To generate cash from say Google Adsense or any other PPL program.Its very important to have a through knowledge of your product what you are selling.And above all knowledge of search engine optimization is needed.This is the way by which you can push your site on the first page of any search engine. Web spider or Web crawler are the software which search the best suited data for search and present you in a fraction of second.By this we come to know the importance of web spider. But when you write a same keyword in different search engine eg. google,yahoo,altvista etc. different result will come.Because web spider of different search work in different way. Now, How the web crawler work.and how to write web crawler friendly article.When you write any keyword in a search box.Spiders search that particular word in all the web pages,website whatever the data present on internet.Web spiders follow the following criteria to rank your web page. 1). Search key word density (If some one wri