Your experience with vermin resists the attacks of swarms.
Prerequisites
Favored enemy (vermin) ability.
Benefit
You gain DR/— equal to half your favored enemy (vermin) bonus against vermin and creatures with the swarm subtype. When attempting Fortitude saves against a swarm’s distraction ability, you gain a bonus on the save equal to the damage prevented by this feat.
Against vermin with the swarm subtype, the amount of damage reduction is equal to your full favored enemy (vermin) bonus.
This is a miscellaneous bonus to damage reduction.