Harvesters were the first Horror created by BodySnatch upon it's ascension to full Nightmare. Like BodySnatch, Harvesters bear a strong resemblence to Ghouls both in appearance and dietary habits. It is possible that BodySnatch is attempting to recreate the path that led to it's own self-actualization and eventual rise to the position of Nightmare. It is also possible that BodySnatch is not as creative as the Gaunt Man claims, and is merely retreading the same old Horror in a desperate and pathetic attempt to eak out the last drop of Fear possible from the idea that something "out there" wants your precious bodily fluids.
Though so far found only working alone - one thing that does distinguish them from Ghouls - Harvesters tend to be very tribal, and align themselves by the type of organ they specialize in taking. (It is also possible that there is only one Harvester per organ, and their tendency to speak in the third person is merely a means to make themselves seem more frightening. Either way the various types have no love for one another, with an outright war existing between the Harvester of Eyes and the Harvester of Kidneys to see who can take the most organs.) Though specilizing only in the taking of single organs, Harvesters lack BodySnatch's ability to remove them bloodlessly, and must rely on brute force instead. Some Harvesters have learned tool use - scalpels, garden implements, the like - but this is very rare.