Swarm Mind
Members of the Swarm are bound together into a singular hive mind by a blend of exuded pheromones, imperceptible movements of antennae and limbs, electrostatic fields, and telepathic communication. All Swarm creatures with 30 feet of each other are in constant communication; if one is aware of a threat, all are. (Such awareness can spread along a “chain” of Swarm creatures under appropriate circumstances, potentially alerting distant Swarm creatures). In addition, once per round when within 30 feet of another Swarm creature, a Swarm creature can roll twice and take the better result on a saving throw against a mind-affecting effect.
Format: Defensive Abilities Swarm mind.
Source
Alien Archive 3 pg. 154