Small, insect-like parasites that took over senior Starfleet officers in 2364, sometimes called bluegills after the gill-like organ visible on their hosts' necks.
The parasites were small crawling creatures that entered a host through the mouth and lodged themselves in the body, leaving a gill-like protrusion at the back of the neck. Infected hosts kept their memories but served the parasites, showing great strength and an odd taste for live grubs.
In Conspiracy, Picard was warned that something was wrong at Starfleet Command. Infested admirals, including Gregory Quinn, tried to bring the Enterprise under their control. Picard and Riker found the mother creature inside Lieutenant Commander Dexter Remmick and destroyed it with phasers, killing the other parasites. Data found the creatures had been signaling an unknown point in space.