Controlling introduced species

Settlers introduced possums to New Zealand for fur farming at the turn of the twentieth century. But there are now 60 million possums in the country. The animals have become a formidable pest, chewing their way through 20 000 tonnes of foliage a night, gorging themselves on birds' eggs and spreading bovine tuberculosis.  Rather than poisoning or shooting them, New Zealand's possum populations could be reined in by sterilising the female possums with genetically modified carrots. Scientists who developed the carrots say they are a humane and environmentally sound alternative to managing wildlife with poisons or viruses.The main risk is that the carrots may sterilise other animals.