“Watching the butterfly go towards the sun
I wonder what I will become”- Hillary Duff
Metamorphosis is the transformation of insects from an immature form to an adult. The process is amazing to behold and is a powerful metaphor for human transformation. Metamorphosis has appeared with regularity in poetry and prose since the Roman Poet Ovid titled his history of the world Metamorphoses (1942 BP = 8 AD).
Most insects undergo complete metamorphosis- that is they have a pupa stage. (Insects that lack a pupa stage have “incomplete metamorphosis”). The immature stage, or larva, molts to a pupa when it completes its growth. The adult (usually with wings) emerges from the pupa. The separation of life stages into a larval feeding stage and an adult reproduction and dispersal stage is an important feature of insect evolution and has allowed insects to greatly diversify in numbers of species. A single stage devoted to feeding and growth allows natural selection to act on adaptations that affect the larva independent of the adult. An adult stage devoted to reproduction and dispersal allows natural selection to act on adaptations that affect the adult independent of the larva. The result is an insect that is better adapted to both feeding/growth and reproduction/dispersal rather than an intermediate that is less well adapted to both.
Insects with complete metamorphosis have 2 sets of genes that control body form. The larval genes are expressed and the adult genes are suppressed in the larvae under the influence of high concentrations of the hormone, juvenile hormone. When juvenile hormone is absent during a molt, the larval genes are suppressed and the adult genes are expressed.
Insect larvae have undifferentiated cells masses scattered throughout the body called imaginal discs. Under high levels of juvenile hormone, these cells remain in an undifferentiated state. When the insect molts to a pupa, the imaginal disc cells will grow and differentiate to produce the adult form. In the metamorphosis process, the cells of the larva break down and release their contents. This provides the nutrients and the structural building blocks (amino acids and sugars) to create a new insect. The adult genes are expressed and guide the growth and differentiation of the cells so that the adult form is produced. The physiology of metamorphosis is complex and the subject of ongoing scientific study. There is a wealth of knowledge to be gained about the biological process of growing new tissue.
At the aesthetic level, few processes are more fascinating than watching a butterfly emerge from its chrysalis and fly away. On that note I will leave you with this metamorphosis song:
Every day is a transformation
Every day is a new sensation
An incarnation, celebration
Every day is a new equation
Every day is a revelation
Onto another destination