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.
Chimeras can use their multi-jointed limbs to climb walls and ceilings, even creep through air ducts where they will hide until living prey draw near. Each limb ends in a razor-sharp, hook-shaped claw. The Chimeras use these claws for climbing and eviscerating their victims. The creatures also have wings on their thoraxes, though they are too small and underdeveloped to allow them to fly. Chimeras can also breed at an impressive rate and have left several larvae within the halls of the Arklay labs. While dexterous and cunning, these monsters aren't as strong as they could have been and can be killed quickly with shotgun fire. A chemical imbalance in the Chimera's genetic makeup causes the creatures to immediately dissolve when they die.