Giant Bugs -- Prehistoric Times

This is not exactly directly related to our readings, but a few weeks ago I was watching something on TV (it may have been on the history channel) about how giant insects existed in prehistoric times. Obviously, this reminded me a lot of Gregor. I was curious about why these insects were so large back then when today the biggest insects we see could typically squeeze under doors. The show I was watching said that some of these insects were literally 5-6 feet long/tall. I could not even imagine the sight of that. Anyway, I wanted to know a little more about why these insects were so big (I didn't watch the whole show), so I just googled it and found that, "During the Carboniferous and Permian periods, atmospheric oxygen concentrations were significantly higher than they are today. Prehistoric insects breathed air that was 31-35% oxygen, as compared to just 21% oxygen in the air you're breathing as you read this. Atmospheric oxygen is the single most limiting factor on insect size." Anyway, I just thought this was really interesting and if you google this, you'll see some replications/fossils of these bugs. It's really crazy.