EXPLAINER

It’s imminent although no one knows exactly when — and there’s nothing to be too worried about, scientists say.

An uninvited guest might soon be invading the New York City area in the United States, according to experts. Just how soon is the question.

The Joro spider, which first made its presence felt in the southern state of Georgia a decade ago, has been slowly migrating northwards. And scientists say it could move into the Great Lakes area, the northeastern US and even Canada in the coming months or years.

But what exactly is the Joro spider? Is it dangerous? And why is it spreading across the US?

What is a Joro spider?

The Joro spider, scientifically named Trichonephila clavata, originates from East Asia and is known for its web-weaving abilities and distinctive appearance. The Joro spider is often confused with the golden silk orb weaver (Nephila clavipes) because they look similar.

A female Joro spider can have a span of 8cm to 20cm (3 to 8 inches) with its legs spread – bigger than the human hand. Female Joro spiders typically have yellow bodies while the male spiders, which are smaller, are muted yellow and black or brown in colour.

How do they spread to new areas?

Joro spiders do not have wings, but their hatchlings can harness the wind to, in effect, fly.

Through a technique called ballooning, baby Joro spiders release silk threads that allow them to ride currents of the wind. That allows them to move to new areas – sometimes travelling more than 160km (100 miles).

Babies hatch in the spring and summer, making these the prime seasons when the spiders expand their territorial reach.

Joro spiders also have another advantage. Research in 2022 by University of Georgia ecologist Andrew Davis and his colleagues found that they have a high metabolism and heart rate, which allows them to survive in colder climates.

Where are Joro spiders in the US?

Since its initial appearance in Georgia about 10 years ago, the invasive species has started to spread north.

According to the nonprofit group INaturalis, the Joro spider has been spotted in Maryland, West Virgina, Tennesse, North Carolina and South Carolina. It has also been seen in the south-central state of Oklahoma.

In research published in November, scientists at Clemson University in South Carolina said the colourful arachnid could soon start moving towards “the Great Lakes region of the US and Canada extending throughout the midwestern and northeastern US, and into eastern Canada”.

Parts of the US Northwest and even northwestern Mexico could also serve as favourable habitats for the Joro spider, the scientists said.

Where do they come from?

The Joro spider typically comes from Japan, China, Taiwan and South Korea.

It is likely that the spider was a stowaway in a shipping container from one of those areas and eventually landed in the seaport in Atlanta, Georgia, according to a 2015 study.

Are these spiders harmful?

According to the study by Davis and his colleagues at the University of Georgia, Joro spiders are not harmful to people and pets.

They are venomous, but their bites are not lethal, and their fangs are too small to puncture human skin.

Like any invasive species, scientists are worried about their impact on crops and trees, but just how Joro spiders behave on farms is still a subject of study.

Should I get rid of Joro spiders?

The Joro spider lifespan is roughly one year, so they don’t live very long. In most instances, scientists said, they can be safely ignored, their presence treated more as a nuisance than an infestation. However, researchers are still observing their behaviour in new locations along with their migration patterns.

The lifespan of spiders differs. Most live for about two years, but there have been instances where spiders have been observed to live up to 20 years.