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FAUNA: The Back-To-School Spider

by Mary Parker Sonis

We all know and recognize this spider. This is the spider that is properly known as Argiope aurantia, and better known as the garden spider or “writing spider.” Every year, these gloriously colored, large black-and-yellow orb weavers appear just when it is time for the children to return to school. I remember seeing them in the shrubs around McDougle Elementary each year as I brought my children on the first day of school. I would often linger around the playground on that first day, just to see which spider was the largest specimen.

Photo by Mary Parker Sonis

The web of the Argiope is beautifully structured and quite symmetrical. It is notable for the pattern of “z”s that run in a vertical line down the center of the web, giving the spider the name “writing spider.” It is unknown exactly why the web has these patterns, or stabilimenta. The stabilimenta of the orb weavers consist of a bright, non-capture silk with UV light sensitivity. Only orb-weaving spiders that hunt by day create these patterns, which may stabilize their webs. The stabilimenta are thought to deter birds that recognize the visual cue that the web will be sticky; on the other hand, these UV light-sensitive patterns may attract certain prey. The downside is that while the color and patterning may attract prey to the web, it may also attract predacious insects that recognize the cues as a food source. The evening hunters such as the barn spider (Charlotte was a barn spider) do not add these patterns.

The Argiope is a fastidious housekeeper. Every evening, the female garden spider eats the center section of her web, and then re-spins a fresh center. Generally, you will find these webs in a conspicuous but wind-protected location, such as between two shrubs or near a doorway. Only the female builds this type of web; the much smaller male Argiope will often build a simple web, adjacent to the web of the female. It is thought that the male is not particularly interested in hunting or eating, as his main purpose is to locate and mate with a receptive female. However, he will often include a long dangling escape line from his web to the main web, just in case his paramour becomes hungry during the mating process.

The female is an efficient hunter and will subdue, with great dexterity, any insect that flies into her web. She envenomates the prey and wraps them in a tight cocoon of silk in a matter of seconds. If you spend time observing these spiders, it will astonish you how quickly the Argiope dispatches her prey. I have seen these spiders eat very large insects; even cicadas cannot escape this web.

Argiope is an excellent parent. As the weather begins to cool, the female will lay her eggs (sometimes more than 1,000) and wrap them in a layer of white silk, followed by a strong protective layer of brown silk. The egg case is circular with a narrow neck at the top, appearing like a tiny gourd in the web. She will guard this egg case well into the fall. The eggs hatch in late autumn, but the baby spiders remain dormant in their case until the following spring. The female will never see her offspring, as she will perish in the cold of the first deep frost. Some egg cases are probably eaten by birds or parasitized by other insects or wasps, but enough survive to ensure the future of the species.

The defenses of the Argiope are not restricted to her carefully constructed web. If you lightly touch the back of the Argiope, she will not run away from her web. She will firmly grasp the web center and give the entire web a grand shake. The web will gyrate vigorously for a number of seconds in a trampoline like fashion. This may serve the purpose of fending off predators, and it may help to ensnare prey more securely. It is a very dramatic display.

Most people have a very visceral response to spiders. Some of us react to these arachnids as Ron Weasley did when he saw Aragog in the forbidden forest of Hogwarts. I belong to the Charlotte’s Web school of thought: When I see the beautiful Argiope in her flawless web, only one word comes to mind – radiant!