Argiope australis 01

On 07 March 2004, while doing the Klein Tuinkop Summit Circuit from Silvermine via the Crassula Path and back via Klein Tuinkloof, I came across this female Black and Yellow Garden Spider (Argiope australis). They are a common spider found in many gardens and in the fynbos and are a member of the orb-web group of spiders.

The orb-web group of spiders were recently divided into two families i.e.:

Araneidae		30 genera in South Africa
Tetragnathidae		7 genera in South Africa

The reason for this division is the way the two families deal with ensnared prey. The Araneidae first wraps its prey in silk after capture and then bites it. The Tetragnathidae first bites and then wraps its prey.

The Black and Yellow Garden Spider (Argiope australis) belongs to the Araneidae family.

The larger female has a yellow and black scalloped abdomen. The legs are thin and black striped. They support the spider to normally hang upside down with its two back and two front legs together. From a distance the spider appears to have four instead of eight legs. The head is silvery grey. The males are far smaller and quite insignificant in comparison.

These spiders are harmless to man.

They construct large wheel-like webs (orbs). As a diurnal species they continually repair their webs, using them for a number of days. The characteristic orb-web has two zig-zag bands of silk radiating outwards from the center to the corners of the web. These are known as the stabilimenta. Each stabilimentum functions to stabilize and strengthen the web. Some experiments have shown that its function is to advertise the presence of their web to birds allowing them to avoid the web. The webs, mainly stretched across bushes, are normally built within one metre of the ground.

The webs occupy the aerial passage amongst vegetation in the path of flying insects. The spider sits on the web waiting for prey to get trapped. As prey is caught, the spider cautiously approaches, wraps it in silk to immobilize it and kills it with a bite. The prey is then moved to the center of the web to be consumed.

The male is attracted by the scent of the female. When the female is eating, the male climbs down onto her abdomen and mates with her, then beats a hasty retreat to prevent her consuming him too!

The females lay eggs in heart-shaped egg sacs from May to June and these hatch in early Summer. Up to 9000 eggs can be produced. However only about 2% survive to maturity.