Sown wildflower areas to enhance spiders in arable fields

Sown wildflower areas (SWA) are cultivated in Switzerland to preserve and enhance farmland biodiversity. Here, the impact of SWA on spider density, diversity and species richness in winter wheat fields was studied. Edge effects and field scale effects of SWA were compared with landscape effects of perennial habitats in general. Adjoining SWA enhanced the densities of crab spiders (Thomisidae), ground spiders (Gnaphosidae), wolf spiders (Lycosidae) and young orb weavers (Araneidae) in wheat fields. In addition, numbers of wolf spiders and ground spiders increased towards field edges. Surprisingly, species richness was unaffected by SWA. Species richness, Simpson diversity, and densities of all spiders, and densities of sheetweb spiders (Linyphiidae) increased with the percentage of perennial habitats in 1.5 km radius. In conclusion, high spider diversity in wheat fields depends on perennial habitats at the landscape scale. To enhance cursorial spider families and orb weavers, SWA should be interspersed between crop fields.