Wednesday, February 28, 2018

Earthworms Gone Bad

Most of us grow up hearing about how great earthworms are for the garden.  Gardeners strive for a garden full of beneficial worms!  They aerate the soil, break down organic matter from the soil surface, and expel their nutrient-full 'castings' (aka 'poop') underground for the benefit of plant roots.  Whenever I found earthworms on our driveway after a rain, I enthusiastically picked them up and placed them in whichever part of the garden I thought needed them the most.

Then came the discovery of the invasive Asian jumping worm.


Asian jumping worm
Believe it or not, here in New England we don’t have any native earthworms, as glaciers wiped them all out several millennia ago.  With no earthworms, our hardwood forests evolved in an environment where fallen leaves collect in a thick layer on the forest floor and decompose slowly.  This leaf litter retains moisture, maintains the soil’s pH level, and supports a rich understory as well as the wildlife that live in such an environment.  

Yellow trout lilies
However, in the 1600’s, European settlers introduced earthworms back to the Northeast.  These non-native earthworms alter woodlands by eating the leaf litter that normally supports native tree seedlings and native wildflowers such as trout lilies, mayflowers, and trillium.  

Trillium cuneatum
The disappearance of this spongy leaf layer leads to the disappearance of insects and amphibians that live in it, which has larger implications in the forest ecosystem.  Thankfully this process is very slow, as the worms do not spread very quickly by themselves.

Enter the Asian jumping worm.


Asian jumping worms have likely been in the South and in northern greenhouses for several decades. However, they were noticed in 2013 in Wisconsin as problematic, and since then awareness has grown about these earthworms, which are.... a little different.

Asian jumping worms are more energetic than other worms.  Hailing from Korea and Japan, they are also known as ‘crazy snake worms’, as they thrash wildly side to side and even jump when handled.These worms have a voracious appetite, able to break down wood mulch and plant debris extraordinarily quickly.  (In one study, researchers from University of Wisconsin - Madison studied plots of forest land newly invaded by worms and found that the worms decreased the leaf litter mass by 84 to 95% in just four months!)


Instead of dwelling in deeper soil, Asian jumping worms live close to the soil surface, right underneath the leaf litter. Their dry, but nutrient-full castings are mostly left in the top two inches of soil, inaccessible to deeper plant roots. They work so quickly that scientists liken it to a dose of quick-release fertilizer.  However these nutrients easily wash away - sometimes to where people do not want it, such as in waterways.  Soil occupied by jumping worms often looks churned, grainy, and dry, and it is more prone to erosion.  


These worms that I had so carefully rescued were Asian jumping worms, of course, and they are changing the soil in my garden. The top layer of my soil in many parts of the garden has turned into a gravelly field of loose, dry little pellets.


While Asian jumping worms do thankfully die off in cold weather, their cocoons survive to hatch the next spring.  Another difference between these worms and others: it takes just one.  Jumping worms can reproduce asexually, thus it takes just one worm to make a colony in a new location.

So how can you tell if you have these crazy worms?

Asian jumping worm
It's difficult to tell with young worms, but the adult jumping worms can be identified by their smooth, light-colored clitellum, which completely circles its body near the head.  (The similar-looking European nightcrawler has a raised clitellum instead of a smooth one.)  They also wriggle wildly (or jump!) when picked up or touched.

So what can be done about these invasive worms?  Several states have launched campaigns to discourage people from dumping worms from fishing bait and vermicomposting in the woods, which exacerbates the problem.  Several organizations in Wisconsins have even cancelled their annual plant sales in order to slow the spread of these worms.  As for us, we can make sure not spread these worms by checking plants that we buy or share with others for worms and destroying any that are found.  Acquire compost only from reputable sources where it has reached properly high temperatures, which would kill any cocoons.


As for me, I will stop rescuing these invasive worms and putting them in my garden.


23 comments:

  1. Great article. Thanks for sharing. Also thanks for posting the pics to help identify them. Our property is in SW Michigan and so far we haven't noticed any when planting. I'll definitely make sure to keep an extra close eye out for them when the growing season starts here.

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    1. That's good you haven't seen any yet - hopefully you won't get any!

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  2. Wow! I'll be on the lookout for these. Although the interweb says they haven't been spotted her in western Washington yet, there have been reports of them in nearby Oregon.

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    1. Hopefully awareness can keep them from spreading so quickly! Hopefully you won't get them there.

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  3. Another gift from Asia. Thanks for the heads up!

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    1. With so much global trade, it's a lot harder to stop invasives!

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  4. Oh dear, sorry to hear they've made it to your garden. This is an excellent post! Yes, indeed, they are here in Wisconsin. I volunteer at the UW-Madison Arboretum--one of the first places in the state where they were found. We frequently find them as we're working in the native plant garden. They really squiggle when you pick them up--I find them quite repulsive. And as you describe, they totally change the soil composition where they are found. Even though I help at the arboretum, I've yet to find them in my own garden, although it's probably only a matter of time, since they're spreading throughout the county and the southern part of the state.

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    1. Oh wow! I sure hope you don't end up with them in your own garden!

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  5. That's terrible! I've heard of these nasty guys, but wasn't aware of the details. I'm pretty sure they are not in our garden ... yet.

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    1. That's good. I hope they stay out!

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  6. Wow! This is new information for me. I don't think I have seen any, but now I will be on the lookout.

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    1. Hope you don't have any, and that awareness can slow them down.

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  7. We need more robins! (to eat the worms) :P

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    1. I agree, ha! I know the robins always come by to eat my holly berries, so hopefully they are getting some worms too!

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    2. Unfortunately, the only thing that eats these thick hided worms are VOLES! another garden pest!

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  8. I've heard these things are on the way. Sorry to hear they've found a home in your garden.
    I rely so much on mulches like lawn clippings and shredded leaves to keep the weeds down. I'll be at a complete loss when these pests get here.

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    1. I mulched one of my gardens, and the worms broke it down so quickly. The soil is so weird and loose now there, and it's right by some woods, which is frightening.

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  9. Oh my goodness, I reckon these jumping worms must originate from North Korea. We have no worms in the garden at the moment. I was thinking of introducing some.

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    1. Just introduce the good kind :) Here I was so pleased that I had so many worms in my garden...

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  10. This was a great but kind of creepy post. Your spring natives and stone garden steps are beautiful by the way. I have not seen one of these worms yet and I hope I don't. Perhaps I should be more forgiving of the wild turkeys that take dirt baths in the garden. Robins are great, but those wild turkeys are eating machines. From the news I thought you might be gone with the wind! I'm so glad to hear that is not the case. PS. What do the cocoons look like?

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    1. Sadly the spring native pictures were not taken at my house, but at the nearby New England Wildflower Society's garden. I have little clumps, though, which I hope will expand! The cocoons are rather hard to distinguish from the castings, unfortunately. They look like tiny, round, brown balls.

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  11. As a Madison, WI gardener thank you for getting this news out to gardeners. It sounds crazy but I now keep ziploc bags with my garden tools. Every time I see one of these worms, I bag them up. Then I set the bag of worms in the sun which seems to kill them. Hopefully I am reducing their numbers while the pros look for solutioms.

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    1. It's an issue that definitely needs more awareness! I kill any earthworm I dig up or find, but I do hope someone comes up with a better solution.

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