Its not until fall that most of us become aware of the spiders in our lives, specifically the orb weavers. Orb weavers erect those large circular webs between tree branches, overhead wires, fence posts, porch posts, across the path your walking on, and just about everywhere else you might happen to be during your daily travels about the landscape. If there’s suitable substrate, something to attach a web to, a spider will do it.
The spiders have been doing their web building all summer long. But, the webs had been too small for most people to notice. By fall (now), many of the spiders who spun those webs are large enough to be noticeable, and so too their webs.
Black and yellow argiope spiders are one example of an orb weaver that reaches maturity at this time of year. Most people will run into an argiope at some time during fall.
Some people call these spiders writing spiders because they, the spiders, include a zig-zag pattern of silk in their webs called a stabilimenta. The purpose of the zig-zag is unknown although many people have theories on the subject.
The zig-zag pattern emanates from the center of the web, often getting wider as it radiates away from the center. During the day, the spider typically positions itself directly at the center of the web. Could the purpose of the zig-zag be camouflage, to help break up the outline of the spider in order to conceal it from potential prey?
Spider webs can be difficult to see if not illuminated at the correct angle by the sun’s rays. The zig-zag makes the web much more visible. Could the zig-zag act as a warning to passing birds, or to people walking along a path, there’s something here, fly (or walk) around? Webs take time to build. A bird flying, or a person walking, through a web could cost the spider hours of work.
If you touch (or poke with a stick) an argiope spider while it sits in the center of its web, it will start to pump itself, like doing push-ups, on the web, sometimes violently shaking the web. The purpose of this behavior seems, to me, to be an attempt to scare whoever poked it into stepping back and leaving the spider be. It usually works. I step back myself, even though I’ve poked these spiders many times, and know what’s coming.
Is this zig-zag pattern simply reinforcement of the center of the web? If the spider tried to shake itself in a web which lacked this “extra” webbing, it would probably destroy the web. A small insect, when flying into a web, often does significant damage to the web leaving large holes where it entangled itself. Surely, a large spider violently pumping itself on the same web, without reinforcement, would tear it to shreds.
Argiope spiders “wrap up” the prey they capture in their webs in a special type of silk which is chemically different than the silk used to construct the web. Interestingly, the silk used for the zig-zag in the web is chemically the same silk as is used for wrapping up prey. It would seem that there is a correlation between the two acts of prey wrapping and web decoration or “writing.” What that correlation is, I can’t say. I feel confident though, that if you were interested in digging deeper into the subject, there is more than one scholarly paper written on the matter somewhere out there on the web (Internet).
Speaking of prey, our local spiders have been doing well in their pursuit of prey. Build a web near a busy insect thoroughfare and you will catch insects in the web. There are no less than three argiope spiders in a small patch of partridge pea in Catch the Wind here at the Museum. Milkweed and other herbaceous plants among the pea patch attracts a wide variety of insects. The spiders have indeed been doing well.
The butterfly in the above photo was attracted by the partridge pea as a host plant for its larvae, it was actively laying eggs on the plant.
The latin or scientific name of this spider is Argiope aurantia. Argiope means silver-face and aurantia means gilded, the gilded, silver-faced spider.