That is one of the interesting things with this traffic, everything in the headers looks legit. The referrer is a valid search engine results page, and the user agent is an exact match for a common web browser. Unless the IP address or block of addresses are identified by some other suspicious activity there is no way for an automated process (such as your analytics software) to filter this out. Even GA records this traffic. On the plus side for whoever runs this bot, on a large site they are virtually guaranteed to be able to access the target site without restriction or detection on most sites since many webmasters don't look this closely at their statistics. On the negative for the webmaster, not only can you not automatically block the traffic, your analytics data will be tainted by false requests that can compose a decent percentage of your traffic.

__________________
The best way to learn anything, is to question everything.
Interestingly Average Security Blog