How much care does a shrub-feeding hairstreak butterfly, Satyrium spini (Lepidoptera: Lycaenidae), need in calcareous grasslands?

Many butterfly target species are associated with early successional stages of grasslands. The Blue-spot Hairstreak, Satyrium spini (Denis & Schiffermuller, 1775), is a target species of grasslands. However, it feeds on Common Buckthorn (Rhamnus cathartica), which is associated with late successional stages of grasslands. If S. spini would also be restricted to late seral stages, there might be a management dilemma due to the contrasting requirements of S. spini and other target species. The aim of this study was to determine the oviposition preference of S. spini in calcareous grasslands, and to give management recommendations to promote this species. Therefore, we studied the oviposition microhabitats of S. spini at three representative patches of the Diemel Valley (Central Germany) by comparing environmental conditions on occupied and control host plants. In total we surveyed 1,889 host plants. Altogether we found 148 batches of S. spini on them containing 396 eggs. Most of the eggs were on plants that grew under the warmest conditions. Females preferred to lay eggs on small (< 1.3 m) shrubs of Rh. cathartica fully exposed to the sun growing on steep south- and west-facing slopes. This butterfly showed no difference in its preference for bushes growing in hedges or solitarily. About 80% of the batches of eggs were laid on the upper surface of a twig fork close to the surface of the ground (< 1 m). Our study showed that S. spini is a species characteristic of mid-successional stages of calcareous grasslands. The survival of suitable habitats for S. spini depends on regular management. To achieve this we recommend traditional rough grazing with sheep and goats, which creates open grasslands with small Rhamnus plants. In addition, the shrubs in tall hedges bordering calcareous grasslands should be subjected to cutting on a rotating basis.