Perhaps they are in a zen-like state where they are one with their environment. Maybe that li'l feller is down there working on Satori while he's watching for Silverfish.
I don't *know* but I suspect they live in the eternal present. That thoughts of the future and past are rare, that a quiet low-stimulus day does not equal bored, it equals, "survived another day, that's cool".
I expect that they can get restless when they need something. That they are capable of actively hunting for something, but I doubt they get bored or impatient or frustrated about it. After all, if it takes a week to find a better web site, so what? It's not like they're missing The Game on tv or something.
I would expect them to be able to feel fear/attraction content/need and various other instinctive feelings as required. I don't know if they ever sit back after a hard days web building and feel pride. I don't think they need pride. They are small enough that they probably don't have a whole lot of neurons available for unecessary emotions like boredom.