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| Argiope | ||||||||||||
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 female and male Argiope appensa
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| Scientific classification | ||||||||||||
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| Diversity | ||||||||||||
| 76 species | ||||||||||||
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| Aranea lobata Pallas, 1772 |
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A. aetherea |
The 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.
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Common Names
In North America, Argiope aurantia is commonly known as the "black and yellow garden spider", or "writing spider," because of the similarity of the web stabilimenta to writing.
In England, Argiope bruennichi, where it is found only on the southern coast, and in other parts of Europe, including Germany, is also known as the wasp spider. The East Asian species Argiope amoena is known in Japan as kogane-gumo. In Australia, Argiope keyserlingi and A. aetherea are known as St. Andrew's Cross spiders, for their habit of resting in the web with legs outstretched in the shape of an X, the cross of St. Andrew. The large white zigzag in the centre of its web is called the stabilimentum or web decoration.
Web
The average orb web is practically invisible, and it is easy to blunder into one and end up covered with a sticky web. The very easily visible pattern of banded silk made by Argiope is pure white, and some species make an "X" form, or a zigzag type of web (often with a hollow center). The spider then aligns one pair of its legs with each of the four lines in the hollow "X," making a complete "X" of white lines with a very eye-catching spider colored bright yellow on a field of black or variegated red white and yellow stripes forming its center. The white patterns are called stabilimentum and reflect UV light. They have been shown to play a role in attracting prey to the web, and possibly to prevent its destruction by large animals. Their centers of their large webs are often just under 1 meter above the ground, so they are too low for anything much larger than a rabbit to walk under. The overtness of the spider and its web thus has been speculated to prevent larger creatures from accidentally destroying the web and possibly crushing the spider underfoot.
Other studies suggest that as the stabilimenta may actually lead predators to the spider, species such as A. keyserlingi place their web predominantly in closed, complex habitats such as among sedges. As Argiope sit in the center of their web during the day, they have developed several other responses to predators, such as dropping off the web, retreating to the periphery of the web, or even rapidly pumping the web in bursts of up to 30 seconds, similar to the motion done by the unrelated Pholcus phalangioides.1
Reproduction
The male spider is much smaller than the female, and unassumingly marked. When it is time to mate, he spins a companion web alongside the female's. After mating, the female lays her eggs, placing her egg sac into the web. The sac contains between 400 and 1,400 eggs. These eggs hatch in autumn, but the spiderlings overwinter in the sac and emerge during the spring. The egg sac is composed of multiple layers of silk and designed to protect its contents from damage; however, many species of insects have been observed to parasitise the egg sacs.
Bite
Like almost all other spiders, Argiope are harmless to humans. Like most garden spiders they eat insects, and they are capable of consuming prey up to twice their size. A. savigny was even reported to occasionally feed on the small bat Rhynchonycteris naso2. They might bite if grabbed, but other than for defense they have no interest in biting humans. Their venom is not regarded as a serious medical problem for humans, although they often contain a library of polyamine toxins with potential as therapeutic medicinal agents.3 Among these, the notable Argiotoxin ArgTX-636 (A. lobata).
Gallery
 A. keyserlingi |
 A. aetherea at the center of its web |
 A. aurantia female and male |
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 A. pulchella |
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Footnotes
References
- Rodríguez RL & Gamboa E. 2000. Memory of captured prey in three web spiders (Araneae: Araneidae, Linyphiidae, Tetragnathidae). Animal Cognition 3, 91–97 PDF (Argiope argentata)
- Craig C.L. et al. (2001). Signal polymorphism in the web-decorating spider Argiope argentata is correlated with reduced survivorship and the presence of stingless bees, its primary prey. Evolution 55(5):986-993. Abstract
- Blamires, Sean J.; Hochuli, Dieter F. & Thompson, Michael B. (2007): Does decoration building influence antipredator responses in an orb-web spider (Argiope keyserlingi) in its natural habitat? Australian Journal of Zoology 55: 1-7. doi:10.1071/ZO06098 — PDF
- Timm, Robert M. & Losilla, Mauricio (2007): Orb-weaving Spider, Argiope savignyi (Araneidae), Predation on the Proboscis Bat Rhynchonycteris naso (Emballonuridae). Caribbean Journal of Science 43(2): 282-284. PDF
External links
- Pictures of Argiope species (free for noncommercial use)
