I'm reading huge bio-signs, so I hope your missiles work...

Adam Malkovich

Arachnus is a species native to SR388. At the near-top of the food chain, they are very fearsome predators. The biped is distinguished by its three-fanged maw, segmented eyes, elongated neck, a hard shell on its back, and the large claws on its forearms. It is known to curl into an armored ball when threatened in order to jump towards its target in an attempt to ram it, and will uncurl periodically to swipe with its claws or spit fireballs from its mouth.

Metroid II: Return of SamusEdit

In Metroid II: Return of Samus, Samus Aran can fight an Arachnus. It is an optional boss and defeating it will give Samus the useful Spring Ball ability. It is found posing as an Item Sphere in the hands of a Chozo Statue. Only Morph Ball Bombs will damage it. An easy way for Samus to defeat it is by trapping it behind the statue on the left side of the room; she can then enter Morph Ball form and lay bombs every time Arachnus attempts to escape.

Metroid FusionEdit


Arachnus-X in Metroid Fusion.

In Metroid Fusion, the first boss Samus encounters is an Arachnus, although this one is actually an X Parasite mimic (she witnesses a Core-X combining with several X to imitate the organism).

Through gene manipulation, the X have not only changed its body's pigmentation and increased its size (making it taller than Samus), but they have also enhanced its abilities (the fireballs now arc toward the ground, causing a wave of flame-pillars to erupt) and given it a new attack that is not normally in its genome (the ability to launch sonic waves from its claws). It possesses increased physical strength as well, given the fact that the Arachnus-X can cause a small earthquake (causing Samus to lose her grip if she is holding onto a ledge) by ramming against a wall in ball form.

It is a relatively easy fight as Arachnus in Fusion is one of few bosses Samus can damage with her basic Power Beam, though her newly recovered Missiles are much more effective. The boss has only 150 health, and the Core X has 30. Once Samus defeats Arachnus and absorbs the Core-X that is left behind, she regains her Morph Ball ability.

Metroid: Samus ReturnsEdit

The Arachnus returns in Metroid: Samus Returns, a remake of Metroid II. The boss's attacks are now more similar to Fusion, including swiping projectiles and ramming into Samus in ball form. It will also lob fireballs at her. The Arachnus can be damaged using Beam shots, Missiles and Bombs, the latter of which will knock the creature out of ball form. When killed, it will leave the Spring Ball behind once again.


Metroid II: Return of SamusEdit

Arachnus artwork

"It will roll up its body like an armadillo, then rush at Samus."

Metroid FusionEdit

"Native life-form of SR388. They will roll themselves into balls and attack. Dodge and attack with missiles."


  • The Arachnus encountered in Metroid II had the ability to jump while curled up in its shell. It may have been using the Spring Ball item that it had acquired beforehand, as the battle takes place near a Chozo Statue and the item emerges from the remains of the creature upon its death. This phenomenon can also be seen in the Ing Sub-Guardians from Metroid Prime 2: Echoes, as they release the power-ups they stole from Samus upon their demise.
  • The X Parasite mimic in Metroid Fusion supports this theory - it is never seen leaping into the air in ball form because it does not possess the Spring Ball. It is possible, however, that the jumping ability is a natural aspect of the species and the Arachnus-X does not display this ability in Fusion due to its increased size. Another example is the X-infected Yakuza from the same game, as it utilizes the Space Jump ability during the second phase of the battle.
  • The Berserker Lord's theme is an arrangement of the Metroid Fusion Arachnus theme. The Berserker Lord also resembles the Arachnus, and both appear as the first bosses of their games.
  • In trailers for Fusion, Samus is seen fighting Arachnus in a much larger area than the final game, featuring scenery from Sector 1.
  • Oums resemble the ball form of an Arachnus. The Griptian acts similar to the Arachnus as well.
  • The Arachnus in Metroid Fusion also bears similarities to the Omega Metroid in the same game. Their death sequences both involve them thrusting their heads back repeatedly while roaring and exploding, both are larger forms of bosses found in Metroid II, they both have clawed mouths and claws on their hands, they both have a partly hunched posture and they both walk forwards slowly towards Samus during their battles with her.
  • The Arachnus in Metroid II does not have its own battle music, although this is changed in Samus Returns. It is also the only boss in Metroid II which is not part of the Metroid life cycle. The Arachnus' theme from Samus Returns can be heard here.
  • In the later Japanese version of Fusion (and likely II as well), this creature is known as the "Marukara" (マルカラ) or "Mulcalah", which carried over to the Metroid Prime & Fusion Original Soundtracks.
  • In Metroid Fusion, the Screw Attack can kill Arachnus in one hit, via hacking. This is likely due to its vulnerabilities being the same as a regular enemy, due to Samus being able to damage it with the basic Power Beam.
  • The Arachnus' artwork for Metroid: Samus Returns is identical to its original Metroid II art.


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