Great Lakes Worm Watch

Forest Ecology and Worms »


People play a big role in the story of exotic earthworm invasions and that story started a long time ago.

Where did exotic earthworms come from?

For most of us, earthworms have always been part of our natural world. In fact, earthworms may have been one of the first critters we discovered as children. What we didn't know was that earthworms were not always part of our Great Lakes landscape. The first earthworms probably arrived with soils and plants brought from Europe.  Ships traveling to North America used rocks and soil as ballast which they dumped on shore as they adjusted the ballast weight of the ship.  During the late 1800’s and early 1900’s many European settlers imported European plants that likely had earthworms or earthworm cocoons (egg cases) in their soils.  As a result, exotic earthworms have been around many human habitations since European settlement. Perhaps that is why so many of us believed earthworms must have always been here.

How do earthworms continue to spread across landscape?

More recently, the wide-spread use of earthworms as fishing bait is apparently an important contributor to the spread of earthworms in this region since the advancing edges of invasion often radiate from lakeshores, fishing resorts, boat landing and road ditches… Read more. All common bait worms are non-native species, including those sold as “night crawlers”, “Canadian crawlers”, “leaf worms”, or “angle worms”.  When anglers dump unused fishing bait on the land or water, they are introducing an exotic species (earthworms CAN live in water for many months because they “breathe” through their skin…though they probably don’t prefer it much). It is better to throw un-used bait in the trash… Read more.

Additionally, earthworms can be unintentionally moved by anything that moves soil. Earthworm cocoons (egg cases) are particularly easy to move unintentionally because they are small, hard to see and can tolerate more extreme temperatures and drying than the worms themselves. Both earthworms and their cocoons can be transported via:

Are exotic earthworms everywhere?

No. Although earthworms have been in the Great Lakes Region for a long time, they are not everywhere. Areas where human activity has been the most intense for the longest period of time, have more than likely been invaded by earthworms. However, some large earthworm-free areas still exist, especially in the more remote areas of our region, and ongoing invasions are occurring in many areas through both the natural spread of established populations and with the aid of humans. Without humans moving them around, earthworms move slowly, less than a half mile over 100 years.  If we stop introducing them we can retain earthworm-free areas for a long time.  Since all common European earthworm species are not everywhere and there are additional non-native earthworms available for sale that could have even more harmful effects, even in areas with earthworms already present, we want to take precautions to prevent introducing any more exotic earthworm specie.

Learn how you can help to stop the spread.

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