Neural parasite (23rd century)

The Denevan neural parasites, discovered by the Federation in 2267, were considered a highly-dangerous lifeform.
They had been migrating through the galaxy for centuries, inducing mass insanity on the planets they touched.

Biology

These flying parasites were roughly disc-shaped, about thirty centimeters in diameter, and two to four centimeters in height. Their edges were thin and yellowish, and towards the center, the creature was thicker and redder. Occasionally, the life forms pulsated. These parasites had no detectable external or internal organs, and they emitted buzzing sounds similar to bees. Spock described these neural parasites as "resembling... a gigantic brain cell." They were resistant to phaser fire, even when sustained and at high power levels.

These parasites were capable of "clumsy" flight. They attacked by making physical contact with a target and stinging it in a similar fashion of an Earth bee. The stinger injected a strand of tissue, which infiltrated the victim's nervous system rapidly, entwining with the nerves. Dr. McCoy described this entwining as "far, far too involved for conventional surgery to remove." Once the parasite infiltrated a host, it pressured the host to obey its commands by inflicting enormous pain. There seemed to be some level of pain even when the host obeyed, but the creature could increase the pain it inflicted to bring an uncooperative host to heel. Though infected, Commander Spock was able to end the pain through his mental discipline, and convinced the crew to let him collect one of the parasites to run tests on. However, for others, the continuous painful stimulation led to insanity and death.

Infected victims cooperated in working towards the parasite's objectives. This, and their enormous resistance to harm, led Spock to theorize that all of the parasites were parts of a single organism.

By the late 2360s, Federation scientists believed that this parasite had possibly originated from the Large Magellanic Cloud.

Destruction

The breakthrough in defeating them came when Captain Kirk theorized that they were vulnerable to visible light. The first attempt at a cure using this approach used exposure to a general spectrum of light at 1,000,000 candles per square inch and it proved effective at killing a parasite. The test proved to be premature, as analysis of the creature's remains revealed that ultraviolet light was sufficient. A constellation of 210 ultraviolet satellites were then placed in permanent orbit 72 miles around the planet. The light they generated reached all parts of Deneva, destroying the entire infestation.