![Argiope sp](https://upload.wikimedia.org/wikipedia/commons/f/fd/Argiope_sp.jpg)
A stabilimentum (plural: stabilimenta), also known as a web decoration, is a conspicuous
silk
Silk is a natural protein fiber, some forms of which can be woven into textiles. The protein fiber of silk is composed mainly of fibroin and is produced by certain insect larvae to form cocoons. The best-known silk is obtained from the coc ...
structure included in the webs of some species of
orb-web spider
Spiders ( order Araneae) are air-breathing arthropods that have eight legs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude silk. They are the largest order of arachnids and rank seventh in total species ...
. Its function is a subject of debate.
Origin
It is likely that the use of stabilimenta evolved independently at least nine different times.
''
Araneus
''Araneus'' is a genus of common orb-weaving spiders. It includes about 650 species, among which are the European garden spider and the barn spider. The genus was erected by Carl Alexander Clerck in 1757.
Description
Spiders of this genus prese ...
'' and ''
Gasteracantha
''Gasteracantha'' is a genus of orb-weaver spiders first named by Carl Jakob Sundevall in 1833. Species of the genus are known as spiny-backed orb-weavers, spiny orb-weavers, or spiny spiders. The females of most species are brightly colored wi ...
'' make silk stabilimenta, while ''
Cyclosa
''Cyclosa'', also called trashline orbweavers, is a genus of orb-weaver spiders first described by Anton Menge in 1866. Widely distributed worldwide, spiders of the genus ''Cyclosa'' build relatively small orb webs with a web decoration. The we ...
'' 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''.
[Eberhard 2006]
Form
Although web decorations are common in a number of spider species in the families
Araneidae
Orb-weaver spiders are members of the spider family Araneidae. They are the most common group of builders of spiral wheel-shaped webs often found in gardens, fields, and forests. The English word "orb" can mean "circular", hence the English name ...
,
Tetragnathidae
Long-jawed orb weavers or long jawed spiders (Tetragnathidae) are a family of araneomorph spiders first described by Anton Menge in 1866. They have elongated bodies, legs, and chelicerae, and build small orb webs with an open hub with few, wide-se ...
and
Uloboridae
Uloboridae is a family of non-venomous spiders, known as cribellate orb weavers or hackled orb weavers. Their lack of venom glands is a secondarily evolved trait. Instead, they wrap their prey thoroughly in silk, cover it in regurgitated digestive ...
, 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.
Argiope argentata
''Argiope argentata'', commonly known as the silver argiope due to the silvery color of its cephalothorax, is a member of the orb-weaver spider family Araneidae. This species resides in arid and warm environments in North America, Central Ameri ...
, more commonly known as silver argiope, are also known for spinning stabilimenta into their web. These stabilimenta can appear as zig-zag lines, and most commonly come in bouts of four creating a center-less X. 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. ''
Azilia vachoni
''Azilia'' is a genus of long-jawed orb-weavers that was first described by Eugen von Keyserling in 1881. It is a senior synonym of ''Cardimia''.
Species
it contains eleven species, found in Central America, South America, Cuba, on Saint Vinc ...
'' construct conspicuous stabilimenta with attached detritus such as egg sacs and insect carcasses (mostly their prey), and also hang debris such as dried leaves from their webs.
Stabilimentalobata.png, The detail of the stabilimentum in the web of a female ''Argiope lobata
''Argiope lobata'' is a species of spider belonging to the family Araneidae. It has a wide distribution encompassing the whole of Africa and stretching to southern Europe and into Asia.
The male of this species is small (body length 6 mm) ...
'' showing its zig-zag structure and rostral location
Argiope aetherea 5055.jpg, ''Argiope aetherea
''Argiope aetherea'' is a common, large orb-web spider (family Araneidae). Like other species of '' Argiope'', it is commonly known as the St Andrew's Cross spider, due to the characteristic cross-shaped web decorations female spiders often inclu ...
'' from Australia build X shaped decorations
Octonoba.yaeyamensis.stabilimentum.1.-.takinawa.jpg, An ''Octonoba yaeyamensis
''Octonoba yaeyamensis'' is a species of cribellate orb weaver in the family of spiders known as Uloboridae. It is endemic to the Yaeyama Islands
The Yaeyama Islands (八重山列島 ''Yaeyama-rettō'', also 八重山諸島 ''Yaeyama-shotō ...
'' with a spiral stabilimentum
Orb weaver spider (Cyclosa sp.) web stabilimentum.jpg, Oval spiral ''Cyclosa sp.'', India
India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
Signature spider (Argiope sp.) female web stabilimentum.jpg, ''Argiope sp.''
Function
There is much controversy surrounding the function of these structures, and it is likely that different species use them for different purposes.
Originally the decorations were thought to stabilize the web (hence the term ''stabilimentum''), though this hypothesis has since been dismissed because it was found that the decoration is only loosely attached to the web so that the actual influence on the stability could be minor.
Notable is the fact that stabilimentum-building spiders are largely
diurnal.
It has been suggested that stabilimenta could provide protection to the spider by either camouflaging it (by breaking up its outline), or making it appear larger (by extending its outline). Another hypothesis is that they make the web visible and therefore animals such as birds are less likely to damage the spider's web. More recent work (2016) has leaned toward this latter hypothesis, further finding that food capture was reduced by their presence. The authors note that regardless of function, there is a high cost to building a stabilimentum, and therefore the benefit must be equally large.
The other dominating hypothesis is that web decorations attract prey by reflecting
ultraviolet light
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...
.
[Craig & Bernard 1990] Light in the ultraviolet part of the spectrum is known to be attractive to many species of insects.
[
Another hypothesis is 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
''Argiope lobata'' is a species of spider belonging to the family Araneidae. It has a wide distribution encompassing the whole of Africa and stretching to southern Europe and into Asia.
The male of this species is small (body length 6 mm) ...
'' and the presence of a stabilimentum. Many other hypotheses have also been proposed, such as thermoregulation, stress, or regulation of excess silk. At least one species has been observed to vibrate the web, while positioned in the stabilimentum, when approached by a body the size of a human.
While many ''Uloborus
''Uloborus'' is a spider genus in the family Uloboridae with 80 described species. Most species occur in the tropics and subtropics, with only few species in northern America and Europe.
The chelicerae of these cribellate spiders are robust, but ...
'' 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. In contrast, the strongly UV-reflecting stabilimentum of the uloborid ''Octonoba
''Octonoba'' is a genus of Asian cribellate orb weavers first described in 1979 by Brent Opell. Members of this genus and those of '' Purumitra'' both have a large concave median apophysis and a conspicuous hematodocha. However, these spiders a ...
sybotides'' was found to be attractive to ''Drosophila
''Drosophila'' () is a genus of flies, belonging to the family Drosophilidae, whose members are often called "small fruit flies" or (less frequently) pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species ...
'' flies.[
Several evolutionary models were proposed for the inconsistency in function across species. Stark argued that although these hypotheses seemingly conflict, they might not be mutually exclusive, and suggested that we could take a hierarchical approach to model this problem: the predominant factor leading to stabilimentum production (i.e., the main function of the decoration) in each population might be different depending on the prey-and-predating context of that population. For example, in an environment where the food is abundant but predation pressure is high, the food resources are less important than prey avoidance. Therefore, it might appear that the stabilimentum has little to no effect on attracting prey but functions well as a distraction of predators. Walter offered a similar but more specific solution. He stated that the function of stabilimenta might not even be pattern or species specific. Instead, he hypothesized that the visual signaling effect of stabilimenta might be derived from some non-signaling trait that is connected to other aspects of web-building behavior, such as silk disposition; this behavior was then selected preferentially to the specific ecological environment, and therefore would be displayed through different patterns and functions among various habitats.
In '' Cyclosa argenteoalba,'' web decorations were found to support Stark's hypothesis above in that they do not attract prey and instead deter predators. This was determined through experiments where the spiders produced longer silk decorations when there was an increased predation risk, but was not affected by the amount of available prey.
]
Materials
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
''Cyclosa'', also called trashline orbweavers, is a genus of orb-weaver spiders first described by Anton Menge in 1866. Widely distributed worldwide, spiders of the genus ''Cyclosa'' build relatively small orb webs with a web decoration. The we ...
''). It seems likely that these decorations camouflage the spider, thus providing protection against predators.
Something different occurs in some species of the golden orb spiders in the genus ''Nephila
''Nephila'' is a genus of araneomorph spiders noted for the impressive webs they weave. ''Nephila'' consists of numerous species found in warmer regions around the world. They are commonly called golden silk orb-weavers, golden orb-weavers, gian ...
''. 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.
In popular culture
It is claimed that E. B. White
Elwyn Brooks White (July 11, 1899 – October 1, 1985) was an American writer. He was the author of several highly popular books for children, including ''Stuart Little'' (1945), ''Charlotte's Web'' (1952), and '' The Trumpet of the Swan'' ...
came up with the idea of a writing spider for his book '' Charlotte's Web'' after observing stabilimenta in a spider web.BugGuide.Net: Family Araneidae – Orb Weavers
/ref>
See also
*Spider web
A spider web, spiderweb, spider's web, or cobweb (from the archaic word '' coppe'', meaning "spider") is a structure created by a spider out of proteinaceous spider silk extruded from its spinnerets, generally meant to catch its prey.
Spid ...
Footnotes
References
* (2004): Web-building spiders attract prey by storing decaying matter. ''Naturwissenschaften'' 91: 245–248.
* (2005): Web decoration polymorphism in ''Argiope'' Audouin, 1826 (Ananeidae) spiders: ontogenetic and interspecific variation. ''Journal of Natural History'' 44: 3833–3845
PDF
* (2006): Silk decorations controversy and consensus. ''Journal of Zoology'' 269: 89–97.
* (1990): Insect attraction to ultraviolet-reflecting spider webs and web decorations. ''Ecology'' 71: 616–623.
* (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.
* (2006): Stabilimenta of ''Philoponella vicina
''Philoponella vicina'' is a species of spider that does not use venom (characteristic of Uloboridae), but instead wraps its prey in hundreds of metres of spider silk to crush it to death. The spider then goes on to regurgitate digestive fluid in ...
'' (Araneae: Uloboridae) and ''Gasteracantha cancriformis
''Gasteracantha cancriformis'' (spinybacked orbweaver) is a species of orb-weaver spider (family Araneidae). It is widely distributed in the New World.
The genus name ''Gasteracantha'' derives from the Greek words (', "belly") and (', "thorn" ...
'' (Araneae: Araneidae): Evidence Against a Prey Attractant Function. ''Biotropica'' 39(2): 216–220.
* (1983): Spider-Web Protection Through Visual Advertisement: Role of the Stabilimentum. ''Science'' 14 January 1983
* (1970): Stabilimentum of orb web spider, ''Argiope argentata'': an improbable defence against predators. ''Canadian Entomologist'' 102: 641–655.
* (1992): Stabilimenta characteristics of the spider ''Argiope argentata'' on small islands: support of the predator-defense hypothesis. ''Behavioral Ecology and Sociobiology'' 31: 309–318.
* (2002): The adaptive significance of stabilimentum in orb-webs: a hierarchical approach. ''Annals of Zoology'' 39: 307–315.
* (2018): Tracing the evolutionary origin of a visual signal: the coincidence of wrap attack and web decorating behaviours in orb web spiders (Araneidae). ''Evolutionary Ecology'' 32: 159–170.
* (1992): Stabilimenta as parasols: shade construction by Neogea sp.(Araneae: Araneidae, Argiopinae) and its thermal behaviour. ''Bulletin – British Arachnological Society'' 9: 42–47.
* (2004): The Effect of Food and Silk Reserve Manipulation on Decoration-Building of Argiope aetheroides.'' Behaviour'' 141: 603–616.
Further reading
* (1999): Do stabilimentum in orb webs attract prey or defend spiders? ''Behavioral Ecology'' 10(4): 372–376.
* (2002): The adaptive significance of stabilimentum in orb-webs: a hierarchical approach. ''Annals of Zoology'' 39: 307–315.
External links
Large format reference photos: Argiope spider orb web with stabilimenta
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