According to EU Directive 2001/18/EC, a general surveillance monitoring must be implemented to detect possible unexpected effects of genetically modified (GM) crops on the environment. Butterflies have been proposed to be suitable indicators for monitoring environmental changes in agricultural landscapes. Using such mobile organisms as indicators for general surveillance is a challenge as their populations vary according to many environmental factors acting at the field, landscape and regional scales. They might thus not be appropriate to detect unexpected effects of GM crops, unless the sources of variation in their populations can be identified and accounted for. In the present study we use a multiscale approach to describe the interactions between butterfly populations, the environment and farming activities. We analysed existing butterfly data from several Swiss agricultural landscapes in order to identify the sources of variation in butterfly populations and to give guidelines for the design of general surveillance protocols for butterflies