Foraging benefits and limited niche overlap promote a mixed species association between two solitary species of spider

Mixed species associations are of general importance because of the diversity of ecological relations they can represent (e.g., mutualisms, commensalisms, exploitative relationships). We test for a non-random association between two normally solitary species of spider, the black widow (Latrodectus mactans) and the orchard spider (Leucage venusta). We use field observations comparing solitary and associated individuals of both species to elucidate what effect the association has on prey capture. We then evaluate what influence the association has on prey consumption, as inferred from change in body mass after a reciprocal removal experiment. From our field census we confirm that these species associate non-randomly in wild populations; furthermore, we failed to detect a difference in the number or kinds of prey which hit solitary and associated webs of either species, suggesting the association is not merely an aggregation to microhabitats which afford higher prey availability. Our observational data on prey capture indicate the association serves to increase the capture efficiency of Le. venusta, in part through ricocheted prey, but we failed to detect a prey capture effect for La. mactans. The results of our reciprocal removal experiment suggest the relationship is a commensalism: benefiting Le. venusta and leaving La. mactans unaffected.