Worker honeybees (Apis melli/era) recovering from CO2 narcotization emitted a distinctive 'quacking' sound consisting of a series of short notes, each possessing multiple harmonics and a fundamental frequency around 400 Hz. Quacking was usually accompanied by a distinctive 'shoving' behaviour. Paired bees 'quacked' more frequently than single bees. The similarity of worker quacking to certain variants of queen piping and worker piping is discussed..