What happens in metamorphosis, exactly?

Not the easiest question to answer, but here we go. Let's talk metamorphosis.

The picture here is of an Orange Barred Sulphur chrysalis about one day before the butterfly emerged. Looking closely at the greenish leaf-shaped pod you can see some of the wing markings of the butterfly within, which are some of the last details of a butterfly to form during metamorphosis. Prior to this, alot is happening in that tiny pod.

From the outside it appears as though the pupa, also known as the chrysalis, is resting. In reality the larval tissues completely break down and reorganize rapidly within the pupal skin.

The first thing that happens is that a lot of the caterpillar’s old body dies. It is attacked by the same sort of juices the caterpillar used in its earlier life to digest its food and 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 insect’s old tissue passes on to its new self.

There is one particular sort of tissue left after histolysis. In a number of places in the insect's 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 disk' or a ‘histoblast'. The imaginal disks begin to reproduce rapidly and develop into wings or legs or antennae, from the largest structure to the most tiny detail of a single hair or scale, building of a new body out of the soup that the insect’s 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' which is the formation of different tissues from undifferentiated cells. 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.

For more information, check out this article written by Dr Lincoln Brower.