The aggregating behaviour of Argiope radon, with special reference to web decorations

The existence of aggregations in taxa that are normally solitary poses questions regarding the costs and benefits of group living. Most orb-web spiders are solitary and are aggressive to conspecifics, but a few species aggregate in large numbers. These spiders benefit by enhancing the prey interception potential, but also suffer costs of increased predation and parasitism. In this study, we report on the natural history characteristics of the orb-web spider, Argiope radon, which not only lives in aggregations but also builds silk decorations. Our results show that A. radon aggregates facultatively and that the main benefit of aggregation that we could identify is enhanced mating potential. We also show that decorations built by A. radon are highly visible to both model prey and predator, and suggest that solitary individuals with longer and more frequent decorations may offset the foraging advantage of being in aggregations.