earthworm 101, with great lakes worm watch

Earthworms, from Great Lakes Worm WatchPERHAPS THE CREATURE the gardener knows best is the earthworm, but how deep does that knowledge go? Lately readers have been emailing me sensational headlines about “bad” earthworms, asking: Aren’t all earthworms “good”? To get an earthworm 101, I invited Ryan Hueffmeier, an environmental scientist at the University of Minnesota-Duluth and Director of Great Lakes Worm Watch, to join me on the radio (October 2013). Our Q&A includes some surprises:

First, some background: Great Lakes Worm Watch is a citizen-science outreach organization, working to map the state of the earthworms—and the habitats they’re living in.

“We want to know where earthworms are across the landscape,” says Ryan—and that means even beyond the Great Lakes area, where the project began.  (There is a Canada Worm Watch, too, for those across the border; researchers at the University of Vermont, at the Cary Institute in Millbrook, New York, and elsewhere are likewise studying earthworm invasion.)

Individuals, schools or garden groups can sign on help collect data on what worms are found when and where. That last bit—the habitat, or “where” aspect–is key, because earthworms are neither good nor bad. The role they play, and whether it’s helpful or harmful, depends on the environment they make their way into.

ROUGHLY SPEAKING, there are two different classes of ecosystems, Ryan explained in our chat:

In manmade environments, such as farms and gardens, worms have proven to be helpful as soil-aerators and as detritivores, super-efficient recyclers who break down organic material and return it to the loosened-up soil.

Natural habitats, such as the hardwood forests of the Northeast and upper Midwest, were historically earthworm-free by design—meaning no native earthworm species and not meant to have earthworms, instead relying on tiny fungi and bacteria to do the recycling tasks.

“The fungus and bacteria do that job really, really slowly,” Ryan explains. “But when earthworms come into such an environment [as they did with the European settlers hundreds of years ago] they do it much, much faster.” They accelerate the order of things—and not in a good way.

The forest floor is meant to be a thick, spongy organic “duff” layer, slow to break down. Not only do earthworms make things decompose too fast, but their castings make forest soil more compacted and dense–and more mineral-rich. The altered medium is inhospitable to tree seedlings and herbaceous plants that used to thrive. Natural forest succession is interrupted, and the diversity of the plant community threatened.

The forest floor can even drop, so what used to be a tree root may suddenly find itself above soil grade—a root no longer, but a branch.

“Researchers have coined the term ‘tree root gingivitis’,” says Ryan, who can tell right away when he enters a woodland whether it has been invaded.  Big trees still tower up above, perhaps, but on the ground: maybe sedges (Carex species) or not much at all.  When the big trees die, what will happen, since there are no saplings in the community?

Asian earthworm in genus AmynthasLATELY, the story of invasive earthworms who can change environments has gotten more complicated—hence headlines such as “The Dark Side of Earthworms” and “Invasion of the Earthworms.”

Asian species in the genus Amynthas (above) have made become more widespread in American soils, including large portions of the East Coast, and lately into the Great Lakes area, with pockets in Minnesota, Ohio and Wisconsin. With help from citizen researchers, Great Lakes Worm Watch is trying to track, and help stop, their march. Why?

“These could be a gamechanger when it comes to earthworms,” says Ryan, referring to potential impact of unchecked spread. “They’re very aggressive, and can live in really high densities,” consuming a lot of organic materials in a very short time.  “Some researchers have coined it ‘Nothing Grows Here Syndrome’ where these worms have been.”

more earthworm 101

Q. Why were there mostly no earthworms here to greet settlers hundreds of years ago in much of the nation?

A.  In the last Ice Age, glaciers “scraped right down to the bedrock,” says Ryan.  In the northern tier of the country particularly, and in Canada: no native earthworms the last 11,000ish years, which is about when the last glacial period ended.

Q. How did European earthworms reach the United States?

A. “The earthworms we have known and grown up with are not originally from North America, they’re from Europe,” says Ryan.

Researchers think they came as a side effect with ballast in ships—soil and rocks were used in ships and then unloaded. Plus European plant species brought with settlers, such as lilacs or buckthorn among many, probably had earthworms in their rootballs. Settlers—noticing the Northern U.S. didn’t have earthworms–may also intentionally have brought them along for soil improvement of farms and gardens.

Today human activity–from soil in tire treads to improperly disposed-of fishing bait and more–continues to spread worms where they don’t belong. The worms sold for composting (read GLWW’s pdf), for instance, often include the aggressive Asian species.

3 ecological groups of earthworms, from Great Lakes Worm Watch website.Q. How can I learn to ID earthworms?

A. Earthworms fit into three general ecological groups (get photos and details)—meaning their have three ways that they feed and burrow:

  • Epigeic types (small, reddish brown species living in the leaf litter);
  • Endogeic types (small to large, with no actual skin pigmentation but appearing gray-blue, yellowish, pink or whitish or even with a greenish cast, and living and feeding in the mineral layer of the soil);
  • Anecic species (very large-sized deep soil burrowers who may feed up in the litter; reddish-brown).  Nightcrawlers are our only anecic species so far.

There are keys to further worm ID on this page of Great Lake Worm Watch’s website.

Use adult worms to do your ID’ing, as it can be even more confusing otherwise. How to tell if a worm’s an adult? Adults have a collar-like clitellum near the front of their bodies.  Basic earthworm-anatomy diagrams.

Q. How can I help Great Lake Worm Watch as a citizen scientist (and how to I get the worms to come up to the surface and be counted, anyhow)?

A. Learn how to join the team (a great project for a garden group, school class, scout troop, etc. in the coming growing season), and also learn how to report worm observations, starting here.

As for how to convince those burrowing worms to come up and be counted? At the Great Lakes Worm Watch, Ryan says they use a recipe of mustard powder and water to irritate the worms and get them to surface, like this.

(All illustrations from Great Lakes Worm Watch.)

  1. Choral Eddie says:

    Thanks for this info. It is pretty obvious that we here in Ancram have the Asian earthworm that is turning the soil mineral. I’m looking forward to the results of the earthworms that you will be shipping to Great Lakes Worm Watch. I’d love to know how to “disinvite” them without using pesticides.

  2. emily says:

    This is really fascinating. When I had composting worms I was always careful to freeze the dirt they created before taking it outside. This was supposed to prevent any of the non-native worms from getting released.
    Recently I was planting in a previously wild part of my yard and discovered absolutely gigantic earthworms. Not only that, they have colored, almost luminescent stripes down their sides. I’ve never seen anything like it before.

  3. Sharon says:

    My garden has a huge amount of earthworms – even digging a small hole reveals at least two. When I use cardboard or newspaper to mulch, they come in droves.

  4. Lacey says:

    Setting aside the risk of introducing another non-native, I may have a creepycrawly solution to the worm march. I spend an hour a day in my yard collecting and dispatching land planarians. These nasty, slimy flatworms eat worms (and apparently not much of anything else), reproduce quickly, and have no predator. They are (supposedly) from China and only made it to the US about 100 years ago.

    I read a news story that these flatworms have wiped out the earthworm population in some farms in the UK. I’ve pulled them off many worms in my garden… yuck. I have a lot of earthworms and I’d like to keep them.

  5. Choral Eddie says:

    Lacey – it may help to identify the worms that you currently have as they may in fact be the Asian earthworm that is eating up all the topsoil nutrients. They, the researchers, have found that one way to get rid of this current Asian earthworm are flatworms!

  6. Lacey says:

    Well lookie there . Maybe I’m on to something. Still, those flatworms are nasty – found one today that is (was) 1/2 across and 18 inches long. Long a snotty rubber band. Vile.
    I’ll ID my worms… not making any promises that I’d pick the flatworms over the earthworms though.

  7. Thankyou for the information Margaret. Our area of Northern NJ has an influx of the large, irradecent worms (I’m guessing they are the Asian species, Ill need to do a positive ID). Some are large enough and move quickly enough that at first glance they look like a small snake moving through the leaves and debris, and I hate to say it, but my garden soil has been lovely thanks to them and their ability to chew through so much debris. I’ve actually been burying compostable food scraps into my beds and they incorporate them rapidly.

    Thanks as always. You provide such great information.


  8. Kassie says:

    I feel so naive…I had no idea, and grew up thinking all worms are wonderful for soil. I even help worms across the sidewalk if they are in danger of drying up! I thought it was bad that I have so few earthworms in the Berkshires, but now must rethink that idea. Thank you for one of the most interesting articles yet on AWTG.

  9. Weedy says:

    Found very active, actually wriggle out of your hands and across the soil worms this year, especially over the septic tank. My soil is clay, in fact there was a pot factory across the road up until the last few years and a potter might like the stuff. They used to sell all sizes of terra cotta pots and spread busted pots all over their parking lot. My son used to fish near their clay pits or in them as they are in a wetland.. Back to the worms, they will jump right out of your hand but my son and I caught a pile of them and they appear to be as attractive to fish as any worm but I’m not certain I like so many in my garden and I do think they are beginning to reduce the leaf litter in my woods.—————-Weedy

  10. Bobbi says:

    Very interesting article.

    I’d love to see an article about cultivating worm compost, but with the correct type of earthworm and find out who are the reputable earthworm dealers.

    Thanks Margaret, enlightening!

  11. Weedy says:

    Well, by the time I Google something, I forget within minutes (I’m seventy seven, a strange sounding age or maybe it just feels that way) anyway if you Google Snake Worm, Crazy Worm, or Burmese Snake Worm there is an article (I don’t know how to add a link—it may not be licit anyway) and it describes Amynthas diffringens an extremely active worm that writhes away from you and will jump right out of your hand and moves like a snake rather than extending and pulling itself up to itself like any sensible earthworm. They also lose their tails which is disconcerting when your trying to get a can of fish bait as they keep wiggling after they drop off and many of them do, but, the fish bite on them anyway.————Weedy

  12. Lynda says:

    I have very strange worm activity in the new residential development I moved into last winter. The soil is about 6″ of sand on top of shale. The development sits alongside farmland and acres of woods as well as ponds and streams. My place has very little grass growing — it is mostly sand with grassy patched. Once the ground warmed in the spring, worms started coming out of the ground where they would crawl around and eventually dry up. This happens every day ! Hundreds of worms every day. This continued until the weather turned cold. It is weird.

  13. Alissa says:

    I have the jumping worm (Asian snake worm) on my property in Wisconsin, which is comprised of deep woods and savanna. I have the characteristic “coffee grounds” soil and have noticed areas where the topsoil has eroded completely, partially compounded by the fact that my property is on a steep hill. I would love to learn more about maintaining a garden – and the land – with the soil changes that the worms bring. So far, I plan to mulch regularly to keep the remaining soil from eroding, but I worry that mulching will just feed the worms further! I have yet to find any good resources that speak to these soil changes, other than some remarks about how there can be “dead zones” where nothing will grow. I had planned to plant a number of native species this fall (just got a big haul from Prairie Moon before I learned about the worm) but I wonder if the seeds will even germinate properly. I also wonder if other amendments – like sand – could help to keep the soil from eroding or help fix the texture. If anyone has resources they can suggest, I am all ears.

    1. margaret says:

      Hi, Alissa. I am investigating but so far have found nothing radically positive as far as a solution. Will be in touch.

  14. Lynne says:

    I started seeing these “muscle worms” in my garden beds several years ago, but every gardener I asked about them looked at me like I was crazy. I knew they weren’t good, but got no verification of that hunch. Now they are everywhere; as soon as I even pull a weed, they wriggle up out of the ground and flee. My mulch disappears over the winter down to bare soil. Worms, combined with ticks, deer, mosquitos, and stilt grass, make gardening a lot less pleasurable than it used to be. Hope there’s a solution, as I have two acres of beautiful forest!

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