Living With Change

Metamorphosis, changing from one life stage to another, is taken to the extreme by insects. The study of the metamorphosis process is fascinating. The changes that occur are substantial and rapid. Many of the pupae of moths and butterflies are at least partially clear. We can see through the clear cuticle, a window on the change that is occurring inside.

A caterpillar has no compound eyes. Caterpillars don’t see much and have limited visual receptors. A few spots of photosensitive cells on the caterpillar head (called stemmata) are the only windows a caterpillar has on the world. Once the pupa forms, we can see the compound eyes of the soon to emerge adult clearly through the cuticle.

A caterpillar has chewing mouthparts: mandibles for cutting bite sized chunks of leaves, a labium to collect the bits of leaf, and maxillae to shove the bits into the food canal. The adult will have straw like sucking mouthparts that are formed by extended growth of the larval maxillae into a long sucking straw for drinking nectar. Each maxilla forms half of the long tube that is then “zipped” and glued together. These mouthparts are clearly visible through the cuticle of the pupa.

The wings of the adult moth form in plain sight on the dorsum (back) of the pupa. The wings are plastered tightly to the body of the adult that is forming inside the pupa. The adult moth will fully develop (in a crinkled form inside its cramped pupa). When it is time to emerge, the pupa will split open, the moth will emerge, then expand its wings and body to its full size.

Those who rear caterpillars will get an opportunity to observe these changes as caterpillars undergo metamorphosis to an adult moth.

Moth Cocoon Pupa: The compound eye, wings and mouthparts of the adult are visible through the cuticle of the pupa

About jjneal

Jonathan Neal is a retired Associate Professor of Entomology at Purdue University and author of the textbook, Living With Insects (2010). This blog is a forum to communicate about the intersection of insects with people and policy. This is a personal blog. The opinions and materials posted here are those of the author and are in no way connected with those of my employer.
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8 Responses to Living With Change

  1. Dale Hoyt says:

    Please excuse me for being pedantic. (I really hate to start a comment with a sentence like that.) Shouldn’t the caption of the photo read “Moth pupa” rather than “Moth cocoon”?

    Again, forgive the nit-picking — I really enjoy your blog and read it almost daily.

  2. jjneal says:

    Technically you are correct.

  3. Lindsey McKnight says:

    Sitting in class and trying to put your words to visual pictures about what the process was going to look like was hard. This blog was interesting because it allowed me to follow along with the picture as you described what would be happening. The metamorphosis of the caterpillar into a butterfly is actually really cool, even better than the metamorphosis of the cars in the movie Transformers (probably because this is actually real!). I have decided to choose a caterpillar as my pet and can’t wait to (hopefully) see this happen and be able to describe to others what stage the caterpillar, or pupae is in.

  4. Tracy Glaser says:

    I think metamorphosis is extremely fascinating. I enjoyed listening in class and watching the videos of how different insects go through this transformation. This blog just helped me understand metamorphosis of a caterpillar a little more. I will have a caterpillar as my pet and I hope I get a chance to see it change into a moth (and don’t miss it for some reason). Thanks for the post, I really enjoyed it!

  5. Tony Leyva says:

    Insects in general sort of creep me out, but the ways in which they change and go through metamorphosis is really interesting. I was having trouble understanding all the ways that caterpillars, and other insects that go through complete metamorphosis, change but this article really helped out. I plan on having a pet caterpillar and hope I’ll get the chance to see all these changes as it begins its transformation into a moth! Thanks for all the info and the post!

  6. Kevin Auer says:

    Even though I chose to rear a cockroach for this semester, I have once reared a caterpillar at a younger age. I wasn’t aware of all of the different aspects of metamorphosis that a caterpillar goes through back then, but this blog has taught me the scientific terms for the various stages and I can now comprehend what’s going on.

  7. Richard Konopasek says:

    Before reading this post I had no idea that you could possibly see some of the changes occurring to the caterpillar. When I choose to have the pet caterpillar I thought it would just sit in its container and I wouldn’t really be able to observe many changes. This is exciting and allows for a much greater understanding of what the metamorphosis process is like.

  8. Seung Hyun Lee says:

    I chose Madagascar Cockroach as my insect pet, but after I read this article, I regretted that I chose Madagascar Cockroach. I never knew caterpillar was this much interesting insect. This blog helped with understanding more about caterpillar.
    Thank you!!

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