Zoros - also known as Zeros - are larvae or caterpillar-like organisms found on the planet Zebes, although some evidence suggests that they are not indigenous to the planet. Zoros seem to grow exponentially fast, shedding their exuvia quickly and often. However, it is also possible but not particularly probable that they use their old moultings as a temporary home. Despite appearing harmless, they are in fact dangerous to the touch, as one would naturally expect on a deadly world like Zebes.
Despite the destruction of Zebes during Samus Aran's second mission there, a cluster of them were found aboard the Biologic Space Laboratory Research Station, although how they got there is up to some debate. These Zoros were quickly imitated by the X Parasites and subsequently modified by them, causing them to become naturally larger and be covered in spines that were deadlier than (presumably) their bite. Zero-X are found in unnatural colors, coming in red in blue as opposed to their natural green tint.
By the time Samus had destroyed the Pogo X in the Tropical Sector (TRO), all Zoros had hardened into a seemingly-indestructible chrysalis. Even later, these chrysalids had become transparent, revealing a living organism just beneath the surface. As it turned out, these hatched into mimicked Ki-Hunters.
They were also found aboard the Bottle Ship where they resided alongside Ki-Hunters. They can only be harmed by Bombs, Power Bombs, the Plasma Beam, and the Screw Attack. If they are hit by any other weapon, they will enter a webbed cocoon, and metamorphose into Ki-Hunters.
- At least in Super Metroid, Zoros have a 99% chance of dropping a Power Bomb and 1% chance of dropping an Energy Capsule when killed.