Web architecture, dynamics and silk investment in the social spider Stegodyphus sarasinorum

Abstract

Animal architecture is diverse in form and structure, and extraordinarily intricate, often facilitated by the collective behaviour of several individuals. Social spider webs are one such example of animal architecture, robustly supporting the collective colony weight and intercepting prey for the entire colony. Thus, these webs are interesting, yet little studied from architectural and behavioural perspectives. In the social spider Stegodyphus sarasinorum we examined the spatiotemporal dynamics of web architecture and tracked web development in different group sizes through controlled experiments and image analysis. Geometrical parameters including coordination number, and pore size remained constant across group sizes. Silk density was highest near the retreat (nest) and decreased with radial distance for all group sizes. We tested the silk conservation hypothesis, a proposed benefit for the evolution of group living, by asking whether (1) total silk investment increases with group size and (2) per capita silk investment decreases with group size. Our results indicate that while larger colonies produced more silk than smaller ones, per capita silk investment did not decline in larger groups. We propose further investigations into the roles of ecological factors and body condition in shaping individuals’ silk investment with consequences for web architecture and colony fitness.