Discipline yourselves, keep alert. Like a roaring lion your adversary the devil prowls around, looking for someone to devour.  (1 Peter 5.8)

If, however, you bite and devour one another, take care that you are not consumed by one another. (Galatians 5.15)

In hell God is not present to feed those who are there.  All created spirits - angels and men's souls - need to eat for sustenance.  Since the demons are denied the heavenly food of Christ they turn to consume each other as well as prowl on men.  Demons and the souls of the damned hate each other as much as they hate God and the saints.  They are filled with hate, envy and despair and thus the place they occupy is properly called Hell.

The warning to us is twofold.  We have a very real enemy who is personally interested in consuming us.  We also, even now, began practicing to live the life of the damned if we disobey Christ's commandment to love our neighbor as ourselves.  "If, however, you bite and devour one another, take care that you are not consumed by one another."  (Galatians 5.15)  Just like the devil consumes his minions and seeks to consume us.