I just wanted to share that I just published a new Bot Blocker module. This takes a more general approach to blocking bot traffic, and as of right now, provides the ability to block requests based on substrings occurring in a user agent, i.e. block self-identifying crawlers, and block older versions of major browsers (which seems to be a trend with this recent increase in bot traffic).
These are both ways I've been able to identify bots in this recent trend, and hope it will help the overall Drupal community. I've added this to the list of tools for Building your own Firewall in Drupal.