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The Racnoss were an ancient race from the Dark Times of the universe who re-emerged after billions of years to threaten Earth in 2007.
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. (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. Even hibernating for billions of years without sustenance will retain their hunger. At least in the case of the Empress, her outer skin was shed when outgrown, she had a crown-like bone structure on her cranium, which denoted imperial Racnoss. (The Runaway Bride)
Most of Racnoss technology was made of a fine, silk-like substance, strengthened and powered by Huon energy, including their spacecraft, amongst other things.
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. (The Runaway Bride)
The Racnoss evolved in the Dark Times of the universe. (The Infinite Quest) they were nearly wiped out by the Fledgling Empires 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 took over the work site after the destruction of Torchwood One during the Battle of Canary Wharf. She used the River Thames as a method of manufacturing Huon particles to awaken the Racnoss and took over the Roboforms to use as soldiers. 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. (The Runaway Bride)
It was believed that a splinter nest of Racnoss may have been the ones that attacked the makers of the Clades. (Peacemaker)
Jack Harkness speculated that an interaction with the Racnoss hibernation field’s huon particles may have resulted in the Blessing, but was forced to admit he had no idea.