Iagnon

The Iagnon was a worm-like creature native to Iagnos which fed on jealousy. Its acolytes captured Rose Tyler and placed it in her ear so it could devour her essence. The Tenth Doctor tried to make her jealous so that the Iagnon would overfeed and expel itself, such as by enlisting Amazastian mercenaries to rescue her and having their leader Phalia pose as Mickey Smith's new girlfriend, finally succeeding when he kissed Jackie Tyler. The Iagnon, trapped by Mickey and jealous of the Doctor, ate itself into oblivion. (COMIC: The Green-Eyed Monster)