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I've done some research into giant arthropods lately. The largest land arthropod currently is the Coconut Crab, but I'm wondering how much bigger an arthropod can get in our current Earth climate and environment (atmosphere, gravity and range of biomes specifically) before needing some drastic evolutionary design changes. For example, how big could the biological design for a spider or an ant be nowadays? I've heard of the insane sizes Myriapods have been in the past, can other arthropods do that too, let alone on our modern-day earth?

I'm aware there is, has, and was larger species of arthropod, but these were either underwater, alive during a time where there was more oxygen in the atmosphere, or both. What could be done on our modern range of land environments here on Earth? Can we get arthropods any larger than a coconut crab in today's climate?

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  • $\begingroup$ You are answering yourself. What is the problem that you weren't able to solve with your research? $\endgroup$ – L.Dutch - Reinstate Monica Aug 3 '20 at 4:50
  • $\begingroup$ Sorry, forgot the final line. $\endgroup$ – TommyProductionsInc Aug 8 '20 at 4:50
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As big as a coconut crab. The arthropod body is incredibly successful and allows for very fast and agile creatures. The drawback of it is that, due to how it feeds oxygen to their tissues (relying heavily on diffusion), their growth is closely tied to the amount of oxygen in the air. The coconut crab is considered the largest any land arthropod can grow in our time with the amount of oxygen available. If you want a spider or ant to grow any bigger than that, you'll need it to undergo quite a few changes to how it gets oxygen and delivers it throughout its body, how it's legs are structured and how heavy their exoskeletons are (along with many other changes to allow them to function, since another drawback of the arthropod body which also applies to any living creature: even without worrying about oxygen or food, you can only grow so much until gravity and the square cube law come for you).

We have made studies to try and find out why they'd grow bigger in the past and how some modern arthropods grow depending on how much oxygen there is. The answer is apparently that some grow more than others in environments richer in oxygen.

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