Social spider webs harbour largely consistent bacterial communities across broad spatial scales.

Social animals that live in domiciles constructed from biomaterials may facilitate microbial growth. Spider webs are one of the most conspicuous biomaterials in nature, yet almost nothing is known about the potential for webs to harbour microbes, even in social spiders that live in dense, long-term aggregations. Here, we tested whether the dominant bacteria present in social spider webs vary across sampling localities and whether the more permanent retreat web harbours compositionally distinct microbes from the more ephemeral capture webs in the desert social spider, Stegodyphus dumicola. We also sampled spider cuticles and prey items in a subset of colonies. We found that spider colonies across large spatial scales harboured similar web-associated bacterial communities. We also found substantial overlap in bacterial community composition between spider cuticle, prey and web samples. These data suggest that social spider webs can harbour characteristic microbial communities and potentially facilitate microbial transmission among individuals, and this study serves as the first step towards understanding the microbial ecology of these peculiar animal societies.