The Khan worm, named by Dean Winchester, was a new type of supernatural creature created by Eve, Mother of All. There was no official name for it, as it was new, and humans had not given it a proper name.
A second form of the Khan worm came into existence, described by Dean as like a "cousin" to the first. This version does not take control of the host body. Instead this version of the worm acts more as a parasite.
The Khan worm was a worm that entered into people's heads through their ears or mouth, and controlled their actions. Dean said it was like a Khan worm on steroids, and referred to it as "twelve inch herpes". When possessing someone, it left dark green sludge in its victim's ears, though it could stop this if it wanted. It also spilled the same sludge out of its victim's nose when it was injured or in pain.
The second version of the Khan worm differed from the first in several respects. This variety absorbed all bodily fluids, causing the host to go mad with thirst and drink any liquids they could find; and eventually forced the host to kill and drink blood from other people. This version of the worm acted more as a parasite, drying out its host and moving on. This version appeared to have originated in the Middle East.
Unlike the first, which entered through the ear, this version forced itself into its host's mouth and down their throat.
Created by Eve, she planted the only known worm inside a trucker, who went on to kill his family. It then passed to one of his co-workers who killed twelve people. While investigating the murders, it infected Dean Winchester, who killed his cousin Gwen Campbell. It then infected Samuel Campbell, and later Bobby Singer, who killed Rufus Turner while possessed. While possessing Bobby, it told Dean and Sam Winchester that it was created by Eve, who intended for supernatural beings to take over the world. It was then electrocuted to death by Dean while still inside Bobby, who managed to survive the experience.
Four years later, a variant of the Khan worm possessed an American soldier held prisoner in Iraq. When two soldiers tried to rescue him, the worm attacked and infected them while its original host was killed. This variant did not take complete control of the body, but compelled the host to drink excessive amounts of liquids to the point that they would drink blood or gasoline before the host dried out and the worm moved on to a new host. This caught the attention of Sam, Dean, and Cole Trenton who tried to save Kit Verson, the worm's surviving host. Kit turned out to have at least three Khan worms inside him and infected Cole with one. Dean killed another, and the last forced Kit to retreat. Sam captured Kit and tried to save him, but was ultimately forced to kill him and the worm in self-defense. Dean managed to save Cole by forcing the worm's exit with rapid dehydration and crushing it.
This creature appeared as a brown worm, and possessed two large black curved fangs.
The second version was smaller and sleeker than the first, had small black pincers at its back end, and a black body leading to a red spot where a pair of large white pincers emerge from its front.
It entered a person's body through the ear and controlled their actions. While possessing a person, it greatly enhanced the strength of its host. The hosts retained no memory of the time when the Khan worm was controlling them.
- Possession - Like angels, demons, or ghosts, it could possess humans. While in possession of a host, it could access all of its host's memories. This was its primary ability, as its true form was extremely weak and delicate. The second variant of the Khan worm did not possess this power in as strong a version: it did not take complete control but instead compelled the host to drink excessive amounts of liquids and to attack others so it could move on when the host was too dry for it to survive. A strong-willed host could resist this for at a time.
- Supernatural strength - It was small and weak in its true form, however it was able to magnify the strength of any host it had taken. The second variant also possessed this power, but was weaker than the first.
- Supernatural Durability - The worm enhanced the durability of its host, and allowed them to survive bullets and withstand considerable damage. The second variant would leave the host if the host was fatally injured rather than remaining however.
- Super agility - When not possessing someone, the worm was incredibly quick and agile, and able to jump from host to host with ease. However, while the variant was still agile, it was less so than the original, and was able to be easily squashed.
- Crushing - Though agile, the Khan worm was vulnerable to being crushed easily.
- Electricity - The Khan worm could be injured by electricity. Prolonged duration exposure could kill it. The variant species, however, was unaffected by electrical shock.
- Extreme Dehydration - A variation of the Khan worm that fed off hydration can be ousted from a body by not consuming any liquids for a prolonged period and being forced near extreme heat sources.
- Fire (presumably) - While possessed by a Khan worm, a man ingested gasoline and set himself on fire, presumably killing all of the Kham worms within him.
- This is the first of two supernatural creatures that Dean Winchester has named, the other being Jefferson Starships.
- The name "Khan worm" is a reference to the movie Star Trek 2: The Wrath of Khan, specifically the scenes involving the parasitic Ceti Eels. Like the Khan worms, the Ceti Eels are worm-like parasites that burrow their way into the victims' ears and take possession of their minds.
- As one can assume that this was an alpha, the weaknesses and abilities of other Khan worms - if they existed - may have been slightly different, as alphas are shown to be superior to others of their species (i.e. Alpha Shapeshifter not being vulnerable to silver, Alpha Vampire having extendable fingernails). This may be why the variant species is weaker and different.
- The variant version of the khan worm looked similar to a Goa'uld, a parasitic alien race from the show Stargate SG-1. The worm even changed hosts in the same manner as the Tok'ra variant of that species. On the spin-off Stargate Atlantis, character Colonel Steven Caldwell was possessed by a Goa'uld. Caldwell was played by Mitch Pileggi who portrayed Samuel Campbell who was possessed at one point by the original version of the Khan worm. The Stargate SG-1 character Samantha Carter also acted as a host to a Tok'ra. Carter was played by Amanda Tapping who would go on to play the angel Naomi on Supernatural.
- The variant version of the Khan worm also bears a striking similarity in function to the slug creatures from "The Price", episode 19 of the third season of Angel.