We are in Missouri at present, but we dealt with spiderwebs on hiking trails in NC all the time. It's mostly a hot summer phenomenon. If you are on trails that get a lot of use, it's much less common since the first hikers of the day will clear them all out just by walking through them. We encountered them on a hike we did in Hot Springs, Arkansas recently, but only on the first few miles, where we were on a trail early in the morning, and no one else had hiked it that day, obviously. It was pretty overgrown and full of webs. Whoever is in front bears the brunt of those. We had flies mostly on southern hikes, even back in the spring. Alabama was particularly bad for flies, as I recall, and we've had some deer flies and house flies here in MO. Could be that the further north you get, the less these problems occur, or maybe it's a matter of how urban you are. We have been in some very rural areas, lots of farms around, etc.

Rattle snakes I never worry about except out west, as that is the only place I've ever heard or seen one. But there are copperheads in the south, and water snakes as well, if hiking near a river. I always watch where I step! I've seen a couple of black snakes on the trail this spring, but they get moving pretty fast if they sense you approaching!