Postman or Piano Key Butterfly, Heliconius melpomene. Rare bilateral gynandromorph form; male form wing on left side, and female form wing on right side. Gynandromorphism, wherein an organism posesses both male and female parts, generally results from a cell division error early in development. It can be bilateral, as in theis butterfly, where half the organism is one sex, or mosaic, where the sexes are distributed piecemeal through the organism.