How caterpillars gruesomely transform into butterflies

The caterpillar’s metamorphosis from a tree clinging, 12-legged pest into the majestic flying butterfly is a frequent metaphor for total transformations. It’s truly a fantastic mechanism developed by nature, yet while it may seem fantastic from the outside, this transformation looks pretty gruesome deep inside the chrysalis. In short, for a caterpillar to turn into a butterfly, it digests itself using enzymes triggered by hormones. Then, sleeping cells (similar to stem cells) grow into the body parts of the future butterfly. So you thought puberty was mean? Wait till you read on.

A tough transformation


Image: Yahoo


Our story begins with a hungry caterpillar who had just hatched from an egg. Soon enough, the little caterpillar (scientifically known as a larva) stuffs itself with leaves, growing little by little. When they’ve outgrown their current skin, a hormone called ecdysone is released, instructing the larva to moult. After it moults about five times, the larva stops feeding, hangs upside down from a twig or leaf, and then either spins itself a silky cocoon or molts into a shiny chrysalis. This process is driven by the same hormone, ecdysone, but this time it works in conjunction with another hormone called the juvenile hormone. It’s actually the lack of the juvenile hormone that triggers the metamorphosis mechanism.

The juvenile hormone acts to delay metamorphosis throughout the whole larva stage.  It works by blocking the genes in the imaginal discstiny disc-shaped bags of cells that kick into action when the caterpillar wraps itself in the chrysalis, eventually turning into an antenna, eye, wing or other butterfly bit. As such, the juvenile hormone is essential to the caterpillar’s survival prior to metamorphosis. You see, once the larva reaches its final moult and begins its metamorphosis, strange things happen to its body. Cells in the larva’s muscles, gut and salivary glands are digested and act as spare parts for the soon-to-be butterfly. Each cell is programmed to self-destruct through the activation of enzymes called caspases.

The caspases tear through the cell’s proteins, releasing prime butterfly-making material. Were it not for the juvenile hormone, this could have happened at any time, killing the caterpillar. Instead, nature programmed the hormone to lower its levels at the ideal moment for metamorphosis. With less juvenile hormone around, instead of inducing a regular moult, the ecdysone now drives the caterpillar to pupate. Once a caterpillar has disintegrated all of its tissues except for the imaginal discs, those discs use the protein-rich soup surrounding them to fuel the rapid cell division required to form the wings, antennae, legs, eyes, genitals and all the other features of an adult butterfly or moth. The imaginal disc for a fruit fly’s wing, for example, might begin with only 50 cells and increase to more than 50,000 cells by the end of metamorphosis.

Metamorphosis isn’t just some beautiful physical transformation, however. It’s a stunning display of evolutionary mechanism at work. Butterflies and caterpillars don’t just look different they behave differently, too. One lives in trees, and the other flies. Most importantly, one eats leaves, and the other solely feeds on nectar. There’s plenty of room for both kinds to coexist in the ecosystem since they don’t interfere with each other’s food stocks. It’s brilliant!

Inside the cocoon

Image: Michael Cook,

Image: Michael Cook,

Unfortunately, there is little footage that shows metamorphosis at work. The incredible photo pictured above was shot by Michael Cook, who managed to catch this Tussah silkmoth (Antheraea penyi) in a rare position – during a failed attempt to spin its cocoon. You can see the delicate, translucent jade wings, antennae and legs of a pupa that has not yet matured into an adult moth—a glimpse of what usually remains concealed within the cocoon.

Luckily, we live in the 21st century. Using modern imaging tech, like CT scans, we can peek inside the cocoon without disturbing this extremely delicate process. The video below was shot by scientists working at London’s Natural History Museum.

47 thoughts on “How caterpillars gruesomely transform into butterflies

  1. Sarah Roney Dalton

    Even the most transcendent experiences have their gross side; my big eye-opener was childbirth. What an awful mess, but you end up with a beautiful baby, hopefully!

  2. Arthur Green

    Every detail of metamorphosis screams that it was designed by a loving creator. There is absolutely no way for metamorphosis to develop a stage at a time for some kind of survival advantage: anything less than complete pupation to a perfect butterfly would cause extinction of the partially “evolved” and pitiful creature. So there is no way that this in any way demonstrates or proves evolution.

    Soli Deo Gloria!

  3. Liny

    I am hard pressed to wonder how many favorable mutations would have taken place all at once in thousands of genes to accomplish this critical transformation from caterpillar to butterfly. It couldn’t have happened slowly one protein changing at a time, over millions of years. Funny how scientific discoveries these days put the favorite theory in jeopardy.

  4. Liny


    I too am hard pressed to wonder how many favorable mutations would have
    taken place all at once in thousands of genes to accomplish this
    critical transformation from caterpillar to butterfly. It couldn’t have
    happened slowly one protein changing at a time, over millions of years.
    Funny how scientific discoveries these days put the favorite theory in

  5. Tibi Puiu

    Yes, these changes happen slowly over millions of years – across thousands of thousands of generations. All living beings alive today exemplify evolution, and prove it. There’s yet to be one single proof – and i can’t stress enough the word “proof” – that counters Darwin’s theory of evolution. The reason why you find it hard to believe may be due to the fact that you do not understand how evolution works in the first place. I’m not patronizing ,btw.

  6. Tibi Puiu

    these changes dont happen all at once. the caterpillar’s metamorphosis is hardly an argument against evolution. In fact, it supports it.

  7. Liny

    I appreciate your article. But, evolution can’t get you metamorphosis. Even, if the eloquent sounding words ‘complex mechanism’ and ‘you cannot understand’ etc. are repeated over and over again. Your faith is based on a different world view and my faith is based on a different world view. That’s all the difference. But, both are faiths because ‘evolution’ is not observable science and certainly metamorphosis is something it cannot explain through slow evolution.

  8. buttcabbage

    a theory doesn’t need to be countered, because it is just that, a THEORY. If it were a LAW, then it could be countered, but trying to counter a theory is like saying “I’m going to disprove whats in the center of a black hole”. Since we only have THEORIES as to what is in the center of a black hole, nothing can be disproved, but new theories can be postulated. I DO believe in evolution, but that doesn’t mean that evolution itself wasn’t conceived by whatever power blinked our universe into existence in the first place. Its funny how people who say they believe in evolution, which by definition relies on TIME to occur, its funny how these people conveniently forget that the stuff that makes up our universe had to come from SOMEWHERE, and that somewhere had to have stuff that came from somewhere too, etc etc. In the end, a higher power/creator myth doesn’t seem crazy at all, especially when you yourself are preaching evolution. What if some being somewhere in another universe/existence EVOLVED to the point where it could create it’s own universes and control their outcome (minus free-will). I think its kind of convenient how these “minds of science” are quick to say that nature can explain everything but then are too obtuse to consider the fact that the laws of nature themselves may have been conceived and created by a hyper-evolved being that has the ability to create it’s own laws of nature. I mean if things are constantly evolving, who’s to say there isn’t a universe somewhere that is 50 trillion years old and contained a race of super-beings that hyperevolved and merged into one giant omega being with the knowledge and power of a 50 trillion year old universe to use? The FACT of the matter is you don’t KNOW anything, all you can do is guess and postulate. A mouse doesn’t know its in a maze, and you don’t know if some crazy hyperintelligent being is controlling your every move (physics wise at least) while only leaving you with your free will, which I can see being one of the first things to evolve in life since it is basically the origin of spontaneous change. Anyway, you should really open your mind, if science has shown us anything its that data is just data, and until you have a perfect approach to analyzing it, you are just as likely to be misled and you are to find the truth.
    I myself believe in science because it is just a system of logic statements. I also believe that there is the possibility of a higher power that arranged for things in our universe to end up the way they are now. I have no idea if this was created for humans in general (considering we seem to be the apex of itinerant life in our corner of the universe, it seems a little strange that with the TRILLIONS and TRILLIONS of possibilities around us, we are the only ones that took life to this level? If you really do believe in science you need to take a hard look at the way you examine and acknowledge data.
    As a final note, NO ONE understands how evolution really works, thats why its still a THEORY and not a LAW. You should stop spewing words to ppl if you don’t know what you are saying, because some poor kid is going to grow up thinking that evolution is a perfectly understood, black and white science when that couldn’t be farther from the truth.

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  11. Joseph

    Wow, thank you very much for this article. I never fully realized how all of this happened. An amazing evolutionary process for the caterpillar indeed!

  12. Mea

    But evolution IS an observable science. Search for Darwin’s finches for an example.

    Evolution has been proven time and time again…

  13. Mea

    Just for clarification: Theories are called that in science because, as more information is assessed, it is added to what is always known so it is constantly being upgraded and re-evaluated. This is as opposed to a rule which, as a rule, are not amended.

  14. John

    I beg your pardon? You evidently have not read Dawkins,s “The Selfish Gene” Nor have you read the Bible with understanding by the sound of it. If Darwin knew anything about the cell, he would realise that evolution is just a pile of bunkum, out, of the soil of feeble human minds. He had no understanding of proteins which are the machinery of living tissues that build the structures and implement the chemical reactions necessary for life. That in itself cannot wait millions of years for the next piece of information to come along to complete the processes required. Just for the eye alone, a typical cell contains thousands upon thousands of different types of proteins. The processes of linking together in exactly the right way cannot rely on chance alone, or accidentally by flopsam and mistakes. Just like cricket, when the ball hits the stumps, or you get caught, even LBW, youR out. And Darwins theory has been caught out, at last.
    Have you heard of “Irreducible Complexity” Why not read Michael Behe’s book Darwins Black Box.

    One of Mr, Dawkins Book admits in a preface that we must take his evolutionary account as impossible to happen, a fary story.

    At last Micro biologist are beginning to see sense.

  15. John

    Adaptation is not Evolution. With 30 years of funding by governments in Europe, scientist endeavoured by means of micro evolution to prove that one kind can evolve into another kind. The result was dismal failure. However, the struggle goes on, or the belief in spontaneous generation from simple lumps of mud being organised by ripples of water at the bottom of some bio soup. One thing that impresses the inquiring mind, is that, they realised that to achieve they’re aim, they needed to immolate the conditions required in order to achieve at least a near enough result, that too failed.

    Just as was mentioned in one study, science must work from what we know through observation and experiment, not from something we do not know, and impossible to achieve.

    No, a finch, is a finch, how ever small or large it’s beak, just as a small person is also a human like a large person.

  16. Will

    This is an amazing answer and I’m really not being sarcastic or anything, its equivalent to physicists studying quantum mechanics, they say you really don’t know it if you say you understand it. The greatest minds are still dumbfounded and people try to say they “know” anything like its a fact

  17. Mea

    Evolution is adaptation on a longer time scale. Please prove to me that evolution does not exist.

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  25. Radar Man

    God ordained this whole process to illustrate what the Apostle Paul stated in 1 Cor 15: 35 -58, when asked what sort of body would we have in Heaven.
    Praise the Lord ………..

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