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(NEXSTAR) — Have you ever walked outside after a spring rain and encountered earthworms writhing and slithering across the driveway or the sidewalk?

Well, that’s nothing compared with the bizarre “tornado of worms” that a woman in Hoboken, New Jersey, witnessed last week.

Surprised by the sight, the woman, who wanted to remain anonymous, took pictures and sent them to Hoboken City Councilmember Tiffanie Fisher, who shared them on Facebook, according to Live Science.

“Has anyone ever seen anything like this? This is a tornado of worms that were out this morning,” Fisher posted. “Clearly worms come out after it rains but this is something I’ve never seen!”

The woman who took the pictures told Live Science that she was out walking in a park near the Hudson River on March 25 when she encountered hundreds of worms along the walkway.

She also said she noticed that many of the worms had formed a spiral shape on the concrete that was reminiscent of a cyclone.  

The photographer said the worms weren’t actively spiraling, but many spread out in a big swirl. She told Live Science that others clung to the wall of a nearby building and some spilled over the curb and onto the road.  

Live Science reported that the phenomenon probably had little to do with the Worm Moon, the supermoon that lit up the sky Sunday.

So why were they above ground in such volume?

According to the University of Wisconsin–Madison, worms, which live in underground burrows, breathe through their skin, and oxygen diffuses about a thousand times slower through water than through air.

“The worms can’t get enough oxygen when the soil is flooded, so they come to the surface to breathe,” Teri Balser, an associate professor of soil and ecosystem ecology at UW–Madison, said in a statement.

Live Science reported that the typically solitary earthworms sometimes form herds when they surface. According to a 2010 report in the International Journal of Behavioural Biology, the worms gather in groups and communicate about where to move. 

Researchers found that one species of earthworms — Eisenia fetida — clusters together and “influence each other to select a common direction during their migration.” The study said such behavior may help them survive environmental threats, such as flooding or arid soil. It could also be way to defend against predators or pathogens, the study found.

The exact cause of the Hoboken worm tornado is unclear, reported Live Science, though one theory is that if the ground was dipped and the water drained in one direction after flooding, the worms could be following a water slope.