Let's take jumping worms seriously

We gardeners are among those who are on the front lines of the interface between human activity and nature. When good things happen, we're among the first non-scientists to notice, and the same goes for adverse occurrences. So when the Master Gardeners of Ontario are warning that jumping worms are a real threat, we need to pay attention. Below, I am reproducing a compelling examination of the jumping worms issue by Claudette Sims, on the premise that step one is to know the enemy.

Claudette notes that the many species of mostly European worms that we welcome into our gardens are in fact destructive invaders. They refashion the layer of organic matter that naturally accumulates atop the soil, to the detriment of native organisms, plants and creatures, including songbirds. Of all the species of worms found in Ontario, only two are native, and they are rare. Yet, we see worms as an indicator of soil health and fertility.

Unfortunately Asian jumping worms are exponentially more of a problem than the worms we know. I corresponded with Michael McTavish of the Smith Forest Health Lab at the University of Toronto, who is quoted by Claudette, to see what gardeners can do. At this stage, not much; our role is to observe and report. Protocols are being set up for a new community science monitoring program to collect more data. I've added his comments and more info on the program to the end of this post.

There have been 20 to 25 jumping worm sightings, the first in 2014 in the Windsor area and in various locations in southern Ontario, including Toronto and Hamilton, in 2021. By themselves, they might move a metre a year. With our help, they can leapfrog across long distances - which is why gardeners everywhere need to be vigilant and exercise caution in transporting plants and soil, for instance, from the GTA to cottage country.

By Claudette Sims Master Gardeners of Ontario 

I’m concerned about the content and tone in this Jumping Worm (JW) article in the latest issue of Landscape Ontario magazine.

Landscape Ontario is usually a trusted source of information that I refer forum members to, but this article was quite disappointing.

While the article generally makes some valid points about Jumping worms, several comments are troubling to me and do not paint an accurate picture of Jumping Worms in particular, and earthworms in general.

Here are the statements causing me grief:

“Earthworms are a familiar friend to gardeners and can have a positive impact on soil health through their digestive processes.”

We have grown up to think that earthworms are good for gardens, but they may not be the friend you think they are. This love of earthworms was likely inherited from the settlers who brought them to Ontario during colonization. But the vast majority of earthworms found in Ontario are non-native and invasive. In fact, there are only two species of earthworms known to be native to Ontario. They are rare and have been identified in isolated areas. We have not really had any earthworms in Ontario for the last 10,000 years. Yet Indigenous people have successfully farmed here for thousands of years and our forests have managed to grow and thrive. Clearly earthworms are not needed to make our soil healthy.

“You may be thinking: ‘So the worms in my garden have a bit more spunk, what’s the problem with that?’ Well, the answer is that these worms aren’t a problem for your garden, but they are damaging the biodiversity of Ontario forests.”

I’ve seen JWs described as invaders, voracious eaters, soil engineers, a threat to gardens, but saying they have spunk is a first and seems to better describe a puppy than the very real threat that JWs pose.

They are such a problem in the U.S., that support groups for gardeners have been formed and there is even recognition of the emotional toll that JWs have on gardeners. JWs feast on all organic matter including mulch, stripping nutrients from topsoil, increasing erosion and killing plants, or at the very least making them difficult to grow. Unlike other invasive earthworms that survive our winters, JWs hatch from eggs each year. This means JWs mature en masse in late summer and voraciously devour all leaf litter and organic matter, whether in forests or your garden.

Dr. Michael McTavish, who studies exotic earthworms, states that “Jumping worms are a new group of non-native earthworms that threaten gardens and natural systems.” He will be conducting a webinar showing their impact in Toronto ravines in September. If you are unable to attend, watch for the recording which I’ll post later.

All invasive earthworms contribute to the decline of forest biodiversity. This can include the loss or decline of native plants, salamanders, songbirds, orchids, soil biota, fungi and invertebrates. Because JWs exist in such large numbers and reproduce so quickly, they also have the potential to release significant amounts of carbon dioxide into the air by removing the entire duff layer where carbon is stored. We already know that increases in CO2 increase global warming so impacts of JWs will affect us all and we need to take them seriously.

“Not only that, but Asian jumping worms are known to frantically travel through soil, their quickened pace grinding the earth to almost coffee grounds-like texture.”

It’s true that one indication of JWS is the coffee ground-like texture of invaded soils. This may be the first change that home gardeners notice. However, JWs are not “grinding the earth” to coffee grounds-like texture by their “quickened pace”. The coffee ground-like soil is a result of their castings (poop). Now you’d think this is a good thing as castings add nutrients to the soil- many of us are familiar with vermicomposting. The very loose texture of the JW castings means that invaded soils don’t hold water well and exacerbate drought conditions in your garden.

The bulk of JW activity is noticed in late summer, when they mature and become very active. Any nutrients in the castings are not really needed for plants in late summer or early autumn as they are winding down for the winter. The poop easily erodes away with winter rains and snow because of its light, loose texture. In spring, there are no nutrients left for emerging plants. Impacts on home gardens are real and cannot be ignored.

“However, Cassin said he likes to emphasize that all earthworms, including the Asian jumping worm, are ‘good for the garden, bad for the forest.”

I admit that this idea that earthworms are good for your garden is widespread, but this doesn’t make it true, no matter how many times you say it. “Emphasizing” that JWs are good for your garden is going one step too far. I do hope that was a misquote because even the Invasive Species Centre website states that: “Garden soil altered by jumping worms is often inhospitable to ornamental plants, posing a threat to garden aesthetics and productivity (Johnson et al., 2021).”

“So in human-modified environments, and landscaping scenarios in agricultural fields, earthworms generally have really positive impacts. Their tunnels can increase soil porosity, and increase gas exchange happening, they can increase water infiltration to water the roots. They do a lot of great things.

Hopefully the author is referring to invasive European earthworms at this point and not JWs, but it’s not really clear as it follows the previous quote of JWs being good for your garden. JWs don’t burrow into the soil. They live on the soil surface so this perceived benefit of tunneling certainly doesn’t apply to them. There may be some truth in this for other invasive worms in agricultural fields, but I would challenge these perceived benefits in landscaping.

Dr. John Warren Reynolds Ph.D., LL.B., the first Canadian oligochaetologist (earthworm specialist) points out: “While both European lumbricid and jumping worms remove the organic horizon, the texture of soils invaded by jumping worms is more stressful for roots, fungi and soil animals. This is because jumping worm activities transform surface soils to a texture similar to ground beef or spent coffee grounds. These changes in the soil lead to increased erosion, nutrient leaching, root desiccation, and plant death.”

He continues: “In addition to deteriorating natural systems, jumping worm impacts are being felt by gardeners, plant nurseries, golf courses and community parks. The deep layer of loose castings created by jumping worms is particularly problematic for perennial plants (both native and horticultural), as well as parks and lawns used for recreation.”

There is clear evidence that non-native plants are positively associated with the presence of invasive earthworms. Non-native plant species that co-evolved with invasive earthworms may prefer similar conditions to those found in earthworm invaded soils. Given the prevalence of exotic non-native plants sold in the nursery trade and used in home gardens, this could explain the perception that earthworms have a positive influence on our gardens.

“Cassin explained how these worms are not as harmful to gardens and should be contained to one area as much as possible and identified before taking further action.”

There is ample evidence that JWs are harmful to gardens, but the suggestion that JWs “should be contained to one area as much as possible…before taking further action” is really misleading. Control options are being explored, but to date, there is no known way of removing JWs once they invade your garden. They are unlikely to be “contained to one area”, as a single egg transferred on garden tools, animals or shoes is all that is needed for them to spread. The best strategy is prevention. All gardeners should be knowledgeable about JWs, what they look like, how they spread and how to avoid them.

The bottom line is that any earthworm you find in your garden is invasive and non-native. Once an area is invaded by a species of earthworm, there is no known way to remove them. JWs are many times more destructive because they occur in greater population densities and devour leaf litter and organic matter at a much more rapid pace. We know they will damage our forests and being complacent about them in our gardens will only increase the danger of spread to our natural areas.

Please learn to identify JWs and stop their spread so we can protect our gardens and our forests.

Note: Claudette has a number of helpful references in her original post, which can be found here.

Further note: Here's advice from Michael McTavish on what we can do. 

Whenever I've spoken to a group about jumping worms, the general advice I give in terms of management is:
1. Be aware of jumping worms and what to look out for. Watch areas around you (e.g., gardens, public parks) and keep an eye open any time you bring in new materials such as mulch, soil, or plants. If you see suspected jumping worms, please report to EDDMapS. https://www.eddmaps.org
2. If you do find jumping worms, if they are in a very small and contained area (e.g., a potted plant, bag of soil, raised garden bed), individual worms can be euthanized in high concentration alcohol and soil and other bulk materials can be sterilized by solarization (e.g., tarping with dark plastic to achieve temperatures of at least 40 degrees C for at least 3 days).
3. If the infestation is in a larger, uncontained area, we currently lack any scientifically supported methods to thoroughly remove adult jumping worms and cocoons hidden in the soil. At this point, the focus should be on containing the infestation and preventing spread to other areas. Approaches to containment include not sharing plants or other materials from infested soils, not dumping waste without solarizing or bagging it, and thoroughly wiping off shoes and tools to avoid hitchhiking cocoons.

There is also a video regarding the community detection project - anyone can join, anyone can search, and negative reportings ("no jumping worms here!") are as helpful as positives. Participants are asked to search at least one area once in September 2022. 
Susannah Varmuza
- 26 September 2022 at 12:14pm

Are JWs susceptible to parasitization by cluster flies?
- 26 September 2022 at 06:06pm

Interesting question! I will inquire
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