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"The Yeerk pool. That vast cavern the size of three Astrodomes. A Yeerk complex underground. Beneath the foundations of half our city. Storage and control center buildings. Docked spacecraft. Diverse alien species moving rapidly about their business, united in a common goal: the conquest of humanity. And there, at the center, was the pool itself. Sludgy, leaden liquid teaming and churning with Yeerk slugs. In their natural state. Vulnerable there, and there only."

The Yeerk pool is a special body of water where the Yeerks must return to every three days to absorb Kandrona rays. A large Yeerk Pool complex was created underneath half of the Animorphs' hometown in California and served as the central hub for the Yeerk Empire during their invasion of Earth. This pool was later destroyed by the Animorphs.


"Yeerk pools are generally large and elaborate. They are an important part of Yeerk life. The centers of their lives, really. The pools are, for the Yeerks, what forests and meadows are to Andalites."

Yeerk pools are the natural home environment of the Yeerks. Naturally formed pools exist on the Yeerk homeworld, where Yeerks live, breed and die. The sun of their homeworld emits Kandrona rays that naturally project into the pools, giving the Yeerks the sustenance they require.[2] The pools are the color and texture of molten lead.[3] Upon their exodus from the Yeerk homeworld, the Yeerk Empire created makeshift pools on their ships, with a Kandrona machine beaming artificial Kandrona rays. They also built large scale Yeerk pools on the surface of many of the worlds they invaded, such as the Hork-Bajir homeworld[2] and the Taxxon homeworld, where unhosted Yeerks resided.[4]

Since the Yeerks needed to return to the pools every three days to acquire the necessary Kandrona rays, the pools were an important part of their lives and a central location of their society. As a result, the Yeerk Empire elected to make their surface Yeerk pools large and elaborate.[5]

California Yeerk Pool[]

"They could have played the Superbowl in there and had room left over for a couple of malls. It was like a giant bowl turned upside down, all carved out of solid rock. At the very top of the bowl was the faint outline of a hole. I thought I could see stars through it. All around the outer edges of the cavern I could see other stairways, like ours. They seemed to come from every direction, appearing out of the rock walls, and leading down to the floor of the cavern. [...] At the very center of the cavern was a pool, like a small lake, maybe a hundred feet across, and perfectly round. Only the water wasn't exactly water. It moved more like melted lead, and was about the same color. [...] Near the edge of the pool were cages. In the cages were Hork-Bajir and human beings. Some of the humans screamed for help. Some cried silently. Some just sat and waited, all hope lost. There were adults there. And kids. Women and men. More than a hundred, packed ten to a cage. The captive Hork-Bajir were kept in separate, stronger cages. They paced and howled and slashed at the air with their bladed arms."

The California Yeerk pool resembled a giant turned bowl[3] that was so large it was described as being the size of three Astrodomes.[6] In the center of the cavern was a large, round Yeerk pool that spanned a hundred feet in length.[3] The pool's liquid, which contained water,[7] was a thick, sludgy substance, with a smell not dissimilar to manure, at least to a fly's senses.[8] The pool also had a gentle, circular current.[9] At the top of the cavern was a hole to the surface, allowing oxygen into the underground complex[3] as well as Kandrona rays, which were beamed from the top of the EGS Tower in the Downtown district, to directly hit the pool.[5]

By 1997,[10] the elaborate California Yeerk pool complex was active, with a multitude of unhosted Yeerks in the pool and a system set in place for infestation and feeding. Two steel piers were installed over the pool, one for Controllers leaving their host bodies to feed and the other for infestation/reinfestation. Near the edge of the pool were two types of cages, one type for humans and the other, which was stronger, for Hork-Bajir. The first pier, dubbed the loading station, was manned by a group of Hork-Bajir-Controllers, who assisted their fellow Controllers in leaving their hosts. They would then drag the hosts to the cages, keeping ten human hosts per cage. The second pier, dubbed the loading station, was where the Yeerks re-entered their hosts, who were removed from the cages by Hork-Bajir-Controllers and had their heads thrust into the pool. The cages were only used for involuntary hosts; voluntary hosts would simply deposit their Yeerk into the pool and then retreat to another section of the pool complex, and then willingly walked down the second pier to become reinfested.[3]

Aside from the central pool and the piers with the cages, the rest of the pool complex contained other buildings, such as sheds,[3][9] offices, storage rooms,[6] and a cafeteria.[5][11] A docking station for spacecraft such as Bug fighters was also installed, where a maintenance crew worked to maintain the ships.[12]

The California Yeerk pool complex contained over a dozen different passageways that connected with various locations in the city. These passageways served as the various secret entrances and exits to the Yeerk pool complex.[3] One of them led into the junior high school where high-ranking Yeerk Iniss 226 worked, although it was sealed off after the Yeerks noticed that the Animorphs had used it.[13] Other entrances included The Gap at the mall, the local movie theater,[5] and few McDonald's locations where managerial stuff and employees were all infested.[9][7][14] When the Yeerks created their own community center, they added several new passageways from the community center leading into the Yeerk pool complex.[6]


Yeerk homeworld[]

To be added

Hork-Bajir homeworld[]

To be added

California Yeerk Pool[]


"This wasn't some little group of alien bad guys we were dealing with. To build this underground city, these guys had power we couldn't even imagine. That's almost what it was. A city. There were buildings and sheds all around the rim of the cavern. And we could see yellow Caterpillar earthmovers and cranes at work on the far side of the cavern."

In 1991, Edriss 562 landed on Earth to study humans and gauge whether they would serve as suitable hosts for the Yeerks.[11] By 1995,[15] she set the foundation for the Yeerk Empire to begin a stealth invasion of Earth,[11] based out of a city in California.[16] As it was a secret invasion, the Yeerks could not create a surface-based Yeerk pool and thus elected to construct an elaborate underground pool complex to serve as their central hub. Digging underneath half of the city, the Empire carved a vast underground cavern out of solid rock.[3]

By 1997,[10] the elaborate California Yeerk pool complex was active, with a multitude of unhosted Yeerks in the pool and a system set in place for infestation and feeding. Two steel piers were installed over the pool, one for Controllers leaving their host bodies to feed and the other for infestation/reinfestation, as well as cages around the pool to contain the hosts while their Yeerks fed.[3]

While the pool, piers and cages remained in the center of the complex, the rest of the cavern housed storage sheds,[3][9] offices, as well as a cafeteria so that human hosts could eat.[5][11] Voluntary hosts also had a section where they could lounge in chairs and watch television as they waited for their Yeerks to finish feeding.[3] Various entry and exits ports for spacecraft were also added, allowing for Bug fighters and other aircraft to enter and dock within the pool complex.[6][12]

Several long staircases were embedded into the rock wall, leading to over a dozen different passageways that led into town. One of them led into a janitor's closet of the local junior high school where high-ranking Yeerk Iniss 226 worked. The janitor's closet entrance was hidden behind a retractable wall, and would open when the faucet was turned to the left and a nearby hook was turned to the right.[3] The Yeerks also added passageways leading into other secret entrances, such as The Gap at the mall and a local movie theater.[5] Despite all of this, the Yeerks were not fully satisfied with the underground city they had built and wished to keep expanding the Yeerk pool complex. In order to aid them in the cavernous expansion, various Caterpillar earthmovers and cranes were brought into the Yeerk pool.[3]

Animorphs' First Visit[]

"This is gigantic. This isn't just under the school. This is under half the town. Those stairways must lead up to a dozen secret entrances. Jake, they have this entire area set up with secret passageways. Oh, man. This is worse... this is so much worse... So much bigger..."
Marco to Jake[src]

On a Monday[3] in 1997,[10] the Animorphs decided to enter the Yeerk pool complex through their junior high school's janitor's closet in order to save Jake's brother Tom. A hundful of Controllers used the school's primary entrance to enter the building after hours; one of these Controllers was a police officer, who had kidnapped Cassie and was dragging her through the hallway into the Yeerk pool entrance. The Animorphs then followed suit and used the janitor's entrance to access the pool. They then descended the various steps for minutes, shocked at the mere size of the underground complex and forced to hear the screams and cries of the various victims who were being tossed in cages.

The Animorphs noticed Cassie being dragged to the infestation pier and decided to save her. As Tobias flew up above in his red-tailed hawk morph, Jake, Rachel and Marco relocated near a shed. Marco pulled Jake behind the shed asking him to not let himself get infested, only to be spotted by a trio of Controllers. Rachel, who had been unspotted, morphed into an African elephant and crushed the Hork-Bajir-Controller and the Taxxon-Controller before tossing the human-Controller across the cavern. Jake and Marco then morphed into a Siberian tiger and Silverback gorilla respectively and attacked the various Hork-Bajir and human-Controllers who started to rush towards them. Defeating them with ease, the Animorphs made their way to the cages and freed the hosts before they managed to prevent Cassie from being infested.

Jake vs

Jake in tiger morph attacks Visser Three

As Cassie morphed into a horse and started to help them herd the freed hosts towards the staircase they had come from, they were impeded by Visser Three, who believed they were Andalites in morph. Visser Three then morphed into an Unnamed Creature with Eight Heads and Eight Legs that could shoot fireballs out of his mouth and began firing them at the Animorphs as well as the freed hosts. His fireballs successfully hit many of the freed Hork-Bajir and human hosts, many of whom either burned to death or were recaptured. As the Animorphs, minus Tobias, ran up the stairs, the Visser followed them, although the stairway passage eventually became too narrow for him. After Tom was knocked off the stairs by Visser Three, Jake attacked the Visser before leaping back to join his friends, along with one freed woman, in escaping the Yeerk pool through the janitor's closet.[3]

Tobias, who had been flying up high within the complex, clung to a hidden rock face to avoid being struck by one of the Visser's many fireballs.[17] He was eventually able to escape, although he remained in morph for over two hours and was permanently trapped in the body of a red-tailed hawk.[3] As the Yeerks noticed that the Animorphs had used the janitor's entrance at the junior high school, they sealed it off in an attempt to prevent the "Andalite bandits" from accessing the pool again.[13]

Destruction of the Kandrona[]

To be added

Oatmeal Warfare[]

To be added

Saving Aftran[]

To be added

Tobias' Torture[]

To be added

Saving Cassie[]

To be added

Unit 0[]

To be added

Gas Explosion[]

To be added

Freeing Eva[]

To be added

Animorphs Captured[]

To be added


To be added

New Pool Construction[]

To be added


California Yeerk Pool:

This section requires expansion


Elfangor eye closeup andalite chron "Someone took a picture of me? Not cool. Do you see what I'm wearing? I'm Spandex-boy. Totally not cool."

The image gallery for Yeerk Pool may be viewed here


  1. According to #54: The Beginning, it is in California. VISSER also reveals it is mid-sized coastal city, with series co-author Michael Grant describing the fictional city as a blend between Orange County and Long Beach.
  2. 2.0 2.1 The Hork-Bajir Chronicles
  3. 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11 3.12 3.13 3.14 3.15 The Invasion
  4. The Andalite Chronicles
  5. 5.0 5.1 5.2 5.3 5.4 5.5 The Stranger
  6. 6.0 6.1 6.2 6.3 The Illusion
  7. 7.0 7.1 The Sickness
  8. The Capture
  9. 9.0 9.1 9.2 9.3 The Underground
  10. 10.0 10.1 10.2 The Andalite Chronicles is said to take place 10 years after the 1966 Yeerk exodus of The Hork-Bajir Chronicles and 21 years before Elfangor met the Animorphs. This places it in 1976, meaning the Animorphs met Elfangor in 1997.
  11. 11.0 11.1 11.2 11.3 VISSER
  12. 12.0 12.1 The Revelation
  13. 13.0 13.1 The Visitor
  14. The Arrival
  15. In VISSER, Edriss 562 launches the invasion of Earth and fakes the death of her host, Eva. In #1, Eva is said to have died/disappeared two years prior. As #1 takes place in 1997, this places Eva's disappearance, and the beginning of the invasion of Earth, in 1995.
  16. The Beginning
  17. The Test
Andalite technology Dome Ship | Escafil Device | Hirac delest | Mirrorwave call | Z-space transponder | Morphing | Mag-Hover Truck | Quantum Virus | Shredder | Gleet Bio-Filter | Prion Virus
Yeerk Technology Anti-morphing ray | Dracon beam | Gleet Bio-Filter | Kandrona | Kandrona Rays | Nova-class Empire Ship | Pool ship | Blade ship | Mag-Lev Train | Hunter Robot | Yeerk Pool | Bug fighter
Ketran Technology Explorer | Time Matrix | Mapping Crystal Quadrant 3 | Uninet | Adge
Other Dropshaft | Ixcila | Pemalite crystal | Pemalite ship | Skrit Na Saucer | Hawjabran Colony Ship | Hawjabran Freighter