Putative microbial defenses in a social spider: immune variation and antibacterial properties of colony silk

Abstract

The accumulation of microbes in and around the large, perennial nests of social arthropods can increase the potential for interactions between individuals and harmful pathogens. Accordingly, many social insects utilize multiple organizational lines of individual and collective defenses against microbes. The interaction between microbes and social spiders, however, has been almost entirely unexplored. Here, we use the social spider Stegodyphus dumicola Pocock 1898 (Araneae: Eresidae) to (1) probe how innate immunity varies among individuals and (2) determine if two types of silk extracted from their colonies can inhibit the growth of the entomopathogenic bacteria Bacillus thuringiensis. Individual spiders’ innate immunity against lyophilized cells of Micrococcus luteus varied negatively with their boldness, a behavioral metric important for individual foraging and the organization of collective behaviors. Further, silk from both the capture webs and retreats of uncontaminated colonies inhibited the growth of B. thuringiensis to a small degree. Thus, web construction might represent a form of collective anti-microbial defense in these social spiders. This preliminary evidence suggests that social spider societies may exhibit antimicrobial defenses on multiple levels of organization, including both individual- and group-level defenses.