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Vol 7 No 1 Apr 2000 St. Andrew's Cross Spider Yellow-bellied Prinia Life in the Mangroves: snippets on plants & animals Divine Diversity Shorebird Population Monitoring (1992-1998) Inundation in the Park Service with a Smile: the Park's frontline staff Field Ornithology training in Sarawak Millenium mementos Butterfly Trail Adoption		Pong Yen Ting reveals the mystery that surrounds the web of the St. Andrew's Cross Spider A cryptic name, a cryptic creature. First glance at the common name of this araneid spider of the genus Argiope, one may think: "Why St. Andrew's Cross?" This is so because this particular spider likes to contort its 20mm (males: 5mm) frame to resemble a cross. It does not care for the gangly eight-legged look that most spiders sport. Rather, it prefers to pair its legs so that it appears to be aligned to the four distinguished arms of the Cross of St. Andrew's. The St. Andrew's soft spot for all things 'X' is further seen on the stabilimentum that takes pride of place at the centre of the 38-50mm wide web of the mature female. The mangrove specimen (Argiope mangal) usually spins two of these silken zig-zag bands named stabilimentum, while the inland counterparts like the Argiope versicolor, will spin four bands to form the shape of a cross. This extraordinary phenomenon of the 'X' has drawn a good amount of speculation as to its significance. For many years, it was thought that the function of the zig-zag bands was to strengthen the web or to conceal the spider which often sits, head downward, at the centre of the stabilimentum. Some scientists in the United States established that the purpose of the stabilimentum is to advertise the presence of the web to birds. The birds will know to avoid the webs if they do not want to risk being entangled in the sticky silk. The spiders thus get to preserve their webs, which they will eat when worn out, as it is a precious source of protein supply for silk production. However, recent research has uncovered a new explanation. The silk which makes up most of the web is a poor reflector of ultraviolet light, except the stabilimentum which reflects it very efficiently. In the same way flowers reflect ultraviolet light to attract pollinating insects, the stabilimentum is believed to attract insects to the web, by mimicking a flower. We do not know for sure the reason for the zig-zag bands. Perhaps it just appeals to this little spider's aesthetic sense? Speaking of aesthetic, many will certainly appreciate the pretty webs of the juvenile St Andrew's Cross Spider. These light brown youngsters weave an exquisite disc of lace in the middle of their abodes. As they mature, they add a cross to the disc. When they finally attain adulthood, they only make the cross, or half a cross, in the case of the Argiope mangal. The orb web of the St. Andrew's Cross spider may be good-looking but more importantly, it plays a major role in the spider's eventual survival. Firstly, with only a relatively small outlay of material, it forms a flexible, strong structure spanning a large area— the ideal trap for flying insects. When an insect hits the web, the spider runs out, shrouds it in fine silk and bites it to death. Then, digestive juices are injected into the wrapped prey and the contents sucked out when the digestive process is complete (in a day or so). The careful geometrical arrangement of the capture threads and the spokes allows the spider to move around the web on the thread without becoming trapped. The web is also a defensive tool for the spider. If disturbed, it can flip from one side of the web to the other with lightning swiftness, thus keeping the web between itself and the would-be attacker. Alternatively, it may shake the web vigorously until it becomes an indistinct blur. Apparently, the St Andrew's Cross Spider is not just literally cross in its physical appearance but can be rather cross in temperament too!
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