Interactions between the social spider Anelosimus studiosus (Araneae, Theridiidae) and foreign spiders that frequent its nests

Because competition for resources generally leads to the spatial exclusion of species using similar resources, it is surprising that foreign spider species are frequently observed in or near the nests of the social spider, Anelosimus studiosus (Hentz 1850) (Theridiidae). In this study, we quantified the frequency of A. studiosus-foreign spider co-occurrence and completed experiments designed to explain the nature of the host-foreign spider species associations. Four families were numerically prominent nest associates of A. studiosus: Salticidae, Anyphaenidae, Araneidae and Tetragnathidae. These families and the Agelenidae (intermediate association rate) and (Philodromidae) (infrequent association rate) were subjected to further study. In choice trials, no foreign spider family discriminated nest silk or A. studiosus, itself, from the foliage the nest is built in. Predation events and maximum inter-individual spacing were significant outcomes of induced pair-wise interactions between host and foreign spiders for all families. Predation events were almost exclusively foreign on host. Field census results show that a close correspondence exists between the rate of loss of A. studiosus nests over time and the association rate of anyphaenids and agelenids at particular sites: these two families were the prominent predators on A. studiosus in laboratory trials. In reciprocal predation tests, juveniles suffered less predation in the presence of a mother; in the reciprocal trials, mothers also suffered less predation from foreign spiders when juveniles were present.