Board Thread:General Discussion/@comment-25266931-20161228230634/@comment-26397825-20161229021542

No. They don't need to kill to eat, which is the reason why animals fight over a kill. They only ever eat if it is a way to kill someone, such as when the Griffon swallowed Roman.

And killing each other is detrimental to their cause of wiping out humanity, as it leaves them with less soldiers to fight with. The only thing they'd learn from killing each other is how to kill other Grimm, which again goes against their goal of wiping out humanity.