Imagine there existed a giant air tight glass dome environment where the atmosphere inside was simulated to mimic the atmosphere of the Paleozoic era. Oxygen levels inside the dome where 30%-40% as opposed to 21% levels of oxygen outside. If the dome has a closed loop environment so food and water from the outside dont have to be brought inside, and modern day arthropods are put inside the dome, could they grow to massive sizes? Could we create dragonflies the size of hawks? Isopods the size of house cats? Maybe the organisms put inside the dome wouldn’t grow to this size in their lifetime, but could they over a few generations?
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Im glad you asked this because I have the same doubt since i was like 10 
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https://research.asu.edu/big-insects-provide-big-answers-about-oxygen
Modern dragonflies placed in a 31% oxygen environment grew to be 15% bigger than normal. I don’t think it was a closed-loop food and water system, though. Luckily, cockroaches didn’t grow any bigger.
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I don’t appreciate your citation of an article which starts its first sentence by claiming that I am not a rational person (nor your skewed perception of cockroaches).
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Cockroaches did used to be bigger than they are now. Check out this cockroach fossil
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And of course americans will use anything but the metric system to compare sizes.
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(Im American and I manly use cm and mm for measuring)
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Same, I couldn’t understand how to read an imperial tape measure, so I just gave it up. It’s just easier to use cm or mm. All my tools are metric now. lol
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Really happy that it’s easy to tell the two ruler markings apart in photos!
Imagine if the scales had the same number of divisions for metric and imperial and observers would forget to note units?
Metric: 10 divisions (spaces)
Imperial: 2, 4, 8 … divisions (spaces)
Looks like you’d get an immediate increase in size in some of the insects (e.g. dragonflies), without any change in genes. If you left the system alone for many, many, many insect generations, you’d get a diversity of evolutionary (gene-based) changes, perhaps including giant size. If you deliberately selected for biggest insects in each generation, the process would be fastest, but it would still take a lot of generations.
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There’s more to it than oxygen levels. But yes, it is the limitating factor.
Arthropod species are bigger in warm regions because the molecular movement (not the amount!) of oxygen is increased and therefore the rate of diffusion (this is of relevance since arthropods are not active breathers).
And then there’s of course the predator issue. In the times of Meganeura nothing else flew. But nowadays, with birds and bats on the outlook, it is of significance not to be the biggest juiciest burger … er … insect. Same with land animals. Back then (devon-carbon), the arthropods had a headstart regarding life on land, whereas the vertebrates were still struggling to settle. They were comparatively sluggish, couldn’t climb, and were highly dependant on nearby lakes, rivers or the sea. So they were no reason for arthropod species not to grow to extraordinary sizes (unlike nowadays, with those nimble, highspeed, climbing, flying vertebrates all around).
So I guess we might be able to artificially create bigger insect species, but it is highly doubtful that they would survive in modern ecosystems, probably with the exception of giant cockroaches …
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That’s an interesting thought that probably everyone who was fascinated by insects as a child had!
I doubt that such a closed-loop dome experiment would have the wanted outcome. There are many more limiting factors than just the oxygen concentration that would impact the size of the dragonflies. Every resource in the dome is limited. The availability of suitable territories or prey could restrict their growth. It could even have the opposite effect similar to the phenomenon of island dwarfism.
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Further to the two latter comments, one of the factors that limits insect size is weight. The exoskeleton can only support a certain amount of weight. I’m not sure how insects got so big in the past, especially considering that they do not have an active system of Oxygen transportation.
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I remember a while ago reading about experiments with mealworm beetles kept in a high-oxygen environment, and yes they did grow bigger than usual.
The increased oxygen in the atmosphere means that the tracheal system could be more efficient. The big limitation on insects isn’t so much weight, it’s the ratio of tracheal space to weight. As they get bigger, the % of their body that needs to be trachea increases, until there isn’t enough internal structure to support the weight. With a higher concentration of oxygen, trachea don’t need to be as densely arranged in the body, and therefore the internal structure can support more weight.
Regarding the dome idea that started this, the high percentage of oxygen would cause problems as well – greatly increased risk of fire and rates of corrosion, for example.
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I agree with the increased Oxygen, but there is also a structural limit to how much weight the exoskeleton can sustain. Internal skeletons can support far more weight.
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If you can get past the knee-jerk reaction, roaches are actually kind of awesome little guys. A snippet from Wikipedia says " About 30 cockroach species out of 4,600 are associated with human habitats.". The majority of the species within this order are not out to invade your pantry. They come in all different colors and patterns. Check out some of these species, Therea olegrandjeani, Blaberus Giganteus, Polyzosteria mitchelli and Pseudoglomeris beybienkoi. This article talks about how these hissers are apparently able to distinguish their keepers from new people.
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Thats true. I guess the dome was talking about is a theoretically giant dome, one bigger than we could ever build.
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Terraform Mars! Make it arthropod Jurrasic World! 
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