It's hard to believe, but it's true - earthworms are not native to the Adirondacks. In fact, earthworms are not native to any region where glaciers once scoured the land. This includes all of the Great Lakes region and the Northeast.
I always thought earthworms were good. In grade school, I learned that earthworms churn and aerate the soil as they wriggle and writhe through the earth. As an environmental educator, I taught that as decomposers, worms help to transform dead and decaying matter into nutrient-rich humus that fuels new plant growth. But in recent years, I learned that while worms in most of the U.S., agricultural systems and the garden can be good and desirable, non-native worms in forests can be invasive and devastating.
How is that possible? Earthworms are ecosystem engineers. These inconspicuous organisms can actually change the form and function of our forests, including the health and diversity of forest plants and animals. What make earthworms beneficial to lands where they are native are the exact traits that make them detrimental to areas where they are introduced. They convert the layer of leaves, seeds and other organic matter on the forest floor, "duff," into soil, but in areas where worms are not native, they transform this layer much too quickly, preventing seed germination, which decreases plant populations over time. Woodland wildflowers like false Solomon's seal, bellwort and trillium are all sensitive to earthworm damage.
A sugar maple’s roots are exposed due to non-native earthworm activity, which depletes the leaf litter on the forest floor.
(Credit — Robert Lee, Bugwood.org)
Removing this important duff layer at an unsustainable rate so that it can't be replenished ultimately alters the soil structure and nutrient availability too, leading to a cascade of other changes in the forest. Many species of small mammals, birds and amphibians rely on the leaf litter for cover as well as for insects and other invertebrates, which are their food source. Salamanders use leaf litter to help regulate their temperature and moisture, too. Disturbance from earthworms can also facilitate invasions of other exotic species such as invasive plants like buckthorn and garlic mustard.
Not all worms are created equal. There are three broad groups that are classified based on what they eat and where they live in the soil: litter and surface dwelling, soil dwelling and deep burrowing. Each group has different impacts based on their feeding and burrowing behaviors. The more species and groups of earthworms found in a site, the greater the potential impacts are, especially to native plant species.
Unaided by humans, natural migration by earthworms happens very slowly, less than half a mile in 100 years, so how did they get here? Most are European and initially arrived with European settlement; others are Asian species. And like other invasive species, they continue to be transported, intentionally and unintentionally, through a range of human activities such as the dumping of unused fishing bait, transport of compost "and mulch and anything else that moves soil.
The distribution of earthworms is still largely unknown, but groups across the Great Lakes and Northeast are starting to track the invasion front to better understand their distribution and impacts. With no known methods to remove or control earthworms, doing what you can to help prevent further introductions can make a big difference. Never dump worms in the woods. Dispose of unwanted bait in the trash. Tell others "the dirt" on earthworms in the Adirondacks. And avoid transporting leaves, mulch, compost or soil from one place to another unless you are confident that there are no earthworms. For stunning images pre- and post- invasion where earthworms are not native, and to learn more, log on to greatlakeswormwatch.org.
Eye on Invasives is a biweekly column that spotlights a top invader when it is easiest to identify. Hilary Smith directs the Adirondack Park Invasive Plant Program, a partnership program housed at the Adirondack Chapter of The Nature Conservancy in Keene Valley.
Find out more about this award-winning program online at