Nanites

Nanites are the microscopic machines that were created by the scientists during the Nanite Event, and spread across the globe at the time of the explosion. Nanites exist within every living being, bonded to their molecular structure. Normally, nanites are completely harmless. Though, when activated, they mutate the biology of their host giving them grotesque physical features and special abilities, these are called E.V.O.s.

Mutations
As previously mentioned activated nanites change the hapless individual into an often monstrous and bizarre creature with special powers manifesting as well. The series has shown how the mutations can vary. In some cases creatures mainly grow greatly in size (seen in various arthropods), and many others shift into something radically different, seen time and time again throughout the episodes. Humans almost always retain some human-like qualities, though a good number of E.V.O.s encountered so far appear mindless and bent on destroying anything they can.