|Anime debut||Episode 1|
|Manga debut||Chapter 1|
Parasites are an unknown organism and are the primary antagonists in the Parasyte series (Excluding Migi, Jaw & Reiko). They are a mysterious organism that appeared on earth from an unknown cause. Their origins, to this point, still remain a mystery.
Parasites go through two main stages of development.
The primal or original form. The primal form resembles a green, almost translucent snake with yellow eyes protruding out of its head, and a cone or drill like appendage on the front of its head. They almost resemble tiny tennis ball with eyes and a tail. Or, in the main character's case, a "Snake".
The second stage is when the parasite finds its desired host and enters its body, maturing over time inside to become in sync with the host. Parasites have skin resembling their host and insides to match, which can be changed as they desire. They can morph into various shapes and extend and harden certain parts of their body as they desire.
After taking control of the brain of a human or an animal, parasites develop the instinct to kill and devour other members of their host species. Parasites living in humans desire to consume other humans, while parasites occupying dogs desire to consume other dogs. Although they can live off of the food that their controlled organism would, they choose not to. Parasites are also only capable of occupying bodies of their first host species, and any new hosts must be of the same gender as the original.
It was explained by Dr. Yui that a parasite's cells double as both muscles and neurons (i.e. "sentient muscle"), meaning that their flesh also doubles as their brain. This was confirmed by Migi during his "division demonstration" and each time he divided himself, his intelligence dwindled.
Parasites also often possess a great degree of knowledge: they may use books, television, and the Internet to acquire the ability to speak as well as a great amount of background knowledge about the world, which they use to their advantage. Some parasites use their intelligence to become leaders of other parasites, and relay instructions and plans to 'lower' parasites.
Parasites often struggle to show emotion and usually must fake them if needed, though parasites that do gain emotions generally only show anger. Only two other parasites have shown to gain emotions other than rage, but both have gone through a change which brought them closer to being human; Migi fused with Shinichi's heart, and Reiko Tamura gave birth to a human child.
Though only two cases have been witnessed, it's notable that parasites who fail to take over the brain of their host appear to lean towards being of the same gender as said host. Also, parasites who fail to take over the brain are often seen as outcasts and most would seek to eliminate them, due to the human brain still being intact.
While answering a letter, Hitoshi Iwaaki stated that a parasite usually splits its head open while feeding, but will unravel its head in a spiral pattern when on the offensive, due to being a quicker alternative.
Abilities & Powers
They can identify other parasites through the wavelengths emitted by their brains. Weak parasites or parasites that failed to occupy their host's brain emit weaker signals, consequently. Parasites are able to sense the mood of other parasites. Most importantly, they can sense their killing intent.
All parasites have the ability to morph into many different sizes and shapes, and can become elastic or hardened into a form stronger than steel. Their ability to morph is most often used to blend in with human society (though their empty gaze and lack of empathy can distinguish them to certain humans), or fight humans or other parasites. Parasite-occupied bodies possess physical capabilities that are exponentially greater than their host's, because they can use the body's full potential.
Certain parasites have been shown to control other parasites, most notably Gotou who controlled a body containing several. This ability is shown to require great focus as Miki could only control three, including himself. As of yet it is unknown whether there is a mental or physical limit as to the maximum amount of parasites able to be contained and controlled within a host.
Parasites also possess enhanced reflexes and perception, as shown throughout the series. As Shinichi tries to stab Migi when the latter was just matured, he quickly reacted by blocking the knife and broke the blade.
The biggest weakness parasites possess is their dependence on the organs and digestive system of the host's body: once cut off or separated, in a matter of minutes a parasite will begin to weaken, shrivel and eventually die.
Another weakness is their intolerance to fire. Migi stated that fire causes their surface cells to react in a way similar to "freaking out". This weakness was exploited during Shinichi's fight with Gotou, causing him to become distracted and unbalanced. Coupled with this, alcohol has shown to be a very formidable offensive weapon against them, causing them to lose their morphing abilities in the affected areas and their thoughts become muddled and disorganized.
The host's body is also an inhibition with combat, the body is easily damaged and can also be destroyed by the occupying parasite if it tries to fight using it. Most notably when Mr. A easily broke his arm when attacking a group of teachers.
Parasites are also still affected by diseases and infections. They also have little to no tolerance for alcohol, it's been stated that even the slightest amount can cause their face to distort and reveal their identity.
- Migi - Alive
- Jaw - Alive
- Parasite Dog - Deceased
- Mr. B - Deceased
- Mr. A - Deceased
- Hideo Shimada - Deceased
- Reiko Tamura - Deceased
- Kusano - Deceased
- Hikawa - Deceased
- Maesawa - Deceased
- Kawada - Deceased
- Miki - Deceased
- Gotou - Deceased
- Nobuko Izumi - Deceased
- Mr. Fujii - Unknown
- Mr. C. - Unknown
- While answering fan mail, Hitoshi Iwaaki hinted at the origin of the parasites, saying the "eggs" seemed to have been carried by the wind and that they appeared to have come from somewhere on earth.
- The only parasite in nature that resemble Parasites in the series (in behavior and function) is Cymothoa exigua A.K.A. the tongue-eating louse. It is a fish parasite that first eats the tongue of a fish and then uses its body to replace the consumed body part, while the fish remains alive and relatively unharmed.
- Parasites have a similar functions, though they eat and replace the host's brain. But Migi and Shinichi share a similar relationship, where in this case, the parasite consumed and replaced a body part, while the host remained alive and intact.
- The parasites are similar to "The Thing", since they are parasitic life forms that can manipulate their bodies in a way similar to the parasites from the series.
- When entering defensive mode, the parasites heavily resemble the Las Plagas parasites from the Resident Evil video game series. This is because the concept of these parasites was inspired from Parasyte. Like them, Las Plagas will erupt from the host's head when defending both itself and the host body, under attack. It sprouts tentacles, multiple, jumbled eyes and even a single tentacle with a bony, scythe-like weapon at the end, greatly resembling a parasite's.