Racnoss
The Racnoss are large and ancient beings, appearing as a half-human half-spider mix, and were first seen in the 2006 Christmas Special (The Runaway Bride). Unlike spiders, they have ten razor-tipped limbs, of which two were used as arms. The Empress of the Racnoss (seen in the 2006 Special) can be identified by the crown structure on the top of her head. The Empress is the one who has the duty of laying eggs to continue the species, so all other Racnoss are descendents of hers. The young Racnoss are born starving, so invariably will invade a planet to feed off all life on that planet.
The Racnoss were nearly all wiped out by the Fledging Empires 4.6 billion years ago, having evolved during the Dark Times. Most of the survivors of the Racnoss race escaped in spaceships at the time Earth was created. This spaceship would form the central rock around which Earth would build. The Empress stayed in her Webstar and went into hibernation at the edge of the universe. The Empress returned to Earth when Torchwood began drilling to the centre of the Earth and awoke the Secret Heart. The Empress took over the drilling work after the destruction of Torchwood One at the end of Series 2.
The Empress used Huon particles to build a key out of companion Donna Noble in order to unlock her young from the centre of the Earth. However, these Huon particles within Donna drew her into the TARDIS which got the Doctor involved in the Racnoss’ activities, and he put a stop to them. Using the pilot fish (first used by the Sycorax in the 2005 Christmas Special), the Empress had an army which could use exploding baubles (from Christmas trees). It was these remote control baubles that the Doctor used to destroy the walls of the building the Racnoss was drilling in, causing it to flood with water from the Thames above them. The young are drowned but the Empress escaped back to her Webstar, but that was blown up by the army on the orders of Mr. Saxon (who would turn out to be the Master). The Doctor revealed that the Time-Lords had beaten the Racnoss previously, and so he and the Master (though the Doctor did not know it was the Master till the end of Series 3) did so again.