Several website URLs that need to be visited, and these are seeds. The crawler of the search engine visits every web page, identifies all the pages’ hyperlinks, and then adds them to the list of places to be crawled. This is a piece of software that crawls the Web in search of and indexes websites for use by search engines (Google, Yahoo, Bing). Never do the spiders rest; they keep clicking from one link to the next. Spiders are also known as robots and crawlers and can be used as a verb in the following context: "That search engine spidered my website last month."The Internet is a dynamic environment that is always evolving and growing.
The total number of web pages on the Internet is unknown; therefore, web crawler bots begin with a seed or a list of previously visited URLs. They start by crawling the pages located at those URIs. Crawlers look for links to other URLs and add those to their list of pages to crawl next. Since so many web pages can be indexed for search, this process may continue endlessly. The policies followed by a web crawler allow it to be more selective in its crawling of certain pages and the order in which those pages should be crawled. For the most part, search engine spiders don’t go through every page of the publicly available Internet looking for useful information. Instead, they prioritize which pages are worth crawling based on factors like how many other pages link to them, how many unique visitors they get each month, and whether or not they contain any additional valuable information.
Many other websites cite and visit a high-quality, authoritative webpage. Hence, a search engine needs to index it – just like a library would maintain many copies of a book that gets checked out by many people. Web content is constantly being updated, deleted, or re-located. So that the most up-to-date version of the material is being indexed, web crawlers will need to return to pages regularly. It is also determined by the robots.txt protocol, which pages should be crawled by web crawlers (also known as the robots exclusion protocol).
The robots.txt file on the web server will be checked before crawling begins. The World Wide Web is another name for the Internet or at least the part most people have access to. We called search engine bots "spiders" because they crawl all over the Web, much like actual spiders do on webs of spiderwebs.