Spring rains often bring scores of earthworms to the surface, where they writhe on top of soil and sidewalks. But recently, heavy rainfall in a town near New York City was followed by something a little more unusual, a wormnado.
New Jersey on March 25, spotted hundreds of worms spread along the walkway. But a number of the worms had formed a cyclone like shape, creating a spiral where the edge of the grass met the concrete.
They weren't actively spiraling, although individual worms still wriggled in place. There were no open pipes nearby, and though most of the worms were spread out in a big swirl, there were plenty of worms extending beyond the outer curve of the wormnado.
So what was the weird wormnado all about?
Worms breathe through their skin, so when heavy or persistent rain saturates the soil with water, the worms must tunnel to the surface or risk drowning, according to the University of Wisconsin–Madison. Earthworms are typically solitary, but they sometimes form herds when they're on the surface . The worms collect in groups and communicate with each other about where to move, researchers reported in 2010 in the International Journal of Behavioural Biology.
The scientists in that study found that earthworms in the species Eisenia fetida would form clusters and influence each other to select a common direction during their migration," and they did so using touch rather than chemical signals. This collective behavior could help earthworms survive environmental threats, such as flooding or arid soil, and it could also be a defense strategy against predators or pathogens, according to the study.
One exceptional example of earthworm herding was captured on video in 2015 by rangers at Eisenhower State Park in Denison, Texas. In the footage posted to the Texas Parks and Wildlife YouTube channel, several enormous masses of pink earthworms wriggle on a road.
But the cause of the Hoboken wormnado is less clear.
Kyungsoo Yoo, a professor in the Department of Soil, Water, and Climate at the University of Minnesota said, this tornado shape is really interesting.
Yoo studies how invasive earthworms transform forest ecosystems, and though worms are known for mass-emerging from soil after rain, he had never seen them form a spiral before.
Aquatic worms, such as the California blackworm (Lumbriculus variegatus), can form an enormous living knot known as a blob of as many as 50,000 worms when they're threatened by dry conditions, according to Worm Blobs, a comic created by the Bhamla Lab at Georgia Institute of Technology's School of Chemical and Biomolecular Engineering, and illustrated by artist Lindsey Leigh. A tightly packed blob of worms is less likely to dry out than one worm on its own, and the worms pull and push to move the blob around, Bhamla Lab researchers wrote in the comic.
Lab leader Saad Bhamla, an assistant professor at Georgia Tech, suggested that sudden changes in the soil's water, in combination with the shape of the landscape, could explain the appearance of a spiraling wormnado. The ground there could be dipped. If the water drained that way after flooding, the worms could be following a water gradient.
It's difficult to tell the worm species from the photos, but Bhamla and his colleagues have observed that type of behavior in the aquatic blackworms they study, which form massive blobs.
Bhamla said, we've seen them follow trails of water and form all kinds of paths and aggregate structures. These aggregations occur once water leaves. However, as it's unknown what type of worms made the spiral, any conclusions about their behavior would be speculation.
Harry Tuazon, a doctoral candidate in Georgia Tech's Interdisciplinary Bioengineering Graduate Program said, local weather reports described heavy rainfall the night before the photos were taken about 1 inch (2.5 centimeters) in all. That would have resulted in a lot of earthworms coming out from the soil for air. I think the circular pattern is much more indicative of water draining and the worms being swept, rather than a type of behavioral locomotion. Perhaps a sinkhole is forming? It would be interesting if a bunch of earthworms provided telltale signs of a forming sinkhole!
In any case, whatever may have caused the Hoboken wormnado didn't last.