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I've had a great idea to leap over the giant boundary of respiration when making giant insects.The largest problem is that insects rely on diffusion through exterior holes (spiracles) to breathe, and the amount of diffusion relies on surface area, so a large insect wouldn't be able to move enough oxygen around its body because the volume of its interior mass would be much larger than surface area, and oxygen would need to travel further into the insect.(This is why the largest insects like meganeura had long, thin, tube-like bodies)

My idea is that since lungs (internal respiration) evolved from the gills of fish (external), perhaps the gills of aquatic nymphs like dragonfly larvae could evolve in much the same way.

As I've tagged, I'm looking for a reality check, as my knowledge of the movement from gills to lungs is not very sound. My question comes in two parts:

  • first, of course, is this idea plausible?

  • and secondly, how would the new internal structures affect the shape of the insect's body?

Edit: To clarify, I know that a new circulatory system would be needed along with the lungs, but that's a topic for a different question.

Also, I had another idea for the development of lungs or equivalent from the book-lungs of arachnids, so if you like you can touch on that in your answer. Nymph gills

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    $\begingroup$ "My idea is that since lungs (...) evolved from the gills of fish" - I am sorry, it is not true. Lungs evolved from the swim bladder. $\endgroup$
    – BartekChom
    May 9, 2016 at 4:21
  • $\begingroup$ thank you for the input, i think this question is basically answered by this comment and the answer below, so I'll try to change it's direction. If not, The Nate can have it $\endgroup$
    – XenoDwarf
    May 9, 2016 at 11:50
  • $\begingroup$ Exactly that happened in land crabs--the gills turned into book lungs, just like the did for arachnids--so a neotenic dragonfly evolving its gills into lungs seems entirely plausible. $\endgroup$
    – Logan R. Kearsley
    Oct 25, 2019 at 18:09

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Diffusion of O into the hemolymph it's only part of the issue. They would also need a heart or equivalent, our they'd need ingress into their tissues, or both.

That said, there are options:

Various plates around the insect could have gaps a flex to act as pumps. This could increase exchange with the atmosphere, but could also account for some circulation to tissues.

They could have exchanges at reasonable intervals along their bodies. These would tend towards vulnerability. (Clogging, infection, and gaps in armor.)

They could have actual hearts and lungs.

The environment could be a better exchange medium than our air.

Bucal breathing is simpler than what we have, and far niftier than insects'. It might be a good topic to check out to get a feel for the spectrum in reality.

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  • $\begingroup$ i am aware that diffusion is not the only problem, i simply stated it was the largest. I also know that a heart would most likely be necessary, i just wanted to centre this question around the lungs. Thanks for the help though, i've looked into buccal breathing and it's very interesting, i might edit my question to account for extra information in answers. $\endgroup$
    – XenoDwarf
    Dec 28, 2015 at 4:50
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    $\begingroup$ The plate pump notion could be similar to our peripheral return system (primarily legs) where their normal activity pumps the fluids, air or hemolymph (henceforth: "blood"), through the related systems. That might mean they get really still or move continuously, since anything between could become damaging. Since that could likely work a lot like bucal breathing, I figured it could help to understand...and it's just nifty. $\endgroup$
    – The Nate
    Dec 28, 2015 at 5:32
  • $\begingroup$ Also: I had no idea what you knew, honestly, and the question was quite technical, so I aimed for the generally educated but not-remotely-expert; that wasn't meant as an insult. $\endgroup$
    – The Nate
    Dec 28, 2015 at 5:33
  • $\begingroup$ i was in no way incriminating, i understand completely why you added information, i was simply informing you $\endgroup$
    – XenoDwarf
    Dec 28, 2015 at 14:22

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