Thursday, February 13, 2020

Cancel Earthworms: The “crazy worms” remaking forests aren’t your friendly neighborhood garden worms

...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...Common species like Lumbricus terrestris, better known as the night crawler, arrived hundreds of years ago with European settlers, and have long been welcomed in gardens and farmland. In the 1980s, however, researchers began to find European worms in the forests of Minnesota and other northern states. One hypothesis is that people spread them when they throw away extra fishing bait next to lakes and streams. The discovery alarmed scientists. In the absence of worms, North American hardwood forests develop a thick blanket of duff—a mille-feuille of slowly decomposing leaves deposited over the course of years, if not decades. That layer creates a home for insects, amphibians, birds, and native flowers. But when worms show up, they devour the litter within the space of a few years. All the nutrients that have been stored up over time are released in one giant burst, too quickly for most plants to capture. And without cover, the invertebrate population in the soil collapses...MORE

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