Joro Spider

The Joro spider shares its name with a folkloric “spider demon” in Japanese culture. Though it was once exclusive to regions like Japan and Korea, it was likely brought to the United States via shipping containers in 2013 and has become an invasive species with thriving populations in some states. When this spider is not building webs, it can travel on wind currents on a string of its own silk.

4 Incredible Joro Spider Facts!

Here are a few facts about the Joro spider:

• Despite being venomous, this spider only poses a threat to humans who are allergic to them. Their bite is relatively harmless.
• It is an invasive species, meaning that it is not a native animal to the places where it lives. Experts believe that they traveled on cargo ships, growing in mass numbers in Georgia and other areas.
• While these spiders can look intimidating, they only eat insects such as mosquitos and stink bugs.
• The largest variations of this species can grow to be up to four inches wide.

Scientific Name

The Joro spider’s scientific name is Trichonephila clavate. The word Trichonephila was first assigned to the arachnid by Friedrich Dahl in the early 20th century, describing spiders that create woven orbs for their webs. Clavata comes from the modern Latin word clavatus, which means “club.”

It is from the Araneidae family of the Arachnida class. At this time, they have no subspecies.

Evolution and History

In Japan, the Joro spider is called “jorōgumo,” which is also the name of a mythical creature in Japanese folklore from the Edo period. The Jorōgumo (the modern translation is “entangling bride”) is a spider who upon reaching 400 years old is able to become a beautiful woman. She then captures men with her web then eats them — which reflects what some female Joro spiders do to males after mating.

Before the Joro spider was introduced to the U.S., the only other known Trichonephila species in the New World was the golden orb weaver (Trichonephila clavipes), also known as the golden silk orb-weaver. The Joro spider and the golden orb weaver spin the same type of orb-shaped web, and the silk they both produce is gold. However, the main difference between these spiders is their physical appearance. While the Joro spider is decorated in gray and dark blue stripes with a red belly, the golden orb weaver is usually brown or black with a silvery or plum-colored abdomen. Both species prefer warm environments, however the Joro spider is native to southeast Asia, and the golden orb weaver is much more widespread and found in Australia, Asia, Africa, North America, and South America.

Appearance

The Joro spider is a quite colorful species. Even though males are often the colorful ones in the animal kingdom, the same is not true of this spider. Males tend to have brown and plain bodies. Females, on the other hand, have asymmetrical patterns along their abdomens in black, red, and yellow, complemented by bands of blue and yellow along the legs.

The males and females are relatively close in size as well, though the females are the larger ones. While males range from 0.7 to 1 cm (0.27-0.39 in), the females typically are more than twice this size at 1.7 to 2.5 cm (0.67-1 in) instead. The largest Joro spiders can get even bigger, measuring 7.6-10.16 cm (three to four inches) in diameter in Georgia. However, its only defense is its ability to bite, which is not life-threatening.

Behavior

While these spiders ordinarily keep to themselves, they have been making headlines since 2013 for their mass numbers collecting around homes and in the woods in 25 different counties in Georgia. Though the Joro spider is a relatively helpful creature to humans, the invasive nature of the species leads many people to become afraid of it.

While the Joro spider can appear rather large and intimidating and its orb-shaped webs tend to take over wherever they are attached, it is relatively harmless. Though it can release venom through a bite (which is different from being poisonous), it is not aggressive. The only time that the spider tends to bite is in an act of protection. For some people, this bite is painful, though the venom is not harmful or life-threatening unless you are allergic to this particular spider species. They’ll only bite as a way to protect themselves from threats — however, these spiders are unafraid to use this defense during mating as well, as the female will often eat the male that she mates with.

Still, these spiders have some sense of peace with other Joro spiders as they are able to live in groups in the same area without any other aggression.

To travel, it will use the wind current to “balloon” on, trailing its silk threads from its body to catch itself in the air and glide on the air currents to go up to 100 miles away. They’ll also use almost anything to travel, even holding onto a car bumper or cargo container.

Habitat

The main area of the world that the Joro spider lives in is within the borders of southeast Asia. They are found in Japan, China, Taiwan, and Korea, though they prefer areas with more humidity. They’ll build their home anywhere they can touch.

Since 2013, the spider has become an invasive species in the United States, primarily present in Georgia and the westernmost areas of South Carolina. They are likely to spread further to the East Coast. They don’t seem to have an adverse impact on the local ecosystems just yet, but the warm and humid environments are perfect for the arachnid to thrive. They consume some of the less beloved species of insects (such as the mosquito), and experts believe that they soon will be naturalized to the area.

Diet

The diet of a Joro spider is relatively helpful to the people around it. They are carnivorous, requiring the protein and other nutrients of insects to keep them healthy. Not much is known about the quantities they need to eat a day, but the fact that they go after common pests tends to make the public a little more welcoming to them.

Their diet is opportunistic of the warm and humid climate they need. Typically, mosquitos are the insect of choice, though they’ll also eat yellow jackets, stink bugs, and more. Their diet doesn’t impact the native species of spiders in the area, eating the insects that other spiders tend to avoid. The web is how they passively capture prey, though other spiders — like the dewdrop spider — have fallen victim to the appetite of this species of spider.

The only time that the Joro spider will go after a human or something outside of their standard diet is if they feel threatened.

Predators and Threats

Some birds go after Joro spiders, but there are no particular bird species that prefer them. While they may be eaten by other animals that eat insects and spiders, they don’t have a specific predator that seeks them out. Perhaps because they are an invasive species, there seems to be no natural threat to Joro spiders right now, so they have managed to spread rapidly.

Reproduction, Babies, and Lifespan

Males reach maturity by the end of August when they are about two months old. Females take a little longer, reaching maturity no later than October at three to four months old. The male will join the female on her basket-shaped web, which hangs between tree branches, to mate. Though she may lay between 400-500 eggs, they are all contained within a single egg sac that is constructed from her silk.

When the baby is still within its egg sac with the others, the adults leave them behind and provide no care as they wait to hatch by summertime. Due to the short lifespan, females typically have no mate for life, coming together only for the continuation of the species. Though there are some cases of multiple males fathering the single egg sac or the female guarding the cocoon, these actions are not widespread enough to say whether it is typical of the species.

At birth, the babies can fend for themselves to eat, walking around just after they emerge. There is no specific name for this baby, though some baby spiders are called spiderlings. On average, both males and females live to be one year old. Adults typically cannot survive the winters as the temperatures drop far below their optimal warmth.

Population

At this time, it is practically impossible to say how many Joro spiders exist in the world. Their recent surge in population in the United States has left many people worried, which is why there are no current efforts to protect them. They are not endangered, and they seem to thrive in warmer regions. Their only threat is humans, but even those encounters have not been enough to bring down the population.