Greenies, so named by Hunter, play a larger role in Plague. Hunter claims one dropped a strange liquid on him during the attack. Later, parasitic wasps begin eating Hunter from the inside out. It is later discovered that the greenies are spreading the parasites. They attack Sam, Dekka, and Computer Jack as the three search for water. One manages to drop liquid on Dekka. The parasites infect her, and she barely survives.
Greenies are the only named mutated animals that were named by Hunter and not Howard; the zekes and Gut-Roaches were named by the latter while the blue bats never receive a name at all.