||This article contains weasel words: vague phrasing that often accompanies biased or unverifiable information. (December 2011)|
A web decoration or stabilimentum (plural: stabilimenta) is a conspicuous silk structure included in the webs of some species of orb-web spider. Web decorations consist of silk ribbons, silk tufts, prey remains, egg sacs, and plant detritus. There are many hypotheses that have been proposed for why web decorations exist but the prey attraction and predator defense hypotheses have been tested significantly. Through these tests, researchers suggested that web decorations improve foraging success because more prey gets attracted to the webs. There is also evidence that depicts that the silk material of the web reduces the amount of web damage. On the other hand there is contradicting evidence that shows that silk decorations from Argiope actually attract other insects. The function of stabilimentum is a subject of debate.
It is likely that the use of stabilimenta evolved independently at least nine different times. Araneus and Gasteracantha make silk stabilimenta, while Cyclosa and the closely related Allocyclosa bifurca make stabilimenta of silk, detritus, and their egg sacs. All those evolved independently from those of Argiope, although some decorations of Allocyclosa bifurca closely resemble those of Argiope.
Although web decorations are common in a number of spider species in the families Araneidae, Tetragnathidae and Uloboridae, they are probably best known from spiders of the genus Argiope. This genus includes a number of species known as the Saint Andrew's Cross spiders, so named for their habit of resting in their webs with their legs outstretched in the shape of an X, the traditional shape of the cross of Saint Andrew. Spiders in this genus also construct web decorations as a vertical line, and juveniles commonly construct disc-shaped decorations. Other spiders construct round structures covering the entire hub of the web.
All spiders have spineretes (most have 3 sets of spinerets) attached to the rear of their abdomens and are capable of spinning webs. The silk is used for all kinds of different purposes such as capturing food, wrapping their prey, and covering egg cases.
Changes in a spider’s environment can also have an effect on its web decoration when it comes to orb web spiders. An orb web is an altering foraging tool, which responds to changes in its respective prey. It consists of a “frame with attached radial threads, sticky spirals, a hub, a free sector and in some species, decorations”.
There is much controversy surrounding the function of these structures, and it is likely that different species use it for different purposes. It has been suggested that they could 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 such as birds are less likely to damage the spider’s web. Originally the decorations were thought to stabilize the web (hence the term stabilimentum), though this theory has since been dismissed. Spectrophotometric data depicts that the silk material of the web decoration reflect light in the ultraviolent range attracting prey. The web material made of detritus, were assumed to provide protection through camouflage from predators. It was assumed because the experiment did not have enough evidence to conclude that the web with plant detritus decorations concealed the spiders from predators. Many other theories have also been proposed such as thermoregulation, stress, regulation of excess silk, or simple aesthetics. At least one variant has been observed to vibrate the web, while positioned in the stabilimentum, when approached by a body the size of a human. Another theory is camouflage as it breaks up the outline of the spider. One theory has been put forward that the purpose of the stabilimentum is to attract the male of the species to the web when the female is ready to reproduce. A limited study carried out in the Calahonda area of Spain in the summer of 1992 showed that there was a positive correlation between the presence of a male in the webs of Argiope lobata and the presence of a stabilimentum.
There two most popular theories presented are the predator defense theory and the prey attraction theory. The Prey Attraction Hypothesis states that a spider creates decorations on its web in order to lure its prey, drawing them into the web. The decorations can obscure the spider’s body and make it appear larger/more dangerous than it really is. The Predator Defense Hypothesis states that the decorations on the webs conceal the spider from its predators. The spider will tend to hide in a zig-zag pattern it created or even on flattened cylinder of egg sacs so that their visibility is decreased. A study done with Argiope aurantia and Argiope trifasciata spiders suggested that the stabilimenta was used, by this species of spiders, as a predator defense mechanism. The foraging success of well-fed spiders were compared with those that were poorly fed. Well-fed Agirope spiders included stabilimenta more often in their webs than poorly fed Agirope spiders. This suggest that the predator defense hypothesis is correct. More research done suggested that stabilimentum building is a defensive behavior that can prevent birds from flying through webs. Yet, because some spiders do not include it in their web, it indicates that there is a cost associated with it.
While many Uloborus species construct stabilimenta, Uloborus gibbosus does not; it usually rests at an edge of its orb and drops to the ground if disturbed. This is thought to support the web camouflage hypothesis. The strongly UV-reflecting stabilimentum of the uloborid Octonoba sybotides was found to be attractive to Drosophila flies.
There is a foraging cost associated with the web decorations. The decreased amount of food gained from having a web with a decoration indicates that the decorations have a foraging cost.
Adaption of spider stabilimenta is an example of a Darwinian puzzle.
|Low Prey Encounters||
|High Prey Encounters||
|Variable Prey Supply||
The table supports that web decorations are an adaptation because based on the number of prey encounters the spiders were subjected to, the spiders changed their behavior. A low amount of prey encounters led the spiders to make a larger web with a few number of decorations and a high amount of prey encounters led the spiders to have more decorations on the web.
While the most conspicuous and well-studied decorations are constructed entirely of silk (for example in Argiope), some spiders combine silk with other items such as egg sacs and debris (for example in Cyclosa). 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.
- Tan, 2010
- Eberhard 2006
- Bruce & Herberstein 2005
- Natural History Museum of Los Angeles
- Blamires, 2011
- Schoener & Spiller 1999
- Herberstein et al. 2000; Bruce 2006; Eisner & Nowicki 1983
- Robinson & Robinson 1970
- Tickner 1992 (unpublished)
- Blackledge, 1998
- Blackledge and Wenzel 1998
- Herberstein et al
- Eberhard 2003
- Bjorkman-Chiswell et al. 2004
- Bjorkman-Chiswell, Bojun T.; Kulinski, Melissa M.; Muscat, Robert L.; Nguyen, Kim A.; Norton, Briony A.; Symonds, Matthew R.E.; Westhorpe, Gina E. & Elgar, Mark A. (2004): Web-building spiders attract prey by storing decaying matter. Naturwissenschaften 91: 245-248. doi:10.1007/s00114-004-0524-x
- Bruce, M.J. & Herberstein, Marie E. (2005): Web decoration polymorphism in Argiope Audouin, 1826 (Ananeidae) spiders: ontogenetic and interspecific variation. Journal of Natural History 44: 3833-3845. PDF
- Bruce, M.J. (2006): Silk decorations controversy and consensus. Journal of Zoology 269: 89-97. doi:10.1111/j.1469-7998.2006.00047.x
- Craig, Catherine L. & Bernard, Gary D. (1990): Insect attraction to ultraviolet-reflecting spider webs and web decorations. Ecology 71: 616-623. doi:10.2307/1940315
- Eberhard, William G. (2003): Substitution of silk stabilimenta for egg sacks by Allocyclosa bifurca (Araneae: Araneidae) suggests that silk stabilimenta function as camouflage devices. Behaviour 140: 847-868. doi: 10.1163/156853903770238346
- Eberhard, William G. (2006): Stabilimenta of Philoponella vicina (Araneae: Uloboridae) and Gasteracantha cancriformis (Araneae: Araneidae): Evidence Against a Prey Attractant Function. Biotropica 39(2): 216-220. doi:10.1111/j.1744-7429.2006.00254.x
- Eisner, T. & Nowicki, S. (1983): Spider-Web Protection Through Visual Advertisement: Role of the Stabilimentum. Science 14 January 1983
- Robinson, M.J. & Robinson, B (1970): Stabilimentum of orb web spider, Argiope argentata: an improbable defence against predators. Canadian Entomologist 102: 641-655. doi:10.4039/Ent102641-6
- Schoener, T.W. & Spiller, D.A. (1992): Stabilimenta characteristics of the spider Argiope argentata on small islands: support of the predator-defense hypothesis. Behavioral Ecology and Sociobiology 31: 309-318. doi:10.1007/BF00177771
- Tan, Eunice, J., Seah, Stanley, W. H., Yap, Laura-Marie, Y.L., Goh, Poi Moi, Gah, Wenjin, Liu, Fengxiang, Li, Daiqin. (2010) Why do orb-weaving spiders (Cyclosa ginnaga) decorate their webs with silk spirals and plant detritus?. Animal Behaviour. 79 (1) 179-186. http://www.sciencedirect.com/science/article/pii/S0003347209004941
- Blamires, Sean, J., Chao, Yi-Chi, Liao, Chen-Pan, Tso, I-Min (2011) Multiple prey cues induce foraging flexibility in a trap-building predator. Animal Behaviour. 81(5) 955-961http://www.sciencedirect.com/science/article/pii/S00033472110002
- Spider Survey - Spider Biology | Natural History Museum of Los Angeles." Spider Survey - Spider Biology | Natural History Museum of Los Angeles. N.p., n.d. Web. 01 Dec. 2014.http://www.nhm.org/site/activities-programs/citizen-science/spider-survey/spider-biology
- Herberstein et al. "The function significance of silk decorations of orb-web spiders: a critical review of the empirical evidence. National Center for Biotechnology Information. U.S. National Library of Medicine, n.d. Web. 01 Dec. 2014. http://www.ncbi.nlm.nih.gov/pubmed/11117202
- Blackledge, Todd A. (1998) “Stabilimentum variation and foraging success in Argiope aurantia and Argiope trifasciata (Araneae: Araneidae)” J. Zool., Lond. (1998) 246 ,21±27 http://www3.uakron.edu/biology/blackledge/PDFs/J_Zool_1998.pdf
- Blackledge, Tood A, Wenzel, John W. (1998) “Do stabilimenta in orb webs attract prey or defend spiders?” Behavioral Ecology (1999) 10 (4): 372-376. http://beheco.oxfordjournals.org/content/10/4/372.full
- Cheng et al, (2009) “Insect Vision as one potential shaping force of web decoration design” Journal of Experimental Biology: 10 (759-764) Accessed December 2014 http://jeb.biologists.org/content/213/5/759.abstract
- Walter et al, (2008) “Wrap Attack activates web-decorating behavior in Argiope spiders” Behavioral Ecology: 19, 04 p799-804. Accessed November 2014 http://beheco.oxfordjournals.org/content/19/4/799.full
- Starks, P.T. (2002): The adaptive significance of stabilimentum in orb-webs: a hierarchical approach. Annals of Zoology 39: 307-315.
|Wikimedia Commons has media related to Stabilimentum.|