Carcino-Gen

The Carcino-Gen are giant mutant crustaceans ranging from two to ten feet tall, found near bodies of water throughout Dominus Columbia. They travel in groups of approximately twelve, nest in waterbeds and soft mud, and fight to the death to defend their nesting sites. Last Hope University has been studying them for years. The researchers have not been able to explain where they came from.
  The physical threat they present is considerable. Their back shells are nearly impenetrable, providing a natural defense that most weapons cannot breach. Their claws are strong enough to crush bone and pin targets in place. But the most dangerous aspect of the Carcino-Gen is not their strength or their armor. It is their screech.
  The mutagenic screech of a Carcino-Gen forces Mutant and Evolved strain members to undergo involuntary physical changes: thin exoskeletons erupting from skin, crustacean claws growing from hands. The screech also destroys weapons held by affected targets. The biological mechanism by which a sound produced by a crustacean can hijack the Infection's mutation pathways and force specific physical transformations in living strains is, to put it plainly, not understood. The phenomenon implies a connection between the Carcino-Gen and the Infection itself that current science cannot explain.
  Their diet adds another dimension to the threat. Carcino-Gen scavenge corpses, including strain corpses, making them a persistent hazard near any body of water where the dead might wash up or be deposited. Their territorial behavior and lethal defense of nesting sites mean that waterfront areas claimed by a Carcino-Gen group become effectively inaccessible without the kind of force that most travelers and settlers cannot muster.
  Twelve of them traveling together, armored, armed, and capable of rewriting the bodies of anyone who gets close enough to hear them scream. The university's inability to explain their origin does not reduce the urgency of understanding what they are. It increases it.