Most of us think of earthworms as beneficial creatures. Gardeners are always happy to spot a worm in the flowerbed because they add fertilizer to the soil. Many anglers say they’re the best thing for catching fish. But scientists are beginning to learn worms aren’t so friendly to Great Lakes forests. The Great Lakes Radio Consortium’s Stephanie Hemphill reports:
Most of us think of earthworms as beneficial creatures. Gardeners are always happy to spot a
worm in the flowerbed because they add fertilizer to the soil. And many anglers say they’re the
best thing for catching fish. But scientists are beginning to learn worms aren’t so friendly to
Great Lakes forests. The Great Lakes Radio Consortium’s Stephanie Hemphill reports.
(fade up Girl Scouts)
This Girl Scout troop is learning about worms. Judy Gibbs is a naturalist at the Hartley Nature
Center in Duluth. She shows the girls how to coax worms out of the soil. They pour water laced
with powdered mustard into the worms’ burrows.
It irritates the worms and they come squiggling up by the hundreds.
“Pour it in. Wait a minute. Here it comes. It doesn’t like the mustard and it comes right up.
Look at this one (laughter). oh, there’s another one. Look at it go!” (shrieks)
On their walk through the woods, the girls look for dead leaves. There aren’t many. Judy Gibbs
“Here’s a leaf stem that’s being pulled into this hole. Who’s doing this? Ants! No. Worms.
There’s big night crawlers. You know what a night crawler is? They grow straight down into the
ground, and they come up at night and pull leaves down into their burrows. And they eat the leaf
right off. That’s why we’re not finding any leaves.”
Worms eating leaves might seem natural, but it turns out these worms aren’t native to these
woods. The last glacier buried most of what is now the Great Lakes region. When it melted,
plants and animals returned to create a community of maples, pines, songbirds, and tender plants
growing on the forest floor, like trillium…but not earthworms.
Cindy Hale is a biologist who studies the native wildflowers that grow in northern hardwood
forests. She loves the spring bloomers that take root in the spongy layer of decaying leaves on
the forest floor. Trillium, bloodroot, solomon’s seal.
Hale says many of these plants are disappearing.
“Sites that forty years ago were carpets of trillium have been slowly over the last two decades
declining to almost nothing, and people were scratching their heads, trying to figure out just
what’s going on.”
Earthworm populations are thickest close to cities. But Hale says people bring worms with them
when they come to the woods.
At first, settlers carried them in, along with the animals and plants they brought from Europe or
the east coast. These days, worms are spread by people who drive in the woods – loggers, ATV
“But in particular, fishing bait is a huge way that worms get moved around in our region.
Because there’s so many lakes and so much fishing.”
Hale and her colleagues set up test plots along an advancing line of worms in the Chippewa
National Forest in central Minnesota. The worms crawl about three yards further into the forest
each year. Hale is studying how the soil and the plants have changed as the worms advance.
Worms eat the decaying leaves on the forest floor. They mix that organic matter into the mineral
soil beneath it. And in time, they can use up all the organic matter and leave only mineral soil
That means the plants that have evolved to take root in the leaves on top of the soil have lost their
Hale says these changes could affect every plant and animal that lives in the woods. She says,
for instance, even birds have declined by nearly 50% in the last fourteen years.
“Because ovenbirds nest in that forest floor, so if you lose the forest floor, then you may well
affect ground-nesting birds such as that. So when you start thinking about it, the potential
ramifications across the ecosystem get really wild.”
Hale says one of the big challenges in studying this problem is that there’s been very little basic
research – like how many worms are there are and where.
To gather more information and to get more people involved, Hale created a web-based learning
program. She’s asking teachers from around the country to have their classes do worm counts
and other research. Hale plans to add their data to the web page.
In Minnesota, the Department of Natural Resources is working with interest groups to try to slow
the spread of worms. Next year’s fishing regulations will include instructions not to dump your
worms at the end of a day of fishing.
For the Great Lakes Radio Consortium, I’m Stephanie Hemphill in Duluth.