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The defiler is a zerg breed that uses toxic substances to support other zerg forces.
The defiler is a relatively rare zerg breed, resembling a silverfish in appearance and acting akin to a 'cancer factory' in function. Its core genus, if it has one, is unknown, as the defiler contains the DNA of all other zerg breeds. It was created from festering, carcinogenic pathogens that were, in essence, leftover genetic chains from other zerg strains. It uses this genetic material to synthesize virus-like biochemicals. These biochemicals are extremely hazardous, resistant to the most effective anti-toxins, and, paradoxically, dangerous even to the zerg. A large amount of energy is expended in the production of these chemicals, and defilers are known to cannibalize other zerg to fuel the metasynaptic processes that generated the compounds, often accompanied by zergling escorts for this very reason. They can also recharge the metasynaptic processes through burrowing.
The defiler's body is host to countless small organisms that live on the carapace, constantly feeding on each other. The defiler can spontaneously launch a number of these creatures to swarm a location that make it difficult to target anything under the ensuing cloud. In addition, defilers can produce corrosive spores and hurl them at a target area, the spores exploding in a dense cloud. The highly toxic mist that results corrodes anything it touches. However, these spores are also prone to igniting due to a flammable accelerant contained in them.
Moving with a slow, intelligent slither, defilers are highly vulnerable to any form of counterattack (especially long-range or air assaults) and as such, usually stay at the rear of zerg formations. The defiler evolved into obsolescence after the Brood War. However, with the need for a specialized support strain, the zerg revisited the defiler template and perfected it with genetic data from an unknown species, preserving its core functions while excising its unnecessary lethality. The result was the viper. Feral defilers still existed after the End War however, and the Defenders of Man used psi-emitters to lure a number of them to Borea.
The following section contains information from StarCraft: Retribution.
Defilers possess the ability to extract and process information from terran minds.