Clumps Of Spiders Are Falling From The Sky In California In A Phenomenon Called ‘Ballooning’

Published October 6, 2023
Updated October 7, 2023

Ballooning happens every year, but experts aren't exactly sure why there have been so many of these spider sightings recently.

Threads Of Silk In The Grass

Stephen Michael Barnett/Wikimedia CommonsThreads of silk cover the grass after a bout of ballooning back in 2014.

It’s a bird, it’s a plane — no, it’s webby white clumps of baby spiders. Residents across the Bay Area have been puzzled by the sight of these tiny white clouds drifting down from the sky, which experts say are baby spiders in the midst of a phenomenon called “ballooning” or “kiting.”

“I woke up this morning. Go out to the back deck, drinking a cup of coffee, and I look at the moon… There’s a strand of white going across it and I’m thinking that is weird,” one resident said according to ABC 7 News.

As the San Francisco Chronicle reports, ballooning happens in the Bay Area every year. Like dandelion seeds, baby spiders float through the wind in silken threads in search of new places to live.

“What they are is strands of silk that spiderlings, baby spiders, use to disperse,” Fred Larabee, an assistant professor of biology at San Jose State University, explained to the San Francisco Chronicle. “To get away from where they’re originally born, they spin these silk strands and they get caught by the wind, which pulls the spiders to a new place to live, to new habitats, so they’re not competing with their siblings.”

Ballooning Spiders

Marcella Joann Sandoval/NBC Bay Area/XA Bay Area resident took this photo of ballooning spiders floating through the sky.

All sorts of spiders use ballooning. Crab spiders, wolf spiders, and orb weaver spiders — which all call the Bay Area home — spin silky threads as babies in order to spread themselves far and wide. These threads can clump together, which explains the webby clouds that people have been seeing. By the time these land, however, the spiders have most likely already left.

“What they do is, when they’ve hatched and gotten to a certain size, they’ll get up on something and reel out a wall of fluffy thread and go flying,” Lynn Kimsey, Distinguished Professor of Entomology at UC Davis, explained of the floating spidery webs to ABC 10. “It’s totally awesome.”

As ABC 10 explains, baby spiders can travel as high as three miles into the air while ballooning, and even across oceans. They don’t only utilize the wind, but also the energy of electric currents in the air.

But why are there so many spiders ballooning in the Bay Area lately? Though baby spiders generally spread this way in the spring and fall in Northern California, experts aren’t entirely sure why there have been so many gobs of white spider webs in the sky in recent weeks.

As the San Francisco Chronicle reports, spider populations go through “boom and bust” cycles which means that ballooning is more obvious in some years than others. The proliferation of ballooning spiders this year could be due to the recent heavy rains in California, which caused more plants to grow, and thus more insects (which the spiders eat). High temperatures could also be a cause, and many people first noticed the ballooning spiders during unusually warm days in October.

Spider Webs On A Bush

Darlene Damm/XSpider webs spotted by a Bay Area resident on a bush. By this point, the baby spiders that floated inside have already left to establish their new homes.

Though the sight of spider webs may be alarming — and the San Francisco Chronicle reports that they were even mistaken as chemical warfare during World War II — they pose no risk to people. In fact, as ABC 10 reports, the only problem they may cause is if they float too far away from home and become an invasive species in a non-native environment.

As such, Bay Area residents seem to be taking the proliferation of spider webs in stride. Many have even commented that they even feel appropriate, as Halloween is just around the corner.

“They look almost like the fake spider web stuff that you buy at the Halloween store,” Bay Area resident Brook Shadwell noted to the San Francisco Chronicle of a web she’d touched. “It was very silky and sticky.”

After reading about how spiders are falling from the sky in California in a phenomenon known as “ballooning,” discover some of the most incredible — and incredibly terrifying — spiders on Earth, including the giant huntsman spider and the desert-lurking camel spider.

Kaleena Fraga
A staff writer for All That's Interesting, Kaleena Fraga has also had her work featured in The Washington Post and Gastro Obscura, and she published a book on the Seattle food scene for the Eat Like A Local series. She graduated from Oberlin College, where she earned a dual degree in American History and French.
Maggie Donahue
Maggie Donahue is an assistant editor at All That's Interesting. She has a Master's degree in journalism from Columbia University and a Bachelor's degree in creative writing and film studies from Johns Hopkins University. Before landing at ATI, she covered arts and culture at The A.V. Club and Colorado Public Radio and also wrote for Longreads. She is interested in stories about scientific discoveries, pop culture, the weird corners of history, unexplained phenomena, nature, and the outdoors.
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Fraga, Kaleena. "Clumps Of Spiders Are Falling From The Sky In California In A Phenomenon Called ‘Ballooning’.", October 6, 2023, Accessed May 28, 2024.