When it comes to joro spiders, don’t believe everything you hear
Flying? Nah. However, it has been shown that some spiders can not only balloon on wind currents, but also electromagnetic fields
By Austin Jones
Guest columnist
Entomology instructor, director of undergraduate education and outreach coordinator
U of A System Division of Agriculture
(1,058 words)
(With graphic and image of Jones)
FAYETTEVILLE, Ark. — "Giant." "Venomous." If those adjectives weren't enough to pique America’s arachnophobic interests, some are also tagging joro spiders as “flying.”
Sensational headlines are popping up across the country about the latest species introduced to the US, the joro spider Trichonephila clavata.
However, these sensationalized claims, just like the spiders themselves, do not have wings, and as with much of the news today, there is less to worry about than headlines suggest.
What are joro spiders?
Joro spiders are an impressive-looking species of orb-weaving spider with females exhibiting bright yellow markings on their body and legs. Orb-weavers create the iconic angular-yet-circular spider webs that are often depicted in everything from children’s books to low budget horror films.
The spider family Araneidae (A-rain-E-ah-day) contains about 3,500 species of orb-weavers, with more than 150 species being native to the US. The closest native relative of the joro spider is very similar in overall body shape, habits, and size, and is known as the golden orb-weaver — Trichonephila clavipes. Golden orb-weavers have actually been farmed for silk production and females can be separated in appearance from joros by coloration that is less striking and presence of obvious tufts of hair on three of their four pairs of legs.
Other native orb-weavers and friends of the garden, the garden spiders — Argiope aurantia and A. trifasciata — could also be mistakenly identified as joros by the public as they are also large and colorful yellow and white orb-weavers. Garden spider females can actually get larger than joros and can be differentiated by how their web contains a zig-zag pattern reminiscent of a zipper that runs right up the middle of the orb web. This structure is called a stabilimentum.
Are they giant and can they fly?
Of course, “giant” is relative, but it would probably only be used to describe the mature females that can reach a body length of about 1.25 inches, not including legs. So, these are not carry-away-your-pets-kind-of-big by any means, but quite a bit larger than jumping spiders or black widows for instance. Females still fall far short of tarantula size and males would not be noticed by most people as they lack the striking coloration of the females and only reach a little over .25 inch in body length.
As for the flying, well technically, no, they cannot fly, and adults will never be airborne unless they have fallen or been picked up by wind, just like any other spider could.
However, baby joro spiders do partake in an activity known as ballooning. This is when the tiny and very lightweight spiderlings push out some web into the breeze and catch it much like a miniature kite. Where ballooning spiders land is generally up to the winds of fate instead of targeted destinations.
It has also been shown that some spiders can not only balloon on wind currents, but also electromagnetic fields. Could a joro spider land in your yard from the sky? Sure, but would an individual be enough for you to notice upon landing? Probably not. Each spring, overwintering egg sacs will spill forth with tiny ballooning daredevils that, if successful, will become mature by fall and will perish in late autumn or winter.
Where are joro spiders found?
Joro spiders are native to Japan and many other parts of Asia and are not known to have been reported in Arkansas at the time of this article. However, a lone report from Bartlesville, Oklahoma, was made on the app iNaturalist with the user mentioning that it was likely transported from a recent road trip to Athens, Georgia, (so it probably came through Arkansas!).
Athens is very close to where the joro was first documented in the U.S. in 2014, and a known hotspot of joro activity. This highlights the ability of these spiders to hitchhike in goods and on vehicles to new areas. With much of the Eastern U.S. habitable to this species of spider it is likely a matter of time before they become more widespread via this type of relocation, both as adults or as egg sacs.
Are joro spiders venomous or dangerous?
For starters, of the more than 40,000 known species of spiders, only one single species is known to feed solely on plants, the rest are predators. Of these predators, only one single family is known to not be venomous. Uloborid spiders vomit on their prey instead of injecting venom and consist of more than 300 species globally.
For practical purposes one could say that all spiders are predators and that all spiders are venomous and be right almost all the time. So, yes, they are venomous, but their venom is of no more danger or potency than native spiders which are nearly all of little concern.
In North America the widows — Latrodectus — and recluses — Loxosceles— are the only two spider genera documented to have medically important bites and between them consist of 10 species Two of those species have also been introduced to the U.S. — the brown widow, Latrodectus geometricus, and the Mediterranean recluse, Loxosceles rufescens.
As populations of joro spiders spread they will compete with native species for prey and may displace or outcompete some leading to conservation issues. Should these spiders outcompete native species assemblages and reach large populations due to a lack of natural predators or disease, it could also impact imperiled pollinator insect groups such as butterflies and bees, but these situations have not manifested yet.
Otherwise, having a joro or two in the yard eating other pestiferous species could potentially be seen as a benefit. After all, spiders are our friends when it comes to eating insects, and if joro spiders lived up to the hype of being giant, flying, venomous homewreckers, gun control laws would likely be less hotly debated.
In a nutshell
- Are joro spiders giant? They are large for web-building spiders, but not near the size of a tarantula.
- Can joro spiders fly? Technically no, but they can balloon. Only juveniles can become airborne and do so by riding the wind with kites made of spider web when they are still quite small.
- Are joro spiders venomous? Yes, but nearly every spider is and their venom is not medically important.
- Are joro spiders dangerous? No, they are not aggressive and would only bite if provoked. They do pose some threat to natural spider populations and ecosystem integrity.
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About the Division of Agriculture
The University of Arkansas System Division of Agriculture’s mission is to strengthen agriculture, communities, and families by connecting trusted research to the adoption of best practices. Through the Agricultural Experiment Station and the Cooperative Extension Service, the Division of Agriculture conducts research and extension work within the nation’s historic land grant education system.
The Division of Agriculture is one of 20 entities within the University of Arkansas System. It has offices in all 75 counties in Arkansas and faculty on five system campuses.
The University of Arkansas System Division of Agriculture offers all its Extension and Research programs and services without regard to race, color, sex, gender identity, sexual orientation, national origin, religion, age, disability, marital or veteran status, genetic information, or any other legally protected status, and is an Affirmative Action/Equal Opportunity Employer.
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Media contact: Austin Jones
akj003@uark.edu