Every Earthworm In Michigan Is Actually An Invasive Species

Earthworms. Everyone knows worms. When it rains, you have to play hopscotch to avoid crushing these poor, slimy things. They make great bait for fishing. The school bully may have even dared you to eat fried worms. Worms are everywhere on our feet, under logs, and under rocks. It's not exceptionally difficult to find a worm if you really try.

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Which isn't shocking considering that earthworms have been found in 97% of soils across North America. However, it is not native earthworms. It's invasive earthworms, which have spread and been introduced around the country over the years. It is a little-known fact that, despite their familiar presence and generally praised role in the environment, Michigan was never supposed to have earthworms, and worms are a relatively new feature in Michigan's history.

The Ice Age’s Role in Michigan’s Worm-Free Past

It’s well known that the Great Lakes are the largest freshwater lakes in the entire world, accounting for 21% of the world's freshwater. This is because Michigan was once completely covered in ice during the Ice Age, making it impossible for organisms like earthworms, which live in soil, to survive. As a result, all native-species of worms in Michigan were completely wiped out.

When the glaciers began to melt some 20,000 years ago, Michigan, as we know it today, with its dense forests, came to be. Forests used to be very different from what we know today, with early explorers describing forest floors as once plush from layers of leaves on the ground. That is, before the earthworms invaded.

For this new section, we'll be looking at two sources. The first is a fantastic video that was released over the weekend by Alexis Dahl, a YoopTuber (a term I just created for a YouTuber who lives in the Upper Peninsula) who makes content about fascinating aspects of Michigan. For a full breakdown of earthworm history in Michigan, give the video below a watch. The other source is a study by Stanford on the "earthworm invasion."

In Alexis' video, she goes into detail about how the ancient forests we discussed earlier developed without the assistance of worms in the soil, long before worms arrived in Michigan. These forests relied on fungi instead to help decompose dead leaves at a slow rate, resulting in what came to be known as the "duff layer," and the base layer on which the rest of the forests grew.

READ MORE: The Reason Michigan Lacks Dinosaur Bones

The Duff Layer: Michigan’s Ancient Forest Floor

When worms, natural decomposers that aerate and move the soil as they slither beneath the surface, made their way into Michigan forests, it completely altered the way forest floors functioned. While worm poop makes great fertilizers for farmers, these old forests weren't accustomed to the new makeup of the soil, leading to long-term suffering for some tree populations, such as sugar maples.

Now, to clarify. Not all worms are harmful, nor are there many inherently "bad worms". The long-term effects of worms in areas that previously lacked them are unknown. Even the Stanford study, which details the impact of the many species of earthworms that have permeated much of North America, acknowledges that there is no denying that many earthworms have proven helpful for the environment.

It's a fascinating concept that has not been extensively researched, and the impact of invasive worms should be closely monitored in the future.