Umbrella developed the Chimera B.O.W.'s by inseminating human ovums with fly DNA, then impregnating women with the mutant embryos. They matured quickly, though their physiology was under-developed. They lacked the exoskeletal chitin of the flies they were based on and their bodies were warped and disfigured, with exposed bones and vitals clearly visible in their torsos. Their intelligence never advanced beyond that of an insect and so they could not be trained to follow orders. Due to these many flaws, Umbrella abandoned the Chimera research, though the specimens in the Arklay Laboratory had yet to be disposed of before the T-virus was scattered within the facility. As the staff were killed off or zombified, the Chimeras in the lab escaped and roamed freely.