Metroids are fearsome, flying parasites resembling jellyfish. The Metroid was discovered on the Planet SR388 in suspended animation, but was revived after 24 hour exposure to beta rays. On the return voyage to the Galactic Federation Headquarters, the GF starship was intercepted by Space Pirates who murdered the crew and stole the Metroids for reproduction as biological weapons.
Metroids latch onto their prey with incredible strength, making them nearly impossible to dislodge. While attached, they completely drain the life energy of their prey, leaving the mummified remains. They can only be removed by freezing the creatures or with the force of an explosive blast, techniques that are usually fatal to the victim. Their gelatinous shells reflect and absorb nearly every kind of attack, leaving them invincible to conventional weaponry.
Metroids will grow in size after consuming large amounts of energy. If enough energy is consumed, they will reproduce through mitosis, splitting into two. Metroids will also split if exposed to beta rays for a period of 24 hours. Their rapid reproductive cycle and the fearsome speed with which they consume their prey make them one of the most dangerous life-forms in the cosmos, potentially capable of destroying all of galactic civilization.
Freeze the Metroids with the Ice Beam, then quickly finish them off with five missiles. Metroids will only remain frozen for three seconds, and if they thaw, your missiles will no longer harm them. For this reason, do not enter Tourian unless Samus is equipped with the Ice Beam: otherwise, it will be impossible to make it through to Mother Brain. Should a Metroid latch onto Samus, quickly roll into a ball and drop bombs to dislodge it. Also, move through Tourian slowly, as Metroids can suddenly emerge from almost anywhere, including the ceiling!
Metroids are the titular enemy of the series.
Their design is loosely inspired by the Facehugger from Alien, which will also latch onto a victim’s head and insert a Xenomorph larva into the victim’s chest. Like the Facehugger, Metroids are nearly impossible to remove without killing their hosts and are a threat to galactic civilization. Although the Metroid latches onto its enemy using claws, the original artwork depicts the Metroids as multi-tentacled monsters.
Metroids are an artificial life-form genetically engineered by the Chozo and designed to eliminate the X parasite infestation on SR388. However, this plot point was not revealed until Metroid Fusion and was detailed in the Metroid manga.
Metroids are programmed to form a bond with the first sentient being they come in contact with.