The buzz-run: how honeybees signal ‘Time to go!’

The explosive take-off of a honeybee swarm when it moves to its new home is a striking example of an animal group performing a synchronized departure for a new location. Prior work has shown that the nest-site scouts in a swarm prime the other bees for flight by producing piping signals that stimulate all the bees to warm up their wing muscles in preparation for flight, but how the bees are ultimately triggered to take flight remains a mystery. We explored the possibility that the buzz-run signal is the critical releaser of flight. Using slow-motion analyses of videorecordings, we made a detailed description of this signalling behaviour: a buzz-runner runs about the swarm cluster in great excitement, tracing out a crooked path, buzzing her wings in bursts, bulldozing between idle bees and periodically performing a conspicuous wiggling movement. It seems likely that the buzz-run signal is a ritualized form of a bee's take-off behaviour, with the wing buzzing greatly exaggerated and other behavioural elements (running, butting and wiggling) added to increase the signal's detectability. The immediate effect of the signal is to disperse and activate otherwise lethargic bees; the long-term effect is probably to stimulate the recipients to launch into flight. It turns out that the scout bees from the chosen nest site are responsible for producing both the piping signal to prime a swarm for take-off and the buzz-run signal to trigger the take-off. We suggest that these bees produce the signal that triggers take-off because they travel throughout the swarm cluster while piping and so are able to sense when the entire swarm is hot enough to take flight. The mechanisms mediating take-offs by honeybee swarms appear to present us with a rare instance where an action of a large social insect colony is controlled by a small set of individuals that actively monitor the global state of their colony and produce a signal triggering the colony's action in a timely way.