Abstract The chemo-stimulatory role of the male hair-pencils in the courtship behaviour of the Queen butterfly has been quantified experimentally in the natural habitat. Approximately 600 individuals were studied. Courtship success is substantially reduced either by removal of the male hair-pencils or by blocking the chemoreceptors on the female antennae. However, mating occasionally occurs with either of these experimental modifications. Two of the three major types of perforated sensilla (the long, curved pegs and the coeloconic sense organs) can be completely blocked without reducing courtship success. Therefore the widely distributed short, thin-walled sensilla alone are capable of receiving the male sex pheromone. Approximately 1000 to 1500 of these sensilla (i.e. about 5 per cent of the total) must be exposed for normal courtship success. It is possible that the female also produces an odour which is important to the male in courtship.