Alien Species

The Metroid is an ectoparasitoidic, predatory life form created by the Chozo to combat the X Parasite on SR388. However, due to their ability to collect life energy and feed off of it, Metroids have been harvested for experiments and use as bioweapons by the Space Pirates and later a corrupt faction of the Galactic Federation.



After colonizing the planet SR388, the Chozo, a race of ancient, advanced avian creatures, discovered the presence of an indigenous race of parasites that infected and took the forms of other creatures to reproduce rapidly - parasites that the Chozo named only "X". Knowing the X would engulf and destroy the ecosystem if left unchecked, the Chozo genetically engineered a race of predators to eradicate the X. They dubbed these creatures "Metroid", a Chozo word meaning "ultimate warrior." The Metroids whittled down the X's numbers, and became the dominant predators of SR388.

However, as time went on, the Chozo began to lose control of their creations. The Metroids began to mutate, growing into larger, more aggressive forms, and turned on their creators, who struggled to hold the rogue Metroids at bay. As a desperate measure, the Chozo developed a mechanism to collect their DNA.

Cultivation and Extinction[]

Long after the Chozo had abandoned the planet, a Galactic Federation scout ship chanced upon SR388, and discovered the Metroid species. However, while en route with a specimen, the scout ship was hijacked by the Space Pirates, who saw potential for the Metroids as bioweapons. Cloning the species en masse in their base on planet Zebes, the Pirates experimented extensively with the Metroids' unique properties, giving little regard for the losses incurred by their own numbers. After their Zebes base was destroyed by bounty hunter Samus Aran, Pirates stationed on the planet Tallon IV discovered a mutagenic substance known as Phazon in its core. The Pirates quickly began to use it in their experiments on the Metroids, yielding numerous sub-species such as the Hunter and Fission Metroid. Additionally, their scans of the planet's depths revealed a large presence gestating deep within the planet - a grotesquely mutated Metroid known as the Metroid Prime.

After Samus thwarted the Pirates' operations on Tallon IV and later Aether, Elysia and their own homeworld, it became clear to the Galactic Federation that the Metroids posed a grave threat to the galaxy at large. After two failed attempts by the Federation's army to eradicate the Metroids on their home planet of SR388, they called on Samus Aran to deal with them, as she had previously been the only person able to survive an encounter with the creatures. Samus destroyed all the Metroids on the planet, including their Queen, save one: A larva that had imprinted Samus as its mother. Samus brought back this larval Metroid to Ceres Space Station to be used for research.

This didn't last long, however. Soon Ridley of the Space Pirates captured the larva Metroid and brought it back to Zebes to be cloned. There, the Space Pirates first unsuccessfully cloned the Metroid, creating the Mochtroids. They did manage to clone the Metroids successfully eventually, only to be destroyed by Samus. During Samus's battle with Mother Brain, the Metroid that believed Samus to be her mother gave Samus back life energy during a critical moment, leaving Samus to destroy the Mother Brain. However, the Metroid did not survive the encounter, leaving the Metroids to be presumably wiped out from the Galaxy. It should be noted that the Metroid which saved Samus Aran was massive, likely due to the considerable amount of energy it was able to feed off of over the short time span since its arrival on Zebes. Effectively it could be called a Super Metroid.

Revival and Aftermath[]

Shortly after Zebes was destroyed by Samus, a group of individuals within the Galactic Federation wished to explore the use of bioweapons, Metroids in particular, much like their enemies the Space Pirates. Secretly collecting DNA from Samus' suit, the ringleaders were able to successfully revive the species onboard a large space station known as the Bottle Ship, among other creatures from Zebes both intentionally and accidentally, and were able to produce a healthy Queen that produced more metroids. Wishing to use the Metroids as less flawed weapons, the scientists on the ship were successful in altering some of the larvae to become resistant to the species' infamous and crippling weakness to cold and ice, and were able to control the larvae with an android named MB, who could control the metroids and other bioweapons similar to Mother Brain of the space pirates.

However, MB became erratic and eventually rebelled, controlling the ship's lifeforms to slaughter the scientists onboard and planning to unleash the unfreezable metroids on the Federation as a whole as part of her "judgement". This plan was foiled when Samus Aran and a Federation Platoon discovered the station, with Platoon leader Adam Malkovich sacrificing himself to self-destruct the section that held the unfreezable metroids, and Samus succeeding in slaying the queen. MB herself was killed by Federation reinforcements, and the entire ship was eventually destroyed.

Once all the Metroids were gone from SR388, the X Parasite could reproduce again, and became a threat to the ecosystem. Samus Aran attempted to fight the parasite, but was unsuccessful. The parasite entered Samus's body, leaving Samus's body integrated with her suit as she passed out and the suit could only be removed while she was awake (very likely a safety protocol). Most of it were surgically removed, but she was dying. There was a solution, however: a Metroid vaccine. The Metroid vaccine killed the X parasite, and saved Samus's life - again.

The larval Metroid that Samus had brought back from SR388 had been cloned again on the BSL Research Station orbiting SR388, presumably by DNA sequences sent to them from the Bottle Ship before its destruction. The Federation managed to clone each form of Metroid up to the Omega Metroid using artificial biospheres of SR388's many ecosystems. Whether they managed to clone a Queen, or why, is unknown. The Metroid cloning center was jettisoned into space and self-destructed after a SA-X breached it. Despite this, a single Metroid was able to escape and devoured every X parasite in its path while Samus roamed the rest of the station and regained her abilities, but by the time that Samus defeated an SA-X and put the station on a collision course with SR388, the Metroid had already evolved into an Omega Metroid in the artificial SR388 ecosystem, where it attacked Samus as she attempted to escape and almost succeeded in killing her.

It failed to accomplish this due to the SA-X returning and attacking the Omega Metroid, only for it to damage it and allow Samus to absorb it and regain her full powers as she combated and killed the Omega Metroid before escaping in her ship just as the BSL research station collided with SR388, destroying the planet and all life on it, including the X Parasites. With that, the Metroids were once again rendered extinct, but due to Samus being the last being to possess Metroid DNA, the possibility of their return wasn't impossible.

Regardless, when all seemed over, the Galatic Federation received an anonymous video transmission showing an X Parasie alive and in the wild, traced back to a planet called ZDR. After sending in seven E.M.M.I. robots, only for them to lose communication, the Federation relunctantly had choice but to call Samus in to investigate due to her being the only one immune to the X due to her Metroid DNA.

Although the Metroids are extinct by the time of this incident, they still impact the plot due to the mechanations of the Chozo leader of the Mawkin tribe, Raven Beak, using the video to lure in Samus so he could use the hacked E.M.M.I. to retrieve the Metroid DNA from within her in order to use it to revive the Metroid species from extinction once more and use them for galatic conquest, due to him belieiving them to be the perfect symbol of power.

Despite knowing how outmatched she was against the Chozo, Samus went through ZDR to recover her abilities from the E.M.M.I. and the X Parasites that had invaded the planet long ago due to an expedition to SR388 that brought the parasite back to the Mawkin homeworld, causing her Metroid DNA to begin to finally activate within her, causing her to obtain the Metroid's ability to siphon energy and eventually, mutating her into the last Metroid through her new "Metroid Suit" that granted her power greater than anything she had ever possessed before. This DNA was suppressed once more by the X carrying the Thoha Quiet Robe's DNA and allowing her to escape ZDR's destruction in time, ending Raven Beak's threat to the universe and preventing his plans for reviving the Metroids, with Samus now being the last trace of their species left in existence.

Biology and Life Cycle on SR388[]

The Metroid has a several-stage lifestyle. Designed to live solely within SR388, a Metroid will not evolve unless on the planet or within an artificial recreation of the planet's ecosystem, otherwise they will remain in larval stage. If the conditions are met, they will go through the following stages:


a metroid egg


Metroids start out as eggs, presumably laid by the Queen. They then eventually hatch into small Metroid infants. The infant is small, and floats in the air. Its tentacles will turn into teeth. Infants largely function as smaller and weaker version of larvae, but have shown imprinting behavior, and seem to be more curious than aggressive at this stage.

Metroid Larvae[]


A Metroid

The Metroid larvae has a thick gelatinous membrane, vaguely resemble the jellyfish of Earth, and floats perpetually via an unknown means of propulsion. Their upper body consists of four red, raspberry-like nuclei enclosed by a rounded, veined membrane typically ranging from blue to green. Their mouths are located on their muscular undersides, and feature four sharp, curved mandibles. The larger, caudal pair is used for gripping bioforms, while it uses the smaller, rostral pair to siphon its prey's energy.

Once attached to their prey, Metroids are very difficult to dislodge and will otherwise drain their victim of all life, leaving the unfortunate creature a colorless, brittle husk. Metroids have a voracious appetite and will feed on any and all living creatures they come across, with the sole exception of their own species. This immense threat is compounded by their resistance or even immunity to most forms of known weaponry. They have only one real weakness: an extreme sensitivity to cold temperatures. Once their membrane is frozen it can be shattered with explosives, such as a small explosive projectile.

When a Metroid takes in energy, it grows in size. Eventually, it will metamorphose to its next form. However, a normal, unaltered larvae cannot metamorphose unless it is on its homeworld of SR388 or an enviroment simulating it. However, they can be "bred" by exposing them to beta-rays, which causes them to divide into two, like cells.

Alpha Metroid[]


an Alpha-Metroid

The Alpha Metroid is the next stage in the Metroid's natural life cycle, which takes place on SR388. While Alpha Metroids can hover like their previous form, they have four limbs, strange tusks, a horn, and two pairs of eyes.

Gamma Metroid[]


The Gamma Metroids are a grown version of the Alpha Metroid. The limbs are now longer and more muscular, the carapace is thicker and bigger, and the horns are stronger and thicker. Another pair of eyes is added to the head of the Metroid. Gamma Metroids also have gained the ability to generate bolts of energy as a means of attack.

Zeta Metroid[]

Zeta Metroid art

a Zeta Metroid

Zeta Metroids are more of a dinosaur-like analog. This form of the Metroid has only a small bit of the blue membrane from the unmorphed Metroid left over. The Zeta has two muscular legs, two short arms with claws at the ends, and a tail. Having lost the ability to hover, they use their legs to leap with great speed as well as strength. The Zeta Metroid has also lost the Gamma Metroid's energy bolt attack, but this shortcoming is compensated by it now being able to spit a powerful corrosive acid.

Omega Metroid[]


Samus Aran facing an Omega Metroid.


a Omega Metroid

Besides the Queen Metroid, this is the fullest a Metroid can naturally evolve. The blue membrane, usually on the underbelly on the Metroids, is now concealed. The legs, arms, and tail are now fully developed. Another pair of eyes are added, making a total of four pairs of eyes. An Omega Metroid's large leg muscles make it a quick runner and a mighty jumper it can breath fire.

Queen Metroid[]

Metroid Queen

the Metroid Queen

The Queen Metroid is so far the only form of Metroid known to be able to reproduce normally. The Queen is much larger than any other form of Metroid, and stands on all fours as opposed to walking on two, like the Zeta and Omega Metroids. The neck of the Queen can extend to impressive lengths, to better protect her young she can also breath fire.

Mutated Evolution[]

Tallon IV Metroid[]


a infant Tallon Metroid


An adult Tallon Metroid


Hunter Metroids

The Metroids from Tallon IV evolve along a different path, transforming into a Hunter Metroid as opposed to an Alpha, although this is due to their exposure to phazon and lack of certain elements from SR-388's environment. Through dedicated research it has been discovered that the process of feeding phazon to metroids is not at all enjoyable to them. Federation scientists have stated that the Metroid's reaction to phazon is "much like a Human's reaction to a cocaine milkshake". The Tallon Metroid exposed to orange phazon evolves into a Fission Metroid.

Hunter Metroid[]

The Hunter metroid is slightly larger than a Tallon metroid, and has a red-orange membrane that is somewhat squid-like in appearance. Its mandibles have turned into tentacles, and it has the ability to vampirize life-energy from a distance. It is the next phase a Tallon Metroid's life cycle.

Fission Metroid[]

This Tallon Metroid variant was exposed to orange phazon and has the ability to reproduce using mitosis. It has only been seen within the impact crater on Tallon IV, where Metroid Prime resides. Initially resembling a Tallon Metroid with a colorless membrane and blue nuclei, it will split into two random colored variations upon being damaged, with the new forms being immune to most forms of attack but weak to a certain type of beam energy(Power beam, Wave beam, Ice beam, or Plasma beam), and all being vulnerable to a phazon-based hypermode blast.

Metroid Prime[]


Metroid Prime's essence.

Main article: Metroid Prime

Metroid Prime´s origin is unknown, though largely assumed to be a Metroid that found its way into the impact crater of the leviathan meteorite. Presumably it was corrupted by phazon to serve as the phazon core's guardian, much like other leviathans, but may instead have devoured the core and gained its ability to produce phazon. Initially appearing as a large 5-legged exoskeletal creature with a black carapace, huge jaws, and menacing red eyes within the pointed shell, Metroid Prime was highly mobile and could rapidly alter its exoskeleton to use various types of energy beams, missiles, and other projectiles. The creature was only vulnerable to damage on its face, and only with the same type of energy it was currently using to attack.

While unencumbered by its exoskeleton, its core essence resembles a humanoid face with an enlarged cranium, glowing eyes, and 6 long tentacles. The membrane is transparent, and several nuclei that looks like a brain is seen within, with several veins traveling down the tentacles as well. Metroid Prime is able to create Tallon Metroids and its variants, make fire wave attacks, and become invisible to various electromagnetic wavelengths, such as visible light, infrared, or x-ray. Metroid Prime's essence is extremely resistant to damage due to phazon mutation, causing it to only be able to be wounded by phazon-based weaponry. Samus used phazon pools created by the Metroid Prime, activated her Phazon Beam and killed it. With its last breath (assuming of course that they breathe) Metroid Prime stole Samus' Phazon Suit from her and while she escaped used it to formed into Samus' new enemy: Dark Samus.

There are rumors that Metroid Prime is part X Parasite; this is false. The reasoning behind the rumor is because when Samus defeated Metroid Prime and it reverted to an spheroid form, people thought it looked like a Core-X. One must keep in mind however that Dark Samus and the many SA-X's are two completely different characters. SA-X seems to have Samus' face. SA-X only uses techniques it copied over from Samus. Dark Samus has its own style.

Dark Samus[]

Main article: Metroid Prime

Using the Phazon suit that it stole from Samus, Metroid Prime evolved into Dark Samus, a Phazon-based clone of the original Samus containing her genetic material. Samus' first encounter with her "evil twin" was on Planet Aether, which was recently damaged by a phazon meteorite. The meteorite created a Dark version of Aether. Somehow, in Dark Aether, a lifeform known as The Ing was born, devastating the true planet Aether.

Dark Tallon Metroid[]


An ing-infected Metroid.

The Ing have parasitic properties and infect potential fighting creatures, using them as a vessel for combat. When the host is killed, the Ing escapes and finds a new host. The Metroid are enemies of the Ing and attack them on sight. However, some ings have managed to successfully infect Metroids, making them even more powerful.

Unfreezable Metroid[]

In the events of Metroid: Other M, a research team had started a Metroid breeding program on a research station called the Bottle Ship. One of the results of the program was the Unfreezable Metroid, a new strain of Metroid that could not be harmed by freezing temperatures, which was identified by its spiked nuclei and dark blue membrane. Without this weakness, the Metroids were nearly invincible, though infants were still vulnerable to freezing. The majority of these Metroids were kept in an area called Sector Zero, which was jettisoned and destroyed by Adam Malkovitch.


An early attempt by Space Pirates to clone metroids on Zebes, which ended in failure. Mochtroids look very similar to true larvae, but have only a single nuclei and notably less muscle tissue. They behave in the same way as true metroids, attaching and siphoning life energy, but have a much weaker grip, and can be easily killed with a variety of weaponry, not just ice beams.

Phazon Mutations[]

Additional strains of metroids have been created due to even higher amounts of phazon corruption than what is observed in Tallon or Fission metroids.

Stage 1: Phazon Metroid[]

The Phazon Metroid is presumably an alteration of a Tallon Metroid, though its origin is only known to come from heavy phazon mutations. It is likely that this particular strain is either native to the planet Phaaze or was placed there by Space Pirates. The Phazon Metroid is bright blue, with a segment of tissue splitting its membrane into two halves, and have more developed fangs. Phazon Metroids are stronger than normal metroids, are able to attack enemies with phazon energy bolts, and their ability to become intangible allows them to evade missiles and phase through walls.

Stage 2A: Metroid Hatcher[]


a Metroid Hatcher

The Metroid Hatcher is an enormous Metroid mutated through phazon exposure. The Metroid Hatcher has a large maw and long tentacles that can be used to lash opponents or drain their energy. It "births" live Phazon 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" (see next).

Stage 2B: Hopping Metroid[]

In this variant of Metroid 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 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 hard shell of the hopping metroid makes it more resilient, though still vulnerable to cold, and it can use its sharp legs to attack, or unleash phazon energy as shockwaves.

Stage 3: Metroid Prime[]


the Metroid Prime

Metroid Prime is currently thought of as the height of Phazon Metroid mutation. Only one has been seen alive, though their may have existed more.

One instance is on Tallon IV, where this creature was found lurking in the Impact Crater. When this Leviathan was near death, sometime after impact, it followed its natural instinct by choosing a creature in close proximity and corrupting it with immense quantities of phazon to cause it to act as a guardian until the planet has been transformed, but ultimately resulting the resulting creature having presumably consumed the core instead to replace it(as no core is seen and Prime's ability to produce phazon rapidly is only seen elsewhere in Cores and Phaaze itself)

The second instance 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. Presumably this means other metroids were mutated into similar creatures due to phaaze being made entirely of phazon, though none were discovered alive.


  • Metroid series