The Mikrax were an alien race genetically engineered to be the perfect non-technological warrior. They were humanoid, except solid black, and instead of having hands they had long clawlike appendges prodtriding down from the end of their arms, and wider feet which gave them increased jumping ability. Mikrax were known for never using technology, but relying entirely on instinct. Individual Mikrax had no personal intelligence, but were controlled by a large central organism, known as the "mikrax mother", which also produced the Mikrax. There was generally only one of these "mothers" for each region of the planets which the Mikrax invaded. They had very tough skin, and thought nothing of pain, but a blow to the heart from most weapons would kill them. The Mikrax could micro-evolve as needed for different situations, the mother producing a new generation better equipped to handle the situation. For example, if a group of warriors fighting the Mikrax discovered the location of thier hearts and was slaying them, a new generation would come to replace the old, with an entirely different heart placement. They had come to Earth, via the Rift, and had since spread to various places across the world. They seemed to place thier nests in or near populated areas, and UNIT believed there to be several such nests dotted across North America.