Question For Those Who Know More About Biology And Paleontology Than Me

[R. U. Sirius]

Something that just occurred to me...the square-inverse law is the reason "attack of the 50-foot whatever" wouldn't work IRL. The larger something is, the bigger around its legs have to be in proportion to its body in order to support its weight.

So...how the hell were insects and arachnids able to grow to such nightmarish sizes millions of years ago, while retaining the exact same proportions?

[Ultimate Paragon]

What period are you talking about?  There were at least two eras when arthropods were gigantic.

[Random Gal]

I believe you're talking about the Carboniferous, and that was mostly due to higher oxygen levels if I remember correctly.

Also, these topped out at 10-foot millipedes and eagle-sized dragonflies. There were never any 50-foot B-movie giant bugs. The issue for the actual giant arthropods was mainly due to how much surface area was available for gas exchange in the arthropod respiratory system, not whether or not the exoskeleton could support the body.

[Sigmaleph]

As an aside, it's a square-cube law, not a square-inverse law. Square-cube is when you have two factors, one which grows proportional to the square of length (like surface area) and one that grows proportional to the cube of length (like volume or mass). Since one grows faster than the other, you have different behaviours at different scales.

Square-inverse is stuff like gravity where a force between two objects is inversely proportional to the square of the distance between those objects.

[SpaceProg]

Dangit, Random Guy beat me to it.   Good answer, Random.