The functional significance of silk decorations of orb-web spiders: a critical review of the empirical evidence

A number of taxonomically diverse species of araneoid spiders adorn their o rb-webs with conspicuous silk structures, called decorations or stabiliment a. The function of these decorations remains controversial and several expl anations have been suggested, These include: (1) stabilising and strengthen ing the web; (2) hiding and concealing the spider from predators; (3) preve nting web damage by larger animals, such as birds; (4) increasing foraging success; or (5) providing a sunshield. Additionally, they may have no speci fic function and are a consequence of stress or silk regulation. This revie w evaluates the strength of these explanations based on the evidence. The f oraging function has received most supporting evidence, derived from both c orrelative field studies and experimental manipulations. This contrasts wit h the evidence provided for other functional explanations, which have not y et been tested as extensively. A phylogenetic analysis of the difficult dec oration patterns suggests that the different types of decorations are as ev olutionary labile as the decorations themselves: the analysis shows little homology and numerous convergences and independent gains. Therefore, it is possible that different types of decorations have different functions: and this can only be resolved by improved species phylogenics, and a combinatio n of experimental and ultimately comparative analyses.