The writing spider (Argiope aurantia) is a common inhabitant of gardens across North America. This species belongs to the genus Argiope, a group of large orb-weaver spiders. The spider’s size and prominent web structure often draw attention in fields and backyards. It is a diurnal creature, meaning it is active during the day, making its presence in sunny areas noticeable.
Identifying the Appearance of the Writing Spider
The female writing spider is visually distinct, displaying a bright pattern of black and yellow coloration on its large, oval-shaped abdomen. This abdomen features symmetrical yellow or orange markings set against a black background. The cephalothorax, the fused head and chest region, is covered with short, silvery-white hairs, which contributes to the species’ scientific name, as Argiope means “silver-face.”
A significant size difference exists between the sexes, a phenomenon known as sexual dimorphism. Females range from 19 to 28 millimeters in body length. Males are considerably smaller, measuring only 5 to 9 millimeters, and often have a less vivid, brownish coloration. The legs of the female are generally black with sections of red or yellow closer to the body. Like all orb-weavers, the spider possesses three claws per foot, which aids in spinning its silk.
The Unique Web Design
This species receives its common name from a distinctive structure woven into the center of its large, circular web, which can reach up to two feet in diameter. This dense, zig-zagging band of non-sticky silk is called a stabilimentum. The structure is often oriented vertically in the web, appearing as a thick, white line that resembles written letters or a zipper.
The function of the stabilimentum has been the subject of several proposed theories. One prominent hypothesis is the “web advertisement” theory, suggesting the bright silk warns birds of the web’s presence, preventing accidental destruction. Another theory, the “prey attraction hypothesis,” proposes that the silk reflects ultraviolet light, which may lure insects that use UV light for navigation. Research also suggests the stabilimentum may help camouflage the spider or serve as a defensive shield against predators.
Where They Live and What They Eat
The writing spider is broadly distributed throughout North America, ranging from southern Canada, across the contiguous United States, and south into Central America. This species prefers to construct its large orb webs in sunny, open areas like gardens, fields, and tall vegetation, often near the eaves of buildings. The web is typically suspended between structural supports like tall plants, fence posts, or shrubs.
As a predator, the writing spider’s diet consists primarily of flying and jumping insects that become trapped in the sticky threads of its large web. It commonly captures prey such as grasshoppers, flies, moths, and wasps. Once an insect is ensnared, the spider quickly rushes to the victim, using its venom to immobilize the prey before wrapping it tightly in a thick cocoon of silk for later consumption.
Understanding Their Safety Profile
Despite its imposing size and bold coloration, the writing spider is not considered a threat to humans. The species is non-aggressive and generally only bites when severely provoked, such as when accidentally grabbed or pinned against the skin. The venom contains neurotoxins designed to subdue small insect prey, and it has a mild effect on people.
A bite from an Argiope aurantia is rare and results in symptoms comparable to a mild bee sting, including slight pain, localized redness, and minor swelling. For a healthy adult, the bite is usually harmless. Individuals with pre-existing allergies should exercise caution, though severe allergic reactions are uncommon.