Sampling design
At 22 dry grassland sites (Fig. 1), three pan traps (yellow, blue, white; 19,6 x 15,4 cm with a 300ml 8%-Formaldehyde-water-dish wash-solution) were attached to sticks approximately 40cm above the ground in a triangle 1m wide triangle. The traps were installed for three sampling campaigns in 2017: May (15/5-18/5/2017), June (12/6-15/6/2017) and August (15/8-18/8/2017), located at representative sites of the patches. Each trap stayed for 48 hours in the field within each sampling campaign. The weather conditions were sunny and dry throughout sampling campaigns.
Specimens were needled and determined to species level using Amiet et al. (1999-2017) and Scheuchl (2000-2006) and van Veen (2010) and Bot and van de Meutter (2019) for the hoverflies.