Apparently if a site gets environmentally totalled (wartime bombsites, poisoned etc), spiders are often the first re-colonisers, because they are happy to eat each other - then they attract the larger predators and so on, while the plant seeds blow in and the whole system gets back on track.
I used to hate them, couldn't sleep in a room if I thought there was one. While I wouldn't go out of my way to pick one up, I'm much better now...