On a sweltering July day, I follow Annise Dobson down an overgrown path into the heart of Seton Falls Park. It’s a splotch of unruly forest, surrounded by the clamoring streets and cramped rowhouses of the Bronx. Broken glass, food wrappers, and condoms litter the ground. But Dobson, bounding ahead in khaki hiking pants with her blond ponytail swinging, appears unfazed. As I quickly learn, neither trash nor oppressive humidity nor ecological catastrophe can dampen her ample enthusiasm.
At the bottom of the hill, Dobson veers off the trail and stops in a shady clearing. This seems like a promising spot. She kicks away the dead oak leaves and tosses a square frame made of PVC pipe onto the damp earth. Then she unscrews a milk jug. It holds a pale yellow slurry of mustard powder and water that’s completely benign—unless you’re a worm.
Seconds after Dobson empties the contents inside the frame, the soil wriggles to life.
“Holy smokes!” she says, as a dozen worms come squirming out of the soil—their brown, wet skin burning with irritation. “Disgusting.” I have to agree. There is something unnerving about their slithering, serpentine style; instead of inching along like garden worms, they snap their bodies like angry rattlesnakes. But the problem with these worms isn’t their mode of locomotion. It’s the fact that they’re here at all.
Until about 10,000 years ago, a vast ice sheet covered the northern third of the North American continent. Its belly rose over what is now Hudson Bay, and its toes dangled down into Iowa and Ohio. Scientists think it killed off the earthworms that may have inhabited the area before the last glaciation. And worms—with their limited powers of dispersal—weren’t able to recolonize on their own.
For someone like me, who grew up in the Midwest seeing earthworms stranded on the sidewalk after every rain, this was a shocking revelation. With the exception of a few native species that live in rotting logs and around wetlands, there are not supposed to be any earthworms east of the Great Plains and north of the Mason-Dixon Line.
But there are, thanks to humans. We’ve been moving worms for centuries, in dirt used for ship ballast, in horticultural plants, in mulch. Worms from South America now tunnel through the global tropics. And European earthworms live on every continent except Antarctica. Dobson, a forest ecologist at Yale University, calls it “global worming.”
But of all the earthworms people have shuttled around the world, the ones Dobson shows me at Seton Falls have scientists most concerned. Originally from Korea and Japan, they are known as jumping worms, snake worms, or crazy worms. And they have the potential to remake the once wormless forests of North America.