We are often told how valuable earthworms are for our gardens with their soil-enriching abilities—but are they truly beneficial? Let’s have a quick look at their history in North America and what this means both for gardeners and conservationists.
While the benefit of earthworms is not entirely a garden myth, there are concerns that can affect the future of our forests.
Earthworms in the Garden
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In North America, gardeners rely on earthworms including Lumbricus terrestris (the common earthworm) to aerate our soil, and convert organic matter into nutrients, while improving soil structure and composition.
There’s even some evidence that worms might be beneficial in reducing carbon emissions.
But, the common earthworm is non-native, and, while well-adapted in cultivated gardens, it is not so welcome in forests.
This worm is widely distributed around the globe and has several common names including ‘the common earthworm’, ‘lob worm’, ‘nightcrawler’, ‘dew worm’, or ‘granddaddy earthworm’.
We have 19 identified earthworm species here in Ontario and all of them originate in other parts of the world.
Worms Used in Vermicomposting
Have you seen indoor worm boxes or compost bins where people keep worms to convert organic matter into fertilizer?
That’s vermicomposting (vermis is Latin for worm).
The worms used for vermicomposting are different species than the common earthworm.
Composting earthworms include red wigglers (Eisenia fetida) and red tigers (Eisenia andrei).
Composting worms reside on the soil surface in organic matter, have excellent appetites, reproduce rapidly, and their outdoor populations seem to be limited/controlled by harsh weather conditions.
The common earthworm burrows deep in the soil, and, with that natural protection has managed to wriggle its way through the continent.
All of these worms are non-native to North America.
When it Comes to Common Earthworms, Location Matters
Earthworms native to North America were wiped out in the ice age approximately 15,000 years ago.
The common earthworm (Lumbricus terrestris) we have today originated in Europe and was introduced with imported plants and soil a few hundred years ago.
Scientists studying forests and forest conservationists are ambivalent about the common earthworm.
While the worms have not been problematic in cultivated gardens, they can affect life on the forest floor.
As the worms eat, nutrients are taken from leafy ground covers and moved deeper into the soil, both altering soil structure and robbing young seedlings of necessary nutrition. This in turn negatively affects or restricts new growth.
Deeper roots can access the nutrients but younger plants are left depleted.
How to Prevent Further Earthworm Damage
We cannot control or remove existing common earthworms from forests, but we can do a few things to help limit further spread.
Never dump worms or soil in natural areas.
Never dump leftover bait worms after fishing.
It is hoped that (over many years) our forests can adapt to the introduction of earthworms, but they will be different and perhaps less prolific.
So next time you hear of someone thinking it’s okay to put leftover soil in country ditch or forest, give them the invasive worm talk!
~Melissa the Empress of Dirt ♛
- Earthworms are not Always Good for the Soil | Oklahoma State | Ag Sciences and Natural Resources
Invasive in the Spotlight: Jumping Worms | NH Extension
Earthworms | Clive A. Edwards, The Ohio State University