The Carpalian Witch was a member of the Endangered Dangerous Species Society.
She was of a spider-like species, capable of incredible patience. She was humanoid in basic appearance, but with mandible-like jaws, retractable claws and long, furry legs. The Carpalian Witch would spend much of her time in a state of waking sleep, wrapped up in her web and conserving her energy. If anything moved, she would detect it with her telepathy and then produce an enticing smell to attract it.
When Sebastiene brought the Carpalian Witch to Planet 1 to hunt the Tenth Doctor, she chose to wait in an abandoned building until the final battle. She found the TARDIS and waited for him there. She took Donna Noble hostage, but once she realised the competition had fallen apart, she attacked Sebastiene instead. She was severely wounded during her fight with Sebastiene. Her final fate is unknown. (PROSE: The Doctor Trap)