Neural Parasites

The Neural Parasites were a species of alien antagonists from the Star Trek: The Next Generation episode "Conspiracy". They would also appear in some other works, such as a few DS9 novels, where they were given the name "Bluegill".

The parasites were small alien beings who could take over the bodies of those they had infected, who included Admirals Quinn, Aaron and Savor, as well as Captain Tryla Scott and Lt. Commander Remmick. When Picard's old friend Captain Keel attempted to warn him of a possible conspiracy in the upper brass of Starfleet, his ship was subsequently destroyed. Picard returned to earth, and the infected Admiral Quinn came aboard the ship. While aboard, the Quinn attempted to infect Dr. Crusher, but Riker caught his attention first, and he tried to infect Riker instead. Riker attempted to fight him off, but was easily overpowered, as were Worf and Geordi La Forge. He was only subdued when Dr. Crusher shot him repeatedly with a phaser set to stun. Upon inspecting Quinn's body, Crusher found that Quinn's body was his own, but he wasn't in control of his actions.

Down on Earth, Picard had dinner with Remmick, Scott and the Admirals, who ate bowls of mealworms, revealing themselves to him. Riker entered the room, and was apparently infected as well. Riker looked as though he was going to eat the worms, but suddenly pulled out a phaser, and he and Picard successfully subdued all of the infected members of Starfleet in the room, causing their parasites to leave their bodies. They followed a parasite that came out of Quinn to a room where Remmick was sitting. Remmick, it turned out, was infected with the mother creature of the parasites. Picard and Riker turned phasers on it, successfully killing it, though Remmick was killed as well, along with all other parasites on Earth.

Back on the Enterprise, Riker revealed that Dr. Crusher had put a fake gill on the back of his neck to simulate the infection and fool the other parasites. As the Enterprise moved on into space, Data theorized that Remmick had been transmitting a homing beacon before he died and that should the parasites receive it, they would know where to find Earth.