The Metroids were a creation of the Chozo, created with the purpose of combating the X Parasite. Their name in Chozo literally translates to "Ultimate Warrior". The Metroids however drew the attention of the Space Pirate organization and the species has since been exploited repeatedly in the hopes of using them as bioweapons against galactic civilizations. As a result, Samus Aran has been hired to exterminate Metroids on numerous missions across various planets.
In Metroid and its remake, Metroids were stated to have been originally discovered by the Galactic Federation while researching SR388. This initial encounter gave a glimpse of the species' powerful abilities but despite the Federation suffering casualties on their side, the latter were nonetheless successful in capturing a small number of Metroids. Soon afterwards, the Space Pirates boarded the Space Research Vessel Marina in which the Metroid specimens were being transported and stole them, taking them to their base deep within the planet Zebes. Inside their headquarters, the Pirates began to multiply the creatures' numbers by exposing them to beta radiation. After several attempts by the Federation to defeat them with frontal assaults, Bounty Hunter Samus Aran was tasked to single-handedly infiltrate Zebes and destroy the Space Pirates along with the Metroids.
Fleeing from Zebes, the Space Pirate frigate Orpheon carrying Metroid specimens eventually landed on the planet Tallon IV. The exposure to the planet's atmosphere triggered changes in the Metroids' physiology, becoming a new breed that would be known as Tallon Metroids. These Metroids are smaller and less durable than those encountered on Zebes; while they retain the weakness to the Ice Beam, Samus is now capable of killing them with any weapon in her arsenal, though they take extensive amounts of time and firepower for her to do so. If Samus carries enough Energy Tanks in her suit, she can also let Tallon Metroids drain her Power Suit's energy until they explode from overfeeding.
Despite these initial flaws, Tallon Metroids react strongly to the mutagen Phazon discovered by the Pirates on Tallon IV. This prompted the Pirates to experiment with their specimens, leading to the creation (both intentional and unintentional) of powerful aberrations in the Metroid species: 'Hunter' Metroids, which have red translucent membranes and two long range energy-siphoning tentacles, 'Fission' Metroids, who's individuals can split into two separate entities when attacked, and finally the heavily Phazon-mutated Metroid Prime. Though this last mutant's origins are kept largely ambiguous, a theory can be found here. All the Metroids encountered on Tallon IV, save for the Metroid Prime, can be dispatched with a single Power Bomb, contrary to other breeds seen elsewhere which require numerous bombings.
Danny Richardson designed several Metroid forms that were not included in Prime.
In Metroid Prime 2: Echoes, the Space Pirates imported Metroids to planet Aether. The planet's environment and stimuli seemingly caused the creatures' membranes to gain a red coloration. Other than this adaptive change, they possess the same attributes as the Metroids from the previous game. The Space Pirates have landed on the planet in the hopes of finding more Phazon energy and to continue their research on the Metroid species.
The Ing, the dominant race of Aether's dark dimension, eventually take control of many Tallon Metroids through darkling possession, creating a unique strain called Dark Tallon Metroids. They feature thick, ridged carapaces covered with numerous orange eyes instead of the smooth, transparent membranes seen commonly in prior Metroids. The transformation grants them far more durability against both conventional and dark matter-based weapons, but consequently gain a high sensitivity to the Luminoth's weaponized Light of Aether. The darkling Metroids are used as soldiers in the Ing Horde patrolling Aether and Dark Aether; the Metroids' animal mindset is allegedly replaced with the high level of intelligence of the Ing controlling them, increasing their threat level.
The Space Pirate base in Agon Wastes contains a room filled with artificially-created Metroid Cocoons. These organic storage chambers carry Infant Tallon Metroids that can instantly grow into the red-colored Tallon Metroids when they make contact with Phazon. This small breed cannot yet absorb energy and instead aggressively ram their targets to damage them. The Space Pirates seem to use this Metroid strain as portable energy sources that can be easily and safely transported in large quantities.
In Metroid Prime 3: Corruption, four additional mutant strains of Metroid are introduced. They all originate from Tallon Metroids that were either heavily exposed to Phazon energy or were infused with the mutagenic during the egg stage. Their importation on a Pirate Homeworld seems to have also played a role on the creation of these new breeds. The Space Pirates are intent on progressing further with their Metroid experiments and research in order to use them for the plans of their new leader, Dark Samus.
The first encounter are with the Phazon Metroids kept in a Pirate lab on Elysia. These powerful, blue-membraned organisms can not only leech life energy but also launch electrical Phazon energy at their prey as well as become intangible, allowing them to traverse without hindrance through barriers, solid matter and weapon fire. The Phazon Metroid's infant stage is the Miniroid, an extremely frail, non-aggressive breed that travels in massive groups in order to increase its chances of survival. Despite the Miniroids' initial weaknesses, they ultimately grow into the dreaded Phazon Metroids prior to metamorphosing into one of the following forms: the Hopping Metroid or the Metroid Hatcher.
Hopping Metroids lose many of their larval form's abilities, but develop sharp limbs and a highly resistant exoskeleton. Their new bodies allow them to enter an amplified state known as Hypermode that multiplies their durability and attack power. They can also spit Phazon venom from their mouths as well. The Metroid Hatcher maintains its flight capability while growing a Phazite-like shell and growing energy-siphoning tentacles. They are capable of spawning live Phazon Metroids from their oral cavity.
A massive population of mutated Metroids are found on planet Phaaze, the source of all Phazon in the universe. Though their presence on the planet may seem strange at first sight, Phaaze's great distance from all other locations in the Metroid series makes it likely that the Space Pirates and/or Dark Samus imported the species upon their arrival.
Metroid Prime 3: Corruption presented various scan data found on the Pirate Homeworld that finally explained the many changes in Metroid physiology as the result of being exposed to different atmospheres and other stimuli such as Phazon. The same room containing these scans features three empty tanks, each referencing a breed from Tallon IV, Zebes and SR388. A close inspection of a dissected Metroid corpse reveals it to be none other than a Dark Tallon Metroid from Aether.
The Space Pirates maintained a supply of larval Metroids, multiplying them in a former medical laboratory on Talvania. The Galactic Federation caught wind of this operation and tasked the Federation Force with destroying the facility via a self-destruct mechanism inside. General Alex Miles also asks the Force to, if possible, bring back some Metroid Eggs for study. While this is an optional bonus objective in-game, it is considered canon. At the end of the game, an unknown individual with armor resembling the Federation-hating Bounty Hunter Sylux infiltrates a GF laboratory, and causes a Metroid Egg in captivity to hatch.
In Metroid II: Return of Samus, seeing the dangers the Metroids posed to the galaxy, the Galactic Federation attempted to destroy them. 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 was the only person able to survive several encounters with the creatures. It was in this specific mission where the natural life cycle of the species was first discovered, with the most well-known form of Metroids from previous incidents revealed as being merely the larval stage.
The game begins with a total global Metroid population of 47, though the number displayed is 39 at first—the last 8 Metroids hatch before Samus engages the Queen Metroid. Samus' goal was to explore SR388 and hunt the Metroids down one by one. As she progresses further into the planet, the Metroids continue along their natural life-cycle, eventually culminating in the Omega Metroids. Samus eventually 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 Queen Metroid.
After the Queen was destroyed, an infant Metroid hatched and imprinted on Samus as its mother (thus raising questions as to the true instinctual intelligence of the average Metroid). Because of Samus's efforts, this infant was the last surviving Metroid in the galaxy. It helped Samus escape from SR388, and she took it back to the Federation Academy for further research.
- "The last Metroid is in captivity. The galaxy is at peace..."
"It is said that Metroids are life forms created by an ancient civilization. Metroids engulf living creatures and absorb their energy. They are very intelligent and quick to reproduce."
In Super Metroid, the Infant Metroid that had imprinted on Samus was studied by scientists on Ceres Station; it was found that the Metroids' potential as beneficial creatures was as great as their destructive powers. Right after Samus left Ceres Station, the Space Pirates besieged it, killing everyone on board. Ridley stole the hatchling, taking it back to the Space Pirates' rebuilt base on Zebes.
The Space Pirates quickly used beta-rays to multiply Metroids out of the last infant. However, this usual method would not be enough for the organization this time; the Pirates were anxious to resupply themselves with as many Metroids as possible, thus pushing them to attempt at genetically cloning the hatchling (and possibly the multiplied specimens) alongside the beta-ray exposure. This ambitious method would end in disappointment: in Maridia, Samus finds the cloned failures named Mochtroids. As their name suggests, these clones are a mockery of the true multiplied larvae that filled Tourian's hallways. Though the Mochtroids could still leech life-energy, the siphoning itself was poor, their membranes were extremely frail and they lacked the strength to properly grip onto prey.
The Metroids found in Tourian could only be dispatched by freezing them then followed with blasts from concussive weaponry. Power Bombs could be used to harm them without the use of the Ice Beam, but did very little damage; in addition to having a slow rate of drops between each Power Bomb, they were far less reliable against Metroids this time around.
Samus eventually finds the missing Infant Metroid, however several unknown factors caused it to mutate into a Giant Larva. Not recognizing Samus at first, the Metroid began devouring her life energy only to remember at the very last moment, causing the creature to flee the scene in shame. At the end of the game, the Giant Metroid sacrificed itself to save Samus by attacking and leeching Mother Brain's energy. It then demonstrated the life-saving properties that could have benefited galactic civilization: transferring energy to living beings instead of simply absorbing it. As it re-energized Samus' depleted Energy Tanks and gave her a new weapon stolen from Mother Brain, the Metroid was killed by none other than the resurrected Pirate leader herself. Its demise meant the apparent extinction of the entire Metroid species; it also demonstrated the Metroids' ability to show compassion.
After Samus Aran completed her second mission on Zebes, she spends a great deal of time in thought, reliving the death of the Baby at the hands of Mother Brain. Adrift in space and in memories, she receives a message codenamed "Baby's Cry", reminding her of her lost "child". Following the signal, Samus arrives at the BOTTLE SHIP.
In the Cryosphere, Samus finds a deceased Gigafraug showing signs of Metroid predation. Samus has doubts since not only would Metroids perish in the Cryosphere's cold temperatures, they were extinct thanks to the efforts of both the Space Pirates and herself.
Soon afterward, MB, posing as Madeline Bergman, tells Samus about "Project Metroid Warriors", in which Metroids were cloned from the Baby's particles that landed on Samus's Power Suit and are located in Sector Zero. She also explains that they made an AI of Mother Brain's intelligence to control them.
Samus heads to Sector Zero but stops short as an Infant Metroid pops up in front of her, reminding her of the Baby. When Samus decides to kill the Metroid, Adam shoots her in the back; the Infant sees her as food, but is also shot.
Adam explains that the cloned Metroids that have reached the mature larval stage are likely to have been re-engineered to remove their vulnerability to cold, making them virtually unstoppable; this also confirms that the dead Gigafraug Samus found earlier was indeed the subject of Metroid predation. He also states that the breeding project was named after him, though he was not actually involved in the project. He was petitioned for the authority to create the project, but he refused. However, scientists co-signed it to get the project running.
Adam shot Samus earlier to prevent her from interfering with his next course of action: because the Metroids are immune to Samus' weaponry, Adam goes to activate a self-destruct protocol on Sector Zero by causing severe damage from within, which detaches the sector from the station before the explosion. Seeing this as a suicide mission, Samus attempts to convince him to let her destroy the Metroids, but Adam ignores her, saying that she has work left on the BOTTLE SHIP. Adam succeeds in his mission to destroy the Metroids at the cost of his own life.
However, a Queen Metroid was kept in another part of the BOTTLE SHIP. It not only attacks Samus, but launches several other Metroids. Ultimately, Samus is forced to resort to an old tactic and uses a Power Bomb in the belly of the beast. it is currently unknown how MB succeeded in making an Infant Metroid reach the Queen stage outside of SR388's environment.
Metroid Fusion takes place shortly after Other M and it is "Metroid IV" in the timeline. On planet SR388, the Metroids had been the top predators, and with them gone the ecosystem was thrown completely out of balance. Samus was hired to protect some Federation scientists who were studying the recovery of the SR388 ecosystem. While they were on the planet, Samus was infected with an X Parasite, a highly dangerous organism who's species is quickly ravaging the planet. She was rushed back to Federation Headquarters with a minimal chance of survival. It had recently been discovered that the Metroids were the sole predators of the X Parasites; without the former to keep them in check, the X are rapidly reproducing and infecting all forms of life, taking their hosts' DNA in order to mimic them before moving on to their next host. Using this information, the Federation saved Samus by injecting her with a Metroid vaccine made from a DNA sample of the deceased hatchling.
With Metroid DNA fused with her own, Samus had gained immunity to the X Parasites and was now capable of absorbing them in their pure forms by merely touching them. She had essentially become the "Ultimate Warrior", making her the only being capable of combating the X and their horrific mimicries of countless bioforms that had now spread out into the Biological Space Laboratories in orbit above SR388. If a single X Parasite were to gain access to a host capable of piloting a space-faring vehicle, a galactic plague would be inevitable. The presence of Metroid genes in her body were not without consequence however, as she had gained the species' vulnerability to sub-zero temperatures, a weakness the X would repeatedly exploit throughout her mission.
Later in Metroid Fusion, it was revealed that the Federation had a secret Metroid breeding program going on (see Restricted Lab), presumably based on clones of the last Metroid. Contrary to the Metroid project on the BOTTLE SHIP, it would seem that the program on the BSL was intended for benevolent purposes. In any case, this program was destroyed by a powerful X Parasite mimicking Samus known as the SA-X. The entire laboratory was detached from the station and ejected into space just after Samus escaped, completely destroying the Federation's research. However, one Infant Metroid had escaped and advanced to Omega level. Worthy of note is the difference in size between this Metroid and the Omegas found on SR388, the latter of which were only slightly taller than Samus. The creature was blocking her path towards escaping the BSL; moments earlier she set course for the station to enter SR388's atmosphere and detonate in order to destroy all X Parasites onboard the BSL and the planet below. The Omega Metroid severely wounds Samus and the SA-X, the latter which had seemingly been drawn to the presence of both Metroids. Samus takes the opportunity in absorbing the SA-X, healing her completely and acquiring the Ice Beam which she uses to kill the Omega Metroid before boarding her ship.
At this point, the only known Metroid DNA remaining in the universe resides within Samus Aran, but any negative side-effects were likely removed during her absorption of the SA-X's "pure" genetic code.
|Zebes||Zero Mission • Raid on Planet Zebes • Final Conflict|
|Aether||Aether incident • Battle of the Hive • Dark Age • Fourth Battle of Torvus • Golden Age|
|Other Topics|| Bryyo dynasties • Cosmic Calendar • Cycle • Horus Rebellion • Metroids • Space Pirates (Assault on the Pirate Homeworld) • Species War |
Tetra Border Wars • The Treaty of Elysia • Year 20X5
|Biographies||Dark Samus • Ridley • Samus Aran|
|Natural Life Cycle|| |
|Zebes Metroids|| |
|Tallon IV Metroids|
|Aether Metroids|| |
|Phazon Metroids|| |
|Cocoons and Eggs|| |
|Artificial Metroids|| |
|Metroid Hybrids|| |
|Specific Metroids|| |
|Metroid Technologies|| |