Hairpencils, wing pouches and courtship of the butterfly Danaus chrysippus was studied in green houses. Before and after courtship, the males were observed to insert their abdominal hairpencils frequently into the wing pouches. Pheromones (Pyrrilizidinone) of the hairpencils are effective odour stimuli to the antennae (chemical communication: see also Hymenocera).

Male Danaus chrysippus: pair of hairpencils, one fully extended (ø 10 mm)     © Seibt Literature Seibt, Uta, Schneider, Dieter & Eisner, T. 1972: Duftpinsel, Flügeltaschen und Balz des Tagfalters Danaus chrysippus (Lepidoptera: Danaidae). Zeitschrift für Tierpsychologie 31, 513-530 Schneider, Dieter & Seibt, Uta 1969: Sex pheromone of the Queen Butterfly: electroantennogram responses. Science 164, 1173- 1174