earthworm 101, with great lakes worm watch
PERHAPS 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 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.
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)?
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.)