The mass departure of a honey bee (Apis mellifera) swarm from its parental nest: Triggering signals, identity of signalers, and functional organization

The timing of departures in group-living animals must be synchronized to assure group cohesion. The mechanisms used by a honey bee colony to organize the departure of a swarm from its nest remain a mystery. We examined the signals and signalers that trigger a swarm’s exodus, and we documented the concurrent changes in bee density, mobility, and nest-site recruitment during the swarming process. Using videorecordings, as well as observations at potential nest sites, we analyzed how bees in three swarming colonies prepared for and then performed their sudden departures. We found that over the 60 min before swarm exodus, the production of piping signals gradually increased, and ultimately peaked at the start of the departure. Also, during swarm exodus, bee density dropped markedly, while the average bee velocity, and the production of buzz-run signals spiked dramatically. Neither waggle runs nor shaking signals showed increases before or during swarm exodus. Additionally, we found that bees start searching for potential nest sites prior to departure, and that nest-site scouts are the first producers of piping and buzz-run signals inside the nest. This explosive swarm departure shows how animals can use the same communication signals in different contexts; we now know that nest-site scouts use piping and buzz-run signals to initiate both a swarm’s departure from its nest and a swarm’s take-off from its bivouac site. This study also demonstrates how a small minority of individuals in a honey bee colony operates as an oligarchy to decide when to swarm.