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 Argiope aetherea - Austin, Texas (USA)
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| 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," after the mistaken idea web stabilimenta were correspondence. Stabilimenta are conspicuous lines or spirals of silk, included by many diurnal spiders at the center of their otherwise cryptic webs. It has been shown spider webs using stabilimenta catch, on average, 34% fewer insects than those without. However, webs with the easily-visible markings are damaged far less frequently by birds flying through the web. It is an evolutionary tradeoff the spider can influence every time it builds a new web. The inclusion of stabilimenta is influenced by many factors, including prey density and web location.[1]
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 (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. These spiders build large webs with centers that are 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 may prevent larger creatures from destroying the web and possibly crushing the spider underfoot.
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.
Harmless
These spiders are harmless to humans. Like most garden spiders they eat insects, and they are capable of consuming prey up to 200% of their size. 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.[2] Among these, the notable Argiotoxin ArgTX-636 (A. lobata).
 Argiope keyserlingi |
 A. bruennichi |
 A. lobata |
 Argiope |
 Ventral View |
 A. aurantia |
 Female and male |
 Australia |
 thumb|180px|left|Melbourne Zoo |
 Mature female and male A. appensa |
References
- ^ http://www.cirrusimage.com/spider_argiope_aurantia.htm Ariope aurantia and Web Stabilimena
- ^ [1] "AMPA receptor ligands: Synthetic and pharmacological studies of polyamines and polyamine toxins" Strømgaard, K.; Mellor, I. Med. Res. Rev., 2004, 589-620.
- 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
External links
- Pictures of Argiope species (free for noncommercial use)
