Crazy Jumping Worms May be Coming to a Woods Near You

By Steve Garske, GLIFWC Invasive Species Coordinator

For many, it comes as a surprise. Those earthworms so common in our lawns, gardens, and forests weren’t always here. Since their arrival on the east coast several centuries ago, they have been busy remaking Turtle Island’s northern hardwood and hardwood-conifer forests, and not for the better.

Long ago, the massive Laurentide ice sheet spread out from the Hudson Bay region to cover most of what is now Canada and the northern United States, as far south as Iowa, Illinois and New Jersey. As glaciers scoured the landscape, any native earthworms that may have been here were wiped out.

Then around 12,000 years ago, the glaciers retreated north from the Great Lakes region, leaving a rocky landscape dotted with glacial lakes. As the climate warmed, plants recolonized the landscape, eventually forming the lush forests and wetlands that we see today.

Because they disperse at a rate of only a few feet per year, native North American earthworms only recolonized the very southern edge of this new habitat. The northern half of North America remained earthworm-free until the arrival of European settlers.

Until the invention of ballast water pumps in the 1880s, soil was used to keep ocean-going ships stable. When European ships reached east coast ports this soil was dumped out, along with earthworms and other soil organisms. Earthworms were soon transported far and wide by human activities including logging, roadbuilding, fishing and horticulture. As they spread into natural forests, they began munching on the thick layer of leaves and spongy “duff” that acts like a blanket over the soil, leaving muddy, bare ground in their wake.

Today, earthworm-infested forests are the rule rather than the exception. The loss of the duff layer exposes the soil to erosion, compaction, freezing, nutrient leaching and increased rainwater runoff. It also destroys many of the fungi and microbes that form symbiotic (mutually beneficial) relationships with plants, and help them to grow and remain healthy. Millipedes, mites, insects, salamanders, voles, shrews, and ground-nesting birds that rely on the litter layer for food and cover have a much harder time surviving when the duff layer is degraded or gone. And seedlings of native forest plants often can’t get a foothold in the exposed soil.

Read more at the Spring issue of Mazina’igan.