The
golden silk orb-weavers (genus
Nephila) are a
genusIn biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of araneomorph
spiderSpiders are air-breathing arthropods that have eight legs, and chelicerae with fangs that inject venom. They are the largest order of arachnids and rank seventh in total species diversity among all other groups of organisms...
s noted for the impressive webs they weave.
Nephila consists of numerous individual species found around the world. They are also commonly called
golden orb-weavers,
giant wood spiders, or
banana spiders. In
North AmericaNorth America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, the golden silk orb-weavers (see also
Nephila clavipesNephila clavipes is a species of golden orb-web spider. It lives in the warmer regions of the Americas. The large size and bright colours of the species make it distinctive...
) are sometimes referred to as
writing spiders due to occasional zigzag patterns (stabilimenta) built into their webs, though these occur much more frequently in the webs of
ArgiopeThe genus Argiope includes rather large and spectacular spiders that have often a strikingly coloured abdomen. These are well distributed throughout the world, and most countries in temperate or warmer climates have one or more species, which look similar....
, such as the St Andrew's Cross spider.
The species
N. jurassicaNephila jurassica is an extinct species of spider in the family Nephilidae, which contains the golden silk orb-weavers. The species is known only from the Middle Jurassic Jiulongshan Formation, part of the Daohugou Beds, near the village of Daohugou in Ningcheng County, northeastern China.-History...
, which lived about 165 million years ago, had a leg span of some 15 cm, and is the largest known fossilized spider.
Etymology
The genus name
Nephila is derived from
Ancient GreekAncient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
, meaning "fond of spinning", from the words (
nen) = to spin (related to
nema νήμα "thread") + φίλος (
philos) = "love".
Appearance and distribution
Nephila spiders vary from reddish to greenish yellow in color with distinctive whiteness on the cephalothorax and the beginning of the abdomen. Like many species of the superfamily
AraneoideaThe Araneoidea are a superfamily of araneomorph spiders. They contain families of eight-eyed spiders:* Anapidae* Araneidae* Cyatholipidae* Linyphiidae* Mysmenidae* Nephilidae* Nesticidae* Pimoidae* Sinopimoidae* Symphytognathidae* Synaphridae...
, they have striped legs specialized for weaving (where their tips point inward, rather than outward as is the case with many wandering spiders). Their contrast of dark brown/black and green/yellow allows warning and repelling of potential predators to whom their venom might be of little danger.
Golden orb-weavers reach sizes of 4.8 - 5.1 cm (1.5 - 2 in) in females, not including legspan, with males being usually 2/3 smaller (less than 2.5 cm, 1 in). The largest specimen ever recorded was a 6.9 cm (2.7 in) female
N. clavipes (which is now debated to have been a new yet undocumented subspecies) from
QueenslandQueensland is a state of Australia, occupying the north-eastern section of the mainland continent. It is bordered by the Northern Territory, South Australia and New South Wales to the west, south-west and south respectively. To the east, Queensland is bordered by the Coral Sea and Pacific Ocean...
, that was able to catch and feed on a small-sized
finchThe true finches are passerine birds in the family Fringillidae. They are predominantly seed-eating songbirds. Most are native to the Northern Hemisphere, but one subfamily is endemic to the Neotropics, one to the Hawaiian Islands, and one subfamily – monotypic at genus level – is found...
.
Golden silk orb-weavers are widespread in warmer regions throughout the world, with species in
AustraliaAustralia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
,
AsiaAsia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
,
AfricaAfrica is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
(including
MadagascarThe Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...
), and
AmericaThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
. One species,
N. clavipesNephila clavipes is a species of golden orb-web spider. It lives in the warmer regions of the Americas. The large size and bright colours of the species make it distinctive...
, occurs in the United States of America, where it ranges throughout the coastal southeast and inland, from
North CarolinaNorth Carolina is a state located in the southeastern United States. The state borders South Carolina and Georgia to the south, Tennessee to the west and Virginia to the north. North Carolina contains 100 counties. Its capital is Raleigh, and its largest city is Charlotte...
to
TexasTexas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
.
Nephila spiders are the oldest surviving genus of spiders, with a fossilized specimen known from 165 million years ago.
Web spin
The name of the golden silk orb-weavers refers to the colour of the
spider silkSpider silk is a protein fiber spun by spiders. Spiders use their silk to make webs or other structures, which function as nets to catch other animals, or as nests or cocoons for protection for their offspring...
, not the colour of the spider itself.
Yellow threads of their web shine like gold in sunlight.
Xanthurenic acidXanthurenic acid is a chemical shown to induce gametogenesis of Plasmodium falciparum, the parasite that causes malaria. It is found in the gut of the Anopheles mosquito....
, two quinones and an unknown fourth compound contribute to the yellow color. Experimental evidence suggests that the silk's color may serve a dual purpose: sunlit webs ensnare bees that are attracted to the bright yellow strands, whereas in shady spots the yellow blends in with background foliage to act as a camouflage. The spider is able to adjust pigment intensity relative to background light levels and colour; the range of spectral reflectance is specifically adapted to insect vision.
The webs of most
Nephila spiders are complex, with a fine-meshed orb suspended in a maze of non-sticky barrier webs. As with many weavers of sticky spirals, the orb is renewed regularly if not daily, apparently because the stickiness of the orb declines with age. When weather is good (and no rain has damaged the orb web), subadult and adult
Nephila often rebuild only a portion of the web. The spider will remove and consume the portion to be replaced, build new radial elements, then spin the new spirals. This partial orb renewal is distinct from other orb-weaving spiders that usually replace the entire orb web. In 2011 it was discovered that the web of Nephila antipodiana contains ant-repellent chemicals to protect the web.
Typically, the golden orb-weaver first weaves a non-sticky spiral with space for 2-20 more spirals in between (the density of sticky spiral strands decreases with increasing spider size). When she has completed the coarse weaving, she returns and fills in the gaps. Whereas most orb-weaving spiders remove the non-sticky spiral when spinning the sticky spiral,
Nephila leave it. This produces a "
manuscript paperManuscript paper is paper preprinted with staves ready for musical notation. Manuscript paper is also available for drum notation and guitar tabulature. The treble clef is used for many band instruments including the saxophone,sitar, trumpet, clarinet and flute...
" effect when the orb is seen in the sun: groups of sticky spirals reflecting light with "gaps" where the non-sticky spiral does not reflect the light.
The circular-orb portion of a mature
N. clavipes web can be more than 1 meter across, with support strands extending perhaps many more feet away. In relation to the ground, the webs of adults may be woven anywhere from eye-level upwards high into the tree canopy. The orb web is usually truncated by a top horizontal support strand, giving it an incomplete look.
Adjacent to one face of the main orb there may be a rather extensive and haphazard-looking network of guard-strands suspended a few inches distant across a free-space. This network is often decorated with a lumpy string or two of plant detritus and insect carcasses clumped with silk. This "barrier web" may function as a kind of early-warning system for incoming prey or against spider-hunting predators, or as a shield against windblown leaves; it may also be remnants of the owner's previous web. At least one reference explains the suspended debris-chain as a cue for birds to avoid blundering into and destroying the web.
Stabilimenta among
N. clavipes are sometimes seen in the webs of immatures nearing molt, hence the names "molting webs" or "skeleton webs" (webs with radial strands but no spiral elements).
Prey-capturing mechanisms
The Australian golden silk orb-weaver (
Nephila edulis) has been observed on windy, rainy days dismantling the lower part of its web to allow strong wind to flow through a large opening in the web without breaking it. Golden Orb Weavers are known to occasionally eat prey as big as small birds.
Parasites
N. clavipes (and many other
Nephila species) are frequently victimized by
ArgyrodesSpiders of the genus Argyrodes , also called dewdrop spiders, occur worldwide. They are best known as kleptoparasites: they steal other spiders' prey. They invade and reside in their host's web even though they can spin their own webs...
, a genus of very small black-and-silver spiders that are
kleptoparasiticKleptoparasitism or cleptoparasitism is a form of feeding in which one animal takes prey or other food from another that has caught, collected, or otherwise prepared the food, including stored food...
. As many as a few dozen may infest a single
Nephila web to feed from the host spider's captured prey. The frequent rebuilding or abandoning of webs by
Nephila may be a tactic for controlling
Argyrodes.
Spiny orb-weaverSpiny orb-weavers is a common name for Gasteracantha, a genus of spiders. They are also commonly called Spiny-backed orb-weavers, due to the prominent spines on their abdomen. These spiders can reach sizes of up to 30mm in diameter...
spiders also inhabit the webs of
Nephila to obtain food.
Spiderlings
Young spiders do not generally build yellow-colored silk, and the young
Nephila themselves can be easily mistaken for young
Orchard Spiders (
LeucaugeLeucauge is a spider genus with pantropical distribution.The body and leg shapes and the silver, black and yellow markings of Leucauge females make identification of the genus relatively easy. They have two rows of long, slender curved hairs on the femurs of the fourth leg...
) in general color and shape (both species sport silver stripes or patches on their abdomens, described in some references as a form of heat control). The best distinction between
Leucauge and
Nephila juveniles is web structure:
Leucauge tends to build a horizontal orb that is a perfect circle, whereas
Nephila build vertical, elliptical orbs that are incomplete (missing the portion of the orb over the hub, the center where the spider sits).
Nephila seem to prefer more open habitat such as second-growth scrub or forest edges. Fences or building overhangs often do just as nicely.
In addition, young spiders demonstrate vibrational motion when approached by a predator. They will oscillate at approximately 40 Hz when the web is plucked—thought to be a response to a potential predator. If a predator persists in an attack, the spider will either run to a web-support strand and thus to nearby vegetation, bail out of the web on a silk line that remains connected to the web, or jump from the web after inducing oscillations in the web that aid the jump.
Toxicity
The venom of the golden silk orb-weaver is potent but not lethal to humans. It has a neurotoxic effect similar to that of the
black widow spiderLatrodectus mactans, the Southern black widow, is a highly venomous species of spider in the genus Latrodectus. They are well known for the distinctive black and red coloring of the female of the species and for the fact that she will occasionally eat her mate after reproduction. The species is...
; however, its venom is not nearly as powerful. The bite causes local pain, redness, and blisters that normally disappear within a 24-hour interval. In rare cases, it might trigger allergic reactions and result in respiratory troubles (in asthmatics) or fast-acting involuntary muscle cramps. As the genus possesses relatively strong
cheliceraeThe chelicerae are mouthparts of the Chelicerata, an arthropod subphylum that includes arachnids, Merostomata , and Pycnogonida . Chelicerae are pointed appendages which are used to grasp food, and are found in place of the chewing mandibles most other arthropods have...
, the bite could leave a scar on hard tissue (such as fingers).
Interaction with humans
These spiders do not seem to form either beneficial or harmful relationships with humans. As they weave their webs in bushes and near flowers, they might present a nuisance for gardeners or flower pickers. Some nests near fruits may repel known pests, such as the
fruit flyDrosophila melanogaster is a species of Diptera, or the order of flies, in the family Drosophilidae. The species is known generally as the common fruit fly or vinegar fly. Starting from Charles W...
, without the need to use
insecticideAn insecticide is a pesticide used against insects. They include ovicides and larvicides used against the eggs and larvae of insects respectively. Insecticides are used in agriculture, medicine, industry and the household. The use of insecticides is believed to be one of the major factors behind...
s.
There were efforts to produce garments from
Nephila silk. The spiders were fastened and the extruding thread coiled up until the spider was exhausted. However, this method did not prove commercially viable.
A possible use of
Nephila silk lies in tissue engineering. A study from the Medizinische Hochschule Hannover reports that processed
Nephila silk is an excellent scaffold material thanks to its biocompatibility, mechanical strengths, and its property to promote cell adhesion and proliferation. In particular, the silk acts as a suitable guiding material for peripheral nerve regrowth.
A unique cloth woven from golden silk of over 1 million golden orb female spiders is on exhibit in the
American Museum of Natural HistoryThe American Museum of Natural History , located on the Upper West Side of Manhattan in New York City, United States, is one of the largest and most celebrated museums in the world...
.
Fishermen on coasts of the indopacific ocean remove
Nephila webs and form them into a ball, which is thrown into the water. There it unfolds and is used to catch bait fish.
Nephila in popular culture
In
Japanese folkloreThe folklore of Japan is heavily influenced by both Shinto and Buddhism, the two primary religions in the country. It often involves humorous or bizarre characters and situations and also includes an assortment of supernatural beings, such as bodhisattva, kami , yōkai , yūrei ,...
,
JorōgumoJorōgumo is a type of Yōkai, a creature, ghost or goblin of Japanese folklore. According to some stories, a Jorōgumo is a spider that can change its appearance into that of a seductive woman....
, a type of
yōkaiare a class of supernatural monsters in Japanese folklore. The word yōkai is made up of the kanji for "otherworldly" and "weird". Yōkai range eclectically from the malevolent to the mischievous, or occasionally bring good fortune to those who encounter them...
, is thought to be a Nephila (
Jorō spider) which can shapeshift its appearance into a seductive woman.
External links
- Spider eats bird, The Cairns Post, October 23, 2008
- Photographer found, The Cairns Post, October 24, 2008
- Studies of the golden silk spider, weaving and catching prey
- Female and Male Nephila clavipes mating
- Studies of female and male Nephila clavipes (banana spider)
- Juvenile banana spiders and vibrational predatory responses
- Australian Nephila edulis
- Australian spiders set to train with astronauts for space shuttle mission
- Description, distribution and picture of N. plumipes
- golden silk spider on the UF
The University of Florida is an American public land-grant, sea-grant, and space-grant research university located on a campus in Gainesville, Florida. The university traces its historical origins to 1853, and has operated continuously on its present Gainesville campus since September 1906...
/
Pictures
Videos