Cover from Animorphs #29: The Sickness, showing Cassie morphing into Illim, a Yeerk.
|Leader(s)||Council of Thirteen
|Home world||Yeerk Homeworld|
|Official language||Galard, English|
Yeerks are a fictional extraterrestrial species from the book and television series "Animorphs" written by K. A. Applegate and published by Scholastic. It is also the main antagonist. A yeerk can infest and take control of many living creatures as long as its brain is large enough.
In the series, a Yeerk is described as a parasite that takes over the body of another being by infesting a host's brain through their ear canal. It resembles a small, grey-green slug about five or six inches long (see The Capture, first U.S. print edition page 150). Yeerks in their natural state have decent senses of smell and touch, but they are blind until they enter a host, as they do not have eyes. They possess antennae-like protrusions called palps, as well as osmosis nodes, small organs that process nutrients in the Yeerks' native pools. Although the presence of a circulatory system of some kind is debatable, apparently Yeerks have no hearts, as evidenced by the description of a human morphing into a Yeerk, in which the human heart stops and dissolves away completely.
Yeerks communicate in their natural state using a language of ultrasonic squeaks, and use sonar to get a basic picture of the surroundings. The process of infestation by a Yeerk is not totally painless, but it does not hurt as much as it seems like it should, as a numbing chemical is secreted to anesthetize and dilate the ear canal itself so that the slug-like Yeerk will not cause any physical harm to the host. It is able to manipulate and puncture a variety of alien ear canal structures including bone and membrane to reach the brain. As the Yeerk reaches the eardrum and other ear canal structures, it pushes them aside.
After the process of infestation, the Yeerk flattens itself into what has been described as "3 parts, two wrinkled, one smooth", which is the brain. From there, all control is submitted involuntarily to the Yeerk (however, the host may fight and very rarely win). At this point, the host has no control over itself, no secrets, and no privacy. The Yeerk can even play with the memories of its former host. Although control can be returned to the host by the Yeerk, this does not occur often as most Yeerks prefer their parasitic relationship to a symbiotic one.
Yeerks cannot stay within their hosts for more than three Earth days. After this period of time, they need to bathe in a Yeerk pool and absorb Kandrona rays, the rays of their home sun. Without these rays, a Yeerk eventually starves.
However, there are two ways for Yeerks to survive without Kandrona rays, one terrible and cruel way being to eat other Yeerks. This cannibalism is not normal, a taboo and is only displayed by one Yeerk, Esplin 9466 the lesser (Visser Three's twin sibling) after being cut off from Yeerk society by his twin. He kills Human-Controllers, opening their heads with brute force and eats the Yeerk inside with his maw.
Yeerks may also survive a lack of Kandrona rays by consuming instant maple and ginger oatmeal, although its effects are narcotic and cause the Yeerk to become insane, dependent and trapped within its host indeterminately, without the need to feed in a Yeerk pool. The host may regain some control of its body from time to time, while the Yeerk has lapsed into narcotic-induced lack of control. Usually the Yeerk is not intelligible after full addiction has occurred, since the chemicals in the oatmeal damage part of its brain stem. The Animorphs discover this upon investigating a man named George Edelman who attempts to commit suicide. Edelman is put in an insane asylum, where the Animorphs follow him and discover the Yeerks' weakness to the oatmeal. The Yeerk in his head has succumbed to this weakness, and Edelman is able to speak and move freely, except when his Yeerk seizes control and rants unintelligibly in alien languages. Yeerks may intake oat flakes by way of their hosts. How the dietary fiber exactly reaches the brain is unknown.
Yeerks reproduce through fusion. Three parent Yeerks merge into a single organism, which then breaks apart into hundreds of separate grubs, destroying the parents in the process. Sometimes twins are born when two Yeerks are born from one grub (Visser Three's twin started a Yeerk website to find out where Controllers lived (his host was the World Wide Web Founder) so he could eat the Yeerk inside making him a Cannibal.) ; thus Yeerks have no living parents.
Yeerks do not have different sexes; presumably any three random Yeerks can reproduce. Nevertheless, the Yeerks normally use gender pronouns (he/she) in the novels based on their host's gender - usually by a human or Andalite (Chapman/Iniss 226 and Visser Three/Alloran, or by the Yeerk adopting the gender personality of their host (Karen/Aftran 942 or Taylor/Sub-Visser 51).
So far, Yeerks have enslaved about 18 different kinds of alien species, completely or partially, including Hork-Bajir, Taxxons, Gedds, the Nahara (never seen in the series), Leerans, Garatrons, and of course, humans. According to a Yeerk named Temrash 114, the Yeerks may also have taken over creatures known as the Sstram and the Mak, neither of which is ever seen in the series.
The Yeerks also have the ability to infest Andalites; however, they are never successful in truly enslaving them. The only Andalite body that the Yeerks have ever manage to take over was War Prince Alloran-Semitur-Corrass, turning him into Visser Three.
The Yeerks have a pseudo-diplomatic relationship with the metamorphic Skrit Na, but do not infest them due to the Skrit Na's lifestyle: The cockroach-like Skrit will sometimes unexpectedly cocoon itself and emerge as a Na over a year later, trapping any Yeerk inside, meaning death by starvation.
The Yeerks have also tried to enslave Hawjabrans and Ongachics, but they have failed on both accounts. One, because the Ongachic race is completely nomadic and spread out through the entire galaxy. Two, because Hawjabran brains are spread out in little nodes throughout their bodies, so the Yeerks can never completely control them.
There are some species that the Yeerks do not know about, and therefore have not tried to infest, such as the Iskoort, since Yoort (yeerk-like part) are really like Yeerks, but civil, and they have never infested anyone else after the Isks (bio-robot bodies) were built for them. The Iskoort species is actually related to the Yeerks, even though they do not look at all similar, but not a lot of them know that, or have even heard of them.
Since the Yeerk has access to all parts of the brain (except with Hawjabrans), it is able to pass flawlessly as its host (now called a Controller) so that nobody else suspects that there is, in fact, a secret invasion of their planet. Another result of this is that hosts and Yeerks can sense each other's thoughts and feelings; while this usually is the extent to the mental connection, it seems hinted that the mental bond between the two can result in identity confusion, as in the case of Taylor. Another case of notice is that of Visser One, who, after marrying and having children through one of her hosts, felt an actual romantic and maternal bond to her "family."
Evidently, morph-capable Yeerks morph with their hosts and are extruded into zero-space along with the host's own morphed mass. This is shown in The Capture, when Jake, as a Controller, morphs into an ant. An ant is far smaller than a Yeerk, so otherwise Jake would have been killed by destruction of his head.
List of controllers
- Jake's brother, Tom (Temrash 114, later unknown)
- Andalite Prince Alloran-Semitur-Corass (Esplin 9466 Primary; Visser Three, later Visser One)
- Marco's mother, Eva (Edriss 562; Visser One)
- Mr. Hedrick Chapman (Iniss 226)
- In #1: The Invasion, the kids are approached by a controller policeman. He later takes Cassie to the Yeerk pool, and he is mentioned by Tobias in book 13, The Change.
- In #6: The Capture, Jake was a Controller (Temrash 114)
- In #8: The Alien, Gary Kozlar (Eslin 359)
- Park Rangers in books 9, 10, 16, and 14 were Controllers
- In #12 The Reaction, Jeremy Jason McCole
- In #13 The Change, a reporter mentioned by Tobias
- In #14: The Unknown, 5 horses were Controllers
- In #16: The Warning, Joe Bob Fenestre (Esplin 9466 Lesser)
- In #19: The Departure, Cassie and a girl named Karen were Controllers (Aftran 942)
- In #20 The Discovery and onwards, David's parents. After #22 The Solution their status is unknown.
- In #22 The Solution, various policemen were Controllers
- In #29: The Sickness, Ax and Cassie were Controllers (Aftran 942), as was Mr. Tidwell (Illim)
- In #33: The Illusion and #43: The Test, Taylor (Sub-Visser 19)
- In #35: The Proposal, William Roger Tennant and a few TV people are human-controllers
- In Megamorphs #4: Back to Before, Tobias was a Controller (Odret 177)
- In #41: The Familiar, Cassie and Marco were Controllers.
- In #54: Ax becomes a Controller known as "The One".
The Yeerk homeworld has various satellites, one of the natural ones is a moon called Madra. Yeerks inhabit a homeworld with a dark green and yellow, lightning-torn sky. The ground is largely dark rich soil, and roughly circular Yeerk pools dot the surface, presumably connected to each other somehow, but this is not explained.
Individual pools have names, such as Sulp Niar. Yeerk pool water is a sludgy grey, filled with nutrients Yeerks need, besides Kandrona rays. There are no more than a hundred animal species on the Yeerk homeworld, among them the Gedds, which became the Yeerks' natural host, nearly a symbiotic relationship. The Yeerk home world is surrounded by Andalite ships that stop anything from coming in or out.
A Vanarx, also known as a "Yeerk-bane", is a big long purple tube-like creature that has a round mouth full of teeth, it is native to the Yeerk homeworld, and appears to be the Yeerks' only natural enemy. It latches itself onto the head of a Controller, sucking out the Yeerk inside and eating it. Visser Three morphs a Varnarx in Book #2: The Visitor as a means to eliminate useless subordinates without apparently killing or hurting the host-body, and to scare Chapman.
Sometime in or before the Earth year 1966 (Yeerk date: Generation 685, mid-cycle; each Generation is roughly two Earth years and divided into three cycles), the first Andalites arrived on the Yeerk homeworld, led by the Prince Seerow. Seerow pitied the Yeerks' physical drawbacks despite their capacity to learn, and set up the Andalite-Yeerk Peace and Cooperation Center on the Yeerk homeworld. He and other Andalites taught the Yeerks how to write down the Yeerk language phonetically, and taught them what lay beyond their green-clouded sky.
Once armed with the knowledge of space-faring technology and similar sciences, certain Yeerks rebelled against the Andalites, taking them off-guard and killing many people during the escape with several small Andalite ships and a few transports. The Yeerks stopped on the far side of their planet to siphon up large quantities of Yeerks from Yeerk pools before fleeing the planet, eventually to become the Yeerk Empire. Andalite forces began to patrol the Yeerk homeworld in orbit to make sure no more Yeerks entered, attempted contact, or attempted to leave.
The Yeerk Empire was gutted devastatingly with the death of seventeen thousand, three hundred and seventy-two Yeerks flushed from the Yeerk Pool Ship's onboard pool during the final blatant attack on Earth. The Empire's loss of Earth was caused largely by the Animorphs, and surrendered Yeerks were given amnesty by the Andalite military if they became nothlits, or trapped in one morph forever. A single Blade Ship (holding the morphing cube) escaped with the intent of creating a new Yeerk Empire, and allied with a dangerous, cult-like, otherworldly entity known only as The One. The One captured Ax when he boarded a dead-in-space ship which concealed the Blade Ship. Not much is known about The One except that it is possible he, or it, is allied with the Kelbrid, he/it is possibly more powerful than the Ellimist, and he/it can assimilate other life forms.
Yeerk names end in numbers, which designate which number grub they are (i.e. Aftran 942 is the nine hundred forty second grub to emerge from the Aftran tri-parent). In the case of twin, both are given the same number, which ends in a double number. For example, Visser Three is Esplin 9466 Primary, and his brother is Esplin 9466 Secondary. The higher twin is considered to be superior to the other.
In the Yeerk military, each of them is ranked one after the other, and are referred to by title and number. The lowest rank apparently does not earn the person a title (for example, the Yeerk Essam 293 is only ever referred to by name). The next rank up is Sub-Visser, which is equivalent to a colonel or some such officer rank; after being promoted above sub-visser level, Yeerks may become one of 47 Vissers, which are equivalent to generals or to Andalite Princes.
As a note, earlier in the series, the name number and rank number were the same thing (for example, Temrash 252 was promoted to being Temrash 114) - Vissers were of the numbers from 1 to 47 and Sub-Vissers from 47 to 100; however, this was later retconned by K.A. Applegate with Yeerks remaining with the same number as their "name", no matter what their rank. For example, Visser Three's "name" is still Esplin 9466 Primary, while Visser Three is his rank.
The head of the Yeerk Empire is the Council of Thirteen, the leader of which is the enigmatic Yeerk Emperor; however, to prevent assassination, his identity is never known by anyone but the Councilors. Of the thirteen council members, two remain always concealed. They wear very dark red, almost black, robes, and those Council members who have Hork-Bajir hosts wear a thin mesh under the robes to prevent them from tearing. Thirteen seems to be a symbolic number for the Yeerks, as trials also have thirteen guards on duty.
There is a faction of Yeerks who have formed an entity known as the Yeerk Peace Faction, which opposes the wars led by the Empire in secret and whose members, who may be Yeerks and/or their hosts, oppose involuntary infestation.
There exists an offshoot of the Yeerks that was taken from the homeworld millennia ago: the Yoort. The Yoort have long since changed from taking hosts, and have created symbionts; they genetically engineered a species, the Isk, with whom they have a symbiotic relationship. The joint species is called Iskoort.
Before becoming symbionts, the Yoorts (like the Yeerks) believed that conquest was the way forward. But over time, they realized that this wouldn't be beneficial, because the Isk (Iskoort) are mostly concerned with profit and society. They made a symbiotic relationship so that the Yoort cannot survive without the Isk and the Isk cannot survive without the Yoort.
The Ellimist sent the Animorphs to their homeworld in hopes to save the species so that someday the Yeerks would meet Iskoorts, and the Yeerks would realize there is a better way to live than parasitism.
Yeerk technology is largely stolen from other races, although the Yeerks themselves appear to have a great capacity to learn and create new technology with pieces of alien technology. Yeerk technology and ships include:
- Dracon beams – Hand-held or cannon weapons that emit a painful red beam of energy. Powered by energy cells, Dracon beams have ten settings, the most powerful of which can punch a hole straight through ten feet of solid titanium. They are modified from Andalite shredders by combining them with Ongachic particle technology to make it more painful.
- Yeerk hand-held computers – Small green squares with a holographic, translucent screen.
- Hunter-killer robots – Medium-sized spheres with a single lens that senses movement as a threat, and fires a killing Dracon beam at the target.
- Killing cylinder – An assassination device concealed within a small metal cylinder; when pressed to the back of a host's neck, it kills both Yeerk and host instantly.
- Genetic scanner – Small hand-held device that scans the target for genetic makeup, but does not harm the target. It was modified from Andalite technology.
- Zero-space engines – Allow a ship to jump from real space to zero-space, taking advantage of the curvature of space to travel great distances much more quickly. It was blatantly stolen from Andalites.
- Anti-morphing ray – A machine that forces a creature to revert its DNA pattern from a morph to that of its natural cells. Only a prototype was constructed; however, while it might have worked, the Animorphs tricked Visser Three into thinking it didn't, and subsequently the project was abandoned, its creators put to death.
- Yeerk torture device – One of presumably many, it consists of three buttons that focus on a box where the target lies. The Yeerks rely on their knowledge of all things neural to force the target to feel extreme pain, extreme happiness, or both at the same time.
- Bug fighters – Basic maximum-of-three-person fighters that resemble a black, oval-shaped beetle or other insect, with two eye-like windows and two serrated spears (the Dracon cannon) jutting out from its front end. The interior is large enough for three crewmembers of various species to walk around in, with a weapons station and navigational controls (the latter often handled by a Taxxon). It is modified from Andalite tail-fighters, and inspired by the Hork-Bajir homeworld, where the Bug fighters were first built.
- Blade Ships – Resemble a black medieval battle-axe, with two broad axe-like wings and a long "handle" with a diamond-shaped bridge on the end. Blade Ships are typically assigned to Vissers.
- Pool Ships – Huge, round, bloated, black ships with three spider-like legs are the engines and a series of thick tentacles hanging from the bottom (sensors and weapons); they are often known as Mother Ships.
- Cruiser-class ships – Shaped like a V or a boomerang. These ships fly with the two pronged ends forward, which hold Dracon cannons.
- Truck Ships – Shaped almost like large black metal manta rays. They are used to siphon large quantities of water or other supplies. These were stolen from Andalites.
- Nova-class Empire ship - Larger than Visser Three's Blade Ship, it has eight pods arranged around a central, cylindrical core. Four massive engines bunch up at its rear, blazing a blue fire. Appears only in book 30, under the command of Visser One.
- Andalite bandit – The common term by which the Yeerks refer to the Animorphs, believing them to be Andalite survivors of Prince Elfangor's Dome ship due to their morphing abilities.
- Anti-Morphing Ray (AMR) – A Yeerk-developed device which can detect morphing energy and reverse the morphing process. Only one was constructed; the prototype was destroyed following an infiltration attempt by the Animorphs. The technology was abandoned by the Yeerks despite it possibly functioning correctly; the Animorphs deceived the Yeerks into believing that this was not the case.
- Blade ship – Visser Three's private command ship. The Blade ship is the visser's usual means of transportation. The ship is described as "shaped like a battle-axe" with its weapons section in the rear, and is colored jet black.
- Blue Band Squad - An elite Hork-Bajir unit. These Controllers are highly trained, and are much faster and much stronger than the average shock trooper. They also wear blue bands on their arms, hence their group's name. The squad leader's name is Grath, which could either be the name of the Yeerk or the Hork-Bajir he controls.
- Bug fighter – The standard Yeerk fighter craft. The Bug fighter resembles a jet-black cockroach without legs. The 'head' of the fighter has two long, serrated, lance-like projections, which house the fighter's complement of Dracon beams.
- Controller – A creature under the control of a Yeerk parasite.
- Council of Thirteen – The head of the Yeerk government. This supreme body of leaders is composed of thirteen members, each with their own host body. Council members dress in elaborate robes. One of the Council members is the Emperor, but the leader is known only to the other Council members.
- Dapsen – According to Ax, dapsen is not a very polite word. This word was used to name a Yeerk front organization, Dapsen Logging Company. This leads the Animorphs to believe that "The Yeerks may have a sense of humor after all..."
- Dracon beam – The main particle weapon used by the Yeerks. It is deployed in hand-held form as well as more powerful starship-mounted variants. The hand-held Dracon beam is capable of punching through significant amounts of titanium. A Dracon beam has multiple power settings, rendering it capable of simply stunning or completely vapourizing organic matter. Yeerk Dracon beams were most likely adapted from the Andalites' shredders.
- Alien Species Grouping System – The Yeerks have a grouping system for different alien species. They are arranged into five Classes:
- Physically unfit species, such as Hawjabrans, Mortrons and Skrit Na are described as Class One aliens.
- Aliens that can be infested, but suffer from physiological disadvantages, like Taxxons and Gedds, are considered Class Two species.
- Class Three aliens such as Hork-Bajir are excellent for infestation, but exist in low numbers and do not breed quickly.
- Andalites are plentiful and would make good hosts, but are very difficult to defeat, and as such are Class Four species. In Visser, it is mentioned that Class Four species are out of reach, for now.
- Class Five aliens are those that are physically fit, can be infested, are extremely adaptable, are numerous, breed quickly, and are unable to resist the Yeerks. Humans were originally thought to be in this category, but were later moved down to Class Four.
- Formula 71 – A chemical designed to destroy free will. However, it is impossible to do such a thing to any species. The Yeerks tried putting it in hamburger meat in order to speed up the invasion of Earth.
- Fugue – 'The fugue' is the death phase, occurring at the end of the three days of a Yeerk's Kandrona starvation. In its final moments, a Yeerk recalls its memories and those of its former hosts, before leaving the host and disintegrating.
- Gashad – A warrant issued by the Council of Thirteen to execute a subject on sight.
- Gleet BioFilter – The Gleet BioFilter is stolen technology, first developed by the Andalites. The purpose of a BioFilter is to eradicate all organic life forms that are not registered in its DNA database. Gleet BioFilters are typically positioned at key entry points to sensitive areas, such as the Yeerk pool, in order to ward off spies. First appeared in book 17.
- Happy Meal with Extra Happy – The secret password to enter the Yeerk pool at McDonald's fast food restaurants. (Book only, the TV series modifies this to a generic diner and the password being "Cheeseburger, hold the cheese.")
- Kandrona – The name of the sun of the Yeerk homeworld. Yeerks must bask in its light every three days in order to obtain essential nutrients, much like the human ability to synthesize vitamin D2 by solar radiation. When away from their homeworld, the Yeerks utilize a Kandrona Particle Generator, which simulates the rays of their home sun, to replenish themselves. Kandrona devices can have many different sizes in order to serve one or more Yeerk pools with different capacities. Known large-size Kandronas were located on the EGS Tower in the Animorphs' home city, and aboard the Yeerk Pool Ship.
- Kandrona Particle Generators, Emergency – A one-use, small Yeerk pool made for emergencies. These are designed to make it more or less easy for the Yeerks to carry around with them. They are usually used by Yeerks on the run.
- Madra - The tiny, bright moon of the Yeerk home world.
- Operation 9466 – A failed Yeerk plan to weaken Earth by causing World War III.
- Project Obedience – Codename for a Yeerk attempt to conquer Earth by stripping humans of their free will. It failed miserably because sentient beings are inseparable from free will. Appears in book 28.
- Ramonite - First seen in Megamorphs 1, a Ramonite box is described by Ax as having "seamless walls on all sides." It is "a metal that can stretch open or be made clear or opaque by molecular realignment." The Yeerks use it for imprisoning morph-capable individuals.
- The Sharing – The Yeerk front organization. On the surface, the Sharing resembles the Scout movement: family, friends, cooperation. However, the Sharing is revealed to be an organization dedicated to advancing the Yeerk invasion on Earth, screening potential Controllers from the larger Sharing membership.
- Vanarx – A large, translucent purple predatory worm that attaches itself to a Controller's head and sucks out the Yeerk within. It apparently comes from the Yeerk homeworld. It is also known as a 'Yeerk-bane.'
- Veleek – The Yeerk word for "pet"; the name given by Visser Three to the Saturnian monster in The Andalite's Gift.
- Visser – A high rank in the Yeerk hierarchy. It equates more or less to a general or an Andalite prince. There are forty-seven Vissers, and many more Sub-Vissers, who are equivalent to colonels.
- Yeerk Peace Movement – Underground movement opposed to the taking of unwilling hosts. It was founded by Aftran 942.
- Yeerk Pool – A body of liquid of variable size that simulates the conditions of the Yeerk homeworld. Controllers return to their local Yeerk pool every three days, so that the Yeerk can be let out into the pool, allowing it to absorb nutrients from the liquid and rays from the Kandrona device.
The Sharing is the front organization for the Yeerks. The purpose of The Sharing is to persuade humans to submit to this infestation voluntarily. Some humans do submit voluntarily, while the Yeerks simply force infestation on those who do not. Members are not allowed to remain free indefinitely, and all members of The Sharing, bar those who have newly joined, are under the control of a Yeerk slug.
The Sharing uses psychological manipulations similar to those used by the cults in the real world, although, unlike most cults, The Sharing is successful in making itself appear mainstream to the larger human society, claiming to be a benign social group. In the Animorphs' town, The Sharing seems to be led by a high-ranking Controller named Hedrick Chapman. The Sharing was founded by Edriss 562 when she was controlling a man named Lawrence Alter, whom she renamed Lore David Altman. She later killed Alter/Altman so that he would be revered as a martyr, noting that humans would lionize a dead leader but seek to tear down a living one.
- Alien invasion
- The Goa'uld from Stargate SG-1, which are extremely similar in nature (although a Goa'uld can stay in a host for as long as it likes. In addition the Iskoort are similar to the "Tok'ra" in the Stargate universe.)
- The Zerg from StarCraft
- The Ceti eel from Star Trek II: The Wrath of Khan
- Conspiracy (Star Trek) from Star Trek: The Next Generation
- The six Migar species from the television series Tracker (although in this case, the human host dies; the alien is only using the body)
- The black oil from The X-Files
- The unnamed aliens from Robert A. Heinlein's novel The Puppet Masters
- Applegate, Katherine A. Animorphs: Visser United States: Scholastic, 1998. Print.