The Darkness (The Well-Mannered War)

The Darkness is a race of fly-like insects introduced in The Well-Mannered War.

Though physically the darkness looks no different from a swarm of regular flies, they evolved a type of hive-mind called the Onememory. They had some psychic powers, but they needed a large enough swarm in one place for it to be effective.

At some point in Earth's future, flies somehow evolved the Onememory and started their feeding cycle. Using their mind-controlling powers, they would cause wars and chaos and then feed on the carrion produced. They particularly liked to feed on humans, since they are naturally a self-destructive species. They somehow escaped the destruction of Earth in 5,000,000,000. Using a massive pyramid-shaped craft, they travelled the universe, alternating between times of feeding and times of sleep. They claimed to have feasted on over 60 billion species and adapted parts of their anatomy for their biological-based craft. Eventually, they discovered the planet Metralubit and it's human population, which they choose as the next feeding ground.

The Darkness was wiped out by the Time Lords, with the last swarm being destroyed by The Doctor.