Biggest junebug I've ever dealt with was as long as my thumb. That is a loud thump against a tent.
Atlas moth does sound pretty cool.
I remember that Chicago had a rocking science museum that had an entire section on various bug species, but the name escapes me. It's not the popular science museum, it's the one that the University of Chicago uses for research.
Crap. Blegh.
In southwest MO we have copperheads, rattlesnakes, water moccasins, brown recluses and black widows. Those are the only really posionous things I know about.
Funny story, I was night fishing on a bank a few years back and I felt some pressure on the side of my foot. I turned on my flashlight to see a water moccasin slithering past me. I just stood still and it went on about its business. Freaking out only scares creatures, and I don't want to be bitten.
The creatures that scare me are ones larger and faster than humans. If you ever see a bear you really get a sense of how quick and how big they are.