The most "failsafe" manner for a beginner to differentiate between Hadrurus sexes is to feed them...a lot. The females will almost continuously eat, whereas the males will stop after their fill. They will get to a hugely noticeable diffenence in thickness quite fast. The male's pedipalps are also slightly smoother grooved than the female's and ever-so-slightly smaller peds on the male. The ped size is not accurate when dealing with scorpions of this genus with completely different sizes, bodywise.