An invasive species of brightly coloured spiders has been steadily spreading across the east coast of the U.S., raising fears that they will someday make their way into Canada. Researchers believe it is only a matter of time before the Joro spider is on our doorstep and once they’re here, there isn’t much stopping them from establishing a population.
The Joro spider is a large arachnid that weaves large, circular webs of gold-coloured silk. Most common house spiders are less than a centimetre across but the giant Joro measures up to eight centimetres when their legs are fully extended. Apart from their size, their most striking feature is their bright yellow and black colouring, making them easy to spot during the peak season between August and September.
The Joro spider is not native to North America. They come from East Asia and a leading theory suggests that they hitched a ride to the U.S. in 2013 on a shipping container.
While these spiders don’t pose a danger to humans, experts are concerned that this invasive species could have a negative impact on ecology and agriculture, though more research is needed to understand their impact.
Where are they and where are they going?
The Joro spider is believed to have first landed in the U.S. in the state of Georgia. That’s where the Joro spider population is the largest, according to a community science organization called Joro Watch, developed by the University of Georgia.
According to a map of Joro sightings compiled by Joro Watch, the spiders have developed a substantial population in northern Georgia and have spread out into the Carolinas and Alabama. A few Joros have been spotted in Tennessee and West Virginia and it appears that a small population of the spiders have established themselves as far north as Maryland.
The spiders have been reported and photographed 21 times in Howard County, Md., just outside Baltimore, meaning the closest Joro spider population is only about 470 kilometres away from the Canadian border near Niagara Falls.
But how did these spiders travel from Georgia to Maryland? And how might they make their way to Canada?
The Joro spiders’ main method of long-distance travel is hitching rides on vehicles. On their own eight legs, they can only travel short distances. But with the help of human intervention, Joros have been able to cross oceans, and they can certainly traverse country borders.
Scientists are still trying to figure out where the Joros are spreading, but many experts agree that it’s only a matter of time before they colonize the eastern seaboard.
David Coyle, an assistant professor at Clemson University, says it may take a year or up to a decade for Joros to spread across the northeast of America, and after that, Canada’s next. Research has found that Joro spiders could survive Canada’s harsh winters, and even thrive here.
A study published last November by Coyle and lead author David Nelsen modelled where the Joros could potentially survive given climate and habitat conditions.
“Our application of these models onto North America suggests that the Great Lakes region of the United States and Canada extending throughout the midwestern and northeastern United States, and into eastern Canada, are potentially suitable for future range expansion,” the study reads.
On top of that, the models suggest that the climate of the northeastern United States and southern Canada is “more suitable” for the Joro spider than their current location in Georgia and southern states, because these regions better mimic the natural climate of the Joro spider in Asia.
“Cooler northern climates will likely not impede continued range expansion,” the study reads.
Given the Joro population in Maryland, it’s possible that Joros could first establish a population in southern Ontario or Quebec.
But the Joros likely won’t stop there. The study found that these spiders would be able to survive in the Great Plains, specifically Alberta, and could even make their way into the Pacific Northwest.
In the opposite direction, Joros could also make a home as far south as northwestern Mexico.
Can they fly?
Sort of.
Baby Joro spiders have the ability to parachute through the air in a way by using their spider silk. This technique is called “ballooning” and only juveniles can do it. Mature adults are far too large to use this method of travel.
The technique involves baby Joro spiders producing a thread of silk that can catch the wind and carry them through the air.
This may sound terrifying, and could conjure images of spiders raining down from the sky — but thankfully that’s not the case. Baby Joro spiders are tiny compared with their adult counterparts so it’s likely you wouldn’t even notice a ballooning Joro.
Are they dangerous?
Joro venom is not dangerous to humans, and luckily, these large spiders are timid and not prone to biting. At worst, a Joro bite might itch or cause an allergic reaction, but the shy creatures tend to stay out of humans’ way.
Andy Davis, research scientist and Joro spider expert at the University of Georgia, told Global News in 2022 that Joro fangs are fairly inefficient and incapable of breaking human skin.
“They wouldn’t even be able to bite you if they wanted to, so no matter what, they’re pretty harmless,” Davis said.
The Joro Watch organization notes that the likelihood of being bitten is quite low, but don’t go around provoking a Joro if you see one.
“From our experience collecting hundreds of these spiders, having them in our hair and wandering on our arms, and interacting with thousands of webs, they have not bit. In general, these spiders are timid and non-aggressive,” the organization writes on its website.
When asked if the Joro spider is harming the local ecosystem, Davis said it’s too soon to know for sure.
“We don’t really have any hard data on it. Anecdotally, it seems like the Joro isn’t wreaking havoc at the moment, like other invasive species,” he said.
But as with any invasive species, scientists worry that their growing numbers could tip the scales of our natural ecosystem. There are concerns that Joro spiders will out-compete native spiders for precious food and resources, but there is also research to indicate that Joros are eating other invasive bug species, and could actually be helpful in that regard.
“I think this is one of those ‘canary in the coal mine’ type species where it’s showy, it’s getting a lot of attention,” said Hannah Burrack, professor and chair of the entomology department at Michigan State University.
Instead, Burrack worries more about introduced pests like fruit flies and tree borers, which can do far more damage to the ecosystem.
“This is a global concern, because it makes all the things that we do in terms of conservation, in terms of agricultural production, in terms of human health, harder to manage,” she said.
— With files from The Associated Press
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