The Problem With Earthworms

Earthworm Are earthworms good for your garden? Many gardeners believe that earthworms are a benefit while those who garden in a very heavy clay soil would be quick to disagree.

  Earthworms Are NOT Native To North America

If you live in North America, you've probably never seen a native earthworm. They used to be everywhere until around 10,000 years ago when the last ice age blanketed huge portions of the continent with glaciers. The era that brought North America the Great Lakes killed off most of its native earthworm species.

But when people move from place to place, they tend to bring hitchhikers with them, and the first European settlers in North America were no exception. The first European earthworms arrived in the 1600s in ships' ballast and the soil of imported plants. And today, a global economy brings soil, mulch, and fishing bait from all over — complete with foreign worms from Asia, Europe, and elsewhere riding aboard.

Read more: How Earthworms Benefit Gardens

If you live in North America, you've probably never seen a native earthworm. They used to be everywhere until around 10,000 years ago when the last ice age blanketed huge portions of the continent with glaciers.

  Earthworms And Soil Aggregates

There are many studies that show earthworm activity helps to form better soil aggregates which in turn will help soil to support better plant growth with less compaction and erosion. Just compare the difference earthworms can make in the production of topsoil. It might take 500 to 1,000 years for nature to produce topsoil in the absence of an adequate soil animal population. However, under favorable conditions earthworms can shorten this process to a little as 5 years. This is because of the ability for earthworms to mix, till and build top soil as they go about their daily business of burrowing through the earth.

Read more:   What Are Soil Aggregates?

  Earthworms and Clay Soils

In heavy soils, earthworm activity seems to make all the problems of a clay soil a little bit worse. The earthworm castings seem to be sticky, gloppy masses of close to concrete, not the type of soil conducive to plant growth.

There is no instant, magical way to eradicate earthworms with a spray or drench. In fact, even trying to do so would be devastating to all living organisms in the soil that help make up the great diverse environment in the soil we cannot see. If you have a heavy soil and find earthworms are not helping, the best solution is to add lots of organic matter.

In effect you will be “feeding the worms” and giving them more organics to break down and improve your non-friable soil. Use coarser organics like grass clippings and chopped leaves to provide lots of munching prior to becoming humus.

Read more:   Clay Soil Gardening

  Earthworms and Hardwood Forests

For nearly 10 millennia, the forests of North America have evolved to get along without earthworms. Trees and smaller plants rely on the thick layer of dead and partially decomposed leaves that blankets the forest floor to help them grow and protect their roots. As any gardener knows, earthworms love chomping through leaves. As a result, there are many forests — especially those with mostly hardwood varieties like maple, red oak, poplar, or birch — that once had a thick organic carpet, but now are left with bald spots, leading to decimated herb species and hardly any tree seedlings taking root.

Researchers also say earthworms also lead to a decline in populations of salamanders, songbirds, and orchids, to name a few, and they're also linked to the growth of invasive plant species.

  What Can Be Done?

Earthworm Soil Formation graphic Before you curse every earthworm you see, it's important to know that there are a lot of earthworm species out there — about 5,000 globally — and not all of them are harmful. According to Scientific American, only about 16 of the European and Asian species are responsible for substantial damage.

There is one that you may be familiar with: the Asian worm called the jumping worm (also known as the Alabama jumper, snake worm, or crazy worm) that you can spot by the wild thrashing that helps it literally jump off the ground.

Read More: YIKES! Jumping Worms!

Unfortunately, once these worms have moved in, there's no getting them out. The best hope is to keep them from spreading.

  We can do a couple of things to help limit further spread:

  Never dump worms or soil in natural areas.
  Never dump leftover bait worms after fishing.

Read More:

 How Earthworms Help Your Garden
 Fertilizer Basics: A Tutorial
 Soil Biology
 Native Plant Root Systems

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