Erasers are half-human, half-wolf mutants. They were bred at The School to be guards, but later on in the series they are used to hunt down and kill flock members. Erasers have the ability to morph into wolves, super-human strength, and in School Out Forever they gain wings that are crudely grafted onto their shoulder blades. Erasers only live as 6 to 7 years before getting an expiration date on the back of their necks. In the third book Itex 'retires' all the Erasers, with exception of Ari, and replaces them with Flyboys.