> DuckDuckGo emphasizes returning the best results, rather than the most results, and generates those results from over 400 individual sources, including key crowdsourced sites such as Wikipedia, and other search engines like Bing, Yahoo!, Yandex, and Yummly.

So basically they don't have their own crawler but aggregate results, mostly from Bing which is (or was) clear from comparing search results. However, a sibling comment claims they run their own spider now so my info may be outdated (quote from Wikipedia).