I don't know. It doesn't seem too common. There are almost no wanderers with say, 6 fertility. It doesn't make sense where one group of nichelings ends, though, since they're all compatible. But lore-wise, they have to come from somewhere, where, at least at one point, their strategy thrived. Yet, they haven't attained world domination in other places. How is their constant invasion sustainable? Are there rogue females hidden away, never seen?
(Goodnight for now, still. It's almost midnight here)