Dragonflies cause spatial and temporal heterogeneity in habitat quality for butterflies

1. Mortality caused by natural enemies is an essential but largely overlooked aspect of habitat quality for herbivorous insects. Quantitative data on mortality sources and their spatiotemporal variation are especially scarce for adult insects. 2. Here we report the results of an extensive field study aimed to quantify spatial and seasonal variation in dragonfly predation on adult butterflies in their natural habitats in temperate calcareous grasslands. We rely on direct observations of actual predation events during standardised transect walks. 3. Dragonflies were found to exert high mortality in butterflies. Their impact on butterflies was dependent on predator abundance, which strongly varied among habitat patches and during the season. This suggests that dragonflies can generate substantial spatiotemporal heterogeneity in habitat quality for butterflies in terms of survival. 4. Obtaining prior knowledge of where and when predators are abundant, and avoiding such sites for butterfly conservation, could considerably improve the efficiency of butterfly conservation practices.