Prador Moon is a novel set in the Polity universe by Neal Asher. It's a first contact gone wrong type of novel. Humanity puts out a welcoming hand, and the Prador bite it off. Even worse, the first few victories by the crab-like Prador lead the aliens to believe that humans are going to be easy prey. And there's nothing like easy prey to stock your larder.

(Source: Night Shade Books)