Long-term, low incidence of web-decorating by spiders in the Mariana Islands, Micronesia.

Abstract

Many orb-weaving spiders build webs invested with curious flags, spirals, or zig-zagging ribbons of bright silk termed "decorations" or "stabilimenta". Web decorating arose some 150 million years ago in nine araneoid lineages, which have diversified into hundreds of species referable to about two dozen genera, with few reversions to non-decorating (Scharff and Coddington 1997; Garrison et al. 2016). But why natural selection might favor spiders weaving decorations remains unclear. Indeed, naturalists have been speculating about the behavior since at least Charles Darwin, who suggested in an 1832 journal entry that the device "strengthened" the web (Darwin 1839, p. 41). Over the nearly two centuries since then, more than a dozen other functions for web decorations have been proposed (Walter and Elgar 2012). Experimental tests began in the late 20th century and provide the strongest support for the device as a visual signal in prey attraction (Craig and Bernard 1990), predator avoidance (Blackledge and Wenzel 1999), or warning to flying birds of the web's location (Eisner and Nowicki 1983), as well as indicate that its function(s) are likely balanced against significant and varied costs (Yeh et al. 2015).