Search engine spiders.
Definition. Search engine spiders are programs that search engines use to automatically read your website content. If they can't access your website because it's been built badly or has poor content then you'll not get a fair chance of being listed in the search engines index or library. "The Google Tree" - search engine spiders. One by one search engine spiders (the worker bees) will crawl your site. The search engine spiders will crawl all over your site and take what they need to index you.  (next)