Frame-web-choice experiments with stingless bees support the prey-attraction hypothesis for silk decorations in Argiope savignyi

Abstract

There is controversy about the function of silk stabilimenta, also called silk decorations, on spiders' webs. Most of the proposed hypotheses have been tested using indirect methods. Protection against predators, advertisement for vertebrates to avoid web damage, and increasing prey attraction are the most popular hypotheses. In this study, I tested the prey attraction hypothesis on the silk decorations of the araneid Argiope savignyi using a trial tunnel built in the field, in which I exposed stingless bees Tetragonisca angustula to decorated and undecorated webs placed on wooden frames. I carried out two experiments: 1) a three-frame choice, consisting of a frame bearing a decorated web, one bearing an undecorated web and a control frame without web and spider; 2) a two-frame choice, in which the bees were exposed to only two frames consisting of “decorated web vs. control,” “decorated web vs. undecorated web,” and “undecorated web vs. control”. In favor of the prey attraction function, I found that decorated webs intercepted more bees than webs deprived of the decoration or controls with no webs. Argiope savignyi's decorations might lure prey to the web by UV-reflectance as it has been suggested for other Argiope species.