To become both a lover and a fighter, the male spider Nephilengys malabarensis snaps off his penis inside his partner while they have sex. He becomes better at fending off other males who try to mate with her, because his now-lightened body can fight for longer without tiring. And while he’s playing the guardian, his detached genitals can continue pumping sperm into the female. Through self-castration, he gets more stamina, and he gets more stamina.