When most people think of earthworms, they probably picture them tunneling through compost or garden soil, turning old banana peels and yard waste into rich, dark soil. One such species is the nightcrawler, Lumbricus terrestris, often found on the surface of the lawn at night or coming up for air after a soaking rain. While earthworms may be helpful in a vegetable garden, aerating the soil softer and making it more arable, they can spell disaster in a forest or other native plant community. Why is that? The earthworms crawling in your garden beds, and in fact pretty much anywhere in the northern tier of North America, are fairly recent imports from other parts of the world. Mainly they come from Europe and Asia, which is also the source of many of our horticultural plants and many of our invasive species. North America’s native earthworms were killed in the northern parts of the continent by the glaciers that blanketed New England and New York, with an extent that stretched across the country to the Great Lakes and the Pacific Northwest in an irregular line. Glacial Extent Map.
Because our forests and other native plant communities evolved for thousands of years without earthworms, adding a new organism into their midst has been detrimental. Many species of forest floor wildflowers require particular conditions to thrive, such as a nice, slowly decomposing layer of leaf litter atop a thick peat like substance called humus. The introduced earthworms can make short work of this important litter layer, turning the forest floor into something resembling a garden bed. And guess what appreciates bare disturbed soils with lots of nutrients? Invasive plants like garlic mustard, bush honeysuckle and other non-native invaders.
So, while many species of earthworms are benign and even helpful in your vermicompost bin or in your veggie patch, they rarely stay in one place. Humans are also spreading them around in plant pots and in mulch or topsoil. Fishers buy a container of worms and go to their favorite spot. And if they don’t have a use for the worms after fishing, out they go at the end of the day; a major source of worms invading northern hardwood forests is actually boat launches and popular fishing sites! Read about that in this article from the American Midland Naturalist where researchers found that 44% of anglers disposed of bait in the trash or on land. Be sure to dispose of bait responsibly here on Nantucket by placing in the Compostable waste bin, so the worms will go through the digester and not make it into the wild or into recycling center compost!
Recently, the NCF Science Staff posted for Invasive Species Week on social media about a “new” worm threat, hoping to educate the public on a group of jumping worms (Amynthas spp.) that are known to be spreading northward, rapidly colonizing yards and forest in New England and the Midwest. Unlike earlier earthworm introductions, these jumping or “crazy” worms are even more active and mobile than earlier introduced species, and rapidly reduce leaf litter to a coffee-grounds like material, altering natural habitats like the forest floor and potentially impacting native wildflowers and trees.
Not long after our social media post, a Nantucket resident contacted us to let us know that she’d found what looked like jumping worms all over a few of her garden beds. Further investigation confirmed this, and when we discussed it, she decided they had likely begun spreading in her yard recently in the last couple years. A sample was collected to be deposited in the Natural Science Collections at the Maria Mitchell Association, where many collections of island biodiversity are housed.
Unlike the earthworms that have been present on island for longer periods of time, some from the arrival of the first European colonists, jumping worms can be identified by their flat rather than raised clitellum (a band around their bodies).
But even more recognizable is their behavior. Rather than remaining deeper in the soil, they inhabit the leaf litter or mulch on the soil surface. When disturbed by digging or raking, they will jump and flail in a side-to-side manner that causes you, or a hungry predator, to jump right along with them! These vigorously jumping worms are more likely to escape becoming a meal and go on to invade a new site. They certainly startle me, and I actually like snakes. Check out this short video of the invasive jumping worms to learn about their movement and spread in North America (note that the range map is outdated and the worms have already spread throughout New England).
So, what can you do about this worm issue? If you observe jumping worms on your property or at a natural area, please let us know! Contact me at firstname.lastname@example.org. We would like to find out where they are distributed across the island and where they might be affecting our conservation properties. An earlier survey by Andrew Mckenna-Foster and Julianna Arntzen, formerly of the Maria Mitchell Association, found that these worms were present at a plot at the Squam Swamp NCF property in 2009. But we have no idea how widespread they are either in landscaped yards or in natural areas on Nantucket. You can also map these worms or other invasive species using the EDDMapS website or by downloading their app to your smartphone (search for Outsmart Invasives where you buy apps).
If you are buying potted plants or getting a transplant from a friend’s garden, it is a good idea to inspect the contents of the pot and any soil or mulch carefully—if you see jumping worms, you will know. They are hard to miss. Unfortunately, once jumping worms have spread in your yard or into the wild, there is no certain, surefire way to effectively manage them. This is definitely a situation where it’s best to prevent the problem rather than allowing it to take up residence in your yard. But if you do have jumping worms in your garden, you can avoid spreading them farther by not moving plants, soil, leaves, or mulch off site. Reducing mulching and watering can also make the habitat less jumping worm friendly.
The Nantucket Conservation Foundation is a private, non-profit land trust that depends on contributions from our members to support our science projects, conservation property acquisitions and land management efforts. If you are not already a member, please join us now!