Intraspecific competition: Competition within the same species
Marine flatworms tend to compete with each other when they are trying to mate. Flatworms are asexual and sexual reproducers, they have both male and female parts. When both male flatworms are trying to mate with each other, they start Penis Fencing. Penis Fencing is when the flatworms wrestle each other to see who can stab the other flatworm with its penis. This process is also known as Intradermal Hypodermic Insemination, and is a characteristic of large marine flatworms.