Joro Spider Ballooning: How this Technique Creates Flying Spiders

Recent news headlines are asking if the Joro spider could invade the entire East Coast. These giant spiders use a technique called ballooning in which they spin a web and ride the air currents to travel around. Some ballooning spiders can travel hundreds of kilometers. Let’s find out about ballooning and see if the whole United States could be covered with these giant parachuting spiders!

What are Joro spiders?

Joro spiders have a leg span that reaches about 3 to 4 inches across.

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Joro spiders are big spiders about the size of the tip of your thumb. Their long skinny legs can reach a span of 3-4 inches. Instead of being all black or all brown like most spiders, their females are very colorful. Their backs are black with yellow stripes and a red splotch, there are red markings on the stomach as well. Joro spiders have striped legs, with bands of yellow and blue. Besides their color what makes them stand out is their giant golden webs. They are part of the orb-weaver family and can weave large intricate 3-D webs. The female Joro’s are the ones that are colorful, while the males are only ¼ inch long and brown.

Are Joro spiders invading the United States?

Joro spiders are from Japan and East Asia that have made their way to the United States. In 2014 people reported seeing this unusual spider and their enormous webs in Georgia. Scientists confirmed that it was the East Asian Joro spider. It is unlikely they ballooned across the ocean to get here. Scientists think it is most likely that these spiders hitched a ride on a shipping container and started reproducing here. It is likely that they used the ballooning technique to disperse through Georgia and South Carolina. A recent study out of the University of Georgia suggests they might be able to survive in cooler temperatures than thought, making their way up the East Coast. They have made their way to northwest Georgia, so they could certainly keep moving west to Alabama and south to Florida as well.

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Why do spiders balloon?

There are a number of reasons that spiders adapted to ballooning:

  • Baby spiders: The majority of ballooning is done by spiderlings. A few days after hatching, large groups of baby spiders will take to the air. Their main purpose is to spread out and find new places to live but they also do it to avoid cannibalism from other spiders and to increase the availability of resources.
  • Adult females: Adult females, sometimes as large as an inch long, can balloon but it is less common. They may balloon to a new area if humans interfere with their current location. If food becomes scarce in one area they may take to the wind to find a new home. Lastly they may balloon during mating season to locate an available mate.

Joro spider ballooning, how does it work?

Flying Spiders
Spiders can create a parachute with their webs and float on the air currents to relocate.

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There has been debate over how spiders can seemingly float through the air. There are some mysteries as to how it actually works. How can some spiders balloon when it is raining? Why do spiders take flight only when there is a slight breeze? How can some larger spiders balloon when they seem to be too heavy to make it work?

Researchers are still studying ballooning but it seems that spider’s balloon with a combination of the correct wind currents and electrical fields.

How do spiders float on air currents?

A researcher in Berlin, Germany was curious how some larger spiders could balloon. Moonsung Cho, who was working at the Technical University of Berlin wanted to observe and record exactly how spiders take to flight. He created two experiments, one with a mushroom-shaped platform for the spiders to launch from and one in a wind tunnel to control the air currents. The videos of the spiders on the platform are fascinating to see the ritual for takeoff!

The spiders would raise their front arms in the air, and then stand up like standing on their tiptoes to gauge the wind (this is called “tiptoeing”). The research showed that they were waiting for the correct wind speed (less than 3 ms−1 ) and optimal updraft. The temperature of the air and the humidity played a role as well. Once they had the correct conditions they quickly spun a series of threads that formed a triangle and floated off the platform. The wind tunnel experiment produced similar results.

Cho used crab spiders, an orb weaver similar to the Joro spider, for the experiments. They are a larger ballooning spider, but not the biggest. The ones in the experiment were 3-6 mm.

Besides “tiptoeing” some spiders use what is called “rafting” to take flight. They climb to a high point in a tree or bush and dangle down from a silk thread and wait for the right conditions. Then they spin their parachute and take off.

How are electrical fields used in Joro spider ballooning?

Later research suggests “that Spiders show a significant increase in ballooning in the presence of e-fields.” E-fields (electronic fields) are thought to be sensed by tiny sensory hairs similar to bumblebees. It must play a role in when a spider decides to take off or wait. This might explain why scientist have a hard time predicting what days might be good days for spider ballooning and what days may not. There are factors involved besides the wind speed and humidity.

How far can a spider balloon?

While most spiders balloon shorter distances some have been documented to travel hundreds of kilometers (100 kilometers=62.1 miles). So technically, yes, they could invade the whole United States over time.

What are the risks of ballooning?

The majority of ballooning in spiders is seen by spiderlings, typically a few days after they hatch. Some researchers think that the risks associated with ballooning might not be worth it for larger adult spiders. Think about an inch-long spider floating by a hungry sparrow. What if they are completely at the will of the wind and land in a large lake, or get snatched by the tongue of a frog. They could also land any number of unsafe places (your windshield for example!). But in cases where food has become scarce or humans have interfered with their webs, adult spiders may need to relocate. Large groups of newly hatched spiders need to disperse so the risks for the whole group are worth it.

What other kind of spiders use ballooning?

Goldenrod Crab Spider
Crab spiders are one of the spider species that uses ballooning to travel to new locations by floating on air currents and using electrical fields.

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  • Araneidae (orb-weaving spiders): These include Joro spiders and banana spiders
  • Linyphiidae (sheet-weaver spiders): Tiny black spiders that weave a sheet-like web. Includes Sheetwebs and Dwarf spiders.
  • Lycosidae (wolf spiders): Some wolf spiders are quite large, but the smaller ones have been documented to balloon.
  • Thomisidae (crab spiders): These were the spiders Moonsung Cho used in his experiment.

Are there flying caterpillars?

Beware of flying caterpillars! The gypsy moth in the caterpillar stage uses ballooning to relocate as well.

Picture CreditMillie Bond – Copyright AZ Animals

The Gypsy moth uses ballooning as well to relocate when it is in the caterpillar stage. They climb to higher parts of trees and then use the same “rafting” technique, hanging from a silk thread until they are whisked away by the wind to a new location. The gypsy moth is still limited to the eastern United States so maybe the US should be worried about giant parachuting spiders and flying caterpillars!

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