An eye for the ladies. Male swallowtails have been found to have a primtive 'eye' or light-sensing organ on the tip of their abdomens. They use these light-sensors for help finding the female's abdomens when initiating pairing. On pairing, the male clasps the female's abdomen and hangs on - often for 12 hours or more. The pairing couple can even fly with the male trailing behind.