Available online at www.sciencedirect.com The buzz-run: how honeybees signal ‘Time to go!’ CLARE C. RITTSCHOF * & THOMAS D. SEELEY † *Department of Zoology, University of Florida yDepartment of Neurobiology and Behavior, Cornell University (Received 7 February 2007; acceptance 27 April 2007; MS. number: A10688) 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 wig- gling 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 wig- gling) added to increase the signal’s detectability. The immediate effect of the signal is to disperse and ac- tivate 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 pip- ing 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 me- diating 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. Ó 2007 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. Keywords: Apis mellifera; buzz-run; centralized control; group movement; honeybee; ritualization; swarm Animals that move about in cohesive groups must possess mechanisms of social coordination that enable them to start and stop their movements in unison. In some cases, the mechanism is despotic, that is, one dominant in- dividual decides and directs the others; while in others it is democratic, that is, a majority of group members decide (Conradt & Roper 2003). Examples of species with des- potic mechanisms include hamadryas baboons, Papio hamadryas, where the exaggerated swagger of an old male is able to precipitate a band’s morning departure (Kummer 1968), and African elephants, Loxodonta afri- cana, where an adult female will lift one leg and repeatedly give long ‘let’s go’ rumbles accompanied by steady ear flapping to incite a stationary group to move off together (Poole et al. 1988). Examples of species with democratic mechanisms include gorillas (Gorilla gorilla), where calling by a majority of a group’s adults signal an impending departure (Stewart & Harcourt 1994), and whooper swans, Cygnus cygnus, where a group takes off when the intensity of head-movement signals reaches a threshold level (Black 1988). Social insect colonies show a high degree of group integration and provide many examples of groups moving as cohesive units (reviewed in Dyer 2000). A vast literature has developed concerning the mechanisms underlying group integration and collective action in social insects (Camazine et al. 2001), but the mechanisms mediating the initiation of their group movements remain poorly studied. Only in the honeybee, Apis mellifera, do we Correspondence: T. D. Seeley, Department of Neurobiology and Behav- ior, Cornell University, Ithaca, NY 14853, U.S.A. (email: tds5@cornell. edu). 189 0003e 3472/08/$30.00/0 Ó 2007 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. ANIMAL BEHAVIOUR, 2008, 75, 189e197 doi:10.1016/j.anbehav.2007.04.026