A recent review by scientists in Australia of 73 historical studies of insect decline concluded that insect biodiversity is threatened worldwide, and 40 per cent of insect species are threatened with extinction over the next few decades. But there is a puzzle. The classes that are declining fastest are butterflies, bees and dung beetles. No one is going out of their way to eliminate them. Other insects that we attack deliberately and for which extinction would be a cause for celebration are doing well.