Giant Joro spiders have arrived in North Georgia, but impact is unknown
Because he spends so much time outdoors in nature for work and pleasure, photographer Alan Cressler rarely comes upon something that shocks him. Yet, that is exactly what happened in early October, when Alan spotted “literally thousands of golden webs with large, female spiders,” draping powerlines near the Chattahoochee River in north Fulton County.
The early morning sunlight perfectly illuminated a massive procession of Joro spiders (Trichonephila clavata): the non-native, invasive species that is currently all the buzz on mainstream and social media outlets.
Seven years ago, these strikingly colorful Asian spiders that “look like Halloween decorations come to life” were discovered in Hoschton, Georgia; they likely arrived via a shipping container from China or Japan. Since then, they have moved rapidly throughout northeast Georgia and into metro Atlanta suburbs – and more recently into the Carolinas.
A Jorogumo is a spiderlike creature or goblin from Japanese folklore, hence the name.
Alan speculates that powerlines are providing easy routes for the Joros to cross obstacles like roads and rivers, as they move quickly and efficiently into new territory. They also travel long distances (50 to 100 miles) by ballooning – using wind power by catching a breeze with the silk threads that they spin. And, like other spiders, they often hitchhike on cars and trucks.
On a recent walk in Chicopee Woods in Gainesville, I observed my first Joro: a palm-sized female on a bright yellow, three-dimensional web of silk that was amazingly strong, as I learned by tugging on it – strong enough, I have read, to capture hummingbirds and massive enough to capture pollinating bees that help maintain genetic diversity in plants and ensure seed production for crops.
Some good news is that these non-native spiders are harmless to people and will eat (the nasty) brown marmorated stink bugs, themselves an invasive that was accidentally introduced; our native spiders apparently have discriminating tastes and do not consume stink bugs. Joros also feed on mosquitos, flies, and yellow jackets.
Impacts Unknown
While some are extolling the “pest control” benefits to be reaped from our new arachnid neighbors, others – including Dr. Bud Freeman with the UGA Odum School of Ecology – are cautioning that much still remains unknown about them. How will they affect local ecosystems? Will they outcompete and displace other orb weaving spiders? Will they reduce important insect populations? Should there be efforts to eradicate these trespassers in an attempt to control their populations, as some suggest?
Joros represent yet another non-native species that must be monitored and evaluated for any unexpected economic and environmental consequences. In their homelands, these spiders are kept in check by local predators and defense mechanisms developed by their prey; however, in a new place, without those checks, they can spread widely, and sometimes with devastating outcomes.
How are invasive species defined and what other types have we experienced in Georgia, both currently and historically? The Georgia Invasive Species Task Force (gainvasives.org) describes them as non-native species that have been introduced – either intentionally or accidentally – into areas outside their natural ranges and that cause economic or environmental harm of impacts to human health.
While most introduced species pose little threat to the environment, many constitute a significant risk. In fact, invasive species rank second only to habitat destruction as a threat to biodiversity – in other words, a threat to every living thing from humans to tiny organisms. In Georgia, we have seen the major impacts that invasives can have on forests, farmland and parks.
Other Georgia Invasives
Historic examples of invasive species in Georgia include the boll weevil: an insect that entered the U.S. from Central America in the 1890s and caused extensive damage to the state’s cotton production. Boll weevil infestation was considered by some to be the biggest disturbance of Georgia’s economy since the end of the Civil War. The chestnut blight fungus entered the U.S. through New York City on imported orchard trees, also in the late 1800s; nearly every mature American chestnut tree in the species’ natural range – literally billions of trees predominant in the Appalachian forest – was killed by the 1940s.
Other invasives that are affecting today’s forests, farmland, and backyards, especially in north Georgia, include the emerald ash borer and the aphid-like hemlock wooly adelgid, which has been responsible for the decline and death of most of Georgia’s Eastern hemlock trees. Hemlocks provide important habitat for songbirds and help regulate the flow and temperature of streams. In their native continent (Asia) the adelgid rarely causes problems because local predatory bugs keep their numbers in check.
Two invasives that are high on my personal dislike list are Japanese stiltgrass (Microstegium vimineum) and Chinese privet (Ligustrum sinense), which grow well (too well) in southern soils. Harmful to native shrubs and plants by outcompeting them, these non-native species can be found in many special natural areas, such as the Chattahoochee River National Recreation Area. Global heating is also helping expand the habitats of invasive species.
Agricultural specialists with U.S. Customs and Border Protection inspect the millions of tons of goods that are delivered annually to Georgia through various ports of entry, seeking to stop any “actionable pests.” Their task is difficult and endless—one that has allowed at least a few Joro spiders to secure a “paw-hold” (yes, spiders have paws) in our state.
What You Can Do
If you spot a Joro spider, take a photo and tag it with the date and location. Then, send it to Dr. Richard Hoebeke at rhoebeke@uga.edu and/or post your observation on the iNaturalist app.