Rutan

The Rutan Host are a race of amorphous green blobs. They have only appeared so far in Horror of Fang Rock, but are mentioned by the Sontarans in other serials.

The Rutan host (singular Rutan) are shaped somewhat like a jellyfish, with a green, glowing body and many light-green tendrils. These tendrils have surprising strength and they can climb walls with them. Rutan host can control and absorb electricity, which they can then use for defense and attack. A Rutan can kill a human with their bio-electricity. Rutan speak in second person, which would imply a sort of hive mind. Rutan host can also shapeshift into other forms, but they need to know this form very well, usually after careful study and dissection.

Rutan host are amphibious and native to a cold planet (Ruta III). They have trouble dealing with climates unlike the ones on Ruta III, such as in hot environments.

The Rutan host have been at war with the Sontarans for many years, though they seem to be losing. They are constantly searching out new ways to win the war. Rutan spaceships are crystalline in structure and seem to be large, glowing orbs.