Queen Leech was engineered as Dr. James Marcus' greatest achievement, and its biology differed radically from that of natural leeches. Like natural leeches, Queen Leech was a hermaphrodite, though unlike natural leeches it was capable of self-fertilisation. Queen Leech possessed a sophisticated olfactory organ which allowed it to communicate with offspring via smells. A damp or humid environment was required for Queen Leech to thrive, as with natural leeches, though direct sunlight had the added effect of inducing pain. Queen Leech In keeping with other leeches experimented on, the Queen Leech was known to cannibalise its offspring. In a form of mimicry far beyond that of the leeches, Queen Leech was able to shape its whole body to mimic that of Dr. Marcus, becoming shorter and gaining arms and legs. As a personal choice, it took the form of Dr. Marcus' younger self, rather than the elderly figure that created it. This ability only surfaced after ten years of maturation, it should be noted, and may not have been foreseen.
On a scale of intelligence, Queen Leech far surpassed that of annelids and may have been intended to rival that of human beings. After parasitising the corpse of Dr. Marcus in 1988, Queen Leech consumed his brain and proved itself sentient in gaining his memories and personality. As a result of this parasitism, Queen Leech rationalised that it was indeed Dr. Marcus and had somehow survived an assassination attempt.[excerpt 1]