Patty Loew:
It's a sure sign of spring when you spot an earthworm. They're good for plants in the garden. In fact, Europeans imported seven different species of earthworms when they first arrived in the new world. And for decades, anglers have been dumping leftover worms. Now the little worms are causing big problems. This week "In Wisconsin" reporter Jo Garrett shows you how earthworms are changing the northwoods, literally right under our feet in Bayfield County.

Jo Garrett:
This is a tale of two forests running on either side of a gravel road. Think of it as forest A and forest B. Two forests that together tell a story.

Man:
We're in the Great Divide District in Bayfield County. This is pretty typical of northern hardwood forest. A sugar maple dominated forest.

Jo Garrett:
Steve Spickerman, a plant ecologist with the United States forest service, is very unhappy with the part of the of the Chequamegon we call forest A.

Steve Spickerman:
This is very unhealthy. You see virtually nothing of what should be here.

Jo Garrett:
Look down.

Steve Spickerman:
The thing that I'm looking at here is the ground.

Jo Garrett:
The story is in the ground.

Steve Spickerman:
Kind of an invasion front moving through the forest.

Jo Garrett:
An invasion in the soil. To see how it works, take a look at the floor of forest B, the healthy forest. Forest B has duff. What is duff?

Steve Spickerman:
Duff is the accumulation of leaves and other organic material that has fallen and it creates a layer over the mineral soil. It can be anywhere from an inch to six or seven inches deep.

Jo Garrett:
Duff is not the same as soil. It sits on top, like frosting. Take a closer look at forest A, the unhealthy forest. Forest A is losing its frosting.

Steve Spickerman:
So what's happened over the course of, say, the past 20, 30, maybe 100 years, is that the soil has literally changed. It's gone from a soil that was very deep in leaf litter and the stuff from the trees to a soil that's literally just dirt.

Jo Garrett:
The duff has vanished. It's down to bare dirt. Contrast with forest B.

Steve Spickerman:
When you have duff, the earth is spongy feeling.

Jo Garrett:
Forest B, the healthy forest, still has the right stuff, duff. What happened to forest A?

Steve Spickerman:
We’ve been wormed.

Jo Garrett:
That's right. Earthworms. To the dismay of foresters and ecologists, the forests of northern Wisconsin have been invaded by seven different species of European earthworms. And they're plowing through this duff layer like contestants at a pie eating contest.

Steve Spickerman:
They literally eat it. They pull it down, they digest it, they consume it.

Jo Garrett:
What? Weren't there always worms wiggling through the northwoods? Answer, no. These trees are rather recent.

Steve Spickerman:
8,000 years ago, 10,000 years ago this was covered by a mile thick sheet of ice. When that ice melted, glaciers retreated. Over several thousand years, this area went from barren to tundra to boreal forest. Probably 3,000 years ago, the species we see here now moved in and established the forest. The forest was established in the absence of earthworms.

Jo Garrett:
In their natural state, the woods are worm-free. And this is where conventional wisdom...

Steve Spickerman:
The assumption is that worms are a good thing.

Jo Garrett:
...collides with reality.

Steve Spickerman:
Many of the plants that evolved in this kind of system need the duff. It won't do well on raw mineral soil.

Jo Garrett:
Without duff, some plants can die. Plants like spring ephemerals.

Steve Spickerman:
White trillium, the violet, wild leeks, spring beauty, bloodroot.

Jo Garrett:
These plants blossom in spring and then they fade. Now they seem to be gone for good.

Steve Spickerman:
Those plants simply ceased to exist here.

Jo Garrett:
Spickerman sifts through the evidence in the wake of the worms.

Steve Spickerman:
Another tell tale sign that there were worms here, what looks like small sticks are the rib of last year's leaves. All they left behind were the ribs of the leaves.

Jo Garrett:
The loss of these downed leaves, the duff, can affect standing trees.

Steve Spickerman:
Take a look at the base of the sugar maple. You can see the moss that should naturally be on the maple. It's a line on the bottom of the tree. The soil has literally gone from here to there. We’ve seen places where the forest floor has literally dropped six, seven, eight inches. You lose the soil around your base and it's going to have some real effects. We've actually seen trees that are maybe half this diameter begin to topple over because they no longer are rooted in what they need to be rooted into.

Jo Garrett:
They need the duff. It's true for standing trees, it's true for seedlings.

Steve Spickerman:
If you imagine something that's younger than this trying to get started out on this bare dirt, the moisture on a summer like this summer where we had almost two months without rain here, a young tree is simply not going to be able to survivor on this bare dirt. You lose that too many summers in a row, you lose a generation of trees.

Jo Garrett:
You lose the animals that burrow and live in these downed leaves.

Steve Spickerman:
Salamanders, spring peepers, wood frogs, small mammals, different types of mice that would be living in the leaf litter that are obviously not here because the leaf litter is gone.

Jo Garrett:
So if the worms around aren’t native, how did they get here?

Steve Spickerman:
When the first farmers came from Europe to North America, they brought plants, they brought animals, they brought worms. Following the cut over here around 1900, this area, a lot of it was sold off as farms. There were farms dotted all through this national forest.

Jo Garrett:
Farming brought worms and fishing brought worms.

Steve Spickerman:
You get done with your day of fishing, pull back up to the boat landing. What do you do with the worms? I'm guilty of this, too. I haven't done it in a number of years now, but, you dump the worms out. Great spot there. Worms are probably going to burrow in, they're going to live. Well, you've just introduced a nonnative invasive species to the northwoods.

Jo Garrett:
We've brought them here. What's next?

Steve Spickerman:
Two years ago we walked over 4,000, 5,000 acres, right in this area and tried really hard to find places that didn't have worms and we were unsuccessful. And our supposition is there might be only 15% of the forest now without worms. I would hate to take a guess how many worms are here but it might be in the hundreds of thousands or millions per acre.

Jo Garrett:
Given those numbers, solutions are in short supply and forest B may soon resemble forest A.

Steve Spickerman:
Worms are something you don't see. They're something you don't typically think about and the changes that they're doing are so profound, changing entire soil structure over multiple states. This is literally a problem from the east coast to the west coast. Being done by species that we can't see. When I first moved here and we bought our farm, the first thing we did is dug in the soil and found worms. The first response was oh, great, we have worms. Now I dig in the soil and I go, oh, great. Worms.

Patty Loew:
The Great Lakes Worm Watch is a website devoted to the environmental threat. And with the Wisconsin fishing opener on Saturday, May 1, it has advice for anglers. You can find the link on our website at wpt.org and then scroll down and click on "In Wisconsin." To combat the problem, it recommends dumping your extra worms into the trash, not into the lake and not on the land.