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Mangrove St. Andrew's
Cross Spider

Argiope mangal


These spiders get their name for the way their hold their eight legs in pairs to form an X shape. The X is called the St. Andrew's cross because it is believed that the saint was martyred on a cross of this shape rather than the conventional + shape.

Besides their standard orb-web, Argiope spiders build additional white opaque zig zag lines on their webs, called stabilimentum.
Mangrove and wetland wildlife at
Sungei Buloh Nature Park
on its web with only two white silk bandsMain features: Small spiders with brightly coloured abdomens; striped white, red, black and yellow.

Male: 2mm. The male lives on the female's web.

Female: 5mm

Status in Singapore: Common in mangroves. This species is only recorded from Singapore.

Classification: Family Araneidae.
Sometimes the zig-zag lines match their leg positions, which lead some people to suggest that this helps give the appearance of longer legs. Some spiders build a single vertical line, yet others a patch of zig zags in the centre of the web. No matter the design, the spider sits right smack in the middle. We do not know the purpose of these lines, but some of the explanations put forward include:
  • They stabilise the web (hence their name!)
  • They warn larger animals in the same way that safety strips on glass doors warn people from walking into them. Thus the web is protected from damage by flying birds.
  • Research has shown that the silk in the stabilimentum reflects ultraviolet well, unlike the silk used in the rest of the web. Thus, the designs may mimic flowers, which also reflect ultraviolet light well, and often have lines to guide insects to honey like airport lights do for airplanes. Instead, the insects are guided to the spider which sits in the centre!!
Like many other spiders, the male is half to one-third the size of the females.

Like many other spiders, only the female Argiope mangal build the webs. These are orbs 38-50mm wide and contain only 2 stabilimentum. Argiope versicolor, which is found inland, makes the "full" cross with 4 stabilimentum. When prey is caught in the web, the spider throws out broad swathes of white silk to immobilise the prey, then rapidly rotates it to tighten the binding before administering the fatal bite. Small spiders which are unable to rotate the prey, run around the prey instead as they throw out binding silk.

close up of st andrew's spider abdomenWhen it is disturbed, Argiope mangal vibrates the web so its outline becomes blurred. Another response to flip to the other side of the web in a blink of the eye, through a gap in the web. Yet another response is to simply drop off the web. Large ones may simple wiggle their abdomens, which have a pair of large black eye-like dots.
close-up of moulting spider
A rare look at
a moulting spider

Role in the habitat: like other predators, the spiders keep the population of their prey in check. They in turn, are eaten by other creatures in the food chain.

LINKS
REFERENCES
  To buy these references & others, visit
Nature's Niche
  • Joseph K H Koh, "Spiders of the Family Araneidae in Singapore Mangroves", The Raffles Bulletin of Zoology, 1991 39(1) (p. 169-182).
  • Joseph K H Koh, "A Guide to Common Singapore Spiders", BP Guides, Science Centre, 1989 (p. 28-30 for other Argiope species: habits, habitat, distribution, photos of spider and web).
  • Peter K L Ng and N Sivasothi, "A Guide to the Mangroves of Singapore II: Animal Diversity", Singapore Science Centre, 1999 (p. 92 on Argiope Mangal: description, habits, habitat, photos).
  • Rod Preston-Mafham, "The Book of Spiders", Chartwell Books, 1991 (95-97: about their webs).
 
By Ria Tan, 2001