Female false black widow spiders, Steatoda grossa, recognize webs based on physical and chemical cues

Females of the false black widow, Steatoda grossa CL Koch (Araneae: Theridiidae), invest significant energy and time weaving cobwebs. We tested the hypothesis that S. grossa females select sites for their webs based, in part, on the presence of con- or heterospecific webs, sensing both physical and chemical web cues. In bioassays, we offered female S. grossa a choice between an empty control frame and a frame bearing the web of a conspecific female or that of a female common house spider, Parasteatoda tepidarium CL Koch (Araneae: Theridiidae), recording (1) the time she spent, and (2) the time she spent inactive (a proxy for settling behaviour) on each frame. We also tested the effect of (1) silk micro- and macrostructure (wrapped-up silk or intact web, each semiochemical-deprived), (2) plastic webs, and (3) silk semiochemical extract on the responses of S. grossa females. Females settled on both con- and heterospecific webs and chose test stimuli based on their chemical and physical characteristics. Even plastic webs in cobweb-like arrangement readily prompted settling behaviour by females. Our results suggest that web architecture, rather than web silk, mediates settling responses by female S. grossa on pre-existing webs which may provide structural support for a new web and indicate habitat suitability.