Dresha was the chief pharmacologist on Triketha. She was stung by the Toraxians and went into a coma. After recovering, she returned to her work, but after some venom was released she could telepathically hear the insects. She started to be affected by the Toraxian minds. She later helped to find a solution to stop the insects, but the Sixth Doctor realised that she was unwittingly working to help the Toraxians. She then fully converted into one. (AUDIO: Colony of Fear)