There was actually someone on a forum I frequent that wanted to try this. They had an oxygen chamber and wanted to try to grow generations of caterpillars in it and see if this had any effect on the size of the moths over a number of generations. Unfortunately, the experiment fell apart not long after it started.

Honestly, you’re not likely to see an increase. The oxygen content of the atmosphere does place a limit on how big insects can get, due to how they transport oxygen through their bodies. Here are some of the world’s largest insects:

A dobsonfly

A weta cricket.

A stick insect.

A scarab beetle.

Have you ever seen an insect that big? Chances are, you haven’t. Oxygen imposes a maximum size that insects can grow to, but most never come close to this limit because there are other things limiting their size, such as needing more food and being more visible to predators. By placing insects into an oxygen chamber, you’re not going to see them grow larger - oxygen is not limiting their current size, other factors are.

Another issue is that even with humans selecting for large size in an oxygen chamber, it would take a very long time with a very large breeding populations to get the necessary mutations to start increasing size. Evolution takes time - millions of years using entire species’ populations as a lab to get these mutations in. This just isn’t the kind of thing you’re likely to see happen. Maybe in a lab with genetic editing you could engineer some insects that would grow larger in higher oxygen, but probably not otherwise.

Thankfully not, if that could happen some evil maniac would be creating an army of super-spiders! 300 million years ago the atmosphere was rich in oxygen, which caused insects to grow to enormous sizes! But as the oxygen levels in the atmosphere lowered, the insects got smaller, i believe this is party something to do with how oxygen is delivered around there bodies (somebody confirm?). The size of the insects didn't just happen over night, as they evolved they gradually got bigger as oxygen levels got higher. I do not think Arthlopleura (A 300 million year old, 2 metre "centipede"!) will return if you stick a centipede in a tank with extremely high oxygen levels, however if you set up a breeding colony, after a couple (hundreds/thousands/more?) of generations you may start to notice some generations are larger than the previous, however these differences would initially be so tiny, you would need specialist equipment to claim that they are getting larger as a result of the high oxygen level, and not just a randomly large centipede.

Shall we just stop and be thankful we do not have centipedes preying on cats and dogs? Most people freak out when we see a spider catching a fly, let alone a huge bug crawling away with Mr.Fluffball the cat.

If you do manage to kick evolution in the face and create a super-bug, do it in Australia where the people have also evolved to survive all the native murderous fauna.

PS: I take no responsibility for the uprising you cause as a result of your bug of mass destruction.

Oxygen is poisonous. Yes, that’s right, too much oxygen can kill you if you get too much of it. It’s a powerful generator of free radicals, it oxidizes lipids (like rancid fat or butter), and it drives oxidative stress that kills cells and is probably responsible for many diseases. A 70% increase in it’s concentration, to about 35% of atmospheric gases at sea level, sounds like a lot to me. Maybe someone else has more quantitative information. But there is such a thing as too much of a good thing. Another example is iron. We have evolved a very efficient mechanism for storing iron in our liver because iron is a scarce commodity if you have to kill animals to get it. Unfortunately, we haven’t evolved a mechanism to stop accumulating iron. There are tragic tales of infants and children who have gotten into mom’s supply of pre-natal iron supplements. At first, it doesn’t seem like a big deal. It’s only iron, right? But eventually the iron overload in the form of too much ferritin in the liver destroys it and death inevitable follows (though I suppose a liver transplant might keep the patient alive for many years).

No more so than you would grow larger breathing pure oxygen. You might not have to breath as often but that’s about it. There was a time when insects that evolved in the presence of higher oxygen concentrations grew bigger. But those are long gone. The insects we have now do OK in our lower oxygen concentration, but just like you they won’t get any bigger with more oxygen. It would be cool, though.

Potentially yes but it might take many many generations

Its kind of like food calories and human height although this is not an exact analogy. If you don’t give enough calories, a human’s adult height will be lower. Give enough calories and the human will grow to the max height allowed by his or her genes. Give too many calories and height won’t increase. However this extra calories over thousands to millions of generations does mean that any mutations that continually increase height will be preserved and won’t be selected against because of not enough calories, unless some other thing selects against it

Same thing for insects. More 02 will allow insects within one generation to max out the growth potential in their genes. Over thousands to millions of generations, the increased O2 will allow mutants that have larger size to not be selected against. Assuming of course that there is no other factor that selects against larger size

Early versions of some insects l;Ike dragon flies way back in the cretaceous era were significantly larger, however many other species found in amber and other ‘traps’ were not much larger than contemporary descendants.

Also, there is an upper limit to how much oxygen a life form from early can be exposed to until the life giving aspect turns into “rusting” away. Oxygen is corrosive, thus iron, copper, silver - etc all tarnish/rust. Further oxygen loves to bond with other elements thus changing carbon into carbon monoxide or carbon dioxide.

Then there is the issue of a little thing we call fire. You think wild fires are bad now, at only 30% oxygen in our atmosphere wild fires would be pretty much unbeatable.

Getting back to insects. The Early to middle cretaceous atmosphere was higher in oxygen which by by the late cretaceous it was getting lower before the impact event of 65 million years ago.

There may also have been a denser atmosphere for Earth, we have to take into account that limestone (a product of critters with shells) was laid down during the early life supporting geologic epochs. Limestone is composed of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate (CaCO^3). Which is calcium, carbon and oxygen. In fact the molecule is three atoms of oxygen.

Petroleum consists all sorts of oxygen and carbon bound molecules in the form of hydrocarbons. There is, of course, more chemicals involved.

While a consistent supply of carbon, oxygen and other atmospheric gases have vented out of volcanoes and other geologic activity, life has been very, very busy taking the molecules of say carbon dioxide and stripping out the carbon and releasing the oxygen (plants do that), but other life forms bond carbon to oxygen releasing carbon dioxide. This is by no means a balanced cycle. More carbon and oxygen gets bond up and “sequestered” in soils, and eventually rocks.

Considering the size of pterodactyls and giant dragonflies and other critters that soared or even had true flight and comparing their muscle attachment points to bones and the size of those bones we end up, bone types, etc there appears to be that a group of scientists are insisting that these critters couldn’t fly in today’s atmosphere. There is a general thought that earth’s atmospheric density was greater than it is today: how could pterodactyls fly atmosphere thick.

There are other arguments about such things as earth’s actual gravity/mass such as “expanding earth theory”. Neal Adams has his website with his animated works which shows a correlation of the continents as being “blown up” like a balloon and not shifting continents that just wander around on the mantel. He has even gone so far to address other bodies in our solar system. Just things to make you go Hmmmm.

If we assume that the Earth was some how smaller, thus less massive with less gravity, it would have been losing atmosphere at a far greater rate than it does today. And that covers where the thicker/denser atmosphere went. Also it allows for the structure of big flying dinosaurs and giant insects. Insects have an exterior skeleton there is a limit on how big they can grow and support their organs.

All in all an increased atmospheric pressure with a slightly higher oxygen content would most likely lead to an increase in size for most insects. If you took them to say Mars and kept them inside your over pressurized oxygen rich dome you may find that they would indeed grow larger over generations.

It is thought that once humans colonize Mars for permanent that the first Martians born and raised on Mars would be taller due to the lower gravity. It is also theorized that those Martians wouldn’t be able to come to earth because in getting taller they would sacrifice bone density and muscle mass. Several generations down the line - Stretched out ‘giants’.

Thus gravity is a serious throttle to how big a creature can get.

Most insects are much smaller than they could be, so their size is determined by their genes, not the oxygen content of the atmosphere. It is unlikely that you would see any difference by raising bugs in a high oxygen atmosphere.

If you look in a longer perspective, then evolution would likely after many generations produce some larger insects for the same reason that it produces other large animals; large animals tend to have fewer predators that eat them. However, most insects, as today, would not benefit with a larger size.

The size of most insects is optimized for the niche they occupy. For example, hair lice would not benefit from becoming larger and easier to detect.

Insects don't have lungs for forced ventilation but rely on oxygen diffusion into their bodies through spiracles and trachea. One might suppose that this limits the size to which insects can evolve. However insects have been much larger in the past, as others have pointed out, and more so than could be accounted for by a mere doubling of the oxygen concentration. It may be that while giant insects are possible, they are less competitive in that size range than then vertebrates with lungs and bony skeletons. Spiracles and exoskeleton work well for tiny organisms, while lungs and bony skeletons work better for larger ones. So after amphibians, reptiles and mammals took over the land and flying reptiles (including birds) took over the skies, insects could only compete in the realm of the tiny.

Go to this link: Meganeuropsis - Wikipedia

This link describes an insect with a wingspan of 28 inches, that lived about 290 million years ago in the Permian Age when oxygen levels were about 80% higher.

So to reverse engineer it, if you could take the largest warehouse in the world and keep it pressurized for hundreds of millions of years with 80% more oxygen, then you could cause a dragonfly to evolve to the size of Meganeuropsis.

A project like this would be ultra-expensive.

It would take thousands of self-replicating robots to keep the structure tight and to keep an entire biome of insects and plants watered and lighted.

I will mention the facts about two insect species where well researched population dynamics information is available.

1. Brassica aphid in conducive ecological conditions is able to reproduce parthanogenetically (with out mating). They do so to avoid waste of time in haste of self multiplication. Sex ratio of population is suddenly changed where all (100%) are females. Every individual is producing a child at rate of one in 3 minutes. The young one is ready to produce its own child with in 8 hour. This gives the idea as how fast a population of insects can grow in favourable conditions.
2. Queen termite lays on an average 80,000 eggs per day (24 hour) non stop. Life of a queen is about 8 to 10 years. It can not afford any thing else other than eating and egg laying during her life span. They have rightly been named as egg laying machines. In case laying capacity of a queen deteriorates, it is killed by serving workers in order to get a new one.

No.

It might effect evolution the opposite way. There is genetic variation in any population of insects. Some will inherit different sizes.

Oxygen may speed up the insects metabolism. So maybe some insects will be able to do more. However, it can’t increase their maximum size.

Oxygen in high concentrations is a poison. Large animals by using up oxygen in their blood live longer than small animals. The oxygen will decrease the probability of the little ones surviving. The natural selection in a high oxygen environment will favor the largest insects.

So over many generations, the average size of an insect in a population will increase. Large insects that reproduce slowly survive longer in a high oxygen environment. Small insects will survive only if they reproduce faster.

One place to go when there is too much oxygen in the atmosphere is under water. Some insects may go back into the water when there is high oxygen. There will be more oxygen in the water that they can use. Further, the bubbles that they carry down will last longer.

So high oxygen levels may have initiated the evolution of certain insects that spend part of their time under water.Again, this would occur over MANY generations.

I must leave a proper Biologist to answer this, but I think the issue about O2 levels applies to paleontology and earlier eras when O2 levels did rise , from memory to around 30% in the Carboniferous v 21% now, and that this allowed insects whose size is limited by a primitive respirtory system ( they have no lungs) to evolve to become much bigger than is possible today. Dragonflies the size of birds. I dont think anyone has suggested that increasing O2 levels in insects evolved to live in present O2 levels would affect the size, as this is genetically determined, and can only result in increased size over hundreds of thousands of years of evolutionary genetic selection . So it would have to be a very long experiment!

Great question. Let’s look at a few species for comparison. A Crazy Ant would become the size of a Carpenter Ant. That’s not too big.
A Fire Ant would become 2 1/2 inches long, their trail would cover significantly more area making them very visible and perhaps more avoidable. Most of the fire ants I’ve ever accidentally sat on were because I didn’t notice them first. LOL. The Carpenter Ant would measure approx. a whopping 5 inches in length. They do not eat wood, like termites, but chew through wood and dead trees and the damage to a house would quickly become significant. An entire colony would reduce an acre of deadwood in a forest to sawdust in less than a week. An invasion in a house or other wood structure would do enough damage to perhaps collapse that building if allowed to chew through support beams and floors. Exterminators would need to develop more aggressive methods of eliminating a giant, fast moving colony. The only upside would be that they would be detected much sooner than a normal size ant. A 5 inch chewing ant would make a lot of noise. Also, with their strong jaws, their bite to humans would cause more harm than just a superficial, irritation. A 5 inch ant with those jaws would draw blood, be more painful and take some time to stop hurting and heal. I hope my answer helps you. It creeped me out just writing it.

The basic experiment's been done already several times with several insects.

The necessary background is that the tracheal system of insects works by diffusion. As insects get larger, its efficacy gets smaller, since there is no active process to let the air flow in; this is why large insects are nevertheless still narrow – they need to keep the muscle sites as close to the tracheae as possible. While larger insects have highly-sophisticated tracheal systems aimed at maximising the efficiency of the diffusion, there is a limit set by the exoskeleton – there is only so much space to build these tubes, since connective tissue is also needed. With that in mind, we can look at the best study done so far, by Kaiser et al. (2007): Increase in tracheal investment with beetle size supports hypothesis of oxygen limitation on insect gigantism

What the Kaiser et al. study showed was that when the beetles were raised in an atmosphere with higher-than-normal oxygen, the amount of energy invested in expanding the tracheal system decreases, despite attaining the same mass. Specifically, they showed that it’s not overall body size that matters, but the growth of certain body parts: the limiting factor is getting oxygen through all the constrictions and twistings of the tracheal system to the head. Look at the figure below and especially the last sentence of the caption.

This subsequently means that if they were to expand their tracheal system, they could reach much larger sizes, and this is what happened in the Permian and Carboniferous, back when oxygen concentrations were much higher – the oxygen was there, and so they could afford to reach large sizes without compromising their breathing systems. Today’s largest beetles are at the very limit allowed by current oxygen levels, 16 cm. Another limitation to consider is that the tracheal system can’t get too complicated, or else water balance regulation in the insect gets compromised, since the tracheae interfere with the haemolymph.

There are a few more experimental studies. Peck & Mandrell (2005) did it with Drosophila, main result in the figure above, and Henry & Harrison (2004) showed that such experimentally-induced size changes hold up over many generations. Klok & Harrison (2009) even showed that these size changes might get encoded genetically after a few generations, even if you bring oxygen levels back to normal.

So, in summary, go ahead and start your diabolical plan (why else would you want to do this?). It will work eventually.

“Is it possible to make a contained environment where we could put a higher percentage of oxygen where over a period of time could breed insects to become giant again?”

Apparently this has been done, and might be in the sources to this paper: Atmospheric oxygen level and the evolution of insect body size … it reads like the insects we have now, will just get larger, if they do not spend a lot of time and resources being able to survive with lower oxygen levels.

I know that if you cultivate fish in water that has very high levels of oxygen, their gills atrophy, and will actually die if you go back to natural aspiration of the water.

If you raise them in a high oxygen environment maybe they would grow a bit larger, but this would not be due to genetic change, just that the current genes would allow them to grow to the fullest. Just like two twins would have different heights if one was raised in poverty one raised with enough nutrients.

Raise them in a high oxygen environment will not per se cause them to evolve into larger size. What will happen is that if over time some mutants arise that have genes to be larger, there would not be a selective pressure based on oxygen against larger size.

There may be many more selective pressures though against larger size such as availability of food and predators or whatever but lets assume the opposite, bigger size confers some tiny survival advantage in this situation. Since there is a tiny survival advantage and the negative survival advantage of it being harder to get oxygen is removed then over many millenia there is a chance that the insects would get larger and larger, depending on what mutations occur.

Somebody did the experiment, with Drosophila (fruit flies, a typical experimental animal model in genetics, possibly the most famous animal model in genetics): Experimental Selection for Drosophila Survival in Extremely High O2 Environments (The paper is open access, too, so the entire article can be read for free).

The authors selected a population of Drosophila flies that can survive and reproduce and live their whole lives in 90% oxygen! These levels are lethal in flies that did not undergo selection, or as we biologists call them, "naive" flies. The normal oxygen levels in air is ~21%. Such hyperoxic conditions are lethal because they lead to very high levels of oxydative stress. But these flies managed to live under these conditions, and the investigators found that they had undergone changes in the expression of a few genes, for example upregulating two genes that produce an antibacterial peptide, and lowering the expression of genes, some of which are involved in metabolic pathways. It's not entirely clear how these changes in gene expression help the flies survive.

But to answer the question about size, these flies were about 20% heavier than normal flies and had bigger bodies as well as a larger wingspan.

Q. If we planted too many trees that the oxygen in our atmosphere became like that of prehistoric Earth, would organisms grow larger in response?

A. Well, golly gee whiz! “If we planted too many trees …” How many are too many? And the vast majority of oxygen comes from ocean life, not terrestrial. So, no, too many trees would have inconsequential effect on oxygen percentage in the air.

“… the oxygen in our atmosphere became like that of prehistoric Earth…” Added oxygen doesn't guarantee organisms will grow larger. When arthropods evolved and emerged to live on land, higher oxygen levels may have supported larger bugs, but they don't breathe like later evolved air breathing tetrapods. 🐞🐜

Oxygen levels before dinosaurs appeared jumped from around 15 per cent to around 19 per cent before dropping later. Higher oxygen levels helped dinosaurs to flourish, experts find

The oxygen levels in the past fluctuated for much of the Earth's history dating back to the Triassic Period where oxygen levels hovered between 10 and 15 percent -- far below today's 21 percent and the 30 percent previous studies suggested characterized the Cretaceous Period, which lasted between 65-145 million years. Dinosaurs Lived in a Low-oxygen World, Study Suggests

If this is fully supported, higher oxygen levels didn't guarantee larger tetrapods (the buoyancy of water does), and higher levels would lead to 'oxygen toxicity'. The excess oxygen at a higher partial pressure (concentration and partial pressure are directly proportional) will cause harmful oxidation to their cells causing them to die. An increase in oxygen will also speed up metabolism. 😱

No — not necessarily: For humans (and other vertebrates) size is limited by the ability for bones and muscle to resist gravity not by respiration. This is why sauropods on land and mammals in the ocean have reached the maximum sizes that physics will allow for bones and muscle.

For insects and crustaceans size is limited by the amount of oxygen that can pass through their exoskeletons. As animals with exoskeletons get bigger, their exoskeletons must get thicker to support their weight. As their outer skeleton gets thicker, less oxygen passes through. When the percent of oxygen is higher, then exoskeletons can be thicker. This means that animals with outer skeletons can therefore grow larger and still be able to breathe.

They don’t grow in one generation large because of the oxygen of the air. Hormones and developmental timing are mediated by genetics, not the concentration of oxygen in the air. The concentration of oxygen in the air determines the maximum (smallest upper bound) of size for an insect.

Meganeura was a dragon size dragonfly that lived in the Carboniferous period. In our current atmosphere, a mutant dragonfly the size of Meganeura would die.

However, a high concentration of oxygen won’t make a dragonfly grow to the size of Meganeura. If the oxygen concentration would rise to the level of the Carboniferous level, the dragonflies would remain the same size for thousands of years. However, de nov mutations that create large dragonflies would survive. So natural selection over millions of years would increase the average size of a dragonfly maybe to Meganeura’s size.

[answering "Could giant insects be grown in a high oxygen atmosphere?"]

Yes, the "experiment" was done about 300 million years ago, during the Carboniferous, when global oxygen concentration peaked around 35% (vs 21% today). The fossil record shows many giant insect species in this period.

Insects lack lungs & gills, so oxygen delivery to deep tissues is by passive diffusion along a microscopic network of tubular tracheae. Larger bodies means longer distances over which oxygen must diffuse to reach every last cell, even as oxygen extraction is occurring along the way, so insects are limited in size. There are two ways around this process: (1) raise O2 concentration; (2) raise temperature, which increases rate of diffusion.

This latter effect explains why the largest insect species today are generally confined to the tropics, where average temperature is highest.

But the details of your question suggest a laboratory experiment lasting "at most a few decades..." incorporating "selective breeding," which I assume means choosing the largest offspring to continue breeding. Here I would defer to expert biologists, which I am not.

I'd guess the total number of generations is on the order of 100 to 1000, which might be enough to produce moderately larger bodies but not a dramatic increase (such as a beetle the size of an armadillo) because of (1) scaling factors that follow from laws of physics; and (2) specific physiologic obstacles that might have to wait for an unrelated variation, in some other part of the genome, that enables additional growth.

The first few generations might well be bigger, as newly-hatched larvae, given abundant food, can immediately grow a little bigger in a high-O2 environment vs room air, even if genetically programmed to only grow so large, but that effect would be independent of genetic changes that presumably underlie "artificial evolution" in the laboratory experiment you propose.

I use quotes around artificial evolution because normally speciation requires millions of generations, plus it involves populations either interbreeding or reproductively isolated -- concepts that might not apply in this lab experiment.

Though I consider David Rosen’s answer as quite valid, I would like to suggest a different perspective to your question.

There is a scientific principle called “Limits of Growths”. It’s concerned with how any natural thing that can grow in number & size would have inner mechanisms (and sometimes outer) that would limit its growth. The principle is valid for engineered things as well. The most serious issue of limits of growth is the population explosion. We should never even hope that the population of the Earth would grow indefinitely. Surely it is clear that long before we reach an inordinate number of people, we will perish because of insufficient food, water and shelter for all. Earth after all, is a limited supply warehouse. My favorite example to the limit of growth principle is delivered in this seemingly innocent question: what is the maximum height to which a mountain could grow? One might say that it can grow to a height that would include all available “mountain-material” on Earth. Let’s say: 20% of the Earth’s crust. That means that it would be the only mountain on Earth. Such a mountain would be hundreds of miles tall, even thousands of miles. But, even if we could make this mountain, it would not stand tall for long! It would collapse! The tallest mountain possible on Earth is barely taller than 50,000 ft (about ten miles). Any taller mountain would simply collapse. Hers’ a scary thought: Mt. Everest and Mt. K-2 have been measured to be growing taller. Imagine the awesome sight when they reach their limit of growth of 50 K feet. You would witness the collapse of two majestic mountains!

Now let us take a look at the limits of growth in your question: how big a tank would you use? What do you do when the insect grows to a volume greater than the tank? Oh, you make a bigger tank. Eventually, you need a tank greater than your lab. So you build a bigger lab. OK, I’m kidding. But consider the ethical questions that arise in doing this project. The Law of Conservation of Matter tells us that the oxygen that you feed the insect has to come from somewhere. The more oxygen you use, the less there would be for others. So to be fair, you make your own oxygen from sea-water. But that would disturb the delicate balance of sea-water that is directly related to climate-change and the seasons. Do you see where I’m going with this? Sooner or later, the limits rule will force you to cease operation. Insects evolved into smaller size for a reason. You have one idea now why that is so.