The Parasite was a large cestoid with a thick, worm-like body that measured approximately forty centimetres in length in the adult stage of the Parasite's life cycle. The Parasite spent its entire life cycle inside and living off a larger animal (such as a human or a Dodo) as a host, before reproducing itself and passing its young to a new host.
The Parasite passed itself on through passing its eggs from the parent Parasite's host on to a new host through a bite or kiss. Parasite larvae would enter a host's bloodstream and feed off the nutrients there, before the Parasite matured.The Parasite would then move up the host body and lay its eggs in the host's saliva to be passed on to a new host. Upon maturing, the Parasite caused the host to become unusually aggressive and easily provoked into biting other potential hosts, in order to increase the chances of the Parasite's eggs being passed on. As well as becoming highly aggressive, the Parasite's host would also become highly sensitive to light; coughing and choking when exposed to bright light such as sunlight. When a Parasite's host was angered or provoked and was feeling the Parasite's aggressive influence, their eyes would dilate and turn a bluish colour, and the flesh just beneath them would sag and turn dark.
Eventually, due to the Parasite destroying the host's internal organs and attacking the central nervous system, the host and the Parasite would both die (though a Parasite was once shown to survive for what was stated to be a matter of hours after its host had died, and to leave in search of a new host). It was possible to surgically remove a Parasite from its host, but the host could only be saved and survive if the Parasite was removed while in its incubation stage. Nick Cutter indicated that once the Parasite matured, death of its host became inevitable. (Episode 1.4)
Incursions and encounters
At least two Parasites were each carried in an infected Dodo through a Spaghetti Junction to a football stadium in the present. One of the infected Dodos died shortly after coming through the Anomaly. During the autopsy, the Parasite exited the Dodo and went after Abby Maitland, but it was trapped by Stephen Hart inside a jar. Without a host, the Parasite then died.
The other infected Dodo was stolen by Tom and Duncan, and Tom was bitten and infected with the Parasite before the Dodo died. Tom subsequently infected a doctor with the Parasite, but the doctor was instructed to have his Parasite surgically removed. Tom, and presumably his Parasite, later died at the football stadium.
- Some fans have speculated that the Parasite may have come from the future: it may have been carried in a host through a future Anomaly to pre-17th century Mauritius.
- The Parasite was the first fictional creature in Primeval, possibly discounting the Carboniferous Arachnids.
- The symptoms of the Parasite are loosely similar to those of vampirism in folklore (shunning sunlight, biting and aggression, increased stamina).
- Due to this, a few fans have suggested that the Parasite may have been another example of creatures influencing human mythology and folklore: there may have been a pandemic of the Parasite in Europe in the 17th - 18th century, and the Parasite contagion may have been incorporated into folklore as vampirism.
- The Parasite vaguely resembled the spawn of the Precambrian Worms in Episode 2.2; the Worm larvae were also large, parasitic cestoids, but while the young Worms simply burrowed through the flesh into new hosts, Parasite larvae passed onto a host from their parent's host by contagion.