Observations in the field and in a flight cage reveal that the courtship of the monarch butterfly consists of an aerial phase and a ground phase, each composed of several behavioral components. These include “nudging” by the male, aerial pursuit, aerial “hairpencilling,” aerial takedown of the female, antennal palpation by the male, copulation, and post-nuptial flight. Nearly all male Danainae have extrusible sex pheromone glands, the hairpencils, located at the tip of the abdomen. With the exception of the monarch, the hairpencils of all species studied contain dihydropyrrolizine compounds obtained from plant sources and serving as aphrodisiacs when applied to the female in flight. A striking feature of the monarch courtship is a sequence in which, without hairpencilling, males grab females in midair, the pair falls to earth, and copulation occurs. Hairpencilling occurs in some courtships, but aerial takedowns predominate. Male monarchs whose hairpencils have been surgically removed show no reduction in sexual vigor or success, whereas in the related queen butterfly hairpencilling is a prerequisite for male success, and de-hairpencilled males are impotent. The evolution of courtship in Danaus is discussed with respect to male monarchs' small hairpencil size, alternate sequences leading to female receptivity, and their apparent growing independence from plant compounds in subduing females.