From searchenginejournal.com
The first trouble is that Google Analytics uses what is called “page tagging technology”. Without getting too deep on this, it is important that we understand this one fact. That is, the program is only capable of recording information on browsers that execute JavaScript.
Automated browsers (including all spiders like Googlebot, Yahoo! Slurp, MSNBot, etc.) never execute JavaScript in your source code. So, while Google Analytics may do a great job of tracking your human visitors, they’re unable to give you the goods on spider behavior.
In order to make the most of your SEO efforts you need to know when a spider is coming in, what pages they’re requesting, and how often they’ll come back. Using this information is how you can launch and optimize new pages, set up the best internal links and prioritize your source code changes.
While it sounds strange, I would go so far as to say that tracking spiders is just as important as tracking your visitors.