A Yeerk is a 1"-2" long gray slug. It looks like a snail without a shell. They are helpless unless they have inhabited a host body. They do this by crawling in through the ear canal until they reach the brain. From there, they wrap themselves around the brain, getting into every crack. The Yeerk can now control every move of the person or being, hence the name "Controllers". It is like being trapped within your own body, because you can no longer control your arms or mouth or even your eyes. Yeerks live off Kandrona rays, which are filtered into a pool. Every three days the Yeerks must return to the pools to feed, or they will shrivel up and die. While the Yeerks feed, the involentarily taken humans are put into cages. The humans who allowed themselves to become Controllers watch T.V. or read in a seperate room. Visser 3 is the only Yeerk to inhabit an Andalite. Visser 1 has inhabited Marco's mother.

There are four known species that the Yeerks have infested: Gedds, Hork-Bajir, humans, and Taxxons. A few Leerans were even taken as Controllers for a short amount of time.

So, that's a Yeerk. Pretty scary, huh? If you have anything at all to add to this description, please e-mail me or put it in the guestbook or message board.