95 Million Killers

New Zealand. Population 4 million.
New Zealand possum population. Approximately 95 Million.
From 1837 until 1959, possums were brought into New Zealand from Australia, the intention being to have another animal for recreational hunting and to create a fur trade. Unfortunately, breeding was out of control and the damage to the vegetation and native bush was devastating. One contentious way to deal with the problem is to dump tonnes of bait laced with 1080 poison in the bush.
This, plus hunting and trapping barely stops the population increasing. Something else was required. Secret experiments to genetically modify the animals as a way to eradicate them went horribly wrong....!
Contains graphic descriptions of bloody terror. You have been warned!