DID YOU know that earthworms in Wisconsin, including the mighty night crawler used by thousands of anglers, are invasive species that can damage the health of forests?

“Opening a can of worms” takes on a whole new meaning when it comes to our forests, which evolved without invasive earthworms that were brought here from Europe and Asia centuries ago.

According to the Department of Natural Resources (DNR), anglers have facilitated the spread of earthworms sold by bait shops by dumping unused worms at the edge of wooded lakes and streams. And once established, there is no way to remove those worms from the woods.

And it gets worse. In recent years, new non-native worms from Asia have been found in Wisconsin. Referred to as “jumping worms,” the parthenogenetic worms have a much higher ability than earthworms of successfully establishing populations from small numbers.

Jumping worms were first identified in Dane County in 2013 and have been reported in 45 counties, including Vilas and Oneida.

Biologists say earthworms and especially the larger night crawler consume leaves on the forest floor — leaves that are essential in protecting the soil and providing the proper environment for tree seedlings and native plants to germinate and grow.

When a forest becomes invaded by earthworms, the soil is exposed and erosion occurs. Often, invasive plants take the place of native plant species.

According to research and depending on soil quality, there can be anywhere from 250,000 to 1.75 million earthworms per acre of land. It is farmland and our forests that rank highest for soil quality.

Biologists say because the typical earthworm can process about 10 pounds of organic material from the forest floor every year, just one acre of worm-infested forest can lose five tons of organic material in a year’s time.

Healthy ecosystems are impacted when such a high volume of leafy material isn’t available to break down and release nutrients into the soil for uptake by plants.

“The key to a healthy forest resides in a fungal-based soil that slowly decomposes its organic matter,” said Bernadette Williams, a DNR biologist. “A healthy layer of leaf litter, also known as ‘duff’ in a northern forest, is woven together with threads of fungi that bind the litter to the soil.”

Finding mushrooms, lichen and other fungus in a forest is great news about the overall health of the soil and its future ability to support tree seedlings and native plant life.

Earthworms, notorious disturbers of soil, create healthy conditions for farms and gardens. But once heavily infested in a forest area, they can strip the land of leaves in a single summer season.

So what do we do?

According to Williams, the public can help slow the spread of these invasives by avoiding the release of live worms on land or in the water. Keep compost contained near native landscapes. Wash shoes and tire treads to avoid spreading worm eggs into worm-free forests.

She said the safest way to dispose of unused worms or crawlers is in the trash. Apparently they won’t hurt the local landfill.

The experts claim earthworms are at home in water, where they can either burrow into the lakebed or swim their way to shore. It is common for night crawlers to enter the water in spring as part of their reproduction cycle.

There were once native earthworms in the North Woods, but glaciers during the last ice age scraped and stripped soil from the bedrock, moving them south. It was the first settlers to Wisconsin who brought invasive worms with them.

Today, earthworms and their cocoons move around in the mud attached to logging equipment, heavy machinery, trucks, cars, ATVs and bicycles, as well as plants purchased in the store.

As a walleye and trout angler who from time to time would carry a flashlight and pail while walking through a cemetery at night picking crawlers, I wondered how worm and crawler surveys were being done during the day.

There’s no intent here to put bait dealers out of the crawler business, but Williams shared the most effective, safest way to harvest night crawlers is in the middle of the day.

She takes one-third cup of mustard powder and mixes it with a gallon of water. She pours it onto a leafless area where bore holes and midden piles show crawler activity.

“Apparently the mixture makes them itch because they come to the surface in a hurry,” said Williams. “Each survey takes no longer than 15 minutes.”

These midden piles have leaf stems sticking out of them because night crawlers literally pull dead maple and birch leaves underground to devour them, eating everything except the non-sweet stem.

It’s never too late in life to learn something new. I had no idea that leftover crawlers should never be dumped in a woods or waterway.

These invasive earthworms are good for lawns and gardens, but bad for forests. Keep that in mind next time you come across a leafless area in the woods.