Okay so I’m sure if you’ve read in history that sometime around Jurassic age that insects were like stupidly big due to O2 saturated environments. why can’t we manufacture an enclosed space with gradually increasing oxygen saturation over a few generations and see how big we can get insects?
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Evolution isn’t a short process and size is determined by genetics moreso than environment. It would (and did) take millions of years for insects to evolve to new size. You might see some slightly larger variants after a couple of thousand of generstions, but only by a centimeter or two.
Insects passively breathe.
Instead of having organs like lungs which pump air in-and-out, they just have a series of tubes all along their sides which allow air to get in and that is how they perform gas exchange.
This is very efficient on the small scale, and it allows them to breathe without using any energy at all. But as the insect gets bigger it’s demand for oxygen increases quicker than the limited amount of surface area in these tubes can supply.
Having an external exoskeleton also limits how much an organism can grow, but since coconut crabs are dramatically larger than the largest insect alive today that is clearly not the biggest limiting factor on insects.
And the truly gigantic insects were before the dinosaurs evolved, long before the Jurassic. They were around when the oxygen levels were higher, so the passive breathing was still able to get more oxygen into their bodies.
Insects don’t have lungs, but absorb oxygen through holes in their exoskeletons. Their blood doesn’t carry oxygen, the air has to get to each cell from the holes only. It doesn’t scale well for large volume-to-surface area.
Insects respire in a more passive way than fish, reptiles or mammals, they have holes in their exoskeleton and air channels inside them which circulate oxygen through them so they can live and consume energy. It’s a perfect system if you have the right volume to surface area/volume and oxygen percentage ratio. Millions of years ago, there was a good deal more oxygen in the air, I believe about 35 percent around it’s peak, and insects could grow much larger before their size became a limiting factor in whether or not they could efficiently perform respiration.
Experiments have been done, with surprising results. Dragonflies do in fact grow larger if raised in a high oxygen environment, without any genetic change.
[Science Daily article ](https://www.sciencedaily.com/releases/2010/10/101029132924.htm)
[Wired article](https://www.wired.com/2010/11/huge-dragonflies-oxygen/)
Evolution works very slowly. It doesn’t just make things bigger – over thousands of years, if being bigger for a species is an advantage, the larger ones will gradually breed more and survive more than the smaller ones and then the species gets larger. The tradeoff is larger animals need more food and burn more energy.
Probably because of the sqare-cube law.
The exoskeleton provides good protection but it’s weight increases by a lot as the size increases. Spider crab is a good example. Big for our normal standards, but it can only move because it’s underwater. If you take one to the surface, it will collapse on it’s own weight.
That’s also probably why we won’t have Gundams
>why can’t we manufacture an enclosed space with gradually increasing oxygen saturation over a few generations and see how big we can get insects?
As the other comment says, it’s been done on a small scale in an experiment by some researchers.
But remember, to do this stuff you need money. You need a scientist to manage the project, you need a large, mostly airtight chamber, you need lots of oxygen to supplement the oxygen levels. And if you want to give insects a chance to evolve bigger to take advantage of high oxygen, you need to keep all this going for several years at least.
And somebody’s gotta pay for all that. Competition for grant money is fierce, and for some inexplicable reason billionaires don’t fund this kind of stuff as a side project (I totally would if I was rich). So a lot of time when you ask “why doesn’t someone try this cool experiment” the answer is “nobody volunteered to pay for it”
If we wanted, we could create a study and situation that slowly increased insect size through selective breeding in an artificial oxygen environment. But why?
They can’t survive outside that environment, so they can’t live outside the lab. We’re not really learning anything too special, as we can already examine insects (and the new ones we make are probably different from their peers).
It’d also take a *long* time. A very long time. And there are lots of other factors to consider. It’s not an on/off switch. While insects may grow slightly bigger in environments with more oxygen, they don’t become giant instantaneously. It’s that, over time, traits for larger sizes may be able to survive and breed to the point a new species evolves that is bigger.
Remember, evolution is a complicated system with a lot of chance involved. That’s why we’d have to selectively breed these things ourselves to make them big. While their may be small slight increases in size (just like human height varies based on nutrition from birth), to get giant insects would be real tough.
TLDR: While potentially possible, it takes too long, costs too much, and really has no purpose.
There are a lot of factors that limit the size of insects. The big one, as you guessed, is oxygen. Since they don’t have lungs, and their blood doesn’t carry oxygen, they can’t grow too big or their inside tissues will die from lack of oxygen.
We could manufacture enclosed spaces with high oxygen levels, and people have done that on a small scale, but making a large scale oxygen chamber creates a huge fire hazard, and there really isn’t much demand for giant insects. They wouldn’t make very good pets, because you’d have to keep them in a sealed oxygen chamber, and insects tend not to live very long. So you might get a giant dragonfly, but it would probably only live a couple of months. Making a chamber big enough for them to reproduce would be a massive undertaking.
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