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In Da Woods

by Melanie B. Fullman, US Forest Service

As the Worm Turns

When some folks see worms, they (the people) squirm. Others grab a fishing pole. Most of us were probably taught that worms are good for the soil.

Sure, they’re slimy and not very flashy. But they aerate our gardens, and feed robins and fish, so they must be beneficial, right?


Not So Fast

Turns out – earthworms are NOT native to the Great Lakes region. Any native North American earthworms that might have been here were frozen out when glaciers covered the Upper Midwest 11,000 - 14,000 years ago. Natural re-colonization by earthworms happens VERY slowly, less than a half-mile in 100 years. So there’s just no way that native worms south of the glacial area, in the southern US, could have gotten to the UP on their own (they would have only moved a mere 40 miles or so).

All the earthworms you have come to know and love are exotic. First brought here by European settlers in the mid-1880s, they continue to be transported, intentionally or unintentionally, by humans. Like when unused fishing bait is dumped along the shore of a lake, or when we transport compost and mulch, buy potted plants from distant locales, or bring in firewood or equipment that has dirt on it.

The widespread use of earthworms as fishing bait is probably the leading cause of their spread: one need only look at the advancing edge of the earthworm invasion that radiates from lakeshores, fishing resorts, and boat landings. Besides, all our common bait worms are non-natives: night crawlers, Canadian crawlers, leaf worms, and angle worms.

“Don’t they just drown when I dump them in the water?”, some might ask. Earthworms can actually live in water for many months because they “breathe” through their skin. So unless those fish that wouldn’t come to the worm on your hook suddenly decide to eat all your dumped worms, chances are some not only survive, but thrive in their new North Woods home.

Dandy Duff

For the past 10,000 years, the forests of the Great Lakes region grew without earthworms. In the absence of such a powerful detrivore (eater of dirt and dead vegetation), natural decomposition of leaf litter was controlled by fungi and bacteria. This decomposition occurs at much slower rate than that of earthworms. As a result, a thick, spongy forest floor, known as “duff”, was able to develop.

In un-wormed areas (there’s still a few left), the natural duff layer is typically 4- 5” thick, MUCH deeper than in areas with worms. Dozens of native understory plants need extra thick duff, including trilliums and other spring flowers. Well-developed duff provides protection from predation and insulation from temperature and moisture extremes. The thick duff is so critical that many understory plants and tree seedlings root exclusively there, since it is where most nutrients are found.

The loss of a forest duff layer also causes changes in the diversity and composition of microscopic animals, insects, fungi, and small mammals, which are the primary food source for hundreds of species of forest birds, other mammals, bigger insects, spiders, amphibians, and reptiles. While earthworms can be a good food source for some of these animals, the loss of cover means they are more vulnerable to becoming prey themselves.

Researchers at the University of Minnesota and elsewhere have documented dramatic changes in native hardwood forest ecosystems when exotic earthworms invade. These changes include losses of native understory plant species and tree seedlings, changes in soil structure, and declines in nutrient availability.

Winning the Worm War

Some large earthworm-free areas still exist, albeit mostly in the most remote areas. Ottawa Forest botanists routinely survey for worms during timber sale planning. Standard contact clauses require contractors to clean their equipment and tools before and after operations, which reduces the risk of both worm and other non-native invasive species transport.

You can help, too.

1.      The best way is to NOT dump bait worms. Put them in the trash instead.

2.      Remove dirt/worms/seeds from your ATV, trailer, pickup, etc. before heading to the woods.

3.      Don't dump compost, leaves, or garden waste in the woods.

4.      Participate in ongoing worm research by joining an existing study or conducting your own as part of the Great Lakes Worm Watch. Visit www.nrri.umn.edu/worms/team/index.html or contact me for more information: 932-1330 x539; mfullman@fs.fed.us.


I can honestly say I never expected to write an article on earthworms, especially one touting their unnatural, undesirable effects on our ecosystem. Something, it turns out, that IS not supposed to be In the Woods. Hope to see YOU there instead!



Polar Bear Cookbook

Thank you to everyone who submitted recipes for the Polar Bear Hockey Cookbook. The cookbooks are now available. The cost for the cookbooks are $10.00 so make sure to grab one for yourself and maybe one or two as a gift. They can be purchased at the Pat O'Donnel Civic Center concession stand or by contacting Kerry Roehm or Micki Sorensen.


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