The Homerus Swallowtail, Papilio (Pterourus) homerus, is an endangered butterfly endemic to Jamaica. We report conspecific male interactions observed in the Cockpit Country. Field observations of the patrolling behavior and the conspecific male circular flights suggest that males are territorial. Unlike most previous reports of male butterfly territoriality, physical contact occurs in the male circular flights, evidenced by the sound of the wings hitting each other, which may contribute to wing damage. We were able to quantify the extensive wing damage accumulated on a single territorial male with photographs; this male lost more than 90 percent of an individual wing, and still patrolled an area. In addition, we discuss the possible variables that might determine the outcome of territorial disputes, the habitat associated with territory establishment, and lekking in this species.