Butterflies take a well-studied tumble

Massive amounts of observation data recorded by amateurs are available for butterfl ies, allowing scientists to study their population dynamics and response to environmental threats. They report serious declines in many rarer species leading to an overall loss in biodiversity. As these declines refl ect the impacts of land use change, climate change and pesticide use, they also provide an alarm system to warn of imminent dangers to other, less visible parts of our natural environment. Michael Gross reports.