For many male spiders, having sex means surrendering one or both of their genitals. In some species, up to 75% of males will experience what's known as sexual cannibalism. But this castration carries an advantage: the males become fearsome warriors.
We've talked about the phenomenon of castrated spider warriors before, but this is an important topic, dammit, and we'll just keep going back to this well over and over again until we find out everything there is to know. Since it's long since been established that spiders fight better without their genitals, the question that remains to be answered is why this should be.