Seasonality mediates local and landscape drivers of ground-dwelling spiders in temperate agro-ecosystems

Agricultural intensification has a strong impact on arthropod diversity, yet predators such as spiders provide key ecosystem services through natural pest regulation. Understanding how local and landscape factors shape spider assemblages throughout the season is essential for designing effective agro-ecological infrastructures that can sustain their services in crop systems. We investigated ground-dwelling spider communities in Belgian winter cereal fields and their margins. Pitfall traps were used across seasons to assess the effects of habitat (field vs. margin), surrounding crop cover, and seasonal dynamics on spider richness, activity-density, and community structure. Results show that spider activity-densities were consistently higher in margins than in fields, whereas species richness showed no significant differences between these habitats. Significant seasonal variations were detected on both spider richness and abundance. The landscape effect of the annual crop cover was context dependent, showing seasonal and species-specific patterns and even positive associations in autumn. Seasonal shifts also reflected life stage and sex-specific phenologies. This study reveals that spider communities in Belgian cereal systems are shaped by interacting local, landscape, and seasonal factors. Margins mainly act as refuges that bolster spider numbers rather than species pools, while the influence of the surrounding landscape depends on the season and the species identity. These findings highlight the need to incorporate temporal and biological context when designing margins and other agro-ecological infrastructures to support natural pest regulation providers such as spiders.