Black Flies – North East – Where is there NOT a blackfly problem in May?

Likely, but I have only been there in summer and in fall. Hard to say. I would guess they would show up a bit earlier in water areas…hmmm….yes, they also run the largest suppresion program in the US.
(Refering to PA.)

Catskills? I've been up there in May and don't recall a black fly problem. In my experience, I've never had black fly issues in the Mid-Atlantic – at least nothing that ruined a trip. I'd be more concerned with ticks that time of year than anything else.

You shouldn't have black fly problems in VA, WV, or PA in May — though I would caution that ticks begin coming out in great numbers.

Maybe I'm crazy, but I've never had the blackflies be so bad in May that they've ruined a trip for me. They're annoying, but nothing that can't be combated relatively easily. I've always found June to be the worst in the northeast, but still… they've never stopped me from going outside entirely.

I wouldn't let the naysayers talk you out of a trip you really want to do, just because some bugs will eat you. That said, I'll probably go for a walk next month and be eaten alive.

I agree with Ryan. Don't let the little suckers keep you out of the woods. A good headnet, shell jacket, shell pants and you are good to go. Dogs on the other hand are harder to protect. You might want to let them sit this one out.

Black fly bites on a dog