The Feeders from Within were the titular creatures from the 2013 novel Feeders from Within by Peter J. Evans.
What the Feeders actually looked like is unknown, but they were stated to be parasitic entities which caused a slow, painful death in their host creature over a period of months, all the while broadcasting infectious thoughts of psychic insanity to others in the vicinity. They may have been servants of the Great Old One Tsathoggua, as they were said to dwell with him in N'kai.
As part of an unspecified plot, alien Mi-go Mr. Stone and a number of Silver Twilight Lodge members travelled to N'kai with the intent of "harvesting" the Feeders from Within. The group were foiled by the combined efforts of Mark Harrigan, Diana Stanley and Carolyn Fern.