Beneficial animals Harmful animals

Earthworms: Friend or Foe?

Chances are, if you’re an outdoor gardener, you come across lots of earthworms during the summer months. Little ones, big ones, short ones, long ones, pink ones, brown ones, beige ones… Have you ever noticed how many there are? Most of them stay hidden in the ground and you can’t even see them. It’s probably the bug you come across the most in your soil!

But is that a good thing? Frankly, we’re so used to seeing them that we assume their presence is normal, but is it really?

Photo : Sippakorn Yamkasikorn

Earthworms: Invasive Exotic Species in Canada

Not a very exotic worm, you might say? And yet, they wouldn’t be here if it weren’t for the colonization of America some 500 years ago. Before that, there weren’t really any earthworms in North America.

Arriving probably in the form of eggs (which are tiny) with the French colonists, they discovered a soil rich not in gold, but in litter. They felt at home here and settled in. There are now 19 species, mostly European, in America.

So Much for the Exotic, but What About the Invasive?

The reality was that our soil was very, very rich in organic matter, as there were very few decomposers as efficient. As a result, the worms reproduced very well. But a worm is still a worm: its annual movement to colonize new environments is estimated at… 10 meters. This means that in 500 years, worms would have established themselves within a radius of… 5 kilometers. Not a very invasive prospect!

How come they’re practically everywhere, then? Even the boreal forest is beginning to have a few individuals!

Well, Gina bought some pretty flowers and planted them in front of her house in the Winnipeg, George went fishing in the Laurentians and got rid of his remaining worms by throwing them into the woods, Paulette went hiking in the Rockies with equipment full of mud and Gerald bought manure for his field in Niagara…

In all cases, worms or eggs were disseminated throughout the province, and then across the country. And since worms are highly adaptable, a small quantity of eggs is enough to colonize an entire environment. That’s the invasive side of the earthworm!

Photo 18+ d’un accouplement de vers. Photo : Beentree

So what’s the answer to the thorny “friend or foe” question?

It comes in two parts.

Friend of Vegetables and Flowers

There’s no denying that the earthworm is a very useful worker in the garden. It digs holes and aerates the soil, makes it loose so that roots can sink deep into it, allows water to penetrate better and recycles organic matter into compost, making nutrients available to plants. Wow! A TRUE friend of the garden and flower beds.

The earthworm eats the soil, gobbling up soil, sand, bits of leaves, wood, bacteria, fungi and more. It then digests what is digestible and defecates the soil (rock particles, therefore non-digestible), but also all the nutrients necessary for plant growth.

A Natural Fertilizer

This “worm manure” is a natural, self-sufficient fertilizer for your garden. Is your plant losing leaves? Let the worms take care of it, and they’ll return the carbon to your plant in no time, enabling it to grow new leaves.

Boom! Magic! Nothing is lost, nothing is created, everything is transformed, as Antoine Lavoisier used to say… (wait, I’m googling this)… Antoine Lavoisier.

(But googling, I learn that he never actually said those words, so I’m a little disappointed. Frankly Antoine, you could have made it sexier than “[…] nothing is created, either in the operations of art, or in those of nature, and we can posit in principle that, in any operation, there is an equal quantity of matter before and after the operation; that the quality and quantity of the principles is the same, and that there are only changes, modifications.”)

Back to my verse, stop bothering me, Antoine!

The recycling work of these little laborers is so rapid that a leaf that fell in autumn, which took 3 to 5 years to decompose before the arrival of the earthworm, now only needs a few months to disappear.

The acceleration of this process, although very useful in the garden, has become a problem in the forest…

Enemy in the Forest

Where it is present, the impact of the earthworm has almost wiped out a layer of the forest floor in Canada: litter.

By rapidly recycling debris on the ground, the spongy, moist and poorly decomposed layer at the surface of the forest floor is being devoured. Yet many species have evolved with and need litter. By removing this important layer of plant debris, the health of the soil, the links between species and even the living environment of some are severely affected.

Photo : Lum3n

To give you an idea of the consequences of this troublesome neighbor:

  • Drier, more exposed soil;
  • Difficult to establish for young seedlings, especially in spring;
  • Worms eat healthy seeds and young plants;
  • They interfere with the beneficial links that fungi form with trees;
  • They release much of the carbon trapped in forest soils into the atmosphere;
  • Soil microbes travel with the worms, moving them to new environments where they could potentially cause harm;
  • Many litter-dwelling species (such as insects, salamanders, toads, small mammals and even ground-nesting birds) lose their habitat;
  • Animals that feed on prey in the litter are starved.

In short, a lot of damage for a single worm!

The next time you’re in the forest, take a look: do you see hard, dry, earthy soil, or soft, moist soil covered with all kinds of debris? Chances are you’ll find fewer worms (or none at all) playing in this beautiful humus than in the “clean” forest.

Photo : Kelly

Different types of earthworms

Our 19 species are divided into three types.

There are those that live on the surface, in the litter on which they feed, and do not dig tunnels. They are called epigeic.

Those that dig networks of horizontal tunnels in the soil to a depth of 50 centimetres and feed by eating the soil and microorganisms found there are called endogeic.

These two groups are very useful in gardens and fields.

The third type of worm is undoubtedly the one that has the greatest impact on America’s forests. They dig a single vertical tunnel two meters deep where they bring leaves to feed. In other words, they “hide” the litter at a considerable depth, don’t stir the soil and only bring to the surface their excrement and… leaf stalks!

If you see what looks like the entrance to an anthill, but instead of a mound of sand, it’s leaf petioles and excrement, you’ve probably found a worm hole.

Illustration : Alain Peeters

This worm is obviously not a nuisance anywhere in the world, and is even very useful in Europe, but as North American forests have evolved with a very thick layer of litter, its disappearance is problematic.

Luck or not, the species of worm often used for fishing is an anecium, since it is larger than the other types. As a result, they have spread rapidly through our forests. Think before you throw your worms into the woods after your fishing trip! In some places, it’s illegal to dispose of your bait by releasing it in the wild.

Common earthworm (Lumbricus terrestris), an anemic species that is highly invasive when mature. Photo : Donald Hobern

So What Do We Do?

As with many invasive species, the damage is already done. We can always prevent the invasion from continuing by being cautious about introducing them into new environments, but that’s about it. You can’t eradicate earthworms.

It’s important to be careful not to introduce new species. In the United States, it’s the Asian jumping worm that’s causing damage, and it’s slowly making its way up to Canada.

Fortunately, all is not doom and gloom. Some species benefit from the presence of worms, such as robins, which eat large quantities. Some plants also root more easily, such as the Jack-in-the-pulpit. Whether we like it or not, earthworms are now part of many of our ecosystems, so we might as well look at the positive!

Photo : Brian Forsyth

Put Worms In Your Potted Plants… Yes, But No.

I see this question come up a lot. I understand that you want to have aerated soil full of worm manure for your houseplants, but it’s not a good idea. The worm might feel cramped in your pot, it might run out of food and attack your plant’s roots. It could even die and rot in your pot! Yuck.

No, really, unless you’ve got a MEGA potted planter with a good layer of mulch and frequently-renewed compost, this isn’t a good idea. In fact, if you have such a gigantic planter, chances are worms have already settled in.

So don’t try to force nature’s hand, and leave the worms to your outdoor plants – they’ll benefit far more than your coleus!

Audrey Martel is a biologist who graduated from the University of Montreal. After more than ten years in the field of scientific animation, notably for Parks Canada and the Granby Zoo, she joined Nature Conservancy of Canada to take up new challenges in scientific writing. She then moved into marketing and joined Leo Studio. Full of life and always up for a giggle, or the discovery of a new edible plant, she never abandoned her love for nature and writes articles for both Nature sauvage and the Laidback Gardener.

10 comments on “Earthworms: Friend or Foe?

  1. Mary L Discuillo

    I am disappointed worms have a downside They are so helpful in the garden and compost bin. I guess that’s most things in life. Thanks for the “downside’ even though it makes me sad

  2. jessica crawford

    Thank you for this thorough article about worms.

  3. marianwhit

    I am in Nova Scotia and dug a 10 x 2 x .5′ trench for something else, but decided to collect and count my earthworms…386. Hard to believe they (like exotic slugs…many of those too) do not have a profound influence on the soil and soil chemistry. So I got curious. I noticed that the tarps I throw my introduced plants to die on fill up with both earthworms and slugs…so I started collecting them, and feeding them to my eager trout in the brook that runs by the house. I have an experimental project to try to grow a native plant grassland/meadow, as it really is hard to imagine what that would have been like before humans influenced the landscape so completely. I moved the tarp around the fairly small space often, and over time, have managed to knock back the population a bit. Know what I got? Mushrooms and orchids. 🙂 There is no end to what can be learned out there. And the degree to which we have utterly casually FOBARed it is gob smacking. I am interested in what it takes to grow and steward some of our native plants.

    Growing some of the smaller grassland species is very, very difficult, because we are still suggesting that it is perfectly ok to make America Europe (and stand by while it is dominated completely and disastrously by things like dandelions and clover). The second great colonization…with the result being an unpredictable biological stew that threatens our forests, natural areas, and…food production…maybe do a piece on what invasive species are costing us now? And then imagine 100 years from now. Apologies for being a wet blanket, but I believe many of our plants and trees have no chance if most of us can’t even see the problem. Spent all day pulling dandelions, clover, and invasive cardamine from a project I am now 5 years into (that required months and months of hand weeding, because there is no machine that can match the human eye or hand), and the orchids and even common grasses are disappearing rapidly indeed.

  4. Joel LeGrand

    In the last twenty years worm composter of vermicomposting has bought many worms into North America. The jumping worm is a bad one.

  5. organik gardener

    I forgot to mention that I also sprinkle grits (cornmeal might work also) over ant hills. The ants will feed this to the queen who either dies or moves on with her brood. Interesting to watch them….

  6. Josephine Mullane

    I apologize but this comment has nothing to do with earthworms, but I am hoping you don’t mind. My property, especially the flower and shrub beds attract a ton of ants each year.  And each year I cover them with diatomaceous earth, and each year I get rid of a lot of them, and each year they return.  I can’t seem to find any information online as to WHY my area attracts these ants.  They have destroyed several plants, sections of my lawn, and small bushes with their anthills.  At the moment, one flower bed (20 x 14 feet) has three small plants (heuchera etc) covered with the diatomaceous earth.  Another heuchera could not be saved and I dug it up and the ants were crawling everywhere.
    I would try anything to eradicate them but I do not want to use pesticides.  I’ve lived here for 43 years but only in the last decade have I had this ant problem.
    I would appreciate any information or insight as to ‘why my property’ as I have asked neighbours but they do not have this huge problem.
    Love all the Laidback Gardener’s articles. Thank you.

    • organik gardener

      Several years ago, living in the hot Southeastern U.S., I had a problem with ants, especially fire ants. I was also hesitant to use pesticides. What finally worked was taking a shovel full of the anthill and placing it on another hill. Since ants seem to be tribal, they then “duke it out” and the specific hill became vacant in a short time. Hope this helps.

    • marianwhit

      I would first make an effort to get an actual ID on your ant…maybe I-naturalist, or a university entomology department with an ant specialist. (E.O. Wilson, where are you?) What you are describing sounds like an invasive species, so check it out. Are birds preying on them? Are they black, red, brown? How big are they? Try to get some good photos of the mound, and the individual ants (there are usually a few types, workers, soldiers, queen (don’t worry about her if you don’t want to dig around in the nest, lol. There are also times that they fly. Gather as much info as you can…do they bite, smell a certain way, or deposit specific things around the base of the mound? There are many ant species and we are also spreading them around the world in a haphazard way.

  7. For me the answer would be foe. Our area is dealing with invasive jumping snake worms. I carry a plastic cup around with me and deposit all worms I run across into it. I use to try and differentiate, but it takes too much time away from my gardening. There are no native worms in our area, so I consider them all invasive. The subject of worms these days is kind of like talking about native plants or lawns – everyone has their own opinion and practice, and that’s a good thing. Thanks for your detailed post about a very trending topic.

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