Friday, September 24, 2004
Black and Yellow Garden Spider
When and where found: I found the one in the photo on September 7 in the dry flower stalks of the daylilies in my garden. If you are doing clean-up work in sunny areas of your garden between now and the first frost you may find one — the females are quite common and easy to spot because of their size. This time I noticed the egg case, which looked like an oak gall, before I noticed the spider.
Identifying characteristics: The body of this spider can be over an inch long — at least for females. (The males are much smaller.) The yellow and black markings on the abdomen vary quite a bit in different photos I have seen but are always bold, striking, and bilaterally symmetrical. The head/thorax, called a cephalothorax, is silver-gray and if you look closely you will see that it is covered with short fine hair. The black and yellow legs are typically held closely together in pairs giving the appearance of a four-legged creature. The overall length of this specimen, including the legs, was about two inches. The spider hangs out in the center of her web facing toward the ground.
Word for the week: Aposematic describes coloration used by animals to warn off predators. The black and yellow garden spider has aposematic coloring.
Web: Up until now I had always referred to spider webs generically as cobwebs but this is not really accurate. This spider is in the orb weaver family, Arenidae, and it makes a well-organized web with a circular pattern unlike the rather messy and disorganized webs of another family of spiders called the cobweb spiders. Orb weaver webs can be up to two feet across and are generally augmented with heavy zig-zag lines radiating from the center, usually vertically. This augmentation is the reason for the common name of writing spider. The "writing" is called a stabilimentum because it was originally thought to improve the structural stability of the web. Only diurnal spiders use stabilimenta and it is now thought that they have some visual purpose such as preventing birds from flying through the webs and breaking them.
Life cycle: Most black and yellow garden spiders in our area live just a year. The spiderlings hatch before the winter and remain inside the egg case until spring. The spiders are mature by the end of summer. After mating, the female builds one to three papery egg cases each of which contains anywhere from 300 to 1,400 eggs. She attaches the egg case near her web where she can watch over it until the first hard frost when she will die. The egg case in the daylilies was about one inch in diameter. It was battered by heavy rain and collapsed. The following day there was no sign of it.
References: University of Michigan, Museum of Zoology at animaldiversity. ummz.umich.edu; University of Kentucky, Dept. of Entomology at www.uky.edu/Agriculture/Entomology/enthp.htm. Search for "argiope" at either site.
In 1758, Timothy Wilkins made a gift of land on the Common for a meeting place of "neighbours and fellow cretures [sic]." In 2001, the Mosquito provided the town with the Biodiversity Corner, a place to get to know some of the town's other life forms. Find some non-human "fellow creture" of the town and write its story. The only requirements are that it exists in the wild and was seen in Carlisle. Send a note to Kay Fairweather at 392 School St.reet, Carlisle MA 01741 or to firstname.lastname@example.org.
© 2004 The Carlisle Mosquito