The Racnoss looked like large half-humanoid, half-arachnid beings, with blood-red skin and a crested skull. They had three pairs of eyes – one pair in the place where humans have theirs, and the remaining ones on the forehead. They had ten razor-tipped limbs, two of which were arms that strongly resembled blades. They had spinnerets at the base of their abdomen, allowing them to produce miles of webbing. (TV: The Runaway Bride)
Born with a ravenous hunger, the Racnoss mastered teleportation, which completely negated the need for them to land their ships when they visited other planets. The Empress apparently was the one who had the duty of laying eggs, which hatched into other Racnoss, meaning that the entire Racnoss race were the children of the Empress. The young were born starving, and so invaded planets to feed off all life on them. (TV: The Runaway Bride)
The Webstar had energy weaponry which was used to kill for meat. It also had scanning equipment which the Empress of the Racnoss used to watch a planet and a teleporter to allow her to travel to and from the planet. (TV: The Runaway Bride)
The Racnoss evolved in the Dark Times of the universe. (TV: The Runaway Bride, The Infinite Quest) They had some form of civilisation on Arcnoy Twelve, which was in ruins by the 51st century. (PROSE: River of Time)
They were nearly wiped out by the Fledgling Empires (TV: The Runaway Bride) in the Racnoss Wars (AUDIO: Empire of the Racnoss) over 4.6 billion years BC. Gallifreyans also had a hand in this. Nearly all of the survivors of the race escaped in their spacecraft, around which the planet Earth would later form. The Empress of the Racnoss stayed in her Webstar, but also went into hibernation at the edge of the universe until she decided to search for her young.
Around 2007, the Torchwood Institute began a drilling attempt to the centre of the Earth. This awoke the Secret Heart, which in turn signalled the Empress of the Racnoss. She came to Earth and used Huon particles manufactured from the River Thames to feed Donna Noble with the right catalysis of particles to awaken her young. The Doctor killed the Racnoss young by flooding the tunnel to the centre of the Earth with water from the Thames while the Empress teleported back to the Webstar plotting revenge. However, she had used up all of her power to attack London and revive her children and was left defenceless to a tank attack ordered by Harold Saxon which destroyed the ship and killed her, rendering the Racnoss extinct. (TV: The Runaway Bride)