Penis fencing is a reproductive behavior observed in certain species of hermaphroditic flatworms, particularly those belonging to the genus Pseudobiceros and Pseudoceros. During this unusual mating ritual, two flatworms engage in combat using their elongated and sharp penises, known as “stylets,” in a competition to inseminate the other. The process begins when two flatworms encounter each other and become sexually aroused. They then extend their stylets, which are typically stored inside their bodies, and engage in a fierce duel. The goal of each flatworm is to pierce the skin of its opponent and inject sperm into its body cavity. The flatworm that successfully inseminates its partner gains reproductive success, while the loser may suffer physical harm or fail to reproduce.
Penis fencing
