I found a bunch of these pests on my grape leaf. I zoomed in a bit, but they're quite small in real life. They also seem to be found on leaves with some kind of white or gray fluff (at first glance it looked like a bunch of old spiderwebs crumpled up together, but they're not spiderwebs).
Oh, and if you'll notice, this leaf (and quite a few others like it) have this grayish whitish discoloration on it, also feels like velvet. Is it related?