Wildflower strip establishment supports beneficial ground-dwelling arthropods and pest control but has limited effects on weed seed control and spillover to adjacent fields.

Arthropod declines in agricultural landscapes can threaten biodiversity and the provision of ecosystem services. Wildflower strips (WFS) can support biodiversity and, despite the mostly positive effects on pollinators and predatory arthropods, myriapods and ecosystem services like weed seed and ground-level pest predation are less studied. In addition, time after WFS establishment is highly relevant, but most experiments are performed in a single season. Here, we evaluated the effects of WFS on ground-dwelling arthropods (carabids, spiders and myriapods) and ecosystem services (pest and weed seed predation) across three years and three crop types. Using a standardized experimental design with paired control and WFS margins in 12 fields, we assessed arthropods and ecosystem services and their spillover into adjacent fields. We found that WFS enhanced spider and carabid richness and total and rodent pest predation in all crop types, whereas benefits on carabid activity-density and insect predation were only observed at certain crops. Spillover patterns were weak, and only carabids were enhanced in parts of the field neighbouring WFS. The benefits of two-year-old WFS reinforce the important role of perennial WFS in supporting beneficial ground-dwelling arthropod groups while also highlighting that limited spillover hinders the design of general measures to support biodiversity within arable fields.