Are worms…that is at least what science claims. It seems the forests surrounding the Great Lakes developed without earthworms. Ten-thousand years ago native species disappeared during the glacier period. Since then, our trees and plants have evolved to live in a wormless soils. In this region, a thick layer of duff, the debris of trees and shrubs, lined the forest floor. Duff normally remained for years, slowly decayed by fungi, and providing a habitat for many ferns, delicate wild flowers, and small animals like salamanders.

Since settlers first moved here, earthworms like the red wriggler used in fishing and for composting, have been introduced into the forest lands. Gardeners usually think of worms as a desirable asset to soil. They eat decaying matter, aerate the soil and leave humus-rich worm castings behind as they burrow. In general they do good things for soil where garden plants grow.

In the forests, however, worms eat the duff in just a few years, lowering the soil’s acidity and making nutrients more available. The plants in our forests survived in the poor fertility and the high acidity of our soils. While this won’t necessarily harm the mature trees growing there, the duff’s absence affects the number of seedlings growing in an area. It also makes an advantageous situation for unwanted invasive species that couldn’t have grown in the original, more acidic soil.

As this debris layer disappeared, so did the habitat for plants like Trillium, lady slippers, Solomon’s seal, blue cohosh, sweet cicely, mayflowers, wild ginger, lady fern, bloodroot, bellworts, and the globlin fern. They adapted to germination and growth in the thick layer of duff. The duff layer provided them nutrients, moisture, protection from extremes in temperature and predators, and a habitat for microorganisms like fungi necessary for the plants’ survival.

It is also believed the loss of the duff effected the salamander population that fed on insects living in the debris. The salamanders in turn, provided food for snakes, shrews, thrushes, and screech owls, so the earthworm invasion effected a whole chain of living organisms.

We introduced worms from dumped fishing bait, on purchased plants’ soil balls. The tires on all of our motorized vehicles’ entering our forests often carry worm eggs, so the most severe invasions are usually near roads.

Once the earthworms infest an area, little can be done to remove them without more harm to the forest. We know many of the previously listed plants grow in worm-infested soil, because we grow them in our gardens, but a study in the Chippewa National Forest in northern Minnesota shows these species do not return to worm-infested forests.

Some ecologists hope the ecosystem of the forest may eventually come to a new balance. In the meantime don’t spread earthworms into wormless areas, don’t dump worm bait in forested lands, and keep your vehicles on roads and trails. Gardeners in wooded areas need to keep compost piles and worm contaminated soil from contaminating the woodlands. These may seem like small measures, but a little thing began this big change.

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