One way to quickly find out what underlying provider a metasearch engine uses is to search for "my user agent". You will then normally see the user agent of the crawler in the result snippet.

Doing this on DuckDuckGo: https://duckduckgo.com/?q=my+user+agent&t=hk&ia=answer , reviles http://www.bing.com/bingbot.htm in the snippet for whatsmyuseragent.org .