The Joro spider, scientifically known as Trichonephila clavata, is a large orb-weaver that originated in East Asia and is rapidly spreading across parts of North America. The female is immediately noticeable due to her brilliant yellow and black coloration. Her substantial size is the primary source of public curiosity regarding this invasive species. Understanding the Joro spider begins with establishing the precise dimensions of its body and legs.
Defining the Dimensions
The most significant factor contributing to the Joro spider’s impressive size is its extreme sexual dimorphism, describing the distinct size difference between the sexes. The adult female is the specimen that most people encounter and is responsible for the spider’s reputation. Her cylindrical body alone can measure up to one inch in length, comparable to the size of a thumb.
When her long, slender legs are fully extended, the female Joro spider can achieve a leg span of up to four inches. This measurement is roughly the size of an average adult human palm, which explains why the spider appears so large. Her appearance is further amplified by bright yellow and gray-blue banding on her abdomen and yellow-striped black legs.
In stark contrast, the male Joro spider is significantly smaller and less colorful, often going unnoticed. The male’s body length is typically only about 0.3 inches, and he possesses a dull brown coloration. This means the female can be more than ten times the size of the male.
The Impact of the Web
The Joro spider’s size is only one part of the visual impact, as the massive webs they construct enhance the perception of their presence. These spiders are orb-weavers, building large, circular webs to capture flying insects. A mature female’s web can span several feet in diameter.
The structural support lines of these webs, which anchor the main orb, can stretch up to ten feet wide between trees, porches, or utility poles. The silk itself is notable for its distinct golden hue, which reflects sunlight and makes the structure highly visible.
In areas with high populations, multiple Joro spiders may build their webs in close proximity, sometimes connecting the structural threads. This creates a dense, three-dimensional matrix of silk that can coat entire sections of vegetation or man-made structures. The cumulative effect of several large, golden-hued webs clustered together contributes significantly to the animal’s reputation.
Contextualizing the Size
To understand where the Joro spider ranks among North American arachnids, it is helpful to compare the female’s four-inch leg span to more familiar native species. A common, large native spider is the Black and Yellow Garden Spider (Argiope aurantia), which is also an orb-weaver known for its striking coloration. While the body length of the female Garden Spider can be similar to the Joro’s, its legs are not nearly as long.
The Argiope species typically has a leg span that reaches up to about 2.5 inches, placing the Joro spider in a distinctly larger size class. The Joro’s closest relative, the Golden Silk Orb-Weaver (Trichonephila clavipes), is another large species found in the southeastern United states and is comparable in size. However, the Joro’s legs often appear longer and its specific pattern of bright yellow and blue-gray banding provides a unique visual marker that distinguishes it from other species. The Joro spider is one of the largest spiders currently found in the United States.