Extradimensional beings inhabiting the deuterium of Bannon's Nebula, who were being destroyed by Starfleet's fuel collection and reached out to Uhura through terrifying hallucinations.
The lifeforms of Bannon's Nebula exist in a higher dimension and occupy the nebula's deuterium, which to Starfleet is merely fuel. They are encountered in the second-season Strange New Worlds episode Lost in Translation.
While the Enterprise and the USS Farragut bring a deuterium refinery into operation, Uhura begins to hear sounds and see horrors, among them the corpse of her late mentor Hemmer. A Farragut officer with the same symptoms sabotages the station and dies. With help from the visiting Lieutenant James Kirk, Uhura grasps that these are messages, shaped clumsily from her own memories by minds with no other way to reach a human brain.
The harvesting is killing the beings. Pike takes her word for it, evacuates the refinery and destroys it. The visions cease.