Parasitic Ice Worm

The "parasitic ice worms" are leech-like creatures with an ammonia-based metabolism and probably extraterrestrial origins. They are believed to have come to Earth in a meteor that fell in Alaska about 250 thousand years ago; remaining dormant under the thick ice sheet until 1993, when a group of scientists brought them back to the surface along with deep ice samples and became infected.

After infecting a host, the worms settle in the hypothalamus and proceed to feed on the host's acetylcholine, affecting with the host's self-control and causing extremely aggressive behavior. Removing the worm will result on the immediate death of the host. The worms reproduce asexually and are highly territorial, unable to tolerate the presence of other members of their species in the same host. Therefore, introducing a second worm in the infected subject actually provides a cure, since the two worms will fight each other until both are dead.

Those originally infected with the worms ended up killing each other and committing suicide until only a dog survived. FBI agents Mulder and Scully were called alongside a team of experts to investigate the occurrence and ultimately managed to isolate the parasitic lifeforms, although unable to prevent two more fatalities: the plane pilot Bear, who had been infected by the dog; and Professor Murphy, who was killed by Dr. da Silva while she was also infected. After the incident the whole place was incinerated by the authorities, supposedly for health control reasons but likely to purposely destroy the evidence of extraterrestrial life.

Behind the scenes

 * The parasitic worms were played by real life superworms (Zophobas morio)
 * The episode "Ice" appears to take inspiration from John Campbell's short story Who Goes There? and its famous movie adaptation by John Carpenter; particularly the paranoia scenes where the characters are isolated from the outside world and try to figure out who among them is infected. One of the scientists at the first scene is named Campbell, possibly a homage to the author.
 * Because of a black substance which is seen squirted by the worm in one scene, some people have speculated upon a connection between the ice parasites and the "black oil", and by extension the Greys.
 * The mechanisms that allow an ammonia-based lifeform accustomed to sub-zero temperatures to survive inside a warm-blooded water-based host are left unexplained. The same goes for the worm's biochemistry.

Appearances

 * The X-Files season 1, "Ice"