Found in a pitfall trap in the leaf litter in the forest here. I randomly offered it some grains of baker's yeast, and it readily started feeding on one.
Small, reddish-mauve creatures, many, running around under there, but couldn't capture them on camera. Dark spots look like frass, lots of it, in the webbing. Best guess is barklice, by comparing photos of their webs on tree trunks, but don't know.