St Andrews Cross Spider

Details

The St Andrews Cross Spider is a striking orb-weaver best known for the bold “X”-shaped silk pattern it builds in the centre of its web. The name is used mainly forArgiope keyserlingi in eastern Australia, along with some closely related cross-marked Argiope species. When the adult female sits at the hub of the web with her legs arranged in four pairs along the arms of the “X”, the silhouette resembles the diagonal cross associated with Saint Andrew.

Taxonomy & Naming

• Common name: St Andrews Cross Spider

• Representative scientific name: Argiope keyserlingi

• Family: Araneidae (orb-weaving spiders)

• Genus: Argiope

Appearance

St Andrews Cross Spiders are colourful and highly recognisable garden orb-weavers:

• Body size: adult females are about 10–16 mm in body length with a relatively large, rounded abdomen;      males are much smaller at around 3–4 mm and are usually found near the edge of the female web;

• Colouration: the carapace is brown to dark brown, while the abdomen shows bright patterns of white,      yellow or silvery bands contrasted with black markings;

• Typical posture: the female often rests at the centre of the web with her legs held in pairs,      forming four arms that align with the silk cross;

• Sexual dimorphism: females are conspicuously larger and more colourful, whereas males are small,      slender and more subdued in colour.

Orb Web & the “St Andrews Cross” Stabilimentum

Like other orb-weavers, this species spins a wheel-shaped orb web, but it is especially famous for its distinctive stabilimentum – a dense band of white silk in the web centre:

• The stabilimentum usually forms an “X”-shaped or partial cross of thick, opaque silk ribbons;

• When the spider sits on the cross with legs aligned along the arms, its outline is partially broken up;

• The structure may help with camouflage, reflect ultraviolet light that attracts insects, or make the web more visible      to birds and larger animals so they avoid flying through it.

The orb is normally built between shrubs, tall grasses, fences or man-made structures. In the early morning, dew on the silk makes the cross and the radiating lines particularly visible.

Distribution & Habitat

St Andrews Cross Spiders are common in eastern Australia, including New South Wales, Queensland and Victoria, and related cross-marked Argiope species occur in nearby regions such as New Guinea and parts of the Pacific.

They are typically found in:

• Urban and suburban gardens, flower beds and hedges;

• Field margins, pastures and roadside vegetation;

• Forest edges, clearings and vegetation along creeks and wetlands;

• Fences, verandas and around outdoor lights where flying insects are abundant.

Behaviour & Diet

St Andrews Cross Spiders are mostly active during the day and at dusk. They aresit-and-wait predators that rely on their orb web to catch flying insects:

• Females usually remain at the hub of the web, monitoring vibrations through the silk;

• Their prey includes mosquitoes, midges, flies, moths, small bees and wasps, leafhoppers and other small insects;

• When prey becomes entangled, the spider rapidly runs to the impact point, bites and wraps the victim in silk, then moves      it to a safer position to feed.

By removing large numbers of flying insects, these spiders are valuable natural pest controllers in gardens and agricultural landscapes.

Venom & Human Significance

Like most orb-weavers, St Andrews Cross Spiders possess venom that is effective on insect prey but generally mild for humans. They are not regarded as dangerous spiders.

Documented bites are uncommon and typically result in:

• Short-lived local pain or discomfort at the bite site;

• Mild redness, swelling or itching that resolves within hours or a couple of days;

• Very rare, minor systemic symptoms in particularly sensitive individuals.

Basic first aid – washing the area and applying a cold pack if needed – is usually sufficient. Serious medical complications from this species are extremely rare.

Human Interactions

Because they are conspicuous yet harmless, St Andrews Cross Spiders are frequently used as examples in nature education and public outreach about spiders. They illustrate both the diversity of web designs and the ecological value of spiders as insect predators.

In most situations, the best way to coexist with them is simply to leave their webs in place, especially in garden corners where they do not interfere with paths. If a web is in an inconvenient spot, it can be gently relocated with a stick or by moving the supporting branches, rather than using insecticide.

References

Craig, L.C. and Bernard, G.D. (1990). Insect attraction to ultraviolet-reflecting spider webs and web decorations. Ecology 71 (2): 616-623.

Eisner, T. asnd Nowicki, S. (1983). Spider web protection through visual advertisement: role of the stabilimentum. Science 219: 185-187.

Elgar, M.A. (1991). Sexual cannabilism, size dimorphism and courtship behaviour in orb-weaving spiders (Araneidae). Evolution 45 (2): 444-448.

Elgar, M.A., Allen, R.A. and Evans, T.A. (1996). Foraging strategies in orb-spinning spiders: Ambient light and silk decorations in Argiope aetherea Walckenaer (Araneae: Araneoidea). Australian Journal of Ecology 21: 464-467.

Main, B.Y. (1973). Spiders. Australian Naturalists Library. Collins, Sydney.

McKeown, K. (1963). Australian Spiders. Angus and Robertson, Sydney.