Worms Eating Up Forest Leaf Litter? That’s Crazy!

They might be coming to a yard or forest near you.

Sounds rather like a horror movie, right? Well, it is actually a bit scary. The Crazy Worm, also called Jumping Worm or Crazy Snake Worm (Amynthas agrestis, Amynthas tokioensis, and Metaphire hilgendorfi), are three species from Korea and Japan who are co-invading our yards and forests here in the Northeast and other parts of the country.

These species are called “crazy worms” or “jumping worms” because they wiggle violently when disturbed. They will even jump out of a shallow dish. When wiggling they often lose a section of their tail, which may be an adaptation to escape from predators. Crawling with a back and forth motion earned them the nickname “snake worms.” You can tell them from other worm species because they feel less slimy and have a milky white clitellum, the reproductive part of the worm.

We have heard about the “Red Wiggler” Worm (Eisenia fetida), which helps to break down our leftover fruit and veggies in our compost piles, and about vertical tunnels created by the European Nightcrawler (Eisenia hortensis), which aerate the soil. These species are beneficial in gardens. But did you know that all the worms here in the Northeast are not native, but have been introduced? There haven’t been worms here since the glaciation from the Laurentide Ice Sheet over 10,000 years ago. Colonists weren’t the only organisms arriving on these shores in the 1600s. Potted plants and soil from ships’ ballast contained worms that also colonized our area. And many worm species have since been introduced through landscape material.

But why are these “crazy” worms invasive? These worms don’t tunnel deep into the ground like some European species. They live in the top leaf litter or duff layer. This is a moist, thick, spongy layer that is slowly decomposed by fungi, bacteria, small isopods, and other invertebrates. These invasive worms ravenously and quickly consume this layer, leaving behind a thick deposit of their castings (waste) that looks like gray, chunky coffee grounds. This new top layer drains quickly and loses nutrients through runoff.

Spring ephemeral plants such as Trillium (Trillium sp.) and tree seedlings can’t survive in this dry layer. I haven’t seen many Redback Salamanders (Plethodon cinereus) lately. This amphibian also lives in this moist duff layer and studies have shown they are also affected by Jumping Worms. Karen Caballos from the New York Master Naturalist Program created a Jumping Worm claymation video that explains this well.

Crazy Worms are extremely successful because they are parthenogenic—they can reproduce without mating. In the fall, the worms die at the first frost, but not before releasing small (2 to 4 mm, about the size of a fruit fly), difficult to detect cocoons that survive through the winter. The cocoons hatch when the soil reaches 50 degrees F (10 degrees C) in April. By July, they become adults that are 6 inches (15 cm) long.

What can you do? First, you can check to see whether you have these worms with a simple test: mix one-third cup (79 ml) of ground yellow mustard seed in one gallon of water (3.75 liters). Clean a section of bare ground and slowly pour this mixture over it (it won’t harm plants). This will drive the worms to the surface where they can be collected and identified.

Next, be really careful that you don’t introduce these worms to your yard. Make sure to buy heat-treated compost and soil amendments. Studies have shown that the cocoons cannot survive above 100 degrees F (38 degrees C). Most commercial composts are required by law to be heated above that. Worms can also be introduced in potted plants from plant sales and swaps, and even nurseries. Look through the soil and refuse these plants if you see the telltale gray, coffee ground-like castings. Even if you don’t see those castings, discard the potted soil in the trash and just plant your new purchase with its roots. You can also buy bare root plants and grow plants from seed.

If you like to fish, don’t buy worms called Alabama or Georgia Jumpers (other names for our bad guys). Never dump excess worms of any kind in the wild. Dispose of them in your trash. When gardening, clean all shovels, forks, spades, and other tools, especially if you garden somewhere else.

Experiments with biochar, a soil amendment that has tiny, sharp edges, and a chemical containing tea seed oil may offer hope for the possible control of these invaders.