search engines that search other search engines are called
A metasearch engine (or aggregator) is a search tool that uses another search engine’s data to produce their own results from the Internet. Metasearch engines take input from a user and simultaneously send out queries to third party search engines for results.
A search engine that queries other search engines and then combines the results that are received from all. In effect, the user is not using just one search engine but a combination of many search engines at once to optimize Web searching. Forexample, Dogpile is a metasearch engine.
The third category includes meta search engines, which search other engines for you. Google, MetaCrawler and Dogpile are all meta engines. Ask Jeeves is a meta engine that allows users to enter queries in the form of a question.
A typical meta search engine pulls off the results from a number of search engines, say Google and Bing, and then apply their own algorithms in some cases to re-order the results.