Yeerk Biology
This page is dedicated to telling you everything
you ever wanted to know about Yeerk biology but because of vague narration or fear for
one's life, were afraid to ask. This is collected from various books narrated by different
people, including Andalites (namely Ax). Because of this, some information may conflict. I
have tried to explain the reason one peice of information blatently contradicts another,
which happens a lot when Yeerks are concerned.
Physiology
Life-and-Death
Feeding Cycles
Hosts & Parasitisim
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Yeerks are most commonly described as looking
like slugs. They are rather large for slugs, gray, with two main "antennae"
feelers and several small leglike appendages. In this, their natural state, they have no
sight, hearing, smell or taste abilties. They navigate their environment solely by touch
and and a special sense which may be like a sonar which works equaly well in air or in
water. They also have sensors called palps which can receive information in a form much
like thought-speak. It is the simple exchange of concepts, usually considered slightly
more advanced than regular speech, but in this case it is more like compensation for lack
of speech. The Yeerks do have a native spoken language, but it is sparse, probably because
there is rarely, maybe never, a time at which all Yeerks are able to speak as well as be
in the same form.
Yeerks are, as you should know, parasites. But they don't rely on
their hosts for food or nourishment, but rather for a body; for hands to build and eyes to
see. How they actually accomplish their parasitism is not exactly stated, though a
collection of best guesses is in the Parasitism section. Somehow they are able to
manipulate their actual forms, to fold and squeeze through various narrow spaces in their
hosts head, then wrap around its brain like a living blanket. Perhaps its exterior body is
made in this state by will, or exposure to certain enzymes present in a host's body.
However it is done, this is one of their most unusual and, in the end, most formidable
features.
The Life and Death Cycle:
For Yeerks life and death is a very circular thing; in order to
give birth they must also give their lives. Yeerks are born by a process done in the Yeerk
Pool. It is accomplished by three parent Yeerks fusing together and joining as one. As far
as we know, this act is nothing like any reproductive process belonging to creatures like
humans and Hork-Bajir and Andalites. It is done presumably without any emotion, and
possibly, knowing how the Yeerk govornment is, on order. When the three parents fuse,
their matter and genetic material is combined and spliced, and then this breaks away into
hundreds of tiny peices, called grubs. These grubs are then named and given a number based
on in which order they formed. Since only three Yeerks makes hundreds of them, though, it
is presumed that most Yeerks don't reproduce; they simply live out their lives, eventually
dying. They do not seem to have an "old age" limit, though no Yeerk has been
reported living extremly long.
Feeding Cycles:
In their natural state, Yeerks would be in their pool on their homeworld, absorbing
various nutrients, namely Kandrona rays which are beamed from their sun and absorbed by
the water or water-like substance that Yeerk pools consist of. They get their nutrients
from osmosis nodes, little things on their "skin" which are somewhat like
vacuoles on plants, letting in the nutrients and processing them as energy. Gradually
though, they were able to move around outside of the Yeerk pool by use of hosts (see Hosts and Parasitisim). There was only one problem to this;
after three days (or roughly the time period three Earth days is, the Yeerks don't think
of it this way of course) out of the pool, the Yeerk is depleted of nutrition. Unless they
return to the pool to absorb the nutrients once again, they will die a horrible starvation
that literally breaks them down, caused them to be forced to vacate the host and crumble
into basic dry matter shortly after death.
Once they have gotten the nutrition they need, the Yeerk can return to its host. With the
Gedds, this might have been accomplished by the Yeerk telling the Gedd to return to the
pool and the not-quite-sentient Gedd never thougth otherwise. With more intelligent hosts
such as Hork-Bajir, though, they had to develop a system, in which the free hosts would be
held in place by Controllers until the Yeerks were ready to re-enter their hosts, which
the Controllers would accomplish forcefully.
Hosts and Parasitisim:
During the course of their development, the Yeerks evolved to be parasites. Their lack of
a body except for a small, sluglike form which only serves to house their neural matter
was compensated by their special ability; to use another creature's body as its own. They
are able to enter the host through some acessible opening that is close to the brain,
usually the ear canal. They secrete a chemical which dilates the passages and numbs the
pain. They squeeze their way throught he various crevaces, displacing small bits of tissue
if nessesary, until they reach the brain. There they wrap around the brain, folding
themselves into the folds and valleys, tying their own neurons to those of they're hosts.
This way, not only can they use the host's body as their own, but they also have access to
everything in their mind, including their thoughts, their memories, language and cognitive
skills, talents, and quirks and mannerisims, which prove useful in pretending to be
that person whose body they have taken, as they are doing now with the humans.
This would be fine if it were not for one little problem; the general rule is the
more useful a creature's body is, the smarter it is. Until a species the Yeerks chose, the
Hork-Bajir, were truely sentient, self-aware, yet since they were docile and technolically
primitive, there was little they could do to defend themselves. This issue, of one
creature taking another's freedom to acheive its own, has been the driving force behind
many heated moral issues and debates. Because, to the Yeerks, their parasitism is just as
essential to their life as the killing of animals is for humans. Humans have found a way
to live without doing this, though many don't wish to change. Perhaps many Yeerks feel
this way. Why should they give up their way of life, their wonderful abilities to move
around in the universe, to have corporal signifigance, for the whim of a host?