bodies. This rebuilding process is called ‘histogenesis'. During this time the insect is very vulnerable because it cannot run away, and this is why insects try to choose somewhere safe to hide away when they are going through this incredible change, still I think you have to be very brave to be a Caterpillar and become a Butterfly or a Moth.