The spider species Argiope aurantia is commonly known as the black and yellow garden spider, writing spider, or corn spider. It is common to the contiguous United States, Hawaii, southern Canada, Mexico, and Central America. They have distinctive yellow and black markings on their abdomens and a mostly white cephalothorax. Males range from 5–9 mm (0.20–0.35 in) females from 19–28 mm (0.75–1.1 in). Like other members of Argiope they are considered harmless to humans.
Garden spiders often build webs in areas adjacent to open sunny fields where they stay concealed and protected from the wind. The spider can also be found along the eaves of houses and outbuildings or in any tall vegetation where they can securely stretch a web. The circular part of the female's web may reach two feet in diameter. Webs are built at elevations from two to eight feet off the ground.
Female Argiope aurantia spiders tend to be somewhat local, often staying in one place throughout much of their lifetime.
The web of the yellow garden spider is distinctive: a circular shape up to 2 feet (60 cm) in diameter, with a dense zigzag of silk, known as a stabilimentum, in the center. The purpose of the stabilimentum is disputed. It is possible that it acts as camouflage for the spider lurking in the web's center, but it may also attract insect prey, or even warn birds of the presence of the otherwise difficult-to-see web. Only those spiders that are active during the day construct stabilimenta in their webs.
To construct the web, several radial lines are stretched among four or five anchor points that can be more than three feet apart. The radial lines meet at a central point. The spider makes a frame with several more radial lines and then fills the center with a spiral of silk, leaving a 5/16 to 3/8 inches (8 to 9.5 mm) gap between the spiral rings, starting with the innermost ring and moving outward in a clockwise motion. To ensure that the web is taut, the spider bends the radial lines slightly together while applying the silk spiral. The female's web is substantially larger than the male's, who builds a small zigzag web nearby. The spider occupies the center of the web, usually hanging head-down, waiting for prey to become ensnared in the web. If disturbed by a possible predator, she may drop from the web and hide on the ground nearby. The web normally remains in one location for the entire summer, but spiders can change locations usually early in the season, perhaps to find better protection or better hunting.
The garden spider can oscillate her web vigorously while she remains firmly attached in the center. This action might prevent predators like wasps and birds from drawing a good bead, and also to fully entangle an insect before it cuts itself loose.
In a nightly ritual, the spider consumes the circular interior part of the web and then rebuilds it each morning with fresh new silk. The radial framework and anchoring lines are not usually replaced when the spider rebuilds the web. The spider may be recycling the chemicals used in web building. Additionally, the fine threads that she consumes appear to have tiny particles of what may be minuscule insects and organic matter that may contain nutrition.
The garden spider does not live in very dense location clusters like other orb spiders such as the golden orb web spider. The garden spider keeps a clean orderly web in comparison to the cluttered series of webs built and abandoned by groups of golden orb spiders.
Yellow garden spiders breed once a year. The males roam in search of a female, building a small web near or actually in the female's web, then court the females by plucking strands on her web. Often, when the male approaches the female, he has a safety drop line ready, in case she attacks him. After mating, the male dies, and is sometimes then eaten by the female.
She lays her eggs at night on a sheet of silky material, then covers them with another layer of silk, then a protective brownish silk. She then uses her legs to form the sheet into a ball with an upturned neck. Egg sacs range from 5/8" to 1" in diameter. She often suspends the egg sac right on her web, near the center where she spends most of her time. Each spider produces from one to four sacs with perhaps over a thousand eggs inside each. She guards the eggs against predation as long as she is able. However, as the weather cools, she becomes more frail, and dies around the time of the first hard frost.
In the spring, the young spiders exit the sac and are so tiny that their collection of bodies look like dust gathered inside the silk mesh. Some of the spiderlings remain nearby, but others exude a strand of silk that gets caught by the breeze, carrying the spiderling to a more distant area.
Females of the species are the most commonly seen in gardens. Their webs are usually characterized by a 'Z' shaped line in the middle extending vertically. The spiders spend most of their time in their webs waiting for prey to become ensnared. When prey becomes caught in the web, the spider may undulate the web back and forth to further trap the insect. When the prey is secure, the spider kills it by injecting its venom and then wraps the prey in a cocoon of silk for later consumption (typically 1–4 hours later). Prey includes small vertebrates, such as geckos and green anoles, as well as insects.
- ^ "Argiope aurantia at the University of Michigan's Animal Diversity Web". http://animaldiversity.ummz.umich.edu/site/accounts/information/Argiope_aurantia.html. Retrieved 2007-07-30. Gorham, J. R. and T. B. Rheney. 1968. Envenomation by the spiders Chiracanthium inclusum and Agriope aurantia. JAMA 206 (9): 1958-1962.