Clan Flem

Often confused with Clan Pestilens, the Skaven of Clan Flem are deeply invested in the arts of plague. They differ from their far more powerful rivals in that they lack the religious trappings of the Plague Monks, though few other Skaven make the effort to notice or distinguish the two clans. Clan Flem walks a dangerous road, knowing full well that Pestilens tolerates their existence and also knowing that it is just a matter of time before Pestilens absorbs them into their sickened fold. Until this happens, Flem knows to follow its betters and always supports Pestilens in all that they do.

Source

 * Warhammer Fantasy RPG 2nd ED -- Children of the Horned Rat (pg. 49).