Plasmavore

The Plasmavores were a race of blood-sucking near-Humans. They were commonly criminals, murdering people across the galaxy and drinking their blood. The name plasmavore comes from the latin word "plasma" meaning 'form or shape' and the latin word "voare" meaning 'to devour'. The word plasma could also be reference to Blood plasma, the yellow-colored liquid component of blood, in which blood cells are suspended.

Biology
Though the Plasmavores were Human-like in appearance, they were actually shapeshifters. By draining the blood of an individual, the Plasmavores could mimic the genetic material of the victim. (DW: Smith and Jones)


 * The fact that "Florence" was not identified as an alien during what was apparently a lengthy hospital stay involving several medical examinations suggests that either the species was either extremely Near-Human or able to modify their biology to fool less sophisticated scanners without the need for assimilated biomatter.

Plasmavores required blood to survive, as their bodies absorbed a lot of salt. (DW: Smith and Jones) While feeding, they produced exotic plasma energy. Though they needed to feed on blood, this blood-sucking could be become addictive, leading them to take risks and develop psychoses. (REF: Doctor Who: The Visual Dictionary)

History
The Plasmavores were known as a dangerous species, travelling the universe and looking for new species to feed on.


 * "Florence Finnegan", the Plasmavore on Earth, described herself as a "survivor", perhaps suggesting that, due to criminal associations, Plasmavores are now a rare species in the galaxy.

One Plasmavore, known as Florence Finnegan, fed on the Child Princess of Padrivole Regency 9 on a whim and was then hunted down by the Judoon. She escaped to Earth and hid in the Royal Hope Hospital, feeding on the Hospital's blood storage. She was protected by two Slabs. When the Judoon took the Hospital to the Moon, she fed on Dr. B. Stoker so that she could fool the Judoon scanners. She planned to kill everyone with an overpowered MRI scanner and then escape on the Judoon's Ship, but she also fed on the Doctor, giving her alien genetic material. This allowed the Judoon to recognize her as an alien and they executed her. (DW: Smith and Jones)