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The Alpha Metroid is the fourth stage of a typical Metroid's life cycle, appearing in three games, Metroid II: Return of Samus, Metroid Fusion and Metroid: Samus Returns.

The creature's insect-like appearance is a large departure from its prior and well-known larval form. This metamorphosis will only occur if a Larva Metroid is inhabiting its homeworld of SR388, or a replica of it. From this stage onward in the species' life cycle, a Metroid can no longer be frozen with the Ice Beam, but can be killed with Missiles regardless. After an unknown period of time, the Alpha Metroid will grow into a Gamma Metroid.

Samus Aran encountered fifteen Alpha Metroids during her mission to SR388.

Physiology Edit

An Alpha Metroid molts from the topside of a Larva Metroid's translucent membrane. The development has granted it new physical features: two blue compound eyes, a central horn, two small tusks, four budding limbs and a plated exoskeleton growing along the dorsal region. The Metroid now resembles an arthropod, and the species' characteristic membrane and red nucleus are now located on its underbelly.

The remake Metroid: Samus Returns has made slight alterations to the Alpha Metroid's appearance. A leech-like mouth has been added between its two compound eyes, the latter which are now red. The tusks and horn now function as an additional set of fangs for the new oral cavity.

Absent nuclei Edit

Unlike Larva Metroids which possess four nuclei within their large membranes, Alpha Metroids' have a single nucleus housed in their smaller membranes; it is unknown what becomes of the other three during the metamorphosis. However, due to the fact that a larva leaves nothing but an empty torn membrane when it becomes an Alpha Metroid, it can be logically assumed that the missing nuclei, along with the larva's fangs and muscle tissue, were re-purposed into creating the organism's new body (similar to stem cells). The remaining nucleus is carried within a new membrane for the rest of the Metroid's life cycle.

Coincidentally, Alpha Metroids and all subsequent forms can no longer be frozen but are readily susceptible to concussive weaponry, contrary to Larva Metroids' near invulnerability unless exposed to cold temperatures. This disparity in defensive strength may be determined by the number of nuclei present on their bodies. As for their newfound immunity to the Ice Beam, it is likely a result of the exoskeleton they develop as they grow.


The Alpha Metroid has very basic and straightforward movements, so it does not pose any large threat. Five Missiles on the tender underside will take this creature down. Its only means of attack is ramming, as it lacks the life energy drain of its predecessor, making it one of the weakest stages of a Metroid's natural life cycle.

The creature can perform new attacks in Samus Returns. They will make large swooping motions in an attempt to ram Samus, which can be parried with her Melee Counter and leave it open for damage. The Alpha Metroids can sometimes deploy a thin layer of electricity over themselves before conducting their ramming maneuvers. They will also drop harmful electrical spheres from their membranes, which Samus can destroy for pickups. These electric-based traits are seemingly a precursor to the Gamma Metroid's more extensive control over the element.


"This the [sic] shape of a Metroid after its first molting."


  • Mochtroids, which are defective clones of Metroids created by Space Pirates, also possess a single nucleus. It is much smaller than an Alpha Metroid's however.
  • In Metroid Prime, there is a Tallon Metroid designated as Metroid: Alpha Type, despite not having any relation to an actual Alpha Metroid.


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