As previous posters have alluded, there are two reasons why there never were airplane size insects, and one reason why, during the Mississippian, Pennsylvanian, and Permian eras ther were larger insects thatn we see now:

o The square-cube law;
o Oxygen concentration.

The squeare cube law says that, as the height or width of a critter grows as the square, its mass (and therefore the needs of its support structure) increase as the cube. What this means is that if a critter is three times as tall as another, it will probably mass nine times as much, and its support structure (say, its legs) much be much larger in proportion to its body thatn the smaller critter. In other words if you scaled u-p a mouse to the size of a horse, its legs would have to be much larger, which would make it look more like an elephant or a hippopotamus.

Now an insect or any critter with an exoskeleton doesn't have any hard and strong internal support structure because it doesn't have an internal skeleton (that's why they're called EXO or 'outside' skeletons). If the mass of the internal organs is measured in milligrams, then they can be held to the exoskeleton by muscular tissure, but it the animal becomes as big as a cat, say, no amount of musculature can keep the internal organs in place and the animal would rupture itself and die.

With internal skeletons, which are like rebar in concrete, there is much more of a foundation for heavy organs like the liver, stomach, lungs, heart, etc., to hold on to, and the animal can gro much more massive without falling apart.

Of course, this is based on the force of gravity on land; marine and aquatic creatures don't have this problem, which is why you can have very large exoskeleton animals as well as molluscs which don't have any skeleton at all!

Oxygen concentration is a key factor, because the way insects 'breathe', using spiracles works fine when the oxygen can cross membraneous barriers to get to the tissues by only going a few millimeters.

Given that it's only a few millimeters from the spiracles to most of the insects' tissues, such an inefficient mechanism works fine, but if the tissues are buried too deeply, the only way the cells could get oxygen is to have smoe means of transporting it over longer distances, i.e., blood and blood vessels, which the insect doesn't have.

During the last three eras before the Mesozoic, the oxygen content was substantially higer (~35%) according to some estimates, which allowed a less efficient method (the spiracles) to work ove a slightly longer distance. so during the Mesozoic, one-foot flying animals, as long as they stayed light and didn't violate the square-cube law, would work.

Street,

It sounded like, in engineerease, you belive that we could grow some types of really big bugs in a 35% oxygen atmosphere? Meaning, it might be, sort of, possible?

balaam says:

"It sounded like, in engineerease, you belive that we could grow some types of really big bugs in a 35% oxygen atmosphere? Meaning, it might be, sort of, possible?"

Yes and no.

If there is a genetic advantage to big arthropods (animals with exoskeletons, including spiders and insects) then, given the fact that spiracle inefficiency would not be quite as much of a barrier, then you could see insects evolve to somewhat larger ones.

But you couldn't have cat-size cockroaches or donkey-size dragonflies, because even with an oxygen-rich atmosphere, the spiracles still aren't that efficient; and, besides, you still have the square-cube law to deal with.

Street,

First thanks for the discussion. Well no one was talking about donkey size dragonflies, I for one am quite against that. Just understanding by discussion, since we have a lower oxygen content in the present atmosphere, and since we have fossils of big bugs, 3ft dragonflies, and 2ft cockroaches, it would be a logical connection to think by increasing the percent of O2 we could get some big bugs, during Human times like the thread is interested in. Has anyone ever done a Oxygen vs. bug size experiment or is everyone just guessing?

I think I will try this. It would make the news, just because it is weird. Just think "local man looses hand to homegrown 2ft cockroaches. Police are now on the lookout for 35 wild cockroaches. Please do not approach them at they are considered armed and dangerous,....ahem.. the cockroaches, not the police. He was rescued by a handsome talking donkey, who refused to make a comment. More at 11."

oh im going to sound silly now are spiders insects? i forgot if they are or not.

Also the BEE thing no i dont think it was those bee's, i think these bee's lived 1000's years ago and were found fossilised or something but they only went extinct recently in our timeline of things...

bit like the giant snakes that went extinct 10000 years ago not an insect i know but there sure were a few extinctions about 10000 years ago was it ice age????

also i would'nt put it past em if some survived we like to think we know everything and say oh we found fossils but not seen any living specimins so we say its extinct yet is is so possible that it might not be, lots of things we thought were extinct are being rediscovered recently makes you think what else it for the finding.

Insects cannot be the size of busses or cars because they're body stucture cant support their weight.

The strengh of their body parts is proportional to the cross sectional area, in (unit length)^2 while their mass is proportional to their size (unit length)^3

their mass gets larger then their body structure can acommodade. If you did somehow create a 50 foot ant with you're un-shrink ray, it'd probly collapes on the ground, crush its own legs, and die

Terapin,
You seem to have some issues?
Now, I got me a kolloge edumakation too. Got it in, in ah.. well what street got his in Eng..Egn...nig...darn..never could speel it..You know were you use math and stuff to design them things that float on the water...ah...boats.

But, growing up on the farm we used a meathod of making animals bigger or smaller all the time, they got a funny name for it, selective breeding. That is how you get miniture pony's without waiting millions of years, for the profits to come in.
What in the world in makes you think that the 2ft fossil record cockroaches are a differant DNA, strain, than the todays little ones? Do you know something that no one else does, because last I heard you could not get DNA from fossills. Since they look a like, except size, what reason do you put forth that the DNA is differant? Got some of them thar facts?

There was also more water vapour in the atmosphere which would have contributed to large growths in organic creatures.

StaggerLee

There was also more water vapour in the atmosphere which would have contributed to large growths in organic creatures

How so? If true, it would be important to the experiment. I do not see the connection. I'm not saying it is not there.

Terapin

Yes, absolutely the DNA is different.

Ok, in that sense of you are right, the DNA, of everything is different. That was not the point. It was in reference, to limits of breeding and species. Meaning, that the genetic make up of the big and little cockroaches are the same structure, just as your example of Husky and Wolf. They can interbreed, where as dog and cat cannot. Selective breeding by man can replace pressure by natural selection. But, my main point is that in a richer oxygen atmosphere, the bug might get bigger, it would be interesting to note how much of an increase per generation, is possible. Granted, that today’s cockroaches may be the same inter-fertile species as big brother, but not contain the necessary information to be that big. Then, again they might? So, the only way to find out is too experiment. Unless, you know of a way to solve two variables with one equation? Structure, just as your example of husky and wolf, they can interbreed, where as dog and cat cannot. Selective breeding by man can replace pressure by natural selection But, even if the DNA becomes a limiting factor, in 35% oxygen you should see a marked difference in spiracles efficiency, thus you should be able to extrapolate the maximum size possible, until you reach spiracles inefficiency. It that clear enough, now?

They have a funny name for it... It is called Evolution.

You can talk all you want that I have issues but when you attempt to make a fool of someone else and indicate your lack of understanding of a subject you only serve to make a fool of yourself.

Terapin, your the one telling me, I am so ignorant as to have never heard the word evolution, do you really think that ? I just asked the question, does more oxygen equall bigger bugs, since oxygen is the limiting factor. Then, you go off and start telling me about Evolution, as if I never heard of it? Your tone is clearly, insulting. As if your the only one with education. Furthermore, I just wanted to know if someone ever did such an experiment? contraa, gave a nice logical answer, that he does not belive so. O.k. fine. That means someone should, and you seem to have somesort of problem, with people even asking the question? Why is that? I thought it would be cool to have a 2ft cockroach in a cage. Do you think you can insult people for asking questions and get away with it? Not, on my watch. How are your insults going to help, anyone find out anything? sheeesh....
So again, does anybody know of any experiments that increase the size of bugs.

Hey thanks Terapin,
Your last post was cool. That is all I was asking for.

Second, I never said raising oxygen levels would "force" insects to grow bigger. If i did please point it out, and I will most certainly retract such an unsupportable leap. I want to know "if" it would, not must.
Third, my question is because of the statement made that, oxygen is the limiting factor. It is plain, that any other limiting factor, would also be limiting.
But, in view of the fact, of 2ft cockroaches, it is possible that cockroaches can grow that big. Can the little one now grow that big? I don't know, which is why I asked the question.

Terapin

The problem is oxegenating the body. The way insects 'breath' is quite different from you and I and getting oxygen into the system is a limiting factor when it comes to size.

Balaam's Donkey (first post)

I saw a two foot cockroach "prehistoric" once, so they can get big. The theroy is that, if you take modern ones, and put them in High O2 atmosphere, they will grow very large. Might be fun. Theroy is that the Earth had a higher 02 level in the old days. Has this ever been tried?

Please note my simple question? "Has this ever been tried?" That was it.
Please also note the use of the word theroy.

Yes, it is great two people voted for you, lots of people voted for Hitler. Appealing to mass opinion does prove anything.
You attacked me, I simply defended myself.
Sorry, I did not know that DNA "might" be found in fossils. I have never claimed to know everything, I just asked a question. It won't happen again.

Thanks again for the last post. Seriously.
This ends my quest for knowledge, I will now go will live ignorance, Thank you.

The largest arthropod that ever lived was the Sea Scorpion ones have been found that are 9 ft in length. Since it lived in water it is not really effected by any land calculation on the size a insect could reach. Though it likely did come on shore for at least part of their life cycle. 9ft thats a pretty huge bug.

I dont know if I realy buy into all these calculations on large insects anyway. Its not like if say a ant evolved into a 9 ft insect over millions of years that it would just be a carbon copy of a smaller ant. Its body would have to change as it grew bigger. Legs would become thicker stronger like any other animal that grew to large sizes. If you ask me the real limiting factor is a lack of lungs or a more oxygen rich enviroment.

The Largest flying insect was the dragon fly Meganerua which had a wing stand over two and a half feet.

Hi Terapin,

I would love to ask you some more questions, but you have shown me this is a very bad idea.
My first question, "has this ever been tried" was met with quite an attack. So, you have convinced me to embrace the ignorance, which you claim to deny. Fare thee well, experimentalism, pondering, and open discussion, my boon companions. We shall never meet again……alas..

I wonder if changing other factors might produce larger insects after several generations, such as an increase in gravity. It would be interesting to see if there have ever been experiments done with non flying insects inside of a large centrifuge.

This has also piqued my interest in seeing if any information is available on insect growth in zero g, although I would think that would lead to a decrease in size. If I find anything I will report it back.

Yes, Yes its all my fault...sigh

"has this ever been done." was a terrible logical assumption, you are quite right. Won't happen again.
Nor will ask, how can the mass-gravity relation change, or how was it tested. If somebody does, it wont be me.

Actually because of the way most insects breathe (absorbing oxygen through holes in their exoskeleton) and because the difusion process necessary to absorb the oxygen requires that certain parts of the creature be certain sizes (thicknesses of membranes mostly). The mass of an insect is limited since at a certain size, this process will no longer work and the creature would suffocate.

(Maybe in the old horror movies where the giant house-sized ants attack the town, the ants aren't really angry, they're just suffocating and stumbling about)

Originally posted by Greyhaven7


(Maybe in the old horror movies where the giant house-sized ants attack the town, the ants aren't really angry, they're just suffocating and stumbling about)

Thats a good one

I wonder like was mentioned before if you raise generations of say fruit flies in very controlled enviroments for example in very oxygen rich enviroment if you would see a increase in size. Or if I wonder what would happen in a zero-G enviroment.

It would be very interesting

there are insects, that are a little bigger than Michal Jordan, they are in the shape of lilypads, but are 7 to 11 foo in diameter and they are aquatic, the undersides are just basicly more legs you can count, they feed on small fresh water fish, like minnows of guppies