ECOSYSTEMS ARE complex things, and monitoring their health is hard. To track every species would be impossible, so ecologists commonly focus on those that, like canaries in coal mines, are thought to indicate when the system as a whole is beginning to suffer. Dung beetles are one such group, and have been relied on heavily for years to monitor the effects of things like logging, grazing and road-building.
When there are lots of species of dung beetles around, and faeces vanish quickly, an ecosystem is assumed to be in good shape. When their diversity drops and faeces hang about unconsumed, it suggests something is wrong. However, as Elizabeth Raine, a zoologist at Oxford University, has realised, the value of this assumption depends on how you go about sampling the beetles. That is done by attracting them with their preferred foodstuff, faeces. And she thinks it is being done badly.
Until now, researchers have assumed that dung beetles will happily tuck into any old pile of dung. As such, they have a cherished tradition of using their own excreta as bait. This makes sense, since a supply is always available. But Dr Raine realised that no one had ever tested how attractive human faeces are compared with those of wild animals.
She and her colleagues therefore set up experiments at three lowland tropical-forest...