How big was the centipede? there are some pretty big buggers in the US.
Just don't ever try picking one up without a lot of protective gear, they are VERY fast, highly aggressive, and pack a hell of a painful bite. even tiny ones, especially the Scolopendra spp. will really let you know about it. I'd really hate to get nipped by the Scolopendras. One of them at least is known to have killed a child. And one of my natural history textbooks actually compares having to handle one to being more like wrestling a snake than insect.
As for the spiders around books I would leave them there. Spiders, with only 1-2 exceptions are ALL exclusive carnivores which will predate upon the little bugs that DO damage books.