It’s bad news for American arachnophobes, as a giant east Asian spider is predicted to significantly expand its range on the US east coast over the coming months and years.
The Joro spider (Trichonephila clavate), a large-bodied orbweaver that measures 2.8cm long, with yellow-banded legs, has been in the US since around 2010. It is thought to have arrived in a shipping container, a common route for invasive insect species.
Since being initially spotted in Georgia, the Joro has spread to at least four other southeastern states already, and is set to move further north still, according to new research by scientists including David Coyle at Clemson University in South Carolina.
Using species distribution models from crowd-sourced data, Coyle and his team predict that the Joro will eventually be found throughout eastern North America and in some areas in the western part of the continent. The time frame of its spread is “impossible to predict”, says Coyle, but “could be very soon” given that adult spiders and their egg sacs can be transported when people move objects such as picnic tables from place to place.
Coyle’s study, which was published in November 2023, looked at 21,000 verified observations logged on iNaturalist, a citizen science app, to understand the distribution of the Joro in both eastern Asia (its native range) and North America. They then considered 20 environmental variables, including temperature and rainfall, in order to create a template for where the species occurs in eastern Asia. By overlaying that template on North America, they were able to predict where Joros are likely to survive.
The good news is that the Joro is neither dangerous to humans nor particularly aggressive. A recent study into the behaviour the species by researchers at the University of Georgia, in fact, found that it to be very timid in response to stimulus.
The bad news is that Joros prey on many native north American orbweaver species, as well as outcompeting them for habitat. This has potentially negative consequences for local ecosystems, but it’s still early days for this research.
“This is still a relatively new invasive species,” says Coyle. “We know little about its biology here in North America. There’s a lot we still don’t know, to be honest.”
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