Films: Parasite (2004)
Location: Ocean/Civilized Area
Height/Weight: Up to twice that of an average human.
Summary: Parasites are the cornerstone of nature's darkest tendencies. Creatures that take what is not theirs and expect their hosts to drain away at their own health so that they may prosper. But sometimes, you don't need possession. You just need size...
History: On the Alpha oil rig, there are investigations and there is just business trying to be conducted. But amidst the controversy going about is the discovery of mutant parasites created by the Carmine Oil company as a means of cleaning everything. Alas, they turned out to be pure predators, and are picking off the folks on the rig one by one, getting bigger the longer they live.
Notable Kills: Nothing special.
Final Fate: The rig, and by extension all of the parasites, are blown up after the biggest one tries to eat the survivors. Carmine Oil's evil doings are then exposed to the public.
Powers/Abilities: Can infest people's bodies, and with the more nutrients they have, the bigger they get.
Weakness: Anything conventional.
Scariness Factor: 3-Sorry, but your threatening worm design is a bit undercut by bad CGI. We don't make the rules around here. We just beg for monsters that look even remotely there. Still, these creatures could have been quite successful had it not been for the small area they were in.
Trivia: -Appearance-wise, these parasites actually bear a resemblance to caecilians, which are actually serpentine amphibians with mostly no eyes, practice internal insemination, and have ROWS UPON ROWS OF SHARK-LIKE TEETH. For eating earthworms most of the time, but still.
-The largest parasitic worm is the Guinea worm with a length of up to 800 millimeters. Its modus operandi is to get into your body after you drink water full of infected water fleas carrying eggs. Then after a year, a long worm emerges out of a blister in your lower region after making walking a Hell. Not the deadliest parasite, but among the least pleasant.