When an Eyon detects an intruder, it will fire a sustained green energy beam from its pupil, which is only capable of vertical movement, until stunned by a bright flash (any of Samus's beams) or until it is destroyed with a powerful blast, such as those created by Samus's Charge Beam. When several Eyons become active at once, the resulting series of beams are an effective blockade against unequipped enemies. A large group of Eyons will awaken only after Samus obtains the Charge Beam, though now Samus will be armed against them.
Apparently, when Eyons die of natural causes they petrify, still latched to the surfaces where they originally existed.
- "Immobile organisms entirely composed of ocular tissue. Capable of launching sustained energy beams when active, the Eyon is sensitive to light and will close shut if a bright flash ignites nearby." — Logbook "Eyon" (Metroid Prime)
- "This petrified organic matter looks like a rock carved into the shape of an eye." —Scan Data (Metroid Prime)