It's a Bird, It's a Plane, It's a ... Flying Spider?

By: Mark Mancini  | 

Flying spider
The lack of wings doesn't stop some arachnids from soaring through the air in a convincing simulation of flight. Max Pixel (CCO Public Domain)

Defined as the "intense and irrational fear of spiders," arachnophobia is one of the more common animal phobias. In a 2017 U.K. poll, 24 percent of the respondents said they were "a little afraid of spiders" — and 16 percent were "very afraid."

We bet those people were just thrilled to see headlines about "flying spiders" pop up on their social media news feeds in 2015.

Here's the good news for arachnophobes: No spider can literally fly. However, that doesn't mean our skies are 100 percent spider-free.

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The Flight Club

Bats and other flying animals use assisted aerial motion, also known as true or "powered" flight. They have wings capable of producing both lift (the upward force needed to counteract their bodyweight) and thrust (the force which propels them in the direction of motion).

Winged insects are a dime a dozen; most people have swatted their fair share of airborne mosquitoes or buzzing houseflies.

But as you might already know, spiders are not insects. Like scorpions, ticks, and mites, they're part of a different class of invertebrates called arachnids. Although some arachnids can swim, none possess wings — and true flight just isn't in the cards for them.

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Falling Flat

What caught the scientific community's attention back in 2015 was an arachnid behavior study published by the Journal of the Royal Society Interface.

The paper dealt with tree-dwelling Selenops spiders native to Central and South America. Nicknamed "flatties" because their bodies are flat in appearance, these arachnids hunt by night and regularly seek shelter under tree bark during the day.

Normally, these guys are found in rainforest canopies. Life's not too easy up there. High winds can push an unlucky or unwary spider clear out of the branches. Sometimes, they jump out on purpose to avoid encounters with aggressive Azteca ants.

Either way, the spiders want to avoid plummeting to the forest floor, which is crawling with predators.

Not to worry. Thanks to that Royal Society paper, we now know the "flatties" have a special trick up their sleeves. When of them falls or leaps off a branch, it can usually steer itself towards the nearest tree trunk while falling and then land somewhere on the bark — instead of hitting the ground.

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Target Acquired

A team led by ecologist Stephen P. Yanoviak rounded up wild Selenops spiders in Peru and Panama. Later, they dropped 59 of the arachnids from either local treetops or manmade platforms situated at canopy level.

In 93 percent of their field tests, the falling spider made it safely to the closest tree trunk, never touching the forest floor.

Flatties sometimes "right" themselves in midair by aiming their flat bellies at the ground. But that's not all. To stick the landing, the spiders essentially become mini torpedoes. Each arachnid maneuvers itself into a face-down position, pointing its head and front legs at the trunk. Meanwhile, the rear legs are splayed backwards (and up).

This body manipulation gives Selenops some control over their descent. They can travel 16.4 feet, or 5 meters, horizontally through the air — and also "steer" themselves in the desired direction.

It's not true flight, not even close. The correct term is "directed aerial descent," a phenomenon never previously documented in spiders. Some arboreal ants use the same basic technique.

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Air Time

Okay, enough about flatties. Lots of other spiders can go airborne under the right circumstances — using a totally different process that involves silk.

If you've read the classic children's book "Charlotte's Web" by E.B. White, or seen one of its movie adaptations, then you already know where we're going with this. The story's title character is a kindly barn spider. After Charlotte passes away, her pig friend Wilbur watches all but three of the arachnid's children float into the distance on little balloons made of silk.

White wasn't just using artistic license here; this "ballooning" behavior is something naturalists have known about since the 17th century.

Various spiders have the ability to travel through the air for literally hundreds of miles (or hundreds of kilometers) by riding strands of their own silk. Doing so helps the species populate new territories.

Ballooning is popular with baby spiders, or "spiderlings," who might run the risk of getting eaten if they hang around their parents and siblings too long. However, some adult spiders use the same transportation method.

Experiments conducted in Berlin indicate that ballooning crab spiders raise their front legs upwards to test the wind before taking flight. It would also seem they'd prefer to stay grounded unless there's a warm breeze outside moving at less than 9.84 feet (3 meters) per second.

Furthermore, at least some spiders use electric fields to acquire lift and become airborne when they go ballooning — as demonstrated by a 2018 paper in Current Biology.

One last thing: Did you know floating spiders have been seen cruising along as high as 2.48 miles (4 kilometers) above ground level?

Yeah, maybe don't tell your arachnophobe friends about that....

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