asian jumping worms: what we know (2018 interview), with uw-madison’s brad herrick
I GET A LOT of questions about invasive species, and lately a week doesn’t go by without at least one asking what to do about so-called crazy worms or Asian jumping worms, which more and more of us are alarmed to be finding in our garden soil. I sought a researcher’s perspective on this really challenging and frankly terrifying pest.
Brad Herrick is Arboretum Ecologist and Research Program Manager at the University of Wisconsin-Madison Arboretum, where the staff first noticed the destructive handiwork of Asian jumping worms in 2013. He’s been studying them ever since. Though our understanding of these organisms is in the very early stages, we talked about their biology, their impact, and what control tactics are being explored by scientists seeking a solution. (Photo of Brad, below, by Eric Hamilton, UW Communications.)
Update: In 2019, a year after this introductory interview, I got updates from Brad on research into the impact of heat on the embryo-filled cocoons that contain next year’s worms-to-be–that may in time help lead to answers in some situations. That newer story includes corrective tactics you can try to reduce the population if your infestation if limited to a small area of a garden. Read it here for even more information.
Read along as you listen to the March 19, 2018 edition of my public-radio show and podcast using the player below. You can subscribe to all future editions on iTunes or Stitcher (and browse my archive of podcasts here).
asian jumping worm q&a, with brad herrick
Q. You must have encountered a lot of different issues as an ecologist. Where does this rank? Is this pretty startling one?
A. Yes. It’s definitely right up there, and it’s one that was right under our noses, but we didn’t realize it until like you said 2013. My background is in plants, so I didn’t know a lot about earthworm. I definitely didn’t know different types of earthworms. We discovered it in 2013, and from then on out, we’ve been on a campaign to learn what we can and help others learn as well what to look for and some of the impacts.
Q. To just kind of backtrack: Of course, gardeners were always taught earthworm equals good because they aerate the soil and blah-blah-blah, and leave behind rich castings and so forth. But things are really changing. You said you didn’t know a lot about earthworms, but I bet you do now. These are kind of the latest invasives, but in the northern United States, especially, we don’t really have a lot of native earthworms, do we, of any kind?
A. That’s correct. Pretty much anywhere that was glaciated during the last glaciation, depending on your latitude around 10,000 years ago, or so are pretty much devoid of any native earthworms. Here in Wisconsin, all of our earthworms are most part European species and more recently this new line of Asian species.
Q. You knew you had earthworms, of course, always at the Arboretum, but you didn’t know you had these Asian species. What was the moment? I can tell you the moment that I experienced when I had this “aha,” but what was the moment for you? What was it like? What was the tell-tale sign?
A. It was interesting. What happened was that we were a site for a conference. It was called the Society for Ecological Restoration conference; they were here in Madison. We held a field trip for folks. We had some help from the DNR [Wisconsin Department of Natural Resources], from their earthworm biologists. We came out and talked about invasive species in general and mostly about plants, and she gave a short talk about invasive earthworms.
We actually went out one of our wooded sites here at the Arboretum, and dug around for folks, to show them what European earthworms look like, and talk about what they can do to the leaf litter and the soil and the structure and the plants.
She mentioned just kind of offhandedly that, “Oh, yes. We also had this new group of earthworms from Asia that we don’t have in Wisconsin yet. They’re just kind of … You know that they’re around. We think they’re going to be a really big problem. We’re really working hard to keep them out of the state.”
Not a minute later, she wiped back some of the leaf litter. We saw maybe half a dozen of these snaking, squirming, wiggling earthworms that had a really weird behavior.
Right away, she said, “Oh my gosh. This is what I was just mentioning. This is the new Asian earthworm that until just now I didn’t think we had.” [Note: The Asian species of concern so far are Amynthas agrestis and A. tokioensis, plus Metaphire hilgendorfi. The first two are the ones that have been studied to date at UW-Madison.]
That really kicked off everything. Since then, we’ve been working closely with our Department of Natural Resources, garden clubs, Master Gardeners, other folks from other states, academics, to learn what we can and do as much outreach as possible.
Q. I think what’s scariest—and I mean, of course, all invasive species, whether plant or insect or another organism, a pathogen of some other kind—they’re all scary when we hear about one or another. But a lot of times, they’re specific to like a species or a genus, but often a species or a couple of species. So that’s horrifying enough, like Emerald Ash Borer or whatever.
But this is like it’s a pest of the precious soil that all plants rely on and therefore we all rely on. This is in some way … this pest freaks me out in a way that … not to say that we could necessarily say oh what’s the worst or better grades of bad, but because this attacks the soil. I wonder if you could just talk about that: the mechanism that’s going on that throws things out of balance because again we all thought, oh earthworms were good. They deposit these castings.
But these guys, they live in big congregations and they go too fast; they do the work too fast. What happens?
A. That’s a great question, Margaret. As you said, for a long time—for decades and decades—we’ve been taught and gardeners have known this that earthworms are supposed to be good for your soil especially for your gardens, urban garden. That is true for a specific group of earthworms and in specific types of gardens.
For example, the European Nightcrawler, that everyone knows about. Those actually are really good at aerating the soil because they create these deep pore spaces. They mix the soil. They create channels and tunnels in the soil so that water can get to the roots, and it can really break up what can be often compacted urban soil. It can really help plants grow in a garden setting.
But what’s really different about these suite of species that are primarily from East Asia—the Korean Peninsula and Japan, is where they’re endemic to—is that most of them, the ones that we have now in North America, do not burrow down very far. They spend their entire life cycle in the top few centimeters of soil.
They’re not providing any of those deep-dwelling benefits turning the soil over, mixing nutrients—they’re not doing any of that. They’re doing all their work in a very small space in the soil profile, on the very top, and they do it quite well. They do it very well actually. They turn. They eat all the organic matter, as much as possible, using the form of leaves or whatever organic matter you have on the top of the soil.
They consume that. Then, like you mentioned earlier, they produce casts, which are their poop. And those casts are really rich in nutrients, and that’s usually a good thing for gardens, but what happened is they produce it so quickly, and they make available those nutrients so quickly, that it’s often lost to the plant because after the next rainstorm—those nutrients are leached away. It’s kind of like if you think of a quick-release fertilizer, a lot happens right away. It happens too fast for the plants to a take advantage of it. You end up with soil that actually has less nutrients in it and that can affect plant growth and plant establishment.
Q. I’ve read in the last couple of years, since I first learned about these worms, that they are not only in the Midwest. I know like a number of states or Minnesota, I think, Wisconsin and Michigan. I don’t know which other states have a problem with them. But the Southeast, the Smoky Mountains park. In the Smoky Mountains, they have an issue with them. In New England, we have increasing reports of issues with them.
I’ve read especially in the Great Lakes Forest, they can actually create almost like, I’ve seen referred to as “tree root gingivitis,” like where they destroy the tilth—I don’t know what you’d call it—of the soil, and stuff can’t even hold in the ground. Like they’ve wasted all the organic matter so quickly that the succession plan of these natural areas like in the Smokies or the Great Lakes is not happening like, even in native areas. Forget a garden. It bad enough that a garden is being destroyed, but these natural areas too, yes?
A. Right. For the Wisconsin Department of Natural Resources, that’s really their big concern is what can we do to keep these critters out of our national forests or nice, pristine state forests. You’re right. That’s what’s happened with the European earthworms, too. People don’t think of European earthworms or as earthworms as being that bad, because they’re everywhere. They’re ubiquitous. You find them in your backyard, you find them in forests. But again, there were glaciations and the Great Lakes for the most part—although these states were almost entirely glaciated—the plant communities that came back after those glaciers receded evolved without any presence of earthworms.
It’s a disturbance in the ecosystem. You’re right. These earthworms whether they’re European or Asian variety, they will literally consume the duff layer, which is that organic, spongy, highly nutritious layer that plants need especially when they’re germinating and getting established, and they’ll get rid of it. It’ll end up going right down to the mineral soil. You’re really left with very little nutritious soil that can hold roots and get plants started.
Even trees have problems when you reduce that buffering spongy layer, and you start to see buttressing roots. There is a lot of research now on the feedback between when that disturbance happens. It often opens the pathway for a new and basic plant like garlic mustard buckthorn to come in. It’s sort of a vicious cycle that once you have a real major disturbance: Native plants tend to get excluded, and the same with native soil biota. That’s been shown in the Smokies as well, that some of the native arthropods don’t do well in the presence of especially these new group of earthworms.
Q. It’s like what’s left of the soil is just its mineral content. Is that correct? Because the organic matter is gone.
A. In the high-abundance area, the high earthworm areas.
Q. They really waste the soil, and compared to much smaller organic-matter processing creatures—whether microbial creatures or even small insects, the guys that are sort of detritivores, or debris recyclers, in a forest community—these are big, hungry, fast-moving, fast-processing guys. As you said, they’re taking that duff layer all those years of fallen leaves that were meant to slowly decay and be crumbled up and have little organisms worked on them gradually. It’s not happening. It’s just being voraciously consumed and wasted quickly.
A. That’s right. They’re really good at what they do. We’ve done some research recently that’s shown that they not only consume that organic matter, but they can also move quickly between years.
A. They can spread into uninfested areas, and they can out-compete or displace other earthworm species, even if there are other non-native species like European species. They have not only are there hungry critters, they’re also very good competitors in other ways. We don’t know what the mechanisms are for how they displace other earthworms, or what that might mean long term. We just don’t know a lot yet about the suite of species. That’s some of the work that we’re doing here at the UW-Madison Arboretum.
Q. Sometimes for me in a garden setting, I wasn’t looking under the leaf litter like your colleague at the Department of Natural Resources who came on that tour and discovered them, but what I noticed was what looked almost like mole hills of coffee ground-like soil particles. Do you know what I mean?
A. Yes. Right. Some of the European earthworms like I mentioned, the deep-going ones, will create these little midden piles are called.
Q. Middens, right.
A. Middens. Yes. If you’re seeing little piles of soil often with kind of skeletal weave stuck in them, those are going to be European species. Those will not be the Asian species. But if you see more of a uniform coffee-ground-like soil signature, very loose and granular, that is a telltale sign that you have this other Asian variety.
Q. All around the edges—yes. That’s what I was seeing like the edge of beds, for instance. Instead of seeing those little piles like you’re mentioning that I had known in the past from time to time, it was like at the edge, there was just coffee grounds coming out from where the turf met the bed.
Q. It’s really weird. When I lifted it and I looked, they were these snake-like worms. Their movements were more snake-like, and they were big. They’re so destructive anyway. Before I just keep complaining and complaining….[laughter]:
So your research at the Arboretum—how do ecologists such as yourself and other researchers, how do you even all sort of get together and say hey this is what we need to do, this is what approach we’re taking and our colleagues over here are going to take that approach. Who’s looking into what? What do we do?
A. For us, our first step was, O.K., we’ve found these critters here at the Arboretum. Where exactly are they? We did a mapping effort, the first spring, just to kind of know what we were working with: the scale of the infestation, the habitats. Then, we kind of worked with the systems that we could. One of the projects that we just got published in the journal of Biological Invasions was a study looking at we had an earthworm invasion and some of our sugar maple dominated forests.
We wanted to track them, track the spread in these forests, and to see what kind of impact they had on the plant communities, on things like soil pH and litter depth and these sort of forest-floor variables. This was actually a master’s student project by Katie Laushman.
What we found in that study was that in two years, we couldn’t really detect any marked changes in the vegetation. I say that with a caveat: that could be because of several reasons. A, there weren’t any, and it’s a real thing; that they’re not affecting some of these woodland plant species. Or it’s a new invasion and we just haven’t studied it long enough. Or the forest also have European species that have been here for a long time and might have already sort of done the damage to the plants that are going to be affected—that these aren’t going to have much more effect.
There’s some caveat there, but what we did find was that they spread in one year about 13 acres by themselves.
Q. Oh, wow.
A. If you think of a football field, it’s about 1.3 acres. That’s quite a lot just for a little earthworm. They also found out that they pretty clearly are displacing other earthworms. Basically, very few plots had both European and Asian. They move in, and other species move out. We’re going to be tracking this long-term just to try and ask other questions about their long-term effects versus short-term effects, litter depths and other soil properties. But that’s one part that we’re working on.
And then just kind of quickly, other projects that we have going on, we have a postdoc that’s looking at how do these critters affect tree hydraulics? How do they affect, for example, the ability of sugar maples—which is a really common tree, obviously—to take up water and nutrients to the roots? A pretty straightforward question, but obviously given how common sugar maple is, that could have ramifications for a lot of our hardwood forests.
Then, a colleague of mine, Marie Johnston, and I are looking at things that sort of dive into the control aspect: Are there things that we can figure out about the life cycle of this earthworm that we can disrupt that might control a population?
We’re specifically interested in the cocoon stage, which is the ones that we have in North America, the earthworms are annual species. They hatch from cocoon, which are little eggs were about 2 millimeters across. They hatch in the early spring, mature throughout the year. Then, when it gets to a certain temperature threshold, usually the first hard freeze, that they’ll die, but the cocoons will survive winter and then hatch again in the spring.
We’re trying to think about are there abiotic factors that might limit the viability of cocoons, of the embryos in the cocoon. We’re testing heat treatments. We’re testing things like flash-freezing, and trying to think of it other ways that we can disrupt a part of the life cycle that would offer some kind of control that either landscapers could use, or composters or even backyard gardeners, to apply a heat treatment and use in a small scale.
Q. As gardeners, what do we do? I think one thing we do is that most of the Cooperative Extensions or university extensions in areas that have these are interested in hearing if a homeowner has an outbreak of them. You want to know where they are, right? [Above: jumping worm field guide from Wisconsin DNR.]
Q. We should report it. We should communicate with our Cooperative Extension [or state Department of Environmental Conservation or Department of Natural Resources]. I found that that’s happening everywhere.
I’ve read about, we could … I’ve read crazy things like put them in plastic bags and let them cook to death in the sun and then put that in the trash and things like that, but there’s a lot of them and like you said, they’re moving 13 acres.
When I first read about them a few years ago, I thought, well, golf-course managers, they’ve always hated middens on a beautiful putting green. They’ve always experimented mostly with horrendous chemicals in the years past, but nowadays, it’s more green. They’re looking for green things. I read that they were using something that came from the camellia plant, like a fertilizer, but I think came from the tea plant (which is a camellia), and some kind of fertilizer made with that, but it was only available commercially. But maybe now it’s available for homeowners. What avenues of control like that are you exploring?
A. This summer actually, we’re going to be doing some trials on a product that is sold under the organic label. It’s basically a very low Nitrogen-based fertilizer, but also has, like you say, extracts from tea seed oil.
Q. Tea seed. Right.
A. Yes, which has saponins, which is basically a toxin that plants produce. Actually, some of those studies—many of them were from Kentucky golf courses—have shown that they this fertilizer with these saponins does greatly reduce the number of midden piles or castes that earthworms create, meaning that they’re diminishing the population of earthworms.
There hasn’t been a lot done on the Asian species yet and that’s something that we’re interested in looking at is using a liquid version of this product or a granular version and coming up with what are the sort of minimum dosage that you would need to maybe reduce the population or get rid of the population—and also more importantly even what are the potential side effects, what are the impacts to other beneficial soil biota?
A. That’s really important, I think, before we start to encourage folks to use one or the other controls. There is not a lot of research yet. We’re all for people trying things, but just know that there are often with it with controls, it’s going to control one thing, but it’s going to hurt something else, benefit something else. There’s always other factors than just the target species. But that’s something that we’re definitely interested in.
Q. I think biochar is another thing, because if it’s like sharp edges or something. It’s another thing it’s going to be explored. Is that another one?
A. Yes. There’s not much in literature on that. I don’t know a lot about biochar as a control, but I’ve heard that as well the physical properties of the biochar,, especially the small granular one that had really sharp edges can physically be destructive, the earthworm body, which obviously doesn’t have much of the hard shell on it. That is an option. Obviously, it’s a common soil amendment anyway that many gardeners would use. It’s an easy one to obtain. But yes, we’re also interested in as well.
Q. Brad, it’s early stages. It’s not that you don’t have the answers—it’s that there are no answers yet because you’re at the forefront and colleagues at other universities around the country that are being affected similarly doing this groundwork study. These are the beginning studies, right?
A. That’s exactly right.
Q. You’re going to come back and tell us what happens …
Q. … along the way because we all need to learn together. I’m so appreciative for you giving us this 101 and telling us kind of where things are at about these Asian jumping worms, the latest invasive that I’m worried about.
more about invasive worms
- UW Arboretum’s jumping worm fact sheet
- Cocoon-stage research at UW-Madison
- My interview with Great Lakes Worm Watch: Earthworm 101
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MY WEEKLY public-radio show, rated a “top-5 garden podcast” by “The Guardian” newspaper in the UK, began its ninth year in March 2018. In 2016, the show won three silver medals for excellence from the Garden Writers Association. It’s produced at Robin Hood Radio, the smallest NPR station in the nation. Listen locally in the Hudson Valley (NY)-Berkshires (MA)-Litchfield Hills (CT) Mondays at 8:30 AM Eastern, rerun at 8:30 Saturdays. Or play the March 19, 2018 show using the player near the top of this transcript. You can subscribe to all future editions on iTunes or Stitcher (and browse my archive of podcasts here).