Wonderful shots!
I've not hard of this phenomenon, but it looks stunning. I have seen it with a hedge completely covered, but I suppose that it's probably easy to miss... I only spotted the hedge (by which I pass daily) after a dew had been frozen on them... unless the spiders were all up late the night before and did them then
I suppose it's not that hard to imagine thousands of little spiders all at it at the same time. I had 2 nests of Orb spiderlings close together, which is thiusand of them just form 2 mummy spiders.