10:16 PM, 48F from calling from grass.
I turned the rock to find a bundle of silk wrapped up (seemingly) in leaves and other detritus. When I began moving it a number of jumping spiders came out. They were tiny maybe an eight of an inch or less (they are in at least two of the pics, but are blurry).
It might have been an egg sac which was just opened? I'm told jumping spiders are cannibalistic and don't hang out communally.
On an oak tree.
crappy pic I know. elusive bird + slow camera
I thought this might have been deer hair at first, but it seemed more like some sort of shell when I flipped it (the white part). But I couldn't tell what they might have belonged to. Most of the nearby trees were oak.
Foraging at night along road.