Mary Beth Breckenridge, a nationally published home and garden writer, wrote an article in the Akron Beacon Journal about the good and “not so good” characteristics of earthworms. Her article was later published in the St. Paul Pioneer Press in 2017. This article on Earthworms blames them for changing the forest floor in ways that threaten the survival of some native plants including our beloved Trilliums.
Non-native earthworms have moved into woodland areas that had evolved to survive without them. The worms speed up the decomposition of the spongy forest floor, disrupting the delicate balance of the animals, plants, and other organisms that depend on it. Biologist Dr. Kathryn Flinn conducts research related to the worms and their impact on the environment. She reports that we have no early history of worms because they left no skeletons or fossils. One theory is that if they did exist is Minnesota in Pre-historic times, they were scrapped away during the time of the glaciers.
Mary Beth explained the difference between the earthworms in the garden and those in the forest floor. In the garden they eat the fallen leaves, twigs, and other organic matter from the ground surface and enrich the soil with their castings. This makes ready nutrients that the plants need as a natural fertilizer.
In normal conditions, leaf litter builds up on the forest floor faster than it can decompose thus forming a thick spongy surface called a “duff layer” that holds moisture and keeps organisms in the soil below from freezing in the winter. All sorts of living things depend on the duff layer. Many animals and insects use it for habitat and food. Some plants need its loose texture for their tender roots to spread. And wild flowers like the Trillium need the spongy surface to protect their seeds from birds and small mammals and to provide the right conditions during the long germination process.
When earthworms move in and eat up the duff area, plants are forced deeper into the soil where it is less suitable for their needs. In highly populated deer areas, they eat the tree saplings and other plants while pounding down the duff layers. There are a few things than can help a little. Dump unused fishing bait in a trash can rather than on the shoreline or in the weeds. Also, hikers are encouraged to scrape off the mud on their footwear before they leave the hiking area to remove any worm cocoons that may have attached to that footwear.