In Memphis, spiders cover ground with blanket of silk. How is this possible?

It's called 'ballooning,' and it's harmless.

It’s an alarming sight for arachnophobes, but the half-mile-long spider web harboring thousands, maybe millions, of spiders in Memphis is – believe it or not – harmless.

"It's a mass dispersal of the millions of tiny spiders that have always been in that field, unnoticed until now,” explained Memphis Zoo curator Steve Reichling to a community gripped by spidery terror. Residents in the northern Memphis neighborhood that’s home to the gigantic web have been trying to kill the tiny arachnids one by one.

"You can't even sit in [a neighbor's] house because they're all on the wall, on the door,” complained resident Debra Lewis to WMC News. “We been killing spiders for about an hour now," she said.

But there’s nothing to fear, as the small creatures, probably sheetweb spiders, said Dr. Reichling, don’t bite. What’s causing the blanket of silk web covering parts of a field in a residential neighborhood is a migration event called “ballooning.” What happens during ballooning is that spiders disperse by shooting out threads of silk. These threads catch wind currents that transport these members of the Linyphiidae family forward several feet at a time.

Thousands of these spiders have probably been living in the field near where the blanket of white has been formed in Memphis.

“This would explain the fact that thousands to hundreds of thousands may take off at the same time,” explained  Susan Riechart, a professor at the University of Tennessee in Knoxville and former president of the American Arachnological Society, to The Washington Post.

“Caught by the air currents, the spiderlings have no control over where they will land, but it is not surprising that they may fall in the same area," said Dr. Riechart.  

Such ballooning events are not unique to Memphis. They can happen all over the Northern Hemisphere – and have been spotted in Britain and Australia – but scientists don’t really know why and when.

But they do say the spiders pose no danger to people. Ballooning is simply, “a spectacular natural history occurrence," explained Robb Bennett, a spider expert at Canada’s Royal British Columbia Museum in Victoria, to National Geographic.

In 2012, for example, record rains and flooding in News South Wales, Australia, caused millions of wolf spiders to shoot their silky way to safety up trees and bushes, covering the city of Wagga Wagga in white.

Though events like this are understandably unnerving to people, they’re an indication of a healthy ecosystem. Memphis residents might feel consoled to know that these spiders feed on many agricultural pests, which is beneficial for farmers.

“I would not want to live in a world where such things were no longer possible,” Reichling from the Memphis Zoo said. “The presence of these spiders tells us that all is well with nature at that location."