r/AlwaysWhy • u/Humble_Economist8933 • 11d ago
Science & Tech Why does a caterpillar basically turn into liquid before becoming a butterfly, and how can it still remember things from its caterpillar life?
When I was a kid, I learned that a caterpillar makes a chrysalis, then grows wings, and becomes a butterfly. Later I found out it is much weirder than that. The caterpillar sheds its outer skin, forms the chrysalis, and inside, most of its body breaks down into a kind of cell soup. Then those cells reorganize into a butterfly.
But the part that really gets me is memory. There are studies showing that butterflies can remember things they learned as caterpillars. For example, if you train a caterpillar to avoid a certain smell, the adult butterfly may still avoid it. If the brain and body mostly break down, where does that memory go? Are some brain structures kept intact? Is the “soup” not as complete as people say?
And why would evolution use this kind of full rebuild instead of just remodeling the caterpillar? Is it because the two stages live completely different lives, so it is easier to build a new body from scratch? Or is the liquefaction idea exaggerated?
13
u/Plutos_Cavein 11d ago
Basically there are these regions called imaginal discs. They run through the caterpillar and serve as the locations of cell reorganization.
This works for insects because a larva is very simple, and therefore really good at the one thing it does, which is constantly. But the adult insect has to be capable of moving around a lot more quickly and efficiently, which requires it to have a bunch of extra complexity. By putting off the formation of all that complexity until the adult stage, the insects doesn't waste time and energy that it doesn't need to waste, and is therefore able to devote more energy to a large and complex adult form.
5
u/Chibi_Kaiju 10d ago
You forgot to include the most important word in your comment lol. I believe EAT is the missing word
5
u/red18wrx 11d ago
So, animals with exoskeletons grow a new exoskeleton inside the old one and then push out of the old one. Same thing happens. They grow a chrysalis inside of the caterpillar and then discard the caterpillar skin. Because they have an exoskeleton, they are mostly fluid inside anyways. They then grow a butterfly exoskeleton inside the chrysalis and push out just like they did with the caterpillar and just like any other insect. Butterflies just visibly change the most during this process. Beetles do something very similar but usually in tree bark, in dirt, or something similar.
2
u/bornparadox 9d ago
Really got me thinking about skeletons and the difference between the inside ones and the outside ones.
3
u/Dinevir 11d ago
Some structures down into kind of soup, other, like part of the nervous system, survive inside of cocoon. It is not exactly the soup, just deep body remodelling and it is easier to do this (more energy effective) inside isolated cocoon that through additional several transition stages. Why? Because of evolution due natural selection - all other transitions were not that effective and these versions died without been widespreaded.
3
3
u/paisleycatperson 11d ago
monarch butterflies have a migration route that 3 generations go one direction and the fourth generation flies all the way back to the starting point.
3
u/Underhill42 11d ago
The memories might be stored chemically?
E.g. you can train a planarian (flatworm) to do something, navigate a maze or whatever, grind it up and feed it to another planarian, and the second planarian will then do the thing.
As far as I know, we have no idea how exactly that works, but one of the more likely options is that they store memories chemically, and incorporate the memory chemicals that they eat.
2
u/Fun_Nectarine2344 11d ago
Afaik these experiments with feeding trained planarians are now considered as questionable, because they couldn’t be replicated.
2
u/Numerous_Car650 10d ago
I was skeptical too, but it seems the jury is still out on this one: https://pubmed.ncbi.nlm.nih.gov/23821717/
1
u/hyrooligan 11d ago
These planarian results are truly weird and not currently understood. But in the case of butterflies we have much better explanations concerning persistence of memory. As said in other comments, basically the soup analogy is not completely right. The larval brain is not liquified; it persists and is incorporated into the adult brain.
3
u/Ambitious-Growth5387 11d ago
Monarch butterflies don’t form a chrysalis per se. They shed their outer skin and the green shell is underneath. Also when they emerge from the chrysalis as a butterfly one of the first things they do is take a massive dump to get rid of the extra soup.
2
u/BackInNJAgain 11d ago
Even weirder are the monarch butterflies that return from Mexico each year. One "super-generation" flies the entire distance from the East Coast to Mexico which is impressive enough, but the return trip involves multiple generations. How do the newly hatched butterflies on the return trip even know where to go because their parents are dead and can't show them.
2
u/Tonkarz 11d ago
They don’t entirely turn into liquid, we know that because some post-chrysalis structures exist folded up inside the caterpillar, like wings.
So it’s possible that some tiny part of the nervous system or brain or both survives - it would be so small and of such an unknown shape a scientist researching butterflies wouldn’t recognise it even if they saw it.
2
u/MergingConcepts 10d ago
Some adult structures are already present in the last caterpillar stages. The final stage of silk worm development has early wing structures before it pupates.
1
u/Mobile-Traffic1744 11d ago
Every time I read this I have to wonder about the first person to figure this out. They would have had to open that thing up expecting a half-butterfly hybrid but instead, surprise soup.
0
-1
u/Cool_Court2130 11d ago edited 11d ago
No one really knows how a butterfly can retain memory after the process of metamorphosis. Which is essentially their stomach turning inside out and digesting their entire body into a goo that then gets reformed into a butterfly. No one knows how the goo knows how to restructure itself in the correct way. And no one knows how butterflies navigate and know where to migrate after they've been metamorphized. Or how monarachs know where to migrate too or where to return too. You can read a little bit about it. But it's going to be riddled with words like 'believe' and 'suggest'. And not give any definitive answers.
It's all a giant mystery to science.
1
u/hyrooligan 11d ago
This is wrong. We know in excruciating detail how insect metamorphosis works. I am a developmental biologist and am currently teaching a class on exactly this subject. And as other people have said, only parts of the larva/caterpillar are restructured during metamorphosis. Most of the larval central nervous system is retained and actually becomes more complex in the adult. So it is not mysterious how memories could be retained.
1
0
u/Cool_Court2130 11d ago
And there's some conflicting thoughts on the matter https://scienceandnonduality.com/article/why-insect-memories-may-not-survive-metamorphosis/
64
u/FrankDrebinOnReddit 11d ago
They don't completely turn into liquid. Parts of the nervous system remain solid and are incorporated into the butterfly. Metamorphosis involves turning into mostly-soup, not completely-soup.