Discoid decorations function to shield juvenile Argiope spiders from avian predator attacks

• Published in: Behavioral ecology 2021-12, Vol.32 (6), p.1230-1239
• Main Authors: Wang, Bingjun, Yu, Long, Ma, Nina, Zhang, Zengtao, Liu, Qian, Fan, Wenrui, Rong, Yu, Zhang, Shichang, Li, Daiqin
• Format: Article
• Language: English
• ISSN: 1045-2249; 1465-7279
• DOI: 10.1093/beheco/arab089

Abstract Decorating behavior is common in various animal taxa and serves a variety of functions from camouflage to communication. One predominant function cited for decoration is to avoid predators. Conspicuous, disc-like (discoid) silk decorations spun by orb-web Argiope juvenile spiders are hypothesized, among others, to defend spiders against visual predators by concealing spider outlines on the web, deflecting attacks, shielding them from view, or masquerading as bird-droppings. However, the direct evidence is limited for a specific mechanism by which discoid decorations may deter predators. Here we evaluate the mechanisms by which discoid decorations may defend Argiope juveniles against naïve chicks. Using visual modeling, we show that avian predators are able to distinguish spiders from discoid decorations. Using chick predation experiments, we found that the naïve chicks readily pecked any objects, ruling out the possibility of their neophobia. Significantly more chicks attacked spiders when they were exposed to chicks, regardless of whether their webs had discoid decorations, but few chicks attacked spiders when they were behind the decorations. We also found that significantly few chicks attacked decorations when spiders were absent or behind the decorations. We thus conclude that discoid decorations function to deter avian predators by shielding the spider from view or distracting, not by deflecting attacks, concealing the spider’s outline, or masquerading as bird-droppings. This study sheds light on the study of other similar anti-predator strategies, in a wide range of spider species and other animals that use decorating strategies. Decorating behavior is common in various animal taxa and serves a variety of functions from camouflage to communication. One common function cited for decoration is to avoid predators. However, the adaptive significance of discoid silk decorations built by juveniles of Argiope orb-weaving spiders remains puzzled. Using spectrometry, visual modeling, and chick predation experiments, we provide the direct evidence that discoid decorations function to deter avian predators by visually shielding the spider from view.