Yesterday morning, I saw a spider nestled in the corner of a door frame. It had surrounded itself with a small pocket of web, just big enough to enclose itself. At the time, it looked as though it might be dead: It wasn’t moving at all.
The next time I took a look, about a half-hour later, it had opened up a hole in the top of the pocket, and departed for parts unknown.
So the question is, what was the purpose of this web? It can hardly have been to hide the spider: The web was barely even visible. To protect it against predators while it slept? I’d imagine that anything that would eat a spider would go right through a web without noticing it. To catch food? Anything that got that close, it could just attack with its limbs. A place to lay eggs? But there don’t seem to be any eggs in it, now that the spider is gone.