Nostrovite

The Nostrovites were a race of metamorphic humanoids. (TW: Something Borrowed)

Biology
The Nostrovites, in their natural form, appeared to vaguely resemble a near-Human, but with red eyes, sharp claws and teeth, and visible blood vessels. However, with the use of their proteus glands, they could adopt other humanoid forms.

Nostrovites were carnivores, but only ate living flesh. They naturally ignored dead bodies unless they were in the process of eating them. The females at least could create a sticky, web-like structure to keep prey alive until they were hungry again. (TW: Something Borrowed)

Life Cycle
The Nostrovites, like many other species, had two sexes - male and female. However, they also required a third member: a host. After fertilising the female's eggs, the male would take the eggs and store them in his body. After finding a potential host, the male would bite them and inject the eggs into the host's bloodstream. The eggs would quickly develop inside the host as if the host was merely pregnant with another of its species.

After a while, the female would track down the host and tear them open to release the young. They became very resiliant, and it was shown that several rounds of bullets had little effect on a female Nostrovite. (TW: Something Borrowed)

History

 * ''The Nostrovites were familar to Jack Harkness, although he never said whether this was to do with prior experiance in his native time or with Torchwood 3. (TW: Something Borrowed)

At some point in their history, some Nostrovites discovered Earth and developed a taste for Human flesh. At least one pair reproduced and found Torchwood operative Gwen Cooper as a host. However, the pair of Nostrovites were killed by Torchwood and the developing young removed by Rhys Williams using the Singularity Scalpel. (TW: Something Borrowed)