Metamorphosis: Chunky Caterpillar Soup Part II
(This post is Part II of ‘Metamorphosis: Chunky Caterpillar Soup’. For Part I and everything that happens before histogenesis, please go here.)
The next step in this magical process of metamorphosis is histogenesis (“histo” meaning cell, and “genesis” meaning growth). Particular cells called imaginal discs will begin to multiply and build up the new moth body. The imaginal discs are pretty amazing. Have you ever had a close look at a caterpillar and noticed pairs of small bumps on its body? Those might have been imaginal discs! These are bundles of cells that are already coded to develop into wings, legs and antennae. They’re also already positioned in the right places on the caterpillar body as they wait for their turn to grow. The imaginal discs use the caterpillar protein-soup cooked up during histolysis to grow into wings and any other bits that the moth will need. An imaginal disc can start with a bundle of about 50 cells which then multiply to around 50 000 cells by the end of histogenesis.
Once the pupa has completed its transformation into a perfectly formed moth the adult insect begins to emerge from its cocoon or underground chamber. This process is called eclosion. Hormones cause the hard outer skin of the pupa to soften and kickstart the nervous system to encourage the moth to move. Immediately after emergence the moth’s wings look small and crumpled. Then, it hangs upside down to pump hemolymph into the veins of its wings to expand them. Moths usually emerge in the morning so that their wings are ready for their first flight in the evening. However, before the moth can fly it has to do one final thing. It expels meconium, waste larval tissues built up during the metamorphic process, or in other words, leftover caterpillar soup!
The moth’s main purpose will be to continue the life cycle of its species. It might even eat some snacks if it is lucky enough to have mouthparts. The most tragic part is that after all of this beautiful change has taken place, most moths only live for a few hours to a few days at most!
So that is the magical process of metamorphosis. I’m sure you can understand my excitement over it. An insect that carries its future potential while it’s still a baby, digests itself and then uses its old self to build its new form is pretty darn incredible! Moths will inspire me forever <3
References and great reading:
3-D Scans Reveal Caterpillars Turning Into Butterflies, a blog post by Ed Yong.
What Happens Inside a Cocoon or Chrysalis?, a fantastic in-depth explanation by Nancy Miorelli that includes an incredible video.
How Do Butterflies/Moths Spread Their Wings After Emerging?, from Reiman Gardens of Iowa State University.
Kellogg, V. L. (1906) Physiological Regeneration in Insects. Science, New Series. Vol. 23 (January), No.578, pp. 149-152.
Gilbert, L. I. and Schneiderman, H. A. (1961) Some Biochemical Aspects of Insect Metamorphosis. American Zoologist. Vol. 1, No. 1, pp. 11-51.