Had Nature Run Amuck?
From the back:
Tall was a hunter-explorer, venturing off the tiny island fortress of his tribe and making his way through wilderness inhabited only by giant insects ten times the size of a man. Loosely protected by chitin-armor, and striking with a spear doubly-barbed with spider venom, Tall fought to find a new home for his people.
But as he roamed he became more and more aware that mankind was a stranger in this insect world, that there were no other creatures remotely like men. Then where had his people come from?
As he followed the trail of the almost-mythical Ten who had founded his tribe, Tall found more and more mysteries—and death in more forms than he had ever imagined.
via my collection
Higher oxygen levels allow insects to grow larger.
But only up to a point.
https://www.quora.com/Why-does-the-square-cube-law-stop-giant-animals-from-existing
Lower gravity helps, of course, but a limit is still reached.
Damn – I gotta find me a copy of this! I love a little guy/big bug book!