Delta Journal
by Bob Thomas

The garden spider (Argiope aurantia), also called the black and yellow argiope, is a common member of the Orb-weaver Spiders (Family Araneidae).

Garden spiders construct their webs much closer to the ground than most other orb weavers, such as the common orbweaver (Araneus) and Golden Silk Spiders. They may place their webs within a window pane, or certainly among the plants of your garden. These spiders are active during the day, and do not retreat to a constructed hibernaculum (hiding place in a curled leaf) as does Araneus. When threatened, however, they will crawl off the web or drop to the ground and hide in the vegetation.

Garden spiders sit in the middle of the web, on the upper surface, with their heads pointing down.

An adult typically builds her web about two feet in diameter, and tilted at a slight angle. In the center of the web, the spider uses silk to construct a visible long, thin, zig-zagged zone that scientists call the stabilimentum (juveniles make a circular stabilimentum that is roughly the size of the spider). It is so named because the first explanation of its purpose was that it helped “stabilize” the web. Later it was theorized that its purpose is to make the presence of the web visually obvious. As the thinking went, these spiders put a lot of energy into constructing their webs, so they don’t want a bird to accidently fly through and cause damage.

Insects see in the ultra-violet light spectrum. When one views the surface of flowers in these wave lengths, one sees a very different image than humans normally see. An insect flies about looking for a flower on which to land, and its target, where it collects a meal of pollen and nectar, reflects ultraviolet light. A study revealed that garden spiders’ stabilimenta reflect ultraviolet light. Along comes an insect looking for a flower. It sees the ultraviolet image of the stabilimentum, flies to it, and gets stuck in the web and serves as a meal for the spider. How cool is that (biologically speaking, of course)?

When E. B. White was penning Charlotte’s Web, there was a garden spider web just outside his window. Because of the zig-zagged stabilimentum, the author thought the spider was “writing” on its web, so the arachnid star of the book became known as the “writing spider.”