211-Invasive Asian Jumping Worms: What Gardeners Need to Know
June 3, 2021 | Care, Podcast
(photo: Eric Hamilton/UW–Madison Communications)
The invasive and destructive Asian jumping worm has been identified and recorded in 37 U.S. states plus Ontario and continues to spread, but it is still a species that many gardeners know little about. To explain what jumping worms are and why they pose such a big problem, my guest this week is ecologist Brad Herrick, an expert on all things jumping worm.
Brad Herrick holds a bachelor's in biology from Luther College and a master's in ecosystems studies from the University of Wisconsin-Green Bay, and he's the research program manager at the University of Wisconsin-Madison Arboretum. Since 2013, he has been studying the effects of jumping worms on plant and soil interactions and backyard gardens, the susceptibility of habitats to invasion and potential control mechanisms. He has been interviewed about jumping worms for various periodicals and news outlets such as The Atlantic, The New York Times, Science News and Vox.
Brad Herrick, University of Wisconsin–Madison Arboretum ecologist and research program manager, has been studying invasive jumping worms since 2013.
Brad says his career took a turn in 2013 when an earthworm expert from the Wisconsin Department of Natural Resources identified Asian jumping worms in the sugar maple forest at the arboretum. "At that point, I thought earthworms were earthworms and they were always here," he recalls. But when he saw jumping worms for the first time, he could instantly tell they were different. That encounter led to the research project that he's now been working on for eight years.
Asian jumping worms, as an invasive species of concern, are on the same scale as emerald ash borer and gypsy moths, Brad says. What makes jumping worms more cryptic is that they can spread unnoticed, changing the soil as they do. "They're right under your feet, but you don't always know it," he says.
The Effects of Earthworms and Jumping Worms on Forests
Brad points out that in areas like Georgia, where I live, there are both native and non-native earthworms, but to the north, including the upper Midwest, New England and Canada, earthworms were wiped out during the Last Glacial Period.
The northern forests that have grown in the 10,000 years since the glaciers retreated are not adapted to the presence of earthworms. The earthworms present today in formerly glaciated regions of North America are mostly European species — for instance, the common nightcrawler.
"They're so ubiquitous that people think they're just part of the system, and they're not," Brad says.
There are many different species of Asian jumping worms, all in the genus Amynthas, and the ones now present in the United States are primarily from Japan and the Korean peninsula. Brad says jumping worms co-exist in their native habitats just fine and are not a problem. Jumping worms in Asia are generally found in grasslands and at forest edges, but in the United States that are found in the forests themselves.
Two Amynthas jumping worm species, showing size variation from species to species. The worm on the left is likely not fully mature as the clitellum isn't pale. (photo: Marie Johnston/UW–Madison Arboretum)
European earthworms are known to decimate the organic layer of forest floors as they eat organic matter, such as leaf litter. That removes both moisture and nutrients and understory plants need, especially herbaceous plants. The new, disturbed environment that the worms create leaves what is basically mineral soil, that only a few plants can survive in — and those few plants tend to be other non-native species, such as garlic mustard and buckthorn.
Asian jumping worms are expected to have the same effect on forests but at a faster rate because they are parthenogenic, which means they do not need a mate to reproduce. Just one jumping worm dropped in a forest can start a new population.
Brad says research also shows that Asian jumping worms displace or out-compete any earthworm that was already there. It could be that jumping worms and earthworms are competing for the same food resources or the jumping worms change the soil chemistry in a way that repels earthworms, he says. The precise cause is unknown, and it is still yet to be known what other consequences displacing earthworms will have.
The boundary of an area invaded by Amynthas jumping worms, with the jumping worms' granular "soil signature" on the left and uninvaded soil on the right. (photo: Susan Day/UW–Madison Arboretum)
Why Jumping Worms Are Not Gardeners' Friends
European earthworms can really help gardeners, especially in urban gardens where the soil may be compacted and in need of amendments. Brad says earthworms, especially deep-burrowing ones like nightcrawlers, are useful because they mix nutrients into the soil and create pore space for aeration and water infiltration.
Invasive jumping worms are endo-epigeic, meaning they only live at the very surface of the soil or in the organic matter, Brad explains. "They're not effective at aerating the soil, they're not effective at infiltrating water, they're not moving nutrients around," he says."They're just working and working and working in the same area of soil, and so the consequence of that is that they create this really loose kind of coffee ground-like granular soil that is mostly earthworm castings, and those castings are the earthworm poop."
Earthworm castings are high in nutrients and typically a good soil amendment, but Brad points out that jumping worm castings sit on top of the soil, where those nutrients are not available to plants. Because other earthworms have been displaced, there is nothing else to pull those nutrients down into the soil, and then the castings erode away in rain.
Brad knows that using organic mulch is important in gardening for a variety of reasons, like retaining moisture and suppressing weeds, but he says that for jumping worms, that mulch is like a buffet, including wood mulch. Jumping worms have an enzyme that allows them to digest wood, which not every earthworm can.
I seriously can't imagine a garden without mulch, and my favorite mulch of all is shredded leaves. Well, Brad has studied what leaves, pine needles and grasses are the most and least palatable to jumping worms and found that they really love leaf mulch — especially maple leaf mulch with its high nitrogen content — and just gobble it up. He also found that jumping worms do not like pine needles or native grasses like big bluestem.
Through their feeding behavior, Amynthas earthworms create a coarsely granular soil structure comprising small nutrient-rich excrement, or "castings," but the castings stay on the soil surface, keeping nutrients out of reach of plant roots. (photo: Susan Day/UW–Madison Arboretum)
An Annual Species
Asian jumping worms are an annual species, which is kind of crazy considering how invasive they are, Brad says. While European earthworms have the ability to burrow deeper and stay under the frost line to overwinter, Asian jumping worms die after the first hard frost.
Jumping worms perpetuate because they produce 2-millimeter cocoons that look like little beads of soil. Those cocoons survive the winter and hatch in March to start the new population.
A mass of writhing jumping worms. (video: Brad Herrick/UW–Madison Arboretum)
How Asian Jumping Worms Spread
Asian jumping worms can't move very far on their own, Brad says. But they do spread far due to human and animal activity.
Researchers believe that Asian jumping worms get around the landscape via their cocoons. The cocoons can stick to shoes and garden equipment, so if footwear and equipment are not cleaned between working at home and then working at a community garden, the worm populations will spread.
Another way they spread is in runoff. Because of their loose, granular castings on the soil surface, when it rains they and their castings will slide down any incline.
One region that appears to be spared from jumping worms, at least for now, is the Southwest, where conditions are drier than jumping worms prefer. However, Brad says he's gotten calls about jumping worms in Arizona, where they probably showed up in bagged mulch.
He added that they also hitchhike on rootstock and other garden and landscape materials from state to state.
How to Recognize Asian Jumping Worms
When jumping worms are mature by the end of June, they are easier to recognize and to tell apart from other worms, but there are other signs. Brad says that if worms are found within leaf litter and mulch or just a few centimeters under the soil surface, they are likely jumping worms.
All earthworms have a reproductive structure called a clitellum. It's a ring around the body that produces cocoons. The clitellum on jumping worms is very distinct — it's milky white and in stark contrast to the rest of their body. It's also much closer to the head than the clitellum on any other earthworm.
Asian jumping worms are easiest to identify based on their behavior. "They're called 'jumping' or 'snake worm' for a reason," Brad says. "They are very active."
A regular earthworm may move around in your hand while a jumping worm will actively flop around and try to get away, going so far as to detach its tail.
In the absence of seeing the worms themselves, the presence of jumping worms can also be identified by their castings that resemble coffee grounds or taco meat. "There's nothing else that is producing that," Brad says.
The clitellum on jumping worms is very distinct — it's milky white and in stark contrast to the rest of their body.(photo: Susan Day/UW–Madison Arboretum)
What to Do After Finding Asian Jumping Worms
A new invasion of Asian jumping worms discovered quickly can be eradicated, Brad says. Because they stay at the soil surface, they are easy to pick out and remove. The trick is to catch them early, before they start to produce cocoons.
For a severe infestation, there are physical, biological and thermal controls.
Concerning the latter, Brad says jumping worm cocoons cannot survive heat in excess of 104° Fahrenheit. "Compost piles regularly get hotter than that," he notes. An infestation can also be heat-treated through solarization, which involves covering a lawn or garden with clear plastic sheets for three days, checking every once in a while with a soil thermometer to ensure that 104° has been reached.
A biological control now being tested on Asian jumping worms is Beauveria bassiana, an entomopathogenic fungus sold under the brand name BotaniGard that affects many garden pests.
Beauveria bassiana can also impact European earthworms, though Brad says it can be applied to the surface or mixed in with mulch rather than dug into the soil where beneficial earthworms are.
Physical control options include biochar, sand and diatomaceous earth. The sharp angular particles could kill the worms when ingested.
The snake-like movement of a jumping worm. (video: Carly Ziter, courtesy UW-Madison Arboretum)
Researchers Need Gardeners
There are far more gardeners and people working the soil out there than there are researchers. Brad asks gardeners and members of the landscaping industry to try these various control methods then let him know the results.
Brad has a new study to discover the impact of jumping worms that gardeners are seeing on plants, from ornamentals to vegetables. He already gets emails from gardeners who note that some plants are doing fine while others are negatively affected. He is looking for more data so he can create lists of plants or plant families that can co-exist with jumping worms.
Gardeners interested in participating in the jumping worm survey can find it on the University of Wisconsin-Madison Arboretum website.
The Mustard Test
One method for identifying the presence of Asian jumping worms is known as the "mustard test." A solution of mustard powder — a third-cup of yellow mustard powder mixed with a gallon of water — poured onto the ground will irritate the skin of jumping worms and cause them to emerge from leaf litter.
The mustard test is how researchers test for jumping worm populations cheaply and easily. For a very new invasion, the mustard powder solution could also potentially be used to get the worms out of the soil to be picked off.
Brad demonstrates a mustard pour. (photo: Eric Hamilton/UW–Madison Communications)
How Gardeners Can Stop the Spread of Asian Jumping Worms
Best management practices for stopping the spread of Asian jumping worms start with education, like knowing how to ID the worms and their castings.
Brad says that when he goes to nurseries and plant sales, he looks at the top of the soil in the pots. Gardeners know what good garden soil or potting mix is supposed to look like, so if they see the soil appears granular or strange, they will know not to bring that pot home.
Brad also encourages gardeners to ask questions of the nurseries and greenhouses, both of which he says are generally great allies in stopping jumping worms. They should be able to give answers on where their compost comes from and if they are treating it.
There is no central repository for information on combating jumping worms yet, Brad says, but there are groups that are spreading awareness and collecting information. For instance, gardeners in the Northeast can turn to JWORM, the Jumping Worm Outreach, Research & Management working Group. In Wisconsin, there's the University of Wisconsin-Madison Extension and Brad's own jumping worm survey (which is open to gardeners everywhere).
To let researchers know where invasive species of all kinds have been spotted, there are two tools: EDDMapS and iMapInvasives.
The first step to combatting jumping worms is raising awareness. (photo: Susan Day/UW–Madison Arboretum)
I hope you enjoyed my conversation with Brad Herrick and learned something new. If you haven't listened yet, you can hear this episode now by scrolling to the top of the page and clicking the Play icon in the green bar under the page title.
Have you encountered Asian jumping worms? Let us know in the comments below.
Episode 144: Understanding Nematodes: Microscopic Worms, Friend or Foe of Your Garden
joegardener Online Gardening Academy™: Popular courses on gardening fundamentals; managing pests, diseases & weeds; seed starting and more.
joegardener Online Gardening Academy Perfect Soil Recipe Master Class: Learn how to create the perfect soil environment for thriving plants.
joegardener Online Gardening Academy Growing Epic Tomatoes: Tomato expert Craig LeHoullier joins me in leading this course on how to grow healthier, productive tomato plants and how to overcome tomato-growing challenges.
University of Vermont study: Biocontrol of invasive pheretimoid earthworms using Beauveria bassiana
University of Wisconsin–Madison Arboretum jumping worm survey
University of Wisconsin-Madison Extension: Jumping Worms
Jumping Worm Outreach, Research & Management working Group
EDDMapS
iMapInvasives
Soil3 – Our podcast episode sponsor and Brand Partner of joegardener.com
TerraThrive™ – Our podcast episode sponsor and Brand Partner of joegardener.com
Disclosure: Some product links in this guide are affiliate links, which means we get a commission if you purchase. However, none of the prices of these resources have been increased to compensate us, and compensation is not an influencing factor on their inclusion here. The selection of all items featured in this post and podcast were based solely on merit and in no way influenced by any affiliate or financial incentive, or contractual relationship. At the time of this writing, Joe Lamp'l has professional relationships with the following companies who may have products included in this post and podcast: Rain Bird, Corona Tools, Milorganite, Soil3, Exmark, Greenhouse Megastore, High Mowing Organic Seeds, Territorial Seed Company, Wild Alaskan Seafood Box and TerraThrive. These companies are either Brand Partners of joegardener.com and/or advertise on our website. However, we receive no additional compensation from the sales or promotion of their product through this guide. The inclusion of any products mentioned within this post is entirely independent and exclusive of any relationship.
How Do I Grow Beets?
How to Create a Productive Raised Bed Garden
Winter: The Best Time to Work on Your Garden