Couple things about snakes:
1. Snakes don't know they are snakes, meaning they don't know they are poisonous to you, they don't know you are afraid of them, and they aren't the brightest, so while they may lay in the trail, they could in fact think they are hiding!
2. Only two types of snakes bite people...scared snakes and angry snakes
3. 80% of snake bites are dry, no venom is injected, this is nearly 95% of all 'surprise' snake bites, when you startle them or step on them
I've seen snakes as far south as Hot Springs, and as far north as Vermont, I would agree that Pennsylvania is probably the state you will encounter the most snakes due to the likely time of year a nobo thru-hiker will be there (June/July) and the amount of rocks for sunbathing.
Strangely, I've hiked PA twice, in summer and only seen one Timber Rattler that I recall, and that might have been northern Virginia, not really sure.
To use any type of precaution towards snakes along the AT is a bit silly in my opinion, we don't even do that here in Australia, and we have dozens of deadly snakes here, snakes that do kill people, and are on the trails in abundance...some people might wear long pants with high gaiters, but that's about it.
Snakes are not your problem...Lyme Disease and Ticks are a real concern, you can't even seem the damn things