I have to do a presentation in my intermediate Italian class tomorrow,:eek: and I have a photo of (I’m not at my desk) something gigantus beetle, accompanying a National. Geo-type short piece with the same question as in my header.
Well, it says, IIRC, about breathing, exo strength, and something else… Any rationale here that can add. I’ve always thought it was an interesting topic.
Isn’t there something about why you could never have elephants two times their current size, because they would burst into flames, from non-scaling of heat dissipation - to -metabolism. I don’t understand that, and wonder if the same would also be up with inssects. I also wonder about the Young’s modulus of the exo, and how that applies. Plus I don’t even know how the suckers breathe…
I don’t have an exact answer, but keep in mind that living things need heat transfer, either warm blooded to get rid of excess heat, or cold blooded to gain needed heat. With less surface area to body mass ratio, you are less able to transfer heat.
That, though, isn’t the limiter on insect size. I seem to remember it has something to do with exoskeleton to oxygen content ratio… I don’t remember how, though.
Edit: Also, is it allowed to sue GQ for homework questions? If so, i totally missed the boat on that one when I was in school.
If I recall, the primary functional limitation on insect size is not mass (the square/cube law) nor surface area (for heat dissipation) but oxygen distribution. They don’t have “lungs” proper, and take in air through spiracles (“holes” in technical parlance) that is distributed through the tissue by tinier and tinier capillary-like airways. At a certain point of bulk, oxygen no longer reaches the tissue effectively.
The theory is that the higher oxygen content of the atmosphere in some prehistoric periods made possible the giant insects whose fossils we see. The greater density of oxygen would permeate further into the tiny channels…or something.
I was going to chime in that it’s probably around 9-10lbs because that apparently how big robber crabs get. However I looked it up and apparently they have some sort of modified gill mechanism that lets them get enough O2 so like the others have said, the limiting factor is probably how big that lets them still get enough O2. (I guess a centipede like insect could weigh more by being long and skinny.)
A factor the affects the scaling of most animals is that muscles are typically strong in proportion to their cross section, but weigh in proportion to their volume - so as they get bigger, their weight increases proportional to the cube of their size, but their strength proportional only to the square of their size - this is more or less why an ant can carry many times its own body weight, but a human can’t.
The fossil record shows that insects grew to downright frightening proportions during the Carboniferous period some 299 to 359 million years ago. The abundance of humidity combined with an oxygen-rich global environment allowed for the development of insects large enough to devour house pets.
There are some pretty complete fossils for organisms such was Arthropleura, which as about the size of a full grown human.
Also, for insects, they don’t have a proper circulatory system - the organs are just bathed in blood (well, hemolymph) inside their bodies - this works fine at the smaller scale, where dissolved gases only have short distances to travel.
Oh sorry about the confusion. Basically insects and crabs are both arthropods and both use the same substance for their exoskeletons (chitin) and feature open circulatory systems. So my point was that if a land crab could get up to 10 lbs then at least from a structural point of view a 10lb insect is possible. However like you say insects don’t have quite as advanced of a respiratory system as a crab. Oh and that’s not counting arthropods that use water to support their weight which gives us even larger guys like spider crabs and lobsters. (But the largest ancient water arthropod were sea-scorpions which could be heavier than a person. Again, that’s not an insect.)
I’m not sure the question is as meaningful as might appear.
By rights you could prove that a giraffe couldn’t possibly exist, because it would be unable to drink. But it exists and it has special modifications that allow it to do what other animals in it’s position wouldn’t be able to do. And the same goes for any number of other creatures.
By this same token, the question about insects presumes that another insect would have nothing over the current crop of insects other than size. But in reality it’s theoretically possible that a super large insect could exist but with some special modification, as above. And there’s no way to speculate about what special mechanism might exist.
If you assume a priori that the hypothetical large insect has nothing over current insects, then the ostensibly theoretical question boils down to simply: “what’s the biggest insect in the world?”
You were absolutely right about a doing a simple google, where entire pages are devoted to my panicky question; because I panicked, I went to you, The People Who Know Everything first.
In class I passed around a few spooky/gross pictures, including “Beetleman,” and messed up every other word in Italian, but at least* I* knew what I was talking about…
