The Joro spider, a large and visually striking arachnid, has recently gained attention across North America, raising questions about its status as an “invasive” species. Understanding the scientific perspective on this new arrival is important for addressing public concerns and fostering informed coexistence.
Identifying Joro Spiders and Their Origins
Joro spiders, scientifically known as Trichonephila clavata, are a type of orb-weaver spider distinguished by their vibrant appearance. Females, which are larger, exhibit bright yellow, black, and blue-gray patterns on their cylindrical abdomens and legs, which can span up to four inches. Males are considerably smaller and have a drab brown coloration. These spiders construct large, wheel-shaped webs with a distinctive golden hue that can span several feet across.
The native range of the Joro spider encompasses East Asia, including countries like Japan, Korea, China, Indochina, and Nepal. Their arrival in North America is widely attributed to accidental transport, likely via shipping containers originating from East Asia. They were first reported in northern Georgia around 2013 or 2014.
The Science of Invasive Species
An “invasive species” is defined by more than just being non-native to an ecosystem. To be classified as invasive, its introduction must cause or be likely to cause economic, environmental, or human health harm. Many non-native species integrate into existing ecosystems without significant disruption. The key distinction lies in demonstrable negative impacts.
Joro Spiders’ Presence and Ecological Role
Since their initial detection in Georgia, Joro spiders have expanded across several southeastern U.S. states, including Tennessee, North Carolina, South Carolina, Alabama, and Florida. Populations have also been observed further north in states like West Virginia, Maryland, Ohio, and Pennsylvania. They are predicted to spread across much of the eastern United States due to their adaptability to temperate climates. Young Joro spiders can disperse over long distances through “ballooning,” releasing silk strands to catch air currents.
Joro spiders are generalist predators, consuming a wide variety of flying insects. Their diet includes common pests such as mosquitoes, stink bugs, yellow jackets, beetles, and biting flies, as well as other insects like butterflies and grasshoppers. They have been observed preying on brown marmorated stink bugs, an invasive pest native spiders typically do not consume. Joro spiders are subject to predation by various animals, including birds, lizards, frogs, bats, and certain wasp species like mud daubers.
The ecological role of Joro spiders in their new environment is still being researched. Some studies suggest potential competition with native spider species for food and web space, possibly leading to displacement. However, other observations indicate they may coexist with native orb-weaving spiders, sometimes attaching their webs to those of local species. While non-native and rapidly spreading, the consensus on their overall ecological harm is still being established. Many experts suggest they are more of a nuisance due to their large webs than a significant ecological threat compared to other truly invasive species.
Dispelling Myths and Coexisting
Joro spiders are not considered dangerous to humans or pets. They are described as shy and non-aggressive, preferring to flee rather than confront. While they possess venom, like all spiders, it is primarily for subduing insect prey and is not medically significant to humans. A Joro spider bite, if it occurs, is typically compared to a bee sting, causing minor redness and pain, and their fangs are often too small to easily pierce human skin.
For those who encounter Joro spiders, the advice is generally to coexist. They do not typically seek to enter homes. If their presence is bothersome, they can be gently removed using a broom or by destroying their webs. Unnecessary use of pesticides is discouraged, as it can harm beneficial native insects and other spiders.