Your experience with vermin resists the attacks of swarms.
Benefit(s): 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 damage reduction does not stack with that from other sources.
Pathfinder Player Companion: Monster Hunter’s Handbook © 2017, Paizo Inc.; Authors: Eric Hindley, Mikko Kallio, Luis Loza, and Christopher Wasko.