Template:Articleissues Template:Mergeto Metroids are a fictional species of parasitic alien creatures from the Metroid video game series created by Nintendo.


Metroids were bio-engineered by the birdlike extra-terrestrials, the Chozo, on the fictional planet SR-388. According to the Metroid Fusion instruction manual, "Metroid" means "ultimate warrior" in the Chozo language.

The Metroid was created as a biological defense against the X Parasite, a virulent form of life that entered the body of other life forms, copying the DNA and splicing it with other infected victims, creating violent and dangerous hybrids. Metroids feed on "life energy", rather than physical matter (like blood), enabling them to absorb the X Parasite without becoming infected.

The X Parasite outbreak was in fact contained (though not eliminated), but the Metroids were themselves a dangerous biological parasite. The Chozo on SR-388 were either destroyed or forced to evacuate the planet when the Metroids began to multiply and attack other forms of life.

Physiology and morphology

The body of a Metroid - in its most common, larval state - consists of a thick, gelatinous, transparent membrane, resembling a jellyfish (only with large fangs instead of tentacles). Enclosed in the membrane are three red, raspberry-shaped nuclei resting in a pyramid shape. Each nucleus has several neuron-like branches that connect to the inner wall of the membrane.

Metroids have two pairs of mandibles. The larger set is primarily used for gripping prey, while the smaller set is inserted into the prey to extract life energy. Once a Metroid has attached itself, it is difficult to dislodge. If not quickly removed, it will drain the prey of its life energy completely, killing it. They have an endless appetite and will feed on any and all living creatures they come across, with the single exception of their own species. The more life energy absorbed by a Metroid, the larger that Metroid becomes. Metroids also have the ability to transfer stored energy into another life form, healing them. It is also possible to harvest the energy stored in a Metroid, allowing them to be used as a near-infinitely rechargeable (though extremely hazardous) energy source.

Standard Metroids are invulnerable to most forms of weaponry. Their only weakness is a sensitivity to extremely cold temperatures. Once their membrane is frozen it can be shattered by concussive weaponry (such as missiles), killing the Metroid. Metroids can also be kept in stasis in sub-zero temperatures.

Immediately after hatching, Metroids have the ability to hover in the air. Metroid Prime 2: Echoes explains that they defy gravity by using kinetic energy stored in their body. As they metamorphose into other forms, they gain limbs as well as weight, so a Metroid's ability to fly is lessened whereas strength and defense are gained.

Though a Metroid's nature is one that is threatening to any organism with a life force, they have been known to show signs of intelligence. A fight-or-flight response can be seen instantly after hatching, for example. They have also been known to show signs of having a memory, and even compassion. At the end of Super Metroid, the grown Metroid that had thought Samus was its mother at the end of Metroid 2: Return of Samus initially attacked her, but after recognizing who she was, the Metroid let her go and later saved her life. A log entry seen in the Space Pirate base in Metroid Prime 2: Echoes says that the Space Pirate Science Team believed Metroids could be tamed (the Pirate who wrote the log entry however seemed to disagree due to death in a large stasis tank).

In addition, in Metroid Prime 3: Corruption, it is revealed in a scan that Metroids evolve differently dependant on their planetary environment. The Space Pirates say to have produced encouraging results in their homeworld labs, and upon further inspection of the area, there are tanks that at one time respectively contained SR-388 Metroids, Zebes Metroids, and Tallon IV Metroids

Life Cycle

Metroids' natural metamorphosis.

In a natural environment, Metroids adopt a hive-like society, with a dominant, egg-laying Queen. Metroids that hatch from eggs are typically smaller, but no less dangerous, than their larger and more common larval forms. A baby Metroid is dangerous from the moment it hatches, but it has been known for a baby to imprint the first thing it sees as a mother figure, as happened to Samus Aran at the end of Metroid II.

Following the infant and larval stages, the Metroid can shed its membrane a number of times, drastically altering its appearance and physical characteristics. It is possible for a Metroid to pass through the entire cycle from larvae to adult in just a few days through a special program developed by the Galactic Federation, as stated by Samus' computer C.O. in Metroid Fusion.

While Metroids are typically born from eggs, a single Metroid exposed to high levels of beta radiation causes it to asexually reproduce by dividing, much like a cell undergoing mitosis. This was discovered by the original research team that found the first recorded Metroid on SR-388, and the information was used by the Space Pirates to breed more Metroids. However, Metroids bred this way do not grow past their larval stage.


The most commonly seen version of a Metroid. Sometimes called "Larval Metroid". It appears in almost all of the games.

Alpha Metroid

Following its first transformation, the Metroid appears "upside-down" with the closed membrane acting as the creature's belly, and the four mandibles sprouting from the top as insect-like legs. The top of the Alpha Metroid is covered in a plated exoskeleton. Three horns and two red compound eyes form a head at the front of the exoskeleton. The Alpha Metroid loses its ability to latch onto prey, but is still capable of moving through the air at great speed.

Gamma Metroid

Larger than the Alpha Metroid, with a thicker exoskeleton covering around half of the membrane, the Gamma Metroid has six red compound eyes and much larger horns than its forebear, although is not too dissimilar in appearance or action. It can discharge concentrated bolts of static electricity to paralyze enemies temporarily.

Zeta Metroid

Roughly the height of an average human being, the Zeta Metroid is a significant departure from the Gamma Metroid. The rear legs have clawed, lizard-like toes, and a distinct muscular structure, allowing the Metroid to walk bipedally and leap great distances. The forelegs also feature two claws, and these are primarily used for attack. The head is separated from the exoskeleton by a short neck, and a leech-like mouth replaces the beak of the Gamma Metroid. A tail has grown from the rear. At this point, the Metroid begins to look like a dinosaur, such as a T-Rex. The Zeta Metroid is incapable of flight, but can leap through the air with incredible speed and strength, and can levitate using jets of air. It can also spit balls of fire, though how it does so is unknown. It could be possible that it uses drained life-force as ammunition as well as nutrition.

Omega Metroid

The final stage of the typical Metroid's lifecycle is the Omega Metroid. Standing at around twice the size of an average human being, this bipedal terror is almost completely plated in impenetrable exoskeletal armour, leaving only a small area of the soft membrane visible through the rib cage. While similar to the Zeta Metroid in appearance, the Omega has longer and more powerful limbs, a shorter tail (in relation to body size), eight compound eyes and a larger mouth. Like the Zeta Metroid, it can levitate using jets of air, as well as spit fireballs. One appears at the end of Metroid Fusion, when Samus is required to escape the station.It is invunrable to all weapons except the ice beam received shortly after Samus-X appears and oddly (although probably driven to fight its natural predator) saves Samus

Queen Metroid

It is not known what causes a Metroid to become a queen, as only one has been discovered. The differences in physical appearance to all other natural forms suggest that it may not stem from the same development path. The Queen is quadrupedal, with multiple-jointed and muscular limbs. Its membrane is completely exposed on its belly, but its exoskeletal armour is so thick that it remains permanently protected. The Queen's dominant feature is a large, jointed mouth filled with serrated teeth. Its head is on the end of a long, extendable neck, used to attack and tear apart intruders to its nest. Unlike Zeta or Omega Metroids, the Queen Metroid looks more like a tortoise of some kind instead of a bipedal dinosaur. As shown above the Queen Metroid form is much larger than any other stage in the life cycle.

Extrapolated Life Cycle Due to Phazon Exposure

Due to heavy experimentation by the Space Pirates on Tallon IV, as well as numerous logs, it can be safely determined that the life cycle of a Metroid is altered by atmospheric conditions. The presence of Phazon will cause a Metroid to undergo many different kinds of mutations, many of them varied.

Stage 1: Phazon/Tallon Metroid

The Phazon Metroid (first seen in Metroid Prime 3: Corruption) is possibly related to the Tallon Metroid (first seen in Metroid Prime 2: Echoes) due to its reliance on Phazon. However, since the Metroid species was bio-engineered by the Chozo, who had never visited Phaaze, it is unknown how the Metroid species came to the Phazon planet.

The Phazon and Tallon Metroids are characterized by their complete dependence on Phazon, and their ability to phase in and out of local timespace, similar to the Hunter Ing. Both emerge from a cocoon as infants. Upon contact with Phazon, Tallon Metroids immediately become fully-grown larval Metroids; it is unknown whether Phazon Metroids experience the same rapid growth. Like most other Metroids, Phazon Metroids are vulnerable to extreme cold. The gelatinous portion of this variant is split into two parts down the middle, and they have a ring of sharp teeth on their underside. Tallon Metroids can be frozen with the Dark Beam similarly to the properties of cold weapons, but do not share the same physical variatians as Phazon Metroids.

Stage 2A: Metroid Hatcher

The Metroid Hatcher, seen in Metroid Prime 3: Corruption, is an enormous Metroid mutated through Phazon exposure. The Metroid Hatcher has a large maw and long tentacles. It "births" live Metroids through its maw. This variant serves to increase the Metroid population quickly without the need for beta-ray fission or egg gestation time. It is unknown whether this variant also lays eggs. It is also unknown what conditions cause the Phazon mutation to lead to this form rather than the "Hopping Metroid".

Metroid Hatchers are extremely large and have hardened exoskeletons that render them invulnerable to most attacks. A Hatcher can use its four tentacles to drain energy from afar or perform a spinning attack with. This Metroid variant is not weak to cold based weapons, but can be defeated by ripping the tentacles off, or by damaging its protected internal core with high-frequency weaponry.

Stage 2B: Hopping Metroid

Also seen in Metroid Prime 3: Corruption, this variant of Metroid is heavily mutated by Phazon exposure. The creature has lost its ability to fly and has gained the use of powerful legs. It is believed that either this form or the "Phazon Metroid" lays eggs, due to their presence being unexplained by the "Hatcher Metroid", which "births" live young. It is also believed that this form can only be found where Metroids are exposed to massive quantities of Phazon, such as Phaaze, or proximity to a Leviathan/Seed.

The Hopping Metroid has also lost the characteristic ability to drain the life force from beings. However, it has an immense amount of Phazon stored within its body, allowing it to enter Hypermode at will. The Hopping Metroid is vulnerable to extreme cold, although less so than its brethren.

Stage 3: Metroid Prime

File:Metroidprimeguide 58.jpg

Metroid Prime in its exoskeletal form

Main article: Metroid Prime (creature)

Metroid Prime is currently thought of as the height of Phazon Metroid mutation. It is a direct mutation of the Hopping Metroid due to obvious similarities and evidence. There have been two documented instances of this creature.

One instance is on Tallon IV, where this creature was found lurking in the Impact Crater. The planet was impacted by an interstellar object originating from the planet Phaaze. This object was presumably a natural Leviathan (lacking the Space Pirate technology gained in later years by the entity Dark Samus; technology which augments the Leviathan into a rapidly acting Phazon seed). Metroid Prime came with the Leviathan, presumebly hiding within the hollows of the giant creature. Chozo lore speaks of the "Worm", Metroid Prime, coming from the stars or the instellar terror that struck with the planet.

This Tallon IV incarnation of Metroid Prime had also fused with many Space Pirate weapons, which made it more powerful. This dangerous creature is much larger than a Queen, and is able to produce larval form Metroids, Hunter Metroids, Fission Metroids and Phazon itself from its body. Unlike other Metroids, Prime is composed entirely of a transparent membrane plus the naturally evolved exoskeleton in which it resides. In place of the internal nuclei is a large and distinct brain, and the mandibles are replaced with long tentacles. A distinct facial structure with two glowing red eyes hangs beneath the brain case. This "core" structure is first encountered in a sealed exoskeleton with multiple insectoid legs and horns similar in look to the Hopping Metroid, but this natural armor is no longer a physical part of the Prime's structure, and it can exist without it. Metroid Prime's core is invulnerable to all forms of weaponry, but may be destabilized by over-exposure to Phazon. The core is also capable of shifting in and out of the visible spectrum and attacking using several different forms of energy. This Metroid is repeatedly referred to as a "worm" by the Chozo, probably due to its parasitic nature and ability to produce Phazon.

Despite its defeat at the end of Metroid Prime, the Metroid Prime originally found on Tallon IV fused with Samus Aran's Phazon Suit and continued to wander the galaxy as Dark Samus.

The second documented instance of this creature is found on the planet Phaaze, where dead husks can be found which are said to be identical to the creature fought in the crater on Tallon IV. This instance is simple to explain. The planet Phaaze is, in essence, entirely Phazon-based. The level of Phazon radiation there is enormous. Their presence confirms that the massive levels of Phazon would eventually mutate each Metroid into a Hopping Metroid, and then into a Metroid Prime. All three forms are present on the planet Phaaze, including vast amounts of Hopping Metroids, therefore presumably there were other Metroid Prime bioforms on the planet, perhaps elsewhere. The presence of husks did not necessarily mean that this instance of the creature had been destroyed, however. It may simply have shed its exoskeleton, though there is no official confirmation on the subject.


Further experimentation by the Space Pirates and exposure to elements not found on its homeworld have caused a large number of mutated Metroid variants to be created.

Hunter Metroid

An adaptation from the larval form, brought on by exposure to the blue Phazon mutagen on Tallon IV in Metroid Prime. Hunter Metroids have a red pigmentation and two energy-extracting tentacles which allow them to drain life force from a distance, as opposed to the close-range tactic used by younger Metroids. Although many believe this to be a mutation, it should be noted that the log data for Hunter Metroids refers to them as "adolescent Metroids," and makes no mention of Phazon. It's possible that this either precedes the Alpha stage, or could possibly be the first stage of a different life cycle.

Fission Metroid

Another development from the larval form, also brought on by exposure to Phazon in Metroid Prime. The Fission Metroid possesses the unique ability to multiply by cellular division when at the brink of death, without the need for exposure to beta radiation. The new creatures also gain invulnerability to all but one of Samus's beam weapons, but they can also be destroyed by a Power Bomb. The weaknesses generated "appear to be random, due to the chaotic nature of the Phazon", according to Samus's scans.

Dark Tallon Metroid

Tallon Metroids, when possessed by the Ing from Dark Aether, mutate into a leathery, spotted, blackish-purple appearing creature with a ring of small fangs instead of the regular four mandibles. Only Tallon Metroids can be possessed by Ing, due to their high levels of Phazon intake.


First encountered in Metroid Prime 3: Corruption, though they look similar to the infant form of Tallon Metroids. This is the infant form of the Phazon Metroid. It does not attack and is docile. Miniroids are usually found in groups of many, and often with Phazon Metroids.


A weakened variant of the Metroid, Mochtroids appear in Super Metroid and are the first attempt by the Space Pirates to clone Metroids. While they possess the same overall shape and energy-draining properties of Metroids, Mochtroids are considerably weaker than Metroids and have only one internal nucleus (as opposed to the usual three or four). Their fangs are elongated and more closely resemble tentacles, and they cannot latch onto their prey. They can also be defeated with normal weaponry instead of the Ice Beam.


The games are shown in story timeline order, rather than in order of release.

Metroid / Metroid Zero Mission

A Metroid discovered by a Galactic Federation research team on the planet SR-388 was taken aboard a research vessel for study. The research vessel was boarded by Space Pirates and the Metroid taken to the Space Pirate base deep within the planet Zebes. The Galactic Federation sends bounty hunter Samus Aran to Zebes to destroy the biological computer Mother Brain and any Metroids that have been bred before a new biological weapon is unleashed.

Samus defeated the Kraid, Ridley, and Mother Brain but several Space Pirate vessels were launched from the planet, each carrying a containment of Metroids.

Metroid Prime

A Space Pirate vessel lands on the planet Tallon IV, and begins researching the Phazon mutagen that has poisoned the planet's ecosystem. The Metroids are exposed to it in controlled conditions, along with many other life-forms, creating the Fission and Hunter Metroid variants. The source of Phazon is discovered to be a giant meteor from a planet called Phaaze (revealed in Metroid Prime 3: Corruption). Metroid Prime was a giant Metroid, mutated by Phazon.

Metroid Prime 2: Echoes

A Space Pirate vessel lands on the planet Aether and introduces a new Metroid variant dependent on Phazon to the planet, the Tallon Metroid, appearing with red membranes. Some also become possessed by the Ing creating Dark Tallon Metroids.

Metroid Prime 3: Corruption

A large swarm of Phazon Metroids attack a security drone examining the remains of a destroyed Federation ship, the Valhalla. As Well, it seems Phazon Metroids are kept in storage on Skytown, and Metroid Hoppers are found on the Galactic Federation homeworld Norion, following a space pirate attack on the planet. A large variant called the Metroid Hatcher, which can spawn Phazon Metroids, can be found in multiple locations in the game.

Metroid II: Return of Samus

An Alpha Metroid in Metroid II

The Galactic Federation attempts to destroy the last remaining Metroids on their homeworld of SR-388. After a number of mission failures by the Federation army, Samus Aran is called in to carry out the call, being the only person to survive several encounters with the Metroids.

The planet's Metroid population, for one reason or another, permanently remains at 39, but many of them have developed into later stages of their life-cycle. Samus makes her way into the Metroid nest at the center of the planet, destroying several larval Metroids before engaging in a final battle with the Metroid Queen.

After the Queen's destruction, an infant Metroid hatched and imprinted Samus as its mother. Because of Samus' efforts, this infant was the last surviving Metroid in the galaxy. It helped Samus escape from SR-388, and as the only "domesticated" Metroid in history, she took it back to the Federation for research.

Super Metroid

Cloned Metroids in Super Metroid

In Super Metroid the Metroid larva that had imprinted on Samus was studied, and it was found that the Metroids' potential as life saving creatures was as great as their destructive powers. Right after Samus left Ceres Station, the Space Pirates besieged it and Ridley stole the Metroid larva, taking it back to the Space Pirates' rebuilt base on Zebes.

The Space Pirates quickly used beta rays to multiply the Metroid into a new army of feral larval Metroids. In Maridia Samus also finds many Space Pirate attempts of clones of the Metroids, called "Mochtroids". While they could leech life, they were weak and could not latch onto their prey. At the end of the game, the Metroid larva sacrificed itself to save Samus, causing the Metroid species to be extinct, or so it would appear...

Metroid Fusion

On planet SR-388, the Galactic Federation has been monitoring the ecosystem following the eradication of the Metroids. Samus was hired to lead one of the teams into the planet, when the bounty hunter became infected with an X Parasite. She lost control of her body and her power suit, and fell into a coma, barely clinging to life. A vaccine made of a DNA sample from the last Metroid caused Samus to recover immediately. It had been discovered that the Metroids were created by the Chozo on SR-388 for the purpose of eradicating the X Parasite, and Samus had now gained the Metroid's absorbing power. This allowed her to absorb Core-X parasites and reattain abilities lost as a consequence of her vaccination and surgery.

The X Parasite escaped on the research vessel, and through her efforts to keep the ship active, Samus discovered that the Federation had a secret Metroid breeding program. The program had been destroyed by a powerful X Parasite that had control of Samus's old power suit, the SA-X. The entire section was detached from the station and ejected into space, just after Samus escaped, completely destroying the Federation's research.

One Metroid escaped the breeding station and went on to metamorphose into an Omega Metroid. Samus discovers the fully evolved Omega Metroid as she heads back to her ship to escape the space station. It attacks Samus and lowers her health down to critical levels. But the SA-X appears and weakens it before being destroyed. Samus absorbs the parasite and gains the ability to use the Ice Beam, despite Federation warnings that her Metroid DNA would prove intolerant to the cold. She uses the Ice Beam to destroy the Omega Metroid and finally escapes the space station before its detonation on the planet below.

It is interesting to note that the lone Metroid that escaped left "shells" behind after each metamorphosis, similar to those seen in Metroid II. They can be seen scattered through the station and right before the battle with the Omega Metroid, but if counted there is one more shell than a single Metroid can produce, implying that there may have been another metroid that got away.


  • In Kirby's Dream Land 3 there is a level with several Metroids in it. If a player kills them all (by freezing, as in the Metroid series), Samus takes off her helmet at the end of the level, otherwise she simply stands by the goal. Metroids will attack Kirby, but do not appear to hurt him.
  • A Metroid trophy is available in Super Smash Bros. Melee.
  • In WarioWare: Twisted!, one mini game involves having to tilt the GBA and fire Samus' gun to destroy Rippers, Weavers, and keep away a Metroid that tries to latch onto her. Another one invlolves tilting the GBA to lead Samus to a Missile Tank.
  • In WarioWare: Touched! for the Nintendo DS, one of the microgames features one, two, or three Metroids (depending on the difficulty level) that attempt to cling on to Samus. The player must use the stylus to drag the Metroids off her to keep her alive until time expires.
  • In Wario Land 2, there is a Metroid as a level treasure.
  • In Animal Crossing: Wild World, it is possible to get a Metroid item from Gulliver, the seagull, who flies around in space in a UFO and can be shot down with a slingshot.
  • In Blaster Master, there are Metroid like creatures that live under water, however you don't have to freeze them to kill them.
  • In the Kid Icarus games there is an enemy "Komayto", that resembles a Metroid, and are said to come from "another planet." "Ko-" is a Japanese prefix for "child", and "mayto" may be an Anglicizations of "Meto", itself from "Metroid." Hence, they would be the "young" form of the Metroid (possibly like that which followed Samus at the end of Metroid II).

External links

Metroid series:
By chronology: Metroid (Zero Mission) | Prime (Prime Pinball) | Prime 2: Echoes | Return of Samus | Super | Fusion
By release order: Metroid | Return of Samus | Super | Prime | Fusion | Zero Mission | Prime 2: Echoes | Prime Pinball
Upcoming: Hunters | Prime 3 | Dread
Universe: Samus Aran | Characters | Chozo | Gunship | Items | Kraid | Locations | Metroid species | Mother Brain | Ridley | Space Pirates | Luminoth | Ing | Dark Samus

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