Kago are small insectoid creatures that coexist with each other within large hives, which are caged inside a web of hardened biomatter. They don't actively cause any damage if their hives are left alone, but if fired on, individuals are expelled to defend their homes.
Kagos are first seen in Crateria, but are also found later on in Norfair. They appear as a green cage with glowing red biomass inside. The Kago colony can be destroyed if shot enough times, and when shot members of the colony will jump out and surround it, hopping around back and forth. Remarkably, Kago hives will violently shake the rooms in which they are found with every hit they take from Samus's weapons, suggesting these structures are strongly fixed to the ground. These can be used to collect energy and weapons, and do little damage in themselves as well. They are of very little threat to Samus, only becoming dangerous if large numbers of them are released.
In Sectors 2, 4, and 5 of the BSL Station, there lies an infected version of this creature and/or a mimicked variant, both caused by the X Parasites. It has a shiny green web cage, and the Kago within now glow with a slight purple tint. That is, if the biomatter within the cage is still a colony of Kago, as none of the insectoid members come out when fired on (although unused sprites exist within the game's code). When another free-floating X merges with one of these Kago-X creatures, it mutates even further, tripling in size and transforming into a towering purple cage with glowing green, pulsating insides. This form is vulnerable to both the Screw Attack and shinespark. They often block off certain areas, but can also be used by Samus if frozen to become very useful platforms.
While Kago insects do not spawn from their cage, they are fully programmed as enemies. They have no code allowing them to escape their cage. 
"Stand back and shoot the hive, then shoot what comes out."
- In Super Metroid, if Samus crashes into a Kago by shinesparking, she will be stopped by it. However, in Metroid Fusion, if she does this, she will pass through the Kago, although the Kago will not be harmed. This supports the theory of the Kago hives being built out of an incredibly solid matter that permanently fixes them to the ground.
- Metroid Fusion: The Official Nintendo Player's Guide refers to the vine Kago as a "living wall".
|Unused Bosses and Species|
|Metroid: Zero Mission||Crocomire • Ridley-2|
|Metroid Prime||Fireflea • Kraid • IceBoss • Ripper • Skree • Maggot • Kihunter • Sova • Chomper Fish • Experiment 7526 • Tallon Chameleon • Carnivorous Plant • Phazon Blastcap • Phazon Burrower • Zebesian|
|Metroid Prime 2: Echoes|| Dark Pirate Aerotrooper • Dark Shriekbat • Dark Sporb • Dark Triclops • Kenobite • Phlogus • Triclops • Zoomer • Sova • Icemite|
Metroid 1.5: Mad AI • Humetroid • Thrash-hunters • Shock beast
|Metroid Prime 3: Corruption||Advanced Pirate Militia • Advanced Shield Militia • Assault Pirate Militia • Assault Shield Militia • Big Metroid • Crocomire • Endocoon • Mantha • Phase Sprite • Phazite Armored Trooper • Phazon Tentacle • Reptilicus-G • Salamander|
|Super Metroid||Bang • Reflec • Stoke|
|Metroid: Other M||Zebesian|
|Metroid Fusion||Geega • "Hive" • Kago spawn • Skree • Toxic Gas|
|3DS Metroid game||Boss Creature|