By Karen Menard

If only the 150 year old oak tree’s roots could talk.  It’s likely to tell a story of how their view of the forest floor has changed over time, thanks to some slippery stowaways. 

Even before that oak sprouted, the writhing, subsurface arthropods were on their way to us from a foreign land, buried deep in the soil of a ship ballast, quietly in tow.

These wriggling invertebrates, otherwise known as “earthworms,” were early transports from Europe, hitching a ride alongside the first settlers.  Fresh soil is all that they needed to keep the next generation going. And, so they did.

After their arrival, these annelids moved very slowly across the landscape and made themselves at home in forested ecosystems, as well as backyards and farms. No competition meant better success, as none of their native counterparts survived the impacts of the last glacier. Surprisingly, our forests in the Great Lakes region actually evolved in the absence of these creatures.

From the perspective of an old oak growing in the presence of earthworms, it, most likely, had witnessed some ecosystem changes in its lifetime--mostly dependent on the total worm density.

Different worm species go to work in different layers of the soil, and based upon their burrowing and feeding characteristics, three main ecological groups exist. In the epigeic (top) layer, these smaller species feed on the surface litter and/or fungi and bacteria on plant rhizomes.

One of the most recent invaders and an inhabitant in this uppermost layer—the Asian jumping worm (Amynthas agrestis), is aptly named for their erratic, thrashing movements. This worm is known for its ability to severely impact an ecosystem in a short period of time, often consuming a high percentage of the leaf litter layer, turning it into loose, pellet-like castings that resemble coffee grounds. Reproducing quickly and maturing twice as fast as other species, individuals are often found existing in greater densities. The soil conditions they create include lots of pore space, leading to dry, eroded environments that cannot support native plants.

The next layer is home to the endogeic group. Lacking pigment, this sizable group burrows and feeds within the soil’s mineral layer.  Last, but certainly not least, remains just one burly species comprising the deepest (anecic) layer. Commonly called night crawlers, these dark, reddish-brown, explorers of the deep may burrow up to two meters below the surface! Sadly, a robust population can consume all of the organic litter produced in a season, negatively impacting native forest floor ecosystems long-term.

From the perspective of the old oak, any earthworm population that has wiggled in and among its lengthy root system over time, had the potential to alter the soil structure, affecting microbes and nutrient profiles, halting the neighboring sugar maple seedlings from growing more than just a couple of inches tall, and allowing more space for invasive garlic mustard and buckthorn to get established.   As a result, associated fungi and fauna could also be disrupted, further causing a domino effect on the lifecycles of small mammals, macroinvertebrates and amphibians as the loss of cover and disappearance of food sources occurs on the forest floor.

Additionally, earthworms are even capable of converting organic forms of nitrogen and phosphorus into very soluble nitrates and phosphates. If these chemicals make their way into nearby wetlands and waterways, sites can also be impacted through nutrient loading.

On the other hand, everything that we learned in Kindergarten about worms was that they were beneficial.  And, in truth, they are—all while working their magic in the appropriate environment.  Gardens, farms, compost piles, and turf grass sites are a win-win for both humans and worms alike due to the fact that worms are skilled soil aerators, creating important pore space for oxygen, nutrients, and water, further utilized by plants. By breaking down the organic material, they also aid in the acceleration of nutrients released, also harnessed by the developing plants. All accomplished in the right space.

It’s not all gloom and doom.  Worms have not invaded everywhere, and in areas that different species have moved into, the population concentrations vary in size. However, in certain forested ecosystems that worms have taken a toll on, the herbaceous vegetation that remains is sparse, low in biodiversity, and often dominated by invasive plants. Once worms have become established, there is not a known removal method. Prevention of invasion is key.

In order to continue to slow the spread of these animals into other woodlands or natural areas, we can all help by taking the following conservation steps. Earthworms are spread primarily by humans. 

Dispose of your fishing bait responsibly—do not purchase jumping worms or toss any unused bait into the water! Worms and cocoons (egg cases) can survive in an aquatic environment for long periods of time. Be wary that tire and hiking boot treads often are perfect crevices for holding soil and cocoons. Keep a scrub brush handy and/or a way to remove the excess soil before transporting worms to other natural areas. Also, before using compost, consider letting it freeze solid for at least one week so that the egg cases and worms aren’t transferred to other areas.

Did you know?

• European worms only move about 30 feet a year, whereas, jumping worms move 17 acres.
• Earthworms in the epigeic (top soil layer) group are pigmented a red-brown color and appear darker on the back and head. Scientists believe that the pigmentation may provide protection from UV rays and also may offer some protection from predators.

Above: Stock Photo

For more information, go to: https://wormwatch.d.umn.edu/