shapeoflife.org

J1pd8 TIL: Species of hermaphroditic flatworms engage in a behavior called "penis fencing," where they use their sharp, dagger-like reproductive organs to duel with each other. The winner is determined by the first stab that inseminates the loser.
GYAA5 TIL that Flatworms participate in “penis fencing” where two hermaphroditic worms try to impregnate the other in order to become the alpha male, rather than having to bear children.