What is a Joro Spider and should I be worried?

Here comes the Joro spider!

The invasive, palm-sized arachnid from Asia is spreading up the East Coast this spring.  You might not even notice them in Florida as they closely resemble the naturalized golden orb weaver Trichonephila clavipes often colloquially referred to as the "banana spider" that's been in Florida for 150+ years.  The Joro (Trichonephila clavate) is about the same size as the banana spider and makes a similar web but it more colorful than the previously naturalized species.

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But in north Florida and Georgia the new Joro spiders are often a scary reminder of how globalization is changing the natural environment of the South.  

The Joro spider first arrived in the USA from Asia around 2013 and has since spread across the Southeast.  New research from the University of Georgia suggests that the invasive arachnids could spread through most of the Eastern Seaboard of the USA.

A Florida naturalized golden orb weaver spider often called the "banana spider," or the "golden silk spider," Trichnoephila clavipes.  The large spider is a female and the smaller spider is the male. 
Photo:  Phillip Lott

A recent study by Andres Davis and Benjamin Frich compares and contrasts the Joro with the naturalized golden orb weaver (pictured above). In Physiological evaluation of newly invasive Jorō spiders (Trichonephila clavata) in the southeastern USA compared to their naturalized cousin, Trichonephilla clavipes, Journal of the Royal Entomological Society, 17 February 2022, Davis and Frich write that the thermal limitations of the naturalized golden orb weaver have constrained its range largely to Florida.  The new invading Joro spider is not as limited by cold and thus will spread much further.  Specifically they found that:

Results show the Jorō spider has a shorter season than its cousin, indicating it can complete its lifecycle within a narrow period of suitable weather. It has an inherently higher metabolism (twice as high), and has a 77% higher heart rate when exposed to low temperature. Finally, Jorō spiders survive better (74% compared to 50%) in a brief freeze. These findings suggest the Jorō spider can exist in a colder climatic region than the southeastern USA.

North Georgia Joro Spider
Photo:  Mary Nouri

Cold-hardiness isn't the only factor helping Joro spiders to spread from their current range:  humans often unknowingly transport the spiders.  In their native Japan, Joro spiders colonize most of the country.  Japan has a very similar climate to the USA and is at approximately the same latitude.  

The first Joros to arrive in the USA were likely stowaways on shipping containers.  Now that they're here, the chances of Joros hitching a ride to a new locale on a car or in luggage are high.

Joro Balloons

Joros can use their silks to carry them across the wind to new locations, a behavior called "ballooning."  Its part of the reason why Joros were able to spread so rapidly across the state of Georgia.  When hatchlings emerge in the spring they ride along to someplace new.  Their offspring do the same thing next year.

What's the Good News About Joros?

The good news is that the Joro spider is beautiful, with bright yellow and black stripes and about the size of a palm of the hand. They also eat pests such as stink bugs, lantern flies and lady beetles.

“These are beautiful spiders which may provide important ecosystem services, including biological control of crop pests such as brown marmorated stink bugs or spotted lanternfly, with which they have an ancient association in their native range in eastern Asia,” said Michael Raupp, an entomologist at the University of Maryland.

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The bad news is their webs are often spun in trees, so it’s possible to walk, run or bike face-first into a web containing a giant spider. The spiders typically don’t bite humans because they are timid and flee from confrontation, although some cases have been reported.

Black Widow vs. Brown Recluse

Which is More Dangerous?

Florida's most dangerous spiders are the black widow (left; Latrodectus mactans) and the brown recluse (right; Loxosceles reclusa).  Both can be deadly.  So far the black widow is winning this struggle for territory ongoing on my front porch ceiling.  Photo:  Phillip Lott

Question and Facts about the Joro Spider

Here are some quick facts about the spider from a conversation with E. Richard Hoebeke, associate curator at the University of Georgia Collection of Arthropods. The interview below, conducted via email, is lightly edited.

How is the Joro spider spreading?

The Joro is an effective hitchhiker. This past fall, I found one under the hood of my vehicle. It can build a web quickly and attach it to an automobile or a trailer or any other conveyance. In addition, if the female is mated and gravid (with eggs), she can lay an egg mass on any object, again a vehicle, box, etc. So I believe the Joro is effectively spreading and expanding its range here in Georgia and beyond because of its hitchhiking capability.

It can also spread when the spiderlings first hatch from the egg sac. These small spiders will spin a long strand of silk that can be carried by air currents and moved great distances (a behavior called ballooning). So between these two means, the spider is expanding its range.

Where is the Joro spider found?

The Joro was first found in the northern part of Georgia and has spread into the very southern counties of Tennessee adjacent to the northern state line of Georgia, and in the very western portion of South Carolina, also bordering Georgia. I am aware of a sighting from North Carolina, very possibly a hitchhiker. Also, I heard of a Joro sighting in Oklahoma, again a likely hitchhiker (the person reporting said she came from Athens and was moving to Oklahoma).  The Joro has also recently been reported in Florida.

Will the spider spread across much of the United States?

The Joro has a fairly high cold tolerance (from reported research, also done here at the University of Georgia) so it might do just fine in more-northern climates of the eastern United States. But only time will tell how far or how quickly it will spread. We will continue to rely heavily on the public for sightings of the Joro outside Georgia.

Is the Joro spider venomous, and can it bite humans if startled?

All spiders are venomous. They use that venom to subdue their prey. But not all spiders are poisonous. I know of a few reported incidences of a Joro biting a human. In one case, the bite site became reddened, swollen and a little painful. The individual sported a mild fever for a while, and the wound site took several days or more to heal. I think because all people are different, some with allergies to arthropod bites, the bite response can be different from one person to another.

I also recommend that a spider not be picked up with your fingers. No sense in taking chances to get bit. Joro spiders appear to be passive, timid spiders. They usually run away when their webs are agitated.

Joro spider webs in the Georgia mountains.

Where are Joro webs commonly found?

I know of many stories through the emails I receive of people running into the webs face-first, either on horseback, bikes or trail machinery. The Joro seems to prefer to make webs in higher locations. Generally, the common yellow garden spider and other native orb weavers seem to make webs closer to the ground in shrubs. You will find webs of Joro spiders high up on telephone poles and power lines, at least we do here in Athens, and it is also documented to do the same in its native range (Japan). Also they make webs among the branches of trees as much as 6 to 10 feet off the ground.

Are the Joro spiders a common sight in Georgia?

The Joro appears to be well established in the north-central and northeast portions of Georgia. They are especially abundant, at least in the past year, in the Athens area and many other areas surrounding metro Atlanta. I received hundreds of emails with attached images from homeowners this past year, indicating how common and abundant the spiders were on their properties.

I’ve read the Joro spider may have entered the United States in a container ship. Is that the leading theory of how it arrived here?

That still appears to be the best guess as to how they entered this country. The fact that a Joro spider and its web was found on the exterior of a freight container in a container yard at Tacoma, Wash., seems to support this hypothesis. This scenario has been responsible for numerous other alien invasions of arthropods into North America.

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How large can the Joro spider grow?

A fully mature female measures up to three inches with legs outstretched. The males are quite small (maybe ½ to ¾ inch in length with legs) and pale by comparison with the female.

Is there a downside or risk to having the Joro spider established in the United States?

This question still arises whether the Joro is outcompeting any of our native orb-weaving spiders. Does it displace some of these? There is still no solid evidence to suggest that they do. So the jury is still out on that concern.

The fact is these spiders are here to stay, and they will continue to spread, undoubtedly. Eventually they may become less feared by the general population. No question the Joro is a beautiful spider, and maybe learning more about it and what it does will help in lessening fear of this new immigrant.