Reo, occasionally written Rio, are small, fly-like creatures that are native to Zebes. They live in the caverns of Brinstar, and will dive at any creature it spots. On the Bottle Ship, they are seen coming out of nests of biomass. Whether this is part of their natural life cycle or a mutation caused by the Galactic Federation is unknown. Also in Other M, the Reo are capable of gripping on to Samus, forcing her to shake them off. The X mimicked Reos on the B.S.L station, they act the same as in previous appearances. They are generally enemies of low threat, but can be dangerous in groups.
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- In older games, Reo is spelled Rio, but has been spelled Reo in all recent games.
Reos swarm around Samus in Other M
- "These are also pretty strong. They zoom down to attack Samus from the upper walls. The red ones are stronger then the yellow ones." Metroid Instruction Booklet, Pg 29