The Joro spider, Trichonephila clavata, is a large orb-weaver spider recently noticed in North America. Its striking appearance and extensive webs have sparked considerable interest. This article provides clear information on its identification, origins, behaviors, and interactions with people.
Identifying the Joro Spider
Joro spiders have distinctive physical characteristics. Adult females are large, with body lengths from 0.67 to 1.25 inches (1.7 to 3.2 cm) and leg spans up to 4 inches (10 cm), roughly the size of an adult human palm. Their abdomens are brightly colored with yellow and blue-green bands dorsally, and yellow and red markings ventrally. Their long, black legs often have yellow bands.
Male Joro spiders are much smaller and less vibrant, measuring 0.25 to 0.3 inches (0.6 to 0.8 cm) in body length, and are typically brown with darker stripes. Both sexes construct large, three-dimensional orb webs with a notable golden hue, visible in sunlight. These webs can span over 6.6 feet (2 meters) wide, often featuring irregular layers.
From Asia to America: The Joro’s Journey
Native to East Asia (China, Japan, Korea, Taiwan, Vietnam), the Joro spider likely arrived in the United States around 2013 or 2014. It probably came as a stowaway on international shipping containers or imported plant materials. First detected in northern Georgia, the species has rapidly expanded across the southeastern United States.
This spider demonstrates adaptability, thriving in various environments from fields and forests to urban and suburban areas. Its spread is facilitated by “ballooning,” where spiderlings release silk threads to catch air currents, traveling long distances. While Joro spiders prefer warmth and humidity, research suggests they can tolerate colder temperatures, indicating potential for further spread to northern states.
Life and Habits of the Joro Spider
Joro spiders are known for their web-building. Adult females spin large, intricate orb webs characterized by golden silk and a multi-layered structure. These robust webs effectively capture various flying insects, including agricultural pests like brown marmorated stink bugs, making them beneficial predators.
The Joro spider’s life cycle spans about one year in temperate regions. Adult females lay one to five egg sacs in the fall, each with 400 to 500 eggs. These egg sacs overwinter, and spiderlings emerge the following spring, usually in May or June. After hatching, spiderlings disperse through ballooning, growing and molting throughout the summer before reaching adulthood by late summer or early fall.
Joro Spiders and You
A common concern is the Joro spider’s potential danger to humans and pets. Despite their large size, Joro spiders are not considered a threat. They are non-aggressive and shy, preferring to flee or drop from their webs if disturbed rather than bite.
Like most spiders, Joro spiders possess venom, primarily used for subduing prey and defense. Their fangs are often too small to pierce human skin. If a bite occurs, effects are typically mild, comparable to a bee sting or mosquito bite, causing minor redness and swelling.
Allergic reactions are possible, but none have been reported in humans or animals. Ecologically, Joro spiders may benefit by preying on certain insects, including invasive pest species. Current observations suggest they do not significantly displace native spider species.