St Andrew's Cross spider fact sheet | Field of Mars EEC

What are St Andrew's Cross spiders and what do they look like?

St Andrew's Cross spiders are orb weaving arachnids. Orb weavers are known for creating circular shaped webs. The St Andrew's Cross spiderweb has an X- shape in the centre. This cross is called a stabilimentum.

The spiders are given their name because the web design looks like the St Andrews Cross on the Scottish flag. The scientific name for these spiders is  Argiope keyserlingi.

Females of this species have yellow, red, black and white striped abdomens and brown and black banded legs which sit together in pairs. Like most spiders, females are larger than the males at approximately 16 millimetres long. Males have a brown and cream colouring and grow up to 4 millimetres in length.

St Andrew's Cross spiders are often found on their webs in an X shape.

Where do St Andrew's Cross spiders live?

St Andrew's Cross spiders can be found on the east coast of Queensland, New South Wales and Victoria. Habitats include backyards, open forests, shrubby bush and the edges of rainforests.

Medium-sized webs are built about one to 2 metres above the ground and can usually be found between shrubs and bushes. Their webs are approximately one metre in diameter.

Females hang upside down in the centre with their legs held in pairs on the arms of the cross. Males will build a web close by or sit on the upper edges of the female's web until she is ready to mate. It is not uncommon to find more than one male living on the web.

Females are active day and night and live permanently on their webs.

What do St Andrew's Cross spiders eat?

St Andrew's Cross spiders eat a range of insects including flies, moths, bees, butterflies, crickets and bugs that have been caught in their web. They wrap the prey in silk and eat it straight away or hang it nearby for later. These spiders can often be seen repairing their webs after catching a meal.

Spiders are an important part of the ecosystem as they control insect populations.

St Andrew's Cross spiders have sensory hairs on their legs to detect movement.

What eats St Andrew's Cross spiders?

Predators of St Andrew's Cross spiders include birds and wasps. Wasps will paralyse spiders to use as a food source for their larvae when hatched.

If St Andrew's Cross spiders are disturbed or feel threatened they will either bungee jump to the ground or bounce the web like a trampoline really quickly. This behaviour is used to confuse would be predators as the vigorous shaking makes the cross and spider appear blurry.

Mud dauber wasps take spiders back to their cells for their newly hatched young to feed on

Why do St Andrew's Cross spiders make their unique webs?

There are many hypotheses as to why St Andrew's Cross spiders create the white silk cross pattern. The first is that it deters predators as it makes them look bigger than they are. The second theory is that the bluish white silk reflects ultra violet light which may attract flying insects to the web.

St Andrew’s Cross spiders quickly spin their prey in silk before biting them.

How do St Andrew's Cross spiders reproduce and what is their life cycle?

Mating season for St Andrew's Cross spiders is from summer to autumn. Male spiders will move slowly and gradually on the underside of the web so as not to be mistaken for prey by the female. The male creates a silk thread which is vibrated to attract her attention. If successful, mating will occur although the male might not live to see another day!

Male spiders are often attacked and eaten after mating.

Females can produce up to 3 egg sacs during the breeding season.

Soon after mating, females will produce an egg sac. The greenish egg sac is then wrapped in silk and hung in foliage nearby. After 30 to 60 days hundreds of tiny spiderlings hatch.  Hundreds of tiny spiderlings hatch from one egg sac.

The tiny spiderlings stay around the egg sac for a few days after hatching. Competition for food is fierce as there are so many of them in a small space. The spiderlings will climb to a high point and use a 'ballooning' technique to travel elsewhere. A silk thread is thrown into the breeze which carries them to a new location.

Juvenile St Andrews Cross spiders are light brown with a yellowish abdomen. They create a web with a circular zig zag pattern to begin with. The familiar X-design begins to take shape as they get older.

St Andrew's Cross spiders have a one year life span.

Young St Andrew's Cross spider's create stabilimentum which look a little like the head of a carnation flower.

Related fact sheets

More invertebrate fact sheets

• Invertebrate fact sheets – overview
• Arachnids fact sheet – overview
• Golden orb weaving spider fact sheet – another orb-weaving spider with a large circular web.
• Leaf-curling spider fact sheet – orb-web spider that hides in a curled leaf in the centre of its web.
• Trapdoor spider fact sheet – contrast with a burrow-dwelling ambush spider.

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