Stingray

Stingrays were creatures that devoured everything on a planet and could travel through wormholes to new ones. They were named "alien stingrays" by UNIT due to their superficial resemblance to the stingrays that lived in Earth's seas.

Biology
Stingrays had a wide head with little eyes and gills, a long tail and fins down their side. They were the size of a small car, but were still capable of flight at speeds of at least 300 miles per hour. They were extreme omnivores, capable of eating meat, plants, rock or metal. Any metal they ate would be extruded into their exoskeleton, making them bullet proof, though not immune to explosives. Stingrays would also go into hibernation when cold.

Their metal exoskeleton allowed them to produce large amounts of static energy when they travelled in groups, which was capable of creating wormholes. After eating everything on the planet, the whole swarm would start to circle the planet. The sheer mass and speed of billions of individuals would rip open the fabric of space, creating a wormhole, allowing them to travel from planet to planet and continue this life cycle. Their metal exoskeleton would allow them to survive the passage. (TV: Planet of the Dead)

History
Circa 2009, the Stingrays opened a wormhole to the planet San Helios, where they ate everything within a year, leaving only barren deserts. They then began making a second wormhole with which to leave the planet. When a Tritovore ship came to the planet to trade, an individual Stingray was trapped within the ship, causing the ship to crash. This individual was put into hibernation by the cold.

The wormhole eventually opened up into Earth, accidentally pulling the 200 to San Helios. Though they saw the Stingrays from a distance, they were unable to identify what they were without the help of the Tritovore's probe. Later, when Christina de Souza went to retrieve the crystal nucleus from the Tritovore ship, her body heat raised the temperature just enough to revive the hibernating individual, after which it tore through the ship and devoured the two Tritovore occupants.

The Tenth Doctor was able to return the 200 just before the Stingrays made it to the wormhole and Malcolm Taylor managed to close the wormhole after them. However, three stingrays made it through. Conventional firearms were useless against them, but UNIT's mounted missile launchers proved more effective. The ones trapped on San Helios could easily make another wormhole, but the Doctor stated he would attempt to guide all their wormholes onto uninhabited planets, where they could feed on natural structures. (TV: Planet of the Dead)