Creeps

The Creeps are a widespread and dangerous gang of mutants. Unlike other mutants, who rely on crude, or no weaponry at all, Creeps are intelligent enough to use firearms, and tactics. These little freaks will scamper around and take pot shots at their foes.

Creeps have a strong dislike of humans, and will mutilate any they see.

Background
The original Creeps were mutated convicts, who were exposed to gamma radiation, due to the awful working conditions they were forced to deal with. The Skulls, a rival gang, treated the Creeps like cattle, due to a lack of food, so the Creeps gut any human they see as payback.

It's unknown where the newer Creeps are coming from, but possibly some survivors may have been exposed to the same level of Gamma radiation as was the original batch.