Andrea the St Andrew's Cross spider
Hello, I'm Andrea, the St Andrew's Cross spider. I'm called a St Andrew's Cross spider because I make a stabilimentum (a tough silk support) in the shape of St Andrew's cross. I live at the centre of the cross.
My web is a medium-sized orb web, and I have built it at the front of a bushy plant that gives me protection at the back. This makes it easy to catch flies, moths, butterflies, bees, and other small flying insects that come to land on the bush.
The silk in my cross reflects ultraviolet light, which attracts insects. If you find me or any members of my family in your garden, don't get rid of us. We help keep down the number of flies and mosquitoes around your house.
Am I dangerous?
You can see me eating a wrapped butterfly lunch in the picture at right. I won't bite humans unless I think you are trying to hurt me, but even if I bite you, it won't harm you much — other than giving you a bit of pain in the area of the bite. Generally I am only dangerous to insects.
Why the zig-zags?
My zig-zag stabilimentum has a few purposes that help me survive. The main one is that it reflects ultraviolet light, which insects are drawn to, so it helps me attract my meals. I use the same type of silk to wrap my food and to construct the stabilimentum.
But it also helps me warn off birds. It makes me look larger than I am, and when I shake my web vigorously I probably look like a large moving animal to birds, so they are more likely to go elsewhere looking for an easier catch.
Why are some crosses incomplete?
Some St Andrew's Cross spiders don't build a full stabilimentum. They may construct one, two, or three arms of the cross instead of the whole four (see photos at right and below). They may suffer because of this. It means they catch fewer insects, so often go hungry, and they are less likely to scare off birds. Friarbirds seem to find us especially tasty.
The spider at right, from the far southern end of the creek, was quite small — only about 8 millimetres (a third of an inch). Her web was empty a few hours after this photo was taken.
Young St Andrew's Cross spiders are especially likely to not make the whole four bars of the stabilimentum.
Trying to get them to finish the job is like trying to get kids to do housework. They are always too busy sleeping or playing to finish the task.
The young one at left was only 7 millimetres, and has put only one bar on her stabilimentum. She will learn as she gets older — unless she starves to death first.
Males much smaller
The males of our species are much smaller than the females. You can see by the photo at right that Andy (top right) is only about a quarter of my size. This photo was taken one evening when I invited him over for dinner after he said I had a great stabilimentum.
Sometimes several males sit around the upper area of my web. They try to get a date with me by constructing a dating thread, which they vibrate. This is their way of telling me they fancy me.
Why I like Calamvale Creek
There are a large number of us St Andrew's Cross spiders around Calamvale Creek. We like it here because of the variety of bugs we can feast on. That feeds us, and it helps control the insect population for local residents.
— Andrea the spider