Sensory exploitation in a sit-and-wait predator: Exploring the functions of stabilimenta in the banded garden spider, Argiope trifasciata
Crowe, A. Susan
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Attracting prey by exploiting a visual sensory bias is a common theme in stationary predators across many taxa, particularly for obligate ambush predators, such as orb-weaving spiders, because they construct complex prey traps. Mimicry of UV-reﬂecting ﬂoral-guides has been suggested as the mechanism behind the tendency for spiders and silk web decorations (stabilimenta) to reﬂect in the UV, to attract pollinators that they then prey upon. Also, many insects are attracted to UV because it most commonly indicates open sky, or a safe ﬂight path. My study focuses on the prey attraction function of stabilimenta, in Argiope trifasciata in eastern Ontario. Decorated webs were no more likely to contain prey than undecorated webs, but for adult spiders, longer stabilimenta were associated with increased likelihood of prey capture. For both adults and juveniles, larger webs were more likely to contain prey in undecorated webs, but for decorated webs, web size was not a predictor of prey presence. I interpret this as evidence for a trade-off between two alternative prey capture strategies: building a web with a large capture area, or building a small web with a stabilimentum. In further support of this trade-off, smaller webs were more likely to contain a stabilimentum, for both juveniles and adults. My data also suggest that close neighbours compete rather than cooperate with each other. Adult webs were spaced farther apart from each other than juvenile webs, more than would be expected based on web diameter difference. For juveniles, webs with a closer neighbour were more likely to be decorated, implying an increased need for prey attraction in the presence of a nearby competitor. For adults, prey was more likely to be found in webs that were more solitary. My results do not support the hypothesis that visually attractive spiders increased prey capture by aggregating.