If you want to track all the robots and crawlers that have been to your site, I would recommend you to use crawltracker.com Google and most other analytics do not track robots and crawlers for many reasons.
Crawltracker is free and very simple to install and use. It is great to track all the robots which have accessed your site.
I use it to see how many pages have been indexed or been visited by google, yahoo and msn bots.