Okay, so upon entering the Fracture in Reality, worlds are broken apart and remade. This exposes lifeforms to lots of Chaos Energy, which tends to lead to lots of mutations. Natural selection makes it so only the viable monstrosities survive, but Chaos Energy tends to follow patterns. For example, Chaos Energy tends to enlarge insects.

Because of this, only two kinds of insects survived; those that weren't affected by Chaos Energy (plenty weren't, oddly enough) and those that survived being enlarged. Anyway, that aside, how big could a caterpillar conceivably get, without magic?

Please assume current oxygen levels for the purposes of this question, though I would also appreciate answers that account for how large caterpillars would be given Cambrian oxygen levels, which enabled beings like Meganeura and Arthopleura.

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    $\begingroup$ I think it can be as tough as you want it to be. Chaos Energy is a massive handwave. If you want your caterpillar to be immune to weapons it will be. If you want caterpillars to be mostly immune but have vulnerable weak spots it will have vulnerable weak-spots. Or if you want it to get squashed like the bug that is then it can be squashed like the bug that it is. $\endgroup$
    – sphennings
    Sep 21, 2021 at 16:13
  • $\begingroup$ Suggestion: Reframe your question to cater to the following: "How large could a caterpillar get?", then ask a follow-up question on durability of the carapace based on the information received. $\endgroup$ Sep 21, 2021 at 18:05
  • $\begingroup$ @ALambentEye: I've done that, thanks for the suggestion! $\endgroup$
    – Alendyias
    Sep 21, 2021 at 20:25
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    $\begingroup$ This is not a complaint, but "chaos energy" essentially equals "magic", so you're basically asking how can magic change this thing without actual magic. I like questions that introduce sensible magic of this sort, but the results might not be what you're looking for! Without the magic of chaos energy to alter something else about them, all the big caterpillars will die pretty quick. Maybe within a day! $\endgroup$
    – elemtilas
    Sep 22, 2021 at 1:05
  • $\begingroup$ I altered my proposed solution to reflect your change in question. I hope it helps somewhat. $\endgroup$ Sep 22, 2021 at 17:16

2 Answers 2


[Revised answer based on revised question]

What you are looking at here is the square cube law. Basically, enlarging a creature while still retaining the same bodily structure will often result in the creature being unable to function.

Example, if you actually took a gorilla and enlarged him to the size of king kong, you would end up with a giant gorilla with busted knees (that's an oversimplification.)

So most realistically, your giant caterpillars would not work, they'd probably deflate or something because their structure couldn't support their size. Going a bit less realistic, I'd simply mention that this chaos energy, while maintaining some form of the existing caterpillar, has altered their structure on a basic level to allow for the larger size.

If you're looking for hard math on how big a caterpillar could get, I'm afraid I can't give that to you. I'm sure though that it wouldn't be too hard to figure out, like I said, look at the square cube law, and then probably some statistics on caterpillars, then tweak it to your liking.

As always with writing, what matters most is what best services the story. If your story works best with a man eating caterpillar, then even if it is unrealistic, go for a man eating caterpillar.

  • $\begingroup$ The question has been reframed to give it more focus, you may want to consider editing your answer to reflect the changes. $\endgroup$ Sep 22, 2021 at 11:30
  • $\begingroup$ Thanks for your thoughtful answers and clear logic! It looks like I'll just have to handwave, but that's okay! I should have expected that with giant bugs. $\endgroup$
    – Alendyias
    Sep 22, 2021 at 17:23

Pretty Big

If there is a constant pressure to enlarge (such as chaos energy), then they will enlarge a lot. There are many limits to caterpillar size, and almost all can be overcome

Firstly is metamorphosis. This could easily be solved by staying as a caterpillar throughout their lives. Another more dubious solution is to skip the pupa and simply go directly into a smaller butterfly. This could reach an edge case where the butterfly can develop in only a tiny portion of the caterpillar, which would end up constantly coughing up butterflies like a jellyfish polyp

Next is gas exchange. This is solved by pumping the tracheae and adding a gas exchange pigment to the blood. They could also complexity the heart into a closed circulation. Most of these changes have occurred in real arthropods

On moulting, the effects can be reduced by shedding the cuticle in parts, perhaps even as fine as dust

Support is the final challenge. It again has a solution: Bones. An internal skeleton would be useful, as it is more efficient and wouldn't need to be shed. You could use tetrapods as a base, but make sure the skull is unique (as the tetrapod skull is exoskeletal in origin). There are also other variations (a vertebral limb like brittle stars could look quite good)

Balance might also be a problem. The most plausible idea would be for the hindmost legs to extend back as a tail or outrigger. I'd say with all those changes a caterpillar could easily reach sizes like the sauropods. While they likely couldn't beat out the largest of sauropods due to oxygen requirements, they could still get close

If you want to get more exotic (and energetic)...

If the energy is there, then anaerobic respiration could allow them to transcend the oxygen requirements, potentially allowing them to beat out the sauropods

Another idea could be hydrogen: There are many organisms that make hydrogen, and these could become symbiotes of the caterpillars. They could provide hydrogen to various air-sacs throughout the body, reducing its density and easing the weight on the feet

There seem to be many structures that are far stronger than bone for their weight. If these materials could be laid down instead of bone, then it could allow the creature to get even bigger

All in all, I wouldn't say it's unrealistic for these caterpillars, with the right support and enough energy, to excede the size of a blue whale

  • $\begingroup$ This is a great answer, but I'd appreciate some more clarification on just how these changes would influence the final result and how this would help them get bigger. In other words, you did great, but I really want some more detail if that's possible. Thanks for the good work! $\endgroup$
    – Alendyias
    Sep 22, 2021 at 22:49

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