Well I googleed your request and I got this site:
How Does the Adsense spider work?
Then I went to Wikipedia and found this:
Adsense
Then on Wiki I also typed this:
Search Engine
Basicly from what I gather. Adsense helps the web crawling bot gather info. So when you type in a google search. It has that info from adsense. Thats what I gather. Do a google. And as for Yahoo! Slurp could not find any info on that. Then again Yahoo! was using Google back in the day until 2004.