New sitemaps were submitted to Google and Bing (the URLs changed, although the old ones remap), and I'm not sure if all of these bots are result. I tried to research some of them. A few claim they are analyzing content for assorted reasons like suitability for advertising. Who knows what they're really up to.
Some bots are what I call win-win. For example, Google and Bing index us so they have a search engine upon which to sell advertising and we get traffic from the search engine.
Many other bots are what I call narcissists; they only serve them selves while using our bandwith and CPU time. Some do things like see if anyone is busting on their client's products or company so they can spin things the other way or analyze the sites our users link to so they can tell their clients which sites are best to advertise on.
I'm blocking the latter, unless they plan to start sending us monthly checks.