Web decorations

Web decorations, sometimes termed stabilimenta, are conspicuous silk structures included in their webs by many species of orb-web spider. There is much controversy surrounding the function of these structures. Some people believe that they provide protection to the spider by either camouflaging it or making it appear larger. Another theory is that they make the spider visible and therefore animals are less likely to damage the spider’s web. A more recent theory is that web decorations attract prey by reflecting ultraviolet light. Light in the ultraviolet part of the spectrum is known to be attractive to many species of insects. Many other theories have also been proposed such as thermoregulation, stress, regulation of excess silk and web stabilisation (the source of the term "stabilimenta").

Although web decorations are common in a number of spider species in the families Araneidae, Tetragnathidae and Uloboridae, most people know them from spiders in the genus Argiope. This genus includes a number of species known as the St Andrew's Cross spider, so named because of the characteristic cross-shaped web decoration. However, spiders in this genus also construct web decorations as a vertical line and juveniles commonly construct disc-shaped decorations.

While the most conspicuous and well-studied decorations are constructed entirely of silk, some spiders combine silk with other items such as egg sacs and debris. It seems likely that these decorations camouflage the spider, thus providing protection against predators. However, one interesting case occurs in some species of the golden orb spiders in the genus Nephila. These spiders commonly attach lines of uneaten prey items to their webs. Recent studies have shown that these items help the spider to attract more prey.