The vast majority of Mutoids seen were all female; quite why this should be is unknown. Similarly obscure is the process by which individuals were selected for mutoid modification, although it may have been a punishment for disobedient slave workers (Rashel referred to 'modification' as a punishment).
It is unlikely anyone would volunteer to become a Mutoid as the process involved the wiping of all previous memories, effectively killing the old personality. Their brains could be repeatedly blanked, programmed only to respond to particular trigger words or phrases. The candidate also underwent a high level of bionic reconstruction giving them enhanced strength and endurance. They became impassive and unemotional as a result of the process.
Rather than eating and drinking, Mutoids drew nutrition directly from blood serum. This was either taken from a flask inserted into a receptacle in the sternum or drawn directly from source via a hypodermic needle mounted in the wrist. Because of this, normal humans referred to them as 'vampires' - for their part, Mutoids referred to humans as 'unmodified'.
Being a cyborg himself, Travis was not prejudiced against Mutoids and preferred them for their lack of emotion. He generally used them as crew (although on Exbar his men were Crimos). He was curious enough to obtain personal information about one of the Mutoids crewing his ship above Amersat, telling the Mutoid her original name, Keera.
After going on the run from the Federation, Travis was given his own crew of Mutoids who would respond only to him.