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.