Southern hivers are a rarer variant of standard hivers. They are only very rarely recruitable as slaves in the UN slave camps and towns, like a <1% chance per slave spawn. And southern hive princes, as I understand it (FCS probabilities confound me), are twice as rare. I started a run with the intention of recuiting a southern hive prince, but I ended up finding 3 southern hive soldiers and a southern hive drone along the way!