Animals that travel in groups must synchronize the timing of impending departures to ensure group cohesion. Until recently, the ultimate and proximate mechanisms used by honey bee (Apis mellifera) colonies to organize the departure of a swarm from its nest remained a mystery. In a series of experiments, we examined the signals that trigger a swarm’s explosive exodus from the parental nest, and identified the type of bees that perform these signals and orchestrate the departure. Furthermore, because honey bee queens polyandrous, the derived genetic structure of multiple patrilines in a colony creates a potential for intracolonial nepotism during swarming, as workers might nepotistically choose between serving a young (sister) queen or the old (mother) queen, preferring the former if she is a full-sister but the latter if the young queen is only a half-sister. We examined honey bee colonies that swarmed, and performed paternity analyses on the young (immature) queens and samples of workers who either stayed with the young queens in the nest or left with the mother queen in the swarm to test the hypothesis of intracolonial nepotism during swarming driven by kin selection. The explosive departure of a honey bee swarm from its parental nest provides a great system to test prediction of kin selection theory, and allows us to examine whether and how animals may use the same communication signals in different contexts. It also shows how a small minority of individuals in a social insect colony can operate as an oligarchy to make an important decision, i.e. when a swarm should leave its nest to found a new colony.