Reos (リオ, Rio) are enemies from the Metroid series.
Reos (also referred to as "Rios" in early Metroid games) are inhabitants of Zebes who resemble flies, and are capable of harming Samus. In large groups, they pose a serious threat. They possess sharp claws and can be resilient. In Other M, Reos are seen appearing from nests of biomass: they can latch onto Samus, forcing her to shake them off.
Reos appear as enemies. They remain stationary in the air, and occasionally attack by swooping down.