Flying to greener pastures: Spider ballooning in the city

Abstract

Spider ballooning is a phenomenon in which spiders employ silk threads to travel through the air for dispersal. While this behaviour has been extensively studied in agricultural areas, limited research has been conducted in urban environments, where green spaces are highly fragmented. However, in cities, aerial dispersal can be advantageous for spiders as it allows them to move to suitable habitat patches. This study aimed to investigate how the urban landscape affects spider ballooning. We collected ballooning spider samples using sticky traps in 10 urban sites within different landscape contexts. By using generalised linear models, we analysed the influence of vegetation cover at both local and landscape scales on spider abundance and family richness. Family composition was similar across the city regardless of the landscape context. More individuals were collected dispersing aerially in areas with low landscape-level green cover. However, a higher local percentage of vegetation cover led to a substantial increase in aerial dispersal in areas with high landscape-level green cover. Our findings highlight the significance of the interaction between vegetation cover at these two scales on aerial spider abundance. Our results support the hypothesis that generalist spiders exhibit increased ballooning in highly fragmented landscapes, actively seeking suitable habitats despite the elevated associated risk. Higher aerial dispersal in areas with greater local vegetation cover suggests an increase in short-distance dispersal, indicating spiders´ active search for better habitats nearby upon arrival at a site with potentially greater habitat availability.