Herbert A. 'Joe' Pase III, Texas A&M Forest Service, Bugwood.org
These are some of the largest and showiest of the spiders commonly encountered in Pennsylvania. They are found in gardens, tall weeds, and sunny areas with bushes and other supporting structures on which they build the large orb webs. Yellow garden spiders are found throughout most of the United States.
Argiope aurantia egg sac. Photo by Steven Jacobs, Penn State Extension
Yellow garden spider females range from 19 to 28 millimeters in length. The carapace is covered with silver hairs, and the eight eyes are procurved with the lateral four eyes nearly joined and seated upon two projections or humps on either side of the front of the carapace. The second, third, and fourth pair of legs are black with the femora yellow to red. The front legs are frequently entirely black. The abdomen is an elongated oval that is pointed to the rear, notched in front, patterned yellow and black, and has two anterior humps or shoulders.
The males are 5 to 8 millimeters in length and their legs are lighter in color than those of the females. The immature spiders have banded legs. The spherical, brown, papery egg sacs are deposited in the late summer.
The web is large (50- to 100-centimeter diameters are not uncommon) and orientated vertically with a white zigzag stripe down the center, which is called the stabilimentum. The exact function of this structure is unclear.
In early spring, the spiderlings, numbering from 500 to 1,000, emerge from the egg sac. Many of them will succumb to cannibalism and predation from mud-dauber wasps. Those that do survive are usually unnoticed by humans until they reach maturity in the late summer.
Although these large, showy spiders sometimes cause alarm to individuals who are uncomfortable with spiders, they are not known to be medically important. People are not likely to be bitten unless they handle a female with an egg sac in the web. Even then, the bite would likely cause no more discomfort than a wasp or bee sting for most individuals.
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