Stingray


 * For the virus see The Swarm (The Invisible Enemy).

The Swarm were creatures that fed on everything on a planet and could travel with wormholes to new planets. They were also named "alien stingrays" by UNIT due to superficial resemblance to the stingrays that live in Earth's seas.

Biology
The Swarm were ray-like creatures, with a wide head, 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). The Swarm would go into hibernation when cold.

The Swarm could travel from planet to planet by use of 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 the wormhole. Their metal exoskeleton would allow them to survive the passage. (DW: Planet of the Dead)



History
Circa 2010, the Swarm 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, several individuals were trapped within the ship, causing the ship to crash. These individuals were put into hibernation by the cold.

The wormhole eventually opened up into Earth, accidentally pulling the 200 to San Helios. Though they saw the Swarm 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 individuals, after which they tore through the ship and devoured the two Tritovore occupants. The Doctor was able to return the 200 just before the Swarm made it to the wormhole and Malcolm Taylor managed to close the wormhole after them. However, three individuals 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 worm hole, but the Doctor stated he will attempt to guide all their wormholes onto uninhabited planets, where they could feed on natural structures. (DW: Planet of the Dead)