The acoustic near field of a dancing honeybee

Summary

The acoustic near field close to honeybees performing the wagging dance was investigated with pairs of small, matched microphones placed in various positions around the dancing bees. The dance ‘sounds’ are produced by the wings, which act as an asymmetrical dipole emitter. Close to the abdomen, the ‘sound’ pressures in the air spaces above and below the plane of the wings are totally out of phase. A zone of very intense acoustical short-circuiting exists close to the edges of the wings, where pressure gradients of about 1 Pa/mm are observed in the dorso-ventral direction (perpendicular to the plane of the wings). The pressure gradients drive air movements with velocity amplitudes up to about 1 m/s. The pressure gradients are much smaller in directions radially away from the bee and decrease rapidly with increasing distance from the wings. The ‘sound’ pressure detected by a stationary probe at one side of the bee is strongly modulated at 12–13 Hz as a result of the bee's side-to-side wagging. Surprisingly little ‘sound’ is found near the dancer's head. The positions of the follower bees reflect the properties of the acoustic field: The follower bees place their antennae in the zone of maximum acoustical short-circuiting where the air particle movements are most intense. These observations suggest 1) how follower bees can avoid mixing up the messages carried by the dance ‘sounds’ when two or more bees are dancing only a few cm apart and 2) how the followers might extract information about a dancer's spatial orientation from the acoustic near field she produces. The observations also provide clues regarding the nature of the putative ‘sound’ receivers.