"Stingrays" is the nickname given to a species of non-sapient alien creatures which look like large flying stingrays with a metallic exoskeleton and sharp teeth.
These voracious creatures travel through the universe in huge swarms, thanks to their natural ability to create wormholes linking distant planets across the cosmos. When they arrive in a new world, the swarm quickly devours as much matter as they can - organic, mineral and metallic alike - leaving a desolated wasteland behind. The non-organic materials consumed are used to synthesize an exoskeleton which allows them to go through the otherwise deadly wormholes unharmed.
When they are finished with a planet, they fly in circles around it continually, increasing velocity until a stable wormhole is created and expanded, after which they all enter the wormhole to their next unfortunate destination. It isn't known how they are able to prevent the formation of wormholes leading to interstellar space, stars or asteroids rather than planets. They are known to go into hibernation in cold temperatures, but even a small increase may be enough to awake them.
At one point the Stingrays devoured all life on the surface of planet San-Helios in the Scorpion Nebula, and formed a wormhole which would lead them to Earth. The invasion was prevented as that wormhole was closed thanks to the efforts of the Tenth Doctor and UNIT physicist Malcolm Taylor. The Doctor acknowledged that the creatures aren't malicious as the destruction they cause is part of their life cycle; and stated that he would try to make sure the next wormholes only lead to uninhabited worlds.
- Doctor Who, new series special "Planet of the Dead" (Tenth Doctor, 2009)