St Andrew's Cross spider

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{{Taxobox | color = pink | name = St Andrew's Cross spiders | image = Saint_Andrews_Cross.jpg | image_width = 200px | image_caption = Argiope spider | regnum = Animalia | phylum = Arthropoda | classis = Arachnida | ordo = Araneae | familia = Araneidae | genus = Argiope | genus_authority = Audouin, 1827 | subdivision_ranks = Species | subdivision = A. aurantia
A. bruennichi
A. pulchella
A. keyserlingi
A. aetherea
A. picta
A. mascordi
}}

The St Andrew's Cross spiders are large and spectacular spiders of the genus Argiope, also commonly called black and yellow argiopes due to the markings on their abdomens.

The genus Argiope is well distributed throughout the world, and most countries in temperate or warmer climates have one or more species, which look similar. In North America, Argiope aurantia is known as the black and yellow garden spider. In England Argiope bruennichi, found only on the southern coast, 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 Andrews Cross spiders.

The spider gained its common name for its habit of resting in its web with its legs outstretched in the shape of an X, the traditional shape of the cross of St. Andrew. The large white zigzag in the centre of its web is called the stabilimentum or web decoration and its function is controversial.

In the eastern United States, St Andrew's Cross spiders are more commonly known as writing spiders, due to the unique patterns that they build in their webs. In years past, it was sometimes called the "McKinley spider" because in the period before the election that brought McKinley to office someone claimed that the stabilimentum of one spider's web spelled out "McKinley."

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 the highly visible spider sitting in the center is bright yellow on a field of black.

These spiders build their webs with their centers about belt high, so they are too low for anything much larger than a rabbit to walk under. It is thought that the advantage to the spider of it and its web being highly visible comes from larger creatures avoiding destroying its web by walking through it. It would be an interesting experiment to see whether animals such as deer walk around them if they are on their path; if a human or other rather large creature walks through a web, then the spider's weaving job is demolished. Additionally, the spider may be accidentally stepped on and killed.

These spiders are spectacular and may be quite alarming if one is not familiar with them, but they are not dangerous. 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 defense they have no interest in biting humans. Their venom is not regarded as a serious medical problem for humans.

The male spider is much smaller than the female, and unassumingly marked. When it is time to mate, it spins a companion web alongside the females. After it mates with the female, she then lays her eggs, places her egg sac in the web. The sac contains 400-1,400 eggs. These eggs hatch in the 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, but numerous species of insects have been observed to parasitise the egg sacs.

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