Re: What's a 'spider'?
Not so much data mining, but indexing the page so its easier to find. Google runs thousands of spiders that read your page and cache the relevant parts into their search engine, so when people search you can get that instant result instead of waiting for a few days while it searches the entire internet.
With SH's forum being so rapidly changing, the spiders like to hang out and watch for new posts or updates, and record them as they happen so everybody can find them using Google or Yahoo.