Hair-pencil

Hair-pencils and Coremata are pheromone signaling structures present in lepidopteran males. Males use hair-pencils in courtship behaviors with females, the pheromones excreted by the hair-pencils serve as both aphrodisiacs and tranquilizers to females as well as repellents to conspecific males. Hair-pencil glands are stored inside the male until courtship begins, at which point they are forced out of the body by sclerotized levers present on the abdomen. Coremata (the singular form being corema) are very similar structures. Their exact definition is confused by early descriptions but they are more specifically defined as the internal, glandular, eversible structures that bear the hair-pencils and can be voluntarily inflated with hemolymph or air.

Behavioral use of hair-pencils

Male moths are attracted from relatively long distances by females releasing pheromones; when they are close enough to the females to begin courtship, the hair-pencils are extruded from the abdominal cavity and pheromones are fanned towards the female. Fanning can occur in various ways including extruding and retracting the hair-pencils, wing or abdominal movement, or flight in front of the female. When the female moth becomes receptive to the male hair-penciling she will flick her antennas rapidly in response to his pheromone cues. If the female likes the male blend of pheromones then she will extend her abdomen and copulation begins.