Eknodine

The Eknodine were a species of aliens that took over the bodies of old people in a dream created by the Dream Lord. The Doctor spoke to them as if he knew of them, indicating that they do exist in the main universe. (DW: Amy's Choice)

Physiology
The Eknodine were aliens inside of human hosts. Only the green eyestalk could be seen when they attacked other species. (DW: Amy's Choice)

Abilities


They could turn people into dust by spraying a green cloud over them. They could also incubate inside humans and use them as hosts, allowing the humans to live longer. (DW: Amy's Choice)

History
The Eknodine that the Doctor, Amy Pond and Rory Williams encountered said that they were driven away from their home planet and came to Earth, where they took hosts to stay inconspicuous. Angered at their loss, they decided to destroy other worlds.

They chased and attacked The Doctor, Amy and Rory after they found out what they were and cornered them in Amy and Rory's house and attempted to gain entry. One, under the guise of Mrs Poggit, killed Rory after climbing up to the top floor window and turned him into dust. Amy and The Doctor decided to kill themselves, hoping that this was the dream, and ran a couple of Eknodine over before crashing into the house and dying. (DW: Amy's Choice)

Behind the Scenes

 * It is possible that the thing that has driven them away from their planet is the Silent Menace, as this has also driven the Saturnynians from their home planet to Earth. Of course, as their presence on Earth was part of a dream, the Silence could not actually have been involved. But the Doctor's knowledge of it could have influenced the dream.