Reproduction in butterflies begins with courtship, during which the male vigorously flaps its wings, releasing a dust of microscopic scales carrying pheromones above the female's antennae. These male pheromones act as a sexual stimulant to the female. Some males release additional pheromones from "hair pencils" under the abdomen. Female butterflies that are ready to mate dispense with courtship. Some species, however, perform complicated courtship maneuvers, probably to find a mate strong enough to endure the rigorous rituals, thereby by increasing the chance of producing healthy offspring. Males usually must wait one or two days after emerging from the chrysalis before they can mate, but then they may mate many times. Females can mate immediately after emerging, some species mating several times. However, it is the last male to mate that fertilizes the eggs. Females of some species mate once only.