Insect sizes

My personal opinion is that the size of modern terrestrial arthropods, including insects, primarily limits vulnerability during molting. Moreover, with increasing size, it increases by orders of magnitude. If some aphid can captivate, start drinking juice in a few minutes, and give birth in another hour, then for a large stick insect or bird-eating spider, molting turns into an epic mystery, during which the animal is completely defenseless for at least a day and can die or be seriously injured even from a weak concussion, not to mention the predators that roam everywhere. It was with the spread and evolution of terrestrial vertebrates that the era of giant arthropods ended. But where there are no predators, palm thieves thrive there, about the size of which stories about the square-cube fly to smithereens. The respiratory hypothesis would have looked plausible if it hadn't been for the fact that arachnids that breathe lungs have almost the same size ceiling as tracheal-feeding insects.

The message was edited INO-13.01.2020 22: 01

personal opinion is good, because hypothesizing is a philosophy that, as you know, covers everything, but the ability to show the reliability of a hypothesis, with acc. experiments, or at least a coherent system of evidence that refers to already established facts-this is already science, so we are waiting(not waiting )megastates with evidence of exoskeleton limitations from a real scientist

Meanwhile, there are already scientific articles about attempts to prove exactly the role of the respiratory system
https://www.semanticscholar.org/paper/Myste...13#paper-header

The topic about the size of insects has already been here, the hypothesis with an exoskeleton is good, but nevertheless, Wikipedia writes that lung bags are primitive, and much worse than trachea, although bird eaters who do not have tracheae grow much larger than araneomorphs with tracheae and lungs.

But the whole bid with the "exoskeletal restriction" is what I already wrote about, molting features that suggest vulnerability to large insects could develop protso because it was not necessary to "invent" other molting principles, since the size was initially limited to "something else" Moreover, many insects seriously molt only once, at the moment of metamorphosis, and it is quite possible to do this secretly, some giant larva could pupate in the ground in a walled-up hole into a huge imago with armor, so you don't even need to invent anything special

Being small is more profitable than being big in general, and also for insects in terms of vulnerability during molting, but the trick is that when everyone is small, there is a benefit to someone to become big, and there are quite a lot of such" smart " ones at a certain point, there is a competition who will outgrow whom and the size will stabilize at the optimal level. Mammals under the dinosaurs, as they say, were also no larger than a rat, and as the dinosaurs became extinct and dimensional niches were freed up, it began
This means that the size depends on many factors

The ratio of the size of the smallest and medium-sized mammal-about 150 cm to 2 cm-75, and the average and smallest insect-about 2 cm and 0.2 cm-only 10 times, and if the extreme ranges-then now thriving mammals also rule, the blue whale and shrew-800 times, reptiles dwarf geckos and false-legged - up to 500 times, and the longest lapochnik 35 cm and micro-riders-115 times.
Even from such simple facts, it can be concluded that all living things tend to increase in size, and insects clearly have problems with this, although it is impossible to call them a non-thriving group

It also seems to me that molting is the main problem of insects. It's about breathing...

Let's say we consider the respiratory system of an ordinary honey bee. Through the spiracles, air enters the large tracheae, from there - into the air sacs, from there - into the small tracheae and is then distributed through the body tissues due to diffusion. In this case, the movement of air into the air sacs is forced, while the propagation of air from the air sacs and large trachea to the tissues is due to diffusion.

IMHO, an air bag system can solve the main problem of tracheal breathing-the restriction on the distance that air can travel due to diffusion. If you make a dense network of large tracheae ending in sacs, and separate small deaf tracheae from them, then air can be pumped forcibly through large tracheae, and through diffusion through small tracheae. At the same time, if the network of large tracheae is thick enough, then the insect will bypass the problem of diffusion. So the security question is, can a giant insect pump enough air?

Let's figure it out... 1 liter of human blood contains up to 300 ml of oxygen. In 1 liter of air - 210 ml of oxygen. That is, blood carries oxygen only slightly better than air... But air is much easier to pump through the vessels because of the lower resistance. This is easy to check by trying to push water through the tube first, then the same volume of air. This means that with the same pressure difference, a giant insect will be able to pump more air, and it is better to supply oxygen to the tissues than vertebrates with their hemoglobin.

And only molting does not allow the insect to grow large.