Argiope bruennichi

The spider builds a spiral orb web at dawn or dusk, commonly in long grass a little above ground level, taking it approximately an hour. The prominent zigzag shape called the stabilimentum, or web decoration, featured at the centre of the orb is of uncertain function, though it may be to attract insects.

When a prey item is first caught in the web, Argiope bruennichi will quickly immobilise its prey by wrapping it in silk. The prey is then bitten and then injected with a paralysing venom and a protein-dissolving enzyme.

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  showing stabilimentum
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During Summer 2006, research was carried out in the UK to find that there has been an influx of these spiders to the UK. The colour is still similar, although the yellow stripes are a bit more cream-coloured.[2]

Besides the nominate subspecies, there is one subspecies currently recognised:

• Argiope bruennichi nigrofasciata Franganillo, 1910 (Portugal)

Argiope bruennichi display a rather large distinction between males and females with males averaging length of approximately 4.5 mm and females averaging 15 mm.[3] The reasons for this large difference has evolutionary and fitness background with regards to mating as well as cannibalism by the females towards the males after copulation.

Egg sac

Wasp Spider Nest, Bulbous bulb silk nest 1

The differences of size of these male spiders actually allows the males to come into contact with the females in relation to their orb webs. The male Argiope bruennichi are able to enter into the female's orb and thus make their webs without being detected as prey and thus eaten before they are able to mate, a major fitness advantage.[3]

Certain male Argiope bruennichi have an adaptation that they have developed to ensure that they will be the only mate with whom the female can produce offspring. Certain males are able to "plug" the female after they have mated with her to prevent other males from copulating with the female. This plugging involves using the entire male's body, thus allowing him to only mate once. This is a major reason as to why these males are always in a rush to mate after the female has completed her final moult.[4] With males always waiting around for the female to reach full maturity, the race is on for the male who is small enough to not be detected, yet is also able to "plug" the female so that no other male can compete for fertilization of her eggs. These spiders have evolved to become monogamous for the most part after mating because of this damage.

If the females are only able to reproduce once they must develop a method to produce more offspring at one time (per clutch). This can be caused by multiple things, including a sex ratio that forces these males to make sure they have at least one female to produce their offspring simply because there are not as many females present.[5] If these females are only able to mate one time, they need to develop this larger clutch size to ensure that their genes are passed down from the surviving of her first clutch.

Females that consumed a small supplement of dietary essential amino acids produced offspring that survived simulated overwintering conditions significantly longer than offspring of other treatments. Results suggest that dietary essential amino acids, which may be sequestered by males from their diet, could be valuable supplements that increase the success of the offspring of cannibalistic females.[6]

The species Argiope bruennichi displays cannibalism when it comes to mating. We can see this because the sex ratio is so biased towards females later in the mating season. With so few females available, the males need to develop their own ways to potentially find and secure a successful mating like small size and proper time to find an immature female. The females, typically much larger in size when compared to the males, almost always consume their male counterpart after copulation. Males can often be seen in or near a female's web waiting for her to complete her final moult, at which time she reaches sexual maturity. At this time her chelicerae (jaws) will be soft for a short time and the male may mate with the female without the danger of being eaten. These males obviously want to avoid getting eaten and this is more or less the only time that they are able to take advantage. Although the cause for this type of dimorphism between sexes seems to have a much larger benefit for the females.[7]

• Ella Davies (22 March 2013). "Cold-tolerant wasp spiders spread to northern Europe". BBC Nature.
• "Argiope bruennichi". Fauna Europaea. 2004.
• Daiqin Li (2005). "Spiders that decorate their webs at higher frequency intercept more prey and grow faster". Proceedings of the Royal Society B: Biological Sciences. 272 (1574): 1753–1757. doi:10.1098/rspb.2005.3160. PMC 1559872. PMID 16096085.