Scientists were scratching their heads after hundreds of writhing worms formed a cyclone shape on a sidewalk in New Jersey.

The strange incident occurred after heavy rains in Hoboken, across the Hudson River from Manhattan, earlier this month. Masses of worms emerging from the soil after downpours is not unusual — but the size of this group and the odd formation baffled experts.

Worms breathe through their skin, and must often tunnel to the surface to survive heavy rains. They also sometimes form “herds” when they surface and can move collectively through some kind of “consensual decision phenomenon,” Belgian researchers noted in 2010.

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“Our results modify the current view that earthworms are animals lacking in social behavior,” noted Lara Zirbes, lead author of the study and a Ph.D. student at the time at the University of Liege in Gembloux. The worms form clusters and “influence each other to select a common direction,” the group of researchers theorized. “We can consider the earthworm behavior as the equivalent of a herd or swarm,” according to Zirbes.

The unusual worm confab drew attention after a New Jersey woman who first spotted the annelids earlier this month sent photos to Hoboken City Council member Tiffanie Fisher, who posted them on Twitter. Fisher later tweeted a link to an article on the Belgian research post by the California Academy of Sciences, and explained that she had learned that “earthworm herding is a thing.”