We had them really bad in my area of PA three years ago. You would see hundreds of them if you looked up in the trees that they like, and those trees would be covered in the sticky stuff that they leave behind. We would kill dozens of them walking at lunch every day (pro tip - they can do a big hop, but it takes them a while to recharge, so if you just follow them after the big hop they are vulnerable). Strangely, last year and this year I have seen a lot less and I'm not sure why. People put sticky tape on tree trunks, which apparently causes the nymphs to get trapped there early in the life cycle when they climb up the trees, and also people were scraping and burning the eggs off of trees, but I'm not sure if either those or the squashing were enough to put a big dent in them. Rumor is that cardinals will eat them, and anecdotally I have seen an increase in the cardinal population. Regardless, it offers a bit of optimism for those of you currently dealing with a monster infestation, as it definitely got better here, although I agree that I can't see how they would ever be eradicated now that they've proliferated so much.