My flat seems to be quite popular with what I take to be pholcidae of some description. Occasionally one will move on from its customary home (usually a corner of the ceiling) and a few days/couple of weeks later what appears to be a different one will take up residence in the same spot. Would a spider reuse a vacant web, or would it destroy it and start again from scratch? Or would it even depend on the species?
This is very much anecdotal, based on what I have seen around my own home, so not wise to assume it is typical...either for the species, or for homes where webs are routinely cleaned away.
I have seen Pholcus invade other spider's webs. This morning I observed an adult & jeuvenile both inhabiting an occupied Steatoda nobilis web. The tiny, sub-adult owner seems none too pleased and is cowering well out of reach. I have seen them hang around some in another adult S nobilis web, but she tends to stand guard & they move on.
I don't really know the interplay between different Pholcus individuals, I guess they make their own webs when they have to, but can be opportunistic and use existing webs as they see fit? They seem to build webs in vantage points, from which they pick off passing prey in close proximity.
I have seen a wolf spider invade a Pholcus web...this doesn't surprise me seing that the wolf spider is an active hunter, catching prey on the run. It didn't turn out well for the wolf spider, as it happens, it was quickly hog tied by a tiny little Pholcus spiderling & dropped out of the web looking rather like a tied up Christmas turkey! ;-)
The adult S nobilis has a few Zygiellas bordering her web, I have seen her invade their webs when they catch prey and vibrations alert her. She takes the prey back to her hiding place. Zygiellas stay out of her way, or flea their own web when she turns up, either returning after she has gone, or starting from scratch somewhere else. Generally though they seem tolerant/accepting of each other's presence. I have seen male S grossa temporarily hang out in S nobilis' web, in very close proximity, she was seemingly unbothered by this. I have often observed Tegenarias in a 'stand off' with another S nobilis on the exterior of the building, they often seem poised to invade the web, but S nobilis obviously drives them away, as they don't stay around long. I have seen an S nobilis individual, without an established web, wandering about trying out other webs (Pholcus, A. diadematus & other S. nobilis) it can find - this individual doesn't seem to be a good web builder. S. nobilis webs can start out quite scruffy & random looking, but they add to them over time and they become quite extensive & complex, serving both as a means to catch prey and as a defensive construction.
Araneus diadematus seems to build/maintain/inhabit it's own webs, as do the Zygiellas. Some orb weavers build fresh webs regularly, they often reside in a spot close to the web, but the web is primarily a means of catching prey close to home, rather then "home" itself.
I guess that whether or not a spider actively hunts prey, without a web, has a bearing on whether it is likely to invade another's web. Conversely, if a spider relies on a web for both food & shelter, it is unlikey to leave it voluntarily, or welcome intruders?